@article{lee_parsons_chen_dungan_kathariou_2023, title={Contrasting Genetic Diversity of Listeria Pathogenicity Islands 3 and 4 Harbored by Nonpathogenic Listeria spp.}, ISSN={["1098-5336"]}, DOI={10.1128/aem.02097-22}, abstractNote={Listeria monocytogenes is a serious foodborne pathogen that can harbor the pathogenicity islands Listeria pathogenicity island 3 (LIPI-3) and LIPI-4. Intriguingly, these have also been reported in nonpathogenic L. innocua from food and farm environments, though limited information is available for strains from the natural environment. ABSTRACT Listeria monocytogenes causes the severe foodborne disease listeriosis. Several clonal groups of L. monocytogenes possess the pathogenicity islands Listeria pathogenicity island 3 (LIPI-3) and LIPI-4. Here, we investigated the prevalence and genetic diversity of LIPI-3 and LIPI-4 among 63 strains of seven nonpathogenic Listeria spp. from the natural environment, i.e., wildlife (black bears [Ursus americanus]) and surface water. Analysis of the whole-genome sequence data suggested that both islands were horizontally acquired but differed considerably in their incidence and genetic diversity. LIPI-3 was identified among half of the L. innocua strains in the same genomic location as in L. monocytogenes (guaA hot spot) in a truncated form, with only three strains harboring full-length LIPI-3, and a highly divergent partial LIPI-3 was observed in three Listeria seeligeri strains, outside the guaA hot spot. Premature stop codons (PMSCs) and frameshifts were frequently noted in the LIPI-3 gene encoding listeriolysin S. On the other hand, full-length LIPI-4 without any PMSCs was found in all Listeria innocua strains, in the same genomic location as L. monocytogenes and with ~85% similarity to the L. monocytogenes counterpart. Our study provides intriguing examples of genetic changes that pathogenicity islands may undergo in nonpathogenic bacterial species, potentially in response to environmental pressures that promote either maintenance or degeneration of the islands. Investigations of the roles that LIPI-3 and LIPI-4 play in nonpathogenic Listeria spp. are warranted to further understand the differential evolution of genetic elements in pathogenic versus nonpathogenic hosts of the same genus. IMPORTANCE Listeria monocytogenes is a serious foodborne pathogen that can harbor the pathogenicity islands Listeria pathogenicity island 3 (LIPI-3) and LIPI-4. Intriguingly, these have also been reported in nonpathogenic L. innocua from food and farm environments, though limited information is available for strains from the natural environment. Here, we analyzed whole-genome sequence data of nonpathogenic Listeria spp. from wildlife and surface water to further elucidate the genetic diversity and evolution of LIPI-3 and LIPI-4 in Listeria. While the full-length islands were found only in L. innocua, LIPI-3 was uncommon and exhibited frequent truncation and genetic diversification, while LIPI-4 was remarkable in being ubiquitous, albeit diversified from L. monocytogenes. These contrasting features demonstrate that pathogenicity islands in nonpathogenic hosts can evolve along different trajectories, leading to either degeneration or maintenance, and highlight the need to examine their physiological roles in nonpathogenic hosts.}, journal={APPLIED AND ENVIRONMENTAL MICROBIOLOGY}, author={Lee, Sangmi and Parsons, Cameron and Chen, Yi and Dungan, Robert S. S. and Kathariou, Sophia}, year={2023}, month={Feb} }
 @article{brown_chen_ivanova_leekitcharoenphon_parsons_niedermeyer_gould_strules_mesa-cruz_kelly_et al._2023, title={Draft Genome Sequences of 158 Listeria monocytogenes Strains Isolated from Black Bears (Ursus americanus) in the United States}, volume={12}, ISSN={2576-098X}, url={http://dx.doi.org/10.1128/mra.00248-23}, DOI={10.1128/mra.00248-23}, abstractNote={Listeria monocytogenes is responsible for severe foodborne disease and major economic losses, but its potential reservoirs in natural ecosystems remain poorly understood. Here, we report the draft genome sequences of 158 L. monocytogenes strains isolated from black bears (Ursus americanus) in the southeastern United States between 2014 and 2017. ABSTRACT Listeria monocytogenes is responsible for severe foodborne disease and major economic losses, but its potential reservoirs in natural ecosystems remain poorly understood. Here, we report the draft genome sequences of 158 L. monocytogenes strains isolated from black bears (Ursus americanus) in the southeastern United States between 2014 and 2017.}, number={7}, journal={Microbiology Resource Announcements}, publisher={American Society for Microbiology}, author={Brown, Phillip and Chen, Yi and Ivanova, Mirena and Leekitcharoenphon, Pimlapas and Parsons, Cameron and Niedermeyer, Jeffrey and Gould, Nicholas and Strules, Jennifer and Mesa-Cruz, J. Bernardo and Kelly, Marcella J. and et al.}, editor={Rasko, DavidEditor}, year={2023}, month={Jul} }
 @article{vishnivetskaya_niedermeyer_guttierrez-rodriguerz_baltzegar_parsons_kathariou_thrash_2023, title={Draft genome sequence of <i>Exiguobacterium</i> sp. from whole cantaloupe, with inhibition capacity against <i>Listeria monocytogenes</i>}, ISSN={["2576-098X"]}, DOI={10.1128/mra.00850-23}, abstractNote={ABSTRACT We report the draft genome sequence of a novel species, Exiguobacterium sp., isolated from a freshly harvested and untreated cantaloupe in North Carolina. The strain Exiguobacterium wild type exhibited inhibitory activity against the foodborne pathogen Listeria monocytogenes, including strains of diverse serotypes and genotypes, both on agar media and in biofilms.}, journal={MICROBIOLOGY RESOURCE ANNOUNCEMENTS}, author={Vishnivetskaya, Tatiana A. and Niedermeyer, Jeffrey and Guttierrez-Rodriguerz, Eduardo and Baltzegar, David and Parsons, Cameron and Kathariou, Sophia and Thrash, J. Cameron}, year={2023}, month={Dec} }
 @article{brown_hernandez_parsons_chen_gould_deperno_niedermeyer_kathariou_2023, title={Tetracycline resistance in Listeria monocytogenes and L. innocua from wild black bears (Ursus americanus) in the United States is mediated by novel transposable elements}, volume={89}, ISSN={["1098-5336"]}, url={https://doi.org/10.1128/aem.01205-23}, DOI={10.1128/aem.01205-23}, abstractNote={ABSTRACT Listeria monocytogenes is a facultative intracellular foodborne pathogen and the causative agent of the severe disease listeriosis. It is found ubiquitously in the environment and exhibits innate resistance to certain antimicrobials, but acquired antimicrobial resistance remains relatively uncommon. Given the potentially dire health outcomes associated with listeriosis, acquisition of antimicrobial resistance (AMR) by this pathogen is of considerable public health concern. AMR in L. monocytogenes has been surveyed frequently in strains of clinical and food origin, but much less commonly in wildlife. We analyzed 158 strains of L. monocytogenes and 27 of non-pathogenic Listeria spp. isolated from wild black bears (Ursus americanus) for resistance to a panel of antimicrobials. AMR was uncommon and noted mostly for tetracycline. Tetracycline resistance was more common in Listeria innocua than in L. monocytogenes. All tetracycline-resistant L. monocytogenes strains belonged to sequence type ST1039 and harbored the Tn916-like tet(M) transposon Tn916.1039 in a conserved chromosomal location. In contrast, three different tetracycline resistance elements, i.e., the tet(M) elements Tn5801.UAM and Tn5801.551 and the tet(S) element Tn6000.205, were identified among tetracycline-resistant strains of L. innocua. The greater prevalence and diversity of tetracycline resistance elements among bear-derived non-pathogenic Listeria strains suggest the potential of the latter to serve as reservoirs for retention and diversification of AMR determinants in this wildlife host and warrant their further monitoring and study. IMPORTANCE Listeria monocytogenes causes severe foodborne illness and is the only human pathogen in the genus Listeria. Previous surveys of AMR in Listeria focused on clinical sources and food or food processing environments, with AMR in strains from wildlife and other natural ecosystems remaining under-explored. We analyzed 185 sequenced strains from wild black bears (Ursus americanus) from the United States, including 158 and 27 L. monocytogenes and L. innocua, respectively. Tetracycline resistance was the most prevalent resistance trait. In L. monocytogenes, it was encountered exclusively in serotype 4b strains with the novel Tn916-like element Tn916.1039. In contrast, three distinct, novel tetracycline resistance elements (Tn5801.UAM, Tn5801.551, and Tn6000.205) were identified in L. innocua. Interestingly, Tn5801.551 was identical to elements in L. monocytogenes from a major foodborne outbreak in the United States in 2011. The findings suggest the importance of wildlife and non-pathogenic Listeria species as reservoir for resistance elements in Listeria. Listeria monocytogenes causes severe foodborne illness and is the only human pathogen in the genus Listeria. Previous surveys of AMR in Listeria focused on clinical sources and food or food processing environments, with AMR in strains from wildlife and other natural ecosystems remaining under-explored. We analyzed 185 sequenced strains from wild black bears (Ursus americanus) from the United States, including 158 and 27 L. monocytogenes and L. innocua, respectively. Tetracycline resistance was the most prevalent resistance trait. In L. monocytogenes, it was encountered exclusively in serotype 4b strains with the novel Tn916-like element Tn916.1039. In contrast, three distinct, novel tetracycline resistance elements (Tn5801.UAM, Tn5801.551, and Tn6000.205) were identified in L. innocua. Interestingly, Tn5801.551 was identical to elements in L. monocytogenes from a major foodborne outbreak in the United States in 2011. The findings suggest the importance of wildlife and non-pathogenic Listeria species as reservoir for resistance elements in Listeria.}, number={11}, journal={Environmental Microbiology}, author={Brown, Phillip and Hernandez, Kevin and Parsons, Cameron and Chen, Yi and Gould, Nicholas and DePerno, Christopher S. and Niedermeyer, Jeffrey and Kathariou, Sophia}, editor={Dozois, Charles M.Editor}, year={2023}, month={Nov} }
 @article{fan_foster_zhao_mukherjee_shrestha_parsons_kathariou_2022, title={Genomic Analysis Reveals That Isolation Temperature on Selective Media Introduces Genetic Variation in Campylobacter jejuni from Bovine Feces}, volume={11}, ISSN={["2076-0817"]}, DOI={10.3390/pathogens11060678}, abstractNote={Campylobacter jejuni is commonly isolated on selective media following incubation at 37 °C or 42 °C, but the impact of these temperatures on genome variation remains unclear. Previously, Campylobacter selective enrichments from the feces of steers before and after ceftiofur treatment were plated on selective agar media and incubated at either 37 °C or 42 °C. Here, we analyzed the whole genome sequence of C. jejuni strains of the same multilocus sequence typing (MLST)-based sequence type (ST) and isolated from the same sample upon incubation at both temperatures. Four such strain pairs (one ST8221 and three ST8567) were analyzed using core genome and whole genome MLST (cgMLST, wgMLST). Among the 1970 wgMLST loci, 7–25 varied within each pair. In all but one of the pairs more (1.7–8.5 fold) new alleles were found at 42 °C. Most frameshift, nonsense, or start-loss mutations were also found at 42 °C. Variable loci CAMP0575, CAMP0912, and CAMP0913 in both STs may regularly respond to different temperatures. Furthermore, frameshifts in four variable loci in ST8567 occurred at multiple time points, suggesting a persistent impact of temperature. These findings suggest that the temperature of isolation may impact the sequence of several loci in C. jejuni from cattle.}, number={6}, journal={PATHOGENS}, author={Fan, Sicun and Foster, Derek and Zhao, Shaohua and Mukherjee, Sampa and Shrestha, Yesha and Parsons, Cameron and Kathariou, Sophia}, year={2022}, month={Jun} }
 @article{brown_kucerova_gorski_chen_ivanova_leekitcharoenphon_parsons_niedermeyer_jackson_kathariou_2022, title={Horizontal Gene Transfer and Loss of Serotype-Specific Genes in Listeria monocytogenes Can Lead to Incorrect Serotype Designations with a Commonly-Employed Molecular Serotyping Scheme}, volume={12}, ISSN={["2165-0497"]}, url={https://doi.org/10.1128/spectrum.02745-22}, DOI={10.1128/spectrum.02745-22}, abstractNote={Listeria monocytogenes is a foodborne pathogen responsible for severe illness (listeriosis), especially in pregnant women and their fetuses, immunocompromised individuals, and the elderly. Three serotypes, 1/2a, 1/2b, and 4b, account for most human listeriosis, with certain serotype 4b clonal complexes (CCs) overrepresented in human disease. ABSTRACT Listeria monocytogenes is a Gram-positive, facultative intracellular foodborne pathogen capable of causing severe, invasive illness (listeriosis). Three serotypes, 1/2a, 1/2b, and 4b, are leading contributors to human listeriosis, with 4b including the major hypervirulent clones. The multiplex PCR scheme developed by Doumith and collaborators employs primers targeting specific lineages (e.g., lineage II-specific lmo0737, lineage I-specific LMOf2365_2059) or serotypes (e.g., serotype 4b-specific LMOf2365_1900). The Doumith scheme (DS) is extensively employed for molecular serotyping of L. monocytogenes due to its high accuracy, relative ease, and affordability. However, for certain strains, the DS serotype designations are in conflict with those relying on antibody-based schemes or whole-genome sequence (WGS) analysis. In the current study, all 27 tested serotype 4b strains with sequence type 782 (ST782) within the hypervirulent clonal complex 2 (CC2) were designated 1/2b/3b using the DS. These strains lacked the serotype 4b-specific gene LMOf2365_1900, while retaining LMOf2365_2059, which, together with prs, yields the DS 1/2b/3b profile. Furthermore, 15 serotype 1/2a strains of four STs, mostly from water, were designated 1/2b/3b using the DS. These strains lacked the lmo0737 cassette but harbored genomic islands with LMOf2365_2059, thus yielding the DS 1/2b/3b profile. Lastly, we investigated a novel, dual 1/2a-1/2b profile obtained using the DS with 21 serotype 1/2a strains of four STs harboring both the lmo0737 cassette and genomic islands with LMOf2365_2059. The findings suggest that for certain strains and clones of L. monocytogenes the DS designations should be viewed with caution and complemented with alternative tools, e.g., traditional serotyping or WGS analysis. IMPORTANCE Listeria monocytogenes is a foodborne pathogen responsible for severe illness (listeriosis), especially in pregnant women and their fetuses, immunocompromised individuals, and the elderly. Three serotypes, 1/2a, 1/2b, and 4b, account for most human listeriosis, with certain serotype 4b clonal complexes (CCs) overrepresented in human disease. Serotyping remains extensively employed in Listeria epidemiologic investigations, and a multiplex PCR-based serotyping scheme is widely used. However, the PCR gene targets can be lost or gained via horizontal gene transfer, leading to novel PCR profiles without known serotype designations or to incorrect serotype assignments. Thus, an entire serotype 4b clone of the hypervirulent CC2 would be misidentified as serotype 1/2b, and several strains of serotype 1/2a would be identified as serotype 1/2b. Such challenges are especially common in novel clones from underexplored habitats, e.g., wildlife and surface water. The findings suggest caution in application of molecular serotyping, while highlighting Listeria’s diversity and potential for horizontal gene transfer.}, journal={MICROBIOLOGY SPECTRUM}, author={Brown, Phillip and Kucerova, Zuzana and Gorski, Lisa and Chen, Yi and Ivanova, Mirena and Leekitcharoenphon, Pimlapas and Parsons, Cameron and Niedermeyer, Jeffrey and Jackson, James and Kathariou, Sophia}, editor={Chousalkar, KapilEditor}, year={2022}, month={Dec} }
 @article{brown_chen_siletzky_parsons_jaykus_eifert_ryser_logue_stam_brown_et al._2021, title={Harnessing Whole Genome Sequence Data for Facility-Specific Signatures for Listeria monocytogenes: A Case Study With Turkey Processing Plants in the United States}, volume={5}, ISSN={["2571-581X"]}, url={http://dx.doi.org/10.3389/fsufs.2021.742353}, DOI={10.3389/fsufs.2021.742353}, abstractNote={Listeria monocytogenes is a Gram-positive foodborne pathogen responsible for the severe disease listeriosis and notorious for its ability to persist in food processing plants, leading to contamination of processed, ready-to-eat foods. L. monocytogenes persistence in various food processing environments (FPEs) has been extensively investigated by various subtyping tools, with increasing use of whole genome sequencing (WGS). However, major knowledge gaps remain. There is a need for facility-specific molecular signatures not only for adequate attribution of L. monocytogenes to a specific FPE but also for improved understanding of the ecology and evolution of L. monocytogenes in the food processing ecosystem. Furthermore, multiple strains can be recovered from a single FPE sample, but their diversity can be underestimated with common molecular subtyping tools. In this study we investigated a panel of 54 L. monocytogenes strains from four turkey processing plants in the United States. A combination of WGS and phenotypic assays was employed to assess strain persistence as well as identify facility-specific molecular signatures. Comparative analysis of allelic variation across the whole genome revealed that allelic profiles have the potential to be specific to individual processing plants. Certain allelic profiles remained associated with individual plants even when closely-related strains from other sources were included in the analysis. Furthermore, for certain sequence types (STs) based on the seven-locus multilocus sequence typing scheme, presence and location of premature stop codons in inlA, inlB length, prophage sequences, and the sequence content of a genomic hotspot could serve as plant-specific signatures. Interestingly, the analysis of different isolates from the same environmental sample revealed major differences not only in serotype and ST, but even in the sequence content of strains of the same ST. This study highlights the potential for WGS data to be deployed for identification of facility-specific signatures, thus facilitating the tracking of strain movement through the food chain. Furthermore, deployment of WGS for intra-sample strain analysis allows for a more complete environmental surveillance of L. monocytogenes in food processing facilities, reducing the risk of failing to detect strains that may be clinically relevant and potentially novel.}, journal={FRONTIERS IN SUSTAINABLE FOOD SYSTEMS}, publisher={Frontiers Media SA}, author={Brown, Phillip and Chen, Yi and Siletzky, Robin and Parsons, Cameron and Jaykus, Lee-Ann and Eifert, Joseph and Ryser, Elliot and Logue, Catherine M. and Stam, Christina and Brown, Eric and et al.}, editor={Brown, PhillipEditor}, year={2021}, month={Oct} }
 @article{lee_parsons_chen_hanafy_brown_kathariou_2021, title={Identification and Characterization of a Novel Genomic Island Harboring Cadmium and Arsenic Resistance Genes in Listeria welshimeri}, volume={11}, ISSN={["2218-273X"]}, DOI={10.3390/biom11040560}, abstractNote={Listeria monocytogenes, the bacterial foodborne pathogen responsible for the severe disease listeriosis, frequently exhibits heavy metal resistance. Concurrent resistance to cadmium and arsenic in L. monocytogenes is strongly associated with the 35-kb chromosomal island LGI2. LGI2 has been encountered repeatedly among L. monocytogenes serotype 4b hypervirulent clones but, surprisingly, not among non-pathogenic Listeria spp. Here we describe a novel LGI2 variant, LGI2-3, in two L. welshimeri strains from an urban aquatic environment. Whole genome sequence analysis revealed that the genomes were closely related except for one prophage region and confirmed a chromosomally integrated LGI2-3. It harbored a cystathionine beta-lyase gene previously only encountered in LGI2-1 of L. monocytogenes clonal complex 1 but was otherwise most closely related to LGI2. LGI2-3 harbored a novel cadAC cassette (cadA7C7) that, like LGI2′s cadA4C4, was associated with lower-level tolerance to cadmium (MIC 50 μg/mL) than other cadAC cassettes (MIC ≥ 140 μg/mL). CadA sequence analysis identified two amino acids that may be important for mediating different levels of cadmium tolerance. Our findings clearly demonstrated the potential for LGI2-like islands to be harbored by non-pathogenic Listeria spp. and generate intriguing hypotheses on the genetic diversity mediated by this island and its transfer among Listeria spp.}, number={4}, journal={BIOMOLECULES}, author={Lee, Sangmi and Parsons, Cameron and Chen, Yi and Hanafy, Zahra and Brown, Eric and Kathariou, Sophia}, year={2021}, month={Apr} }
 @article{parsons_azizoglu_elhanafi_kathariou_2021, title={Mutant Construction and Integration Vector-Mediated Genetic Complementation in Listeria monocytogenes}, volume={2220}, ISBN={["978-1-0716-0981-1"]}, ISSN={["1940-6029"]}, DOI={10.1007/978-1-0716-0982-8_14}, abstractNote={Genes that play a role in stress response mechanisms and other phenotypes of Listeria monocytogenes can be identified by construction and screening of mutant libraries. In this chapter, we describe the construction and screening of mutant libraries of L. monocytogenes using the plasmid pMC38, carrying a mariner-based transposon system (TC1/mariner) and constructed by Cao et al. (Appl Environ Microbiol 73:2758–2761, 2007). Following screening of mutant libraries, putative mutants are identified and the transposon is localized, leading to identification of the genes responsible for the phenotype of interest. To confirm the role of the transposon-harboring gene in the relevant phenotype, transposon mutants are genetically complemented with the wild-type gene using the site-specific temperature-sensitive integration vector pPL2, constructed by Lauer et al. (J Bacteriol 184:4177–4186, 2002).}, journal={LISTERIA MONOCYTOGENES, 2 EDITION}, author={Parsons, Cameron and Azizoglu, Reha and Elhanafi, Driss and Kathariou, Sophia}, year={2021}, pages={177–185} }
 @article{lopez-perez_sai_sakamachi_parsons_kathariou_ninomiya-tsuji_2021, title={TAK1 inhibition elicits mitochondrial ROS to block intracellular bacterial colonization}, volume={118}, ISSN={["0027-8424"]}, DOI={10.1073/pnas.2023647118}, abstractNote={Significance We have found that bacterial inhibition of host TAK1 inflammatory signaling elicits an alternative host defense mechanism involving production of mitochondrial reactive oxygen species through caspase 8 and RIPK3. This finding allows a reinterpretation of mouse phenotypes harboring tissue-specific gene deletion of Tak1, many of which die from tissue damage previously ascribed to impaired TAK1-dependent tissue homeostasis. We suggest that these phenotypes arise from misrecognition of compromised TAK1 as pathogen invasion. Mitogen-activated protein kinase kinase kinase 7 (MAP3K7), known as TAK1, is an intracellular signaling intermediate of inflammatory responses. However, a series of mouse Tak1 gene deletion analyses have revealed that ablation of TAK1 does not prevent but rather elicits inflammation, which is accompanied by elevation of reactive oxygen species (ROS). This has been considered a consequence of impaired TAK1-dependent maintenance of tissue integrity. Contrary to this view, here we propose that TAK1 inhibition–induced ROS are an active cellular process that targets intracellular bacteria. Intracellular bacterial effector proteins such as Yersinia’s outer membrane protein YopJ are known to inhibit TAK1 to circumvent the inflammatory host responses. We found that such TAK1 inhibition induces mitochondrial-derived ROS, which effectively destroys intracellular bacteria. Two cell death–signaling molecules, caspase 8 and RIPK3, cooperatively participate in TAK1 inhibition–induced ROS and blockade of intracellular bacterial growth. Our results reveal a previously unrecognized host defense mechanism, which is initiated by host recognition of pathogen-induced impairment in a host protein, TAK1, but not directly of pathogens.}, number={25}, journal={PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA}, author={Lopez-Perez, Wilfred and Sai, Kazuhito and Sakamachi, Yosuke and Parsons, Cameron and Kathariou, Sophia and Ninomiya-Tsuji, Jun}, year={2021}, month={Jun} }
 @misc{parsons_brown_kathariou_2021, title={Use of Bacteriophage Amended with CRISPR-Cas Systems to Combat Antimicrobial Resistance in the Bacterial Foodborne Pathogen Listeria monocytogenes}, volume={10}, ISSN={["2079-6382"]}, url={http://dx.doi.org/10.3390/antibiotics10030308}, DOI={10.3390/antibiotics10030308}, abstractNote={Listeria monocytogenes is a bacterial foodborne pathogen and the causative agent of the disease listeriosis, which though uncommon can result in severe symptoms such as meningitis, septicemia, stillbirths, and abortions and has a high case fatality rate. This pathogen can infect humans and other animals, resulting in massive health and economic impacts in the United States and globally. Listeriosis is treated with antimicrobials, typically a combination of a beta-lactam and an aminoglycoside, and L. monocytogenes has remained largely susceptible to the drugs of choice. However, there are several reports of antimicrobial resistance (AMR) in both L. monocytogenes and other Listeria species. Given the dire health outcomes associated with listeriosis, the prospect of antimicrobial-resistant L. monocytogenes is highly problematic for human and animal health. Developing effective tools for the control and elimination of L. monocytogenes, including strains with antimicrobial resistance, is of the utmost importance to prevent further dissemination of AMR in this pathogen. One tool that has shown great promise in combating antibiotic-resistant pathogens is the use of bacteriophages (phages), which are natural bacterial predators and horizontal gene transfer agents. Although native phages can be effective at killing antibiotic-resistant pathogens, limited host ranges and evolved resistance to phages can compromise their use in the efforts to mitigate the global AMR challenge. However, recent advances can allow the use of CRISPR-Cas (clustered regularly interspaced short palindromic repeats-CRISPR-associated proteins) to selectively target pathogens and their AMR determinants. Employment of CRISPR-Cas systems for phage amendment can overcome previous limitations in using phages as biocontrol and allow for the effective control of L. monocytogenes and its AMR determinants.}, number={3}, journal={ANTIBIOTICS-BASEL}, publisher={MDPI AG}, author={Parsons, Cameron and Brown, Phillip and Kathariou, Sophia}, editor={Brown, PhillipEditor}, year={2021}, month={Mar} }
 @misc{parsons_lee_kathariou_2020, title={Dissemination and conservation of cadmium and arsenic resistance determinants in Listeria and other Gram-positive bacteria}, volume={113}, ISSN={["1365-2958"]}, DOI={10.1111/mmi.14470}, abstractNote={Metal homeostasis in bacteria is a complex and delicate balance. While some metals such as iron and copper are essential for cellular functions, others such as cadmium and arsenic are inherently cytotoxic. While bacteria regularly encounter essential metals, exposure to high levels of toxic metals such as cadmium and arsenic is only experienced in a handful of special habitats. Nonetheless, Listeria and other Gram‐positive bacteria have evolved an impressively diverse array of genetic tools for acquiring enhanced tolerance to such metals. Here, we summarize this fascinating collection of resistance determinants in Listeria, with special focus on resistance to cadmium and arsenic, as well as to biocides and antibiotics. We also provide a comparative description of such resistance determinants and adaptations in other Gram‐positive bacteria. The complex coselection of heavy metal resistance and other types of resistance seems to be universal across the Gram‐positive bacteria, while the type of coselected traits reflects the lifestyle of the specific microbe. The roles of heavy metal resistance genes in environmental adaptation and virulence appear to vary by genus, highlighting the need for further functional studies to explain the mystery behind the array of heavy metal resistance determinants dispersed and maintained among Gram‐positive bacteria.}, number={3}, journal={MOLECULAR MICROBIOLOGY}, author={Parsons, Cameron and Lee, Sangmi and Kathariou, Sophia}, year={2020}, month={Mar}, pages={560–569} }
 @article{parsons_niedermeyer_gould_brown_strules_parsons_bernardo mesa‐cruz_kelly_hooker_chamberlain_et al._2020, title={Listeria monocytogenes
            at the human–wildlife interface: black bears (
            Ursus americanus
            ) as potential vehicles for
            Listeria}, volume={13}, ISBN={1751-7915}, ISSN={1751-7915 1751-7915}, url={http://dx.doi.org/10.1111/1751-7915.13509}, DOI={10.1111/1751-7915.13509}, abstractNote={Listeria monocytogenes is the causative agent of the foodborne illness listeriosis, which can result in severe symptoms and death in susceptible humans and other animals. L. monocytogenes is ubiquitous in the environment and isolates from food and food processing, and clinical sources have been extensively characterized. However, limited information is available on L. monocytogenes from wildlife, especially from urban or suburban settings. As urban and suburban areas are expanding worldwide, humans are increasingly encroaching into wildlife habitats, enhancing the frequency of human–wildlife contacts and associated pathogen transfer events. We investigated the prevalence and characteristics of L. monocytogenes in 231 wild black bear capture events between 2014 and 2017 in urban and suburban sites in North Carolina, Georgia, Virginia and United States, with samples derived from 183 different bears. Of the 231 captures, 105 (45%) yielded L. monocytogenes either alone or together with other Listeria. Analysis of 501 samples, primarily faeces, rectal and nasal swabs for Listeria spp., yielded 777 isolates, of which 537 (70%) were L. monocytogenes. Most L. monocytogenes isolates exhibited serotypes commonly associated with human disease: serotype 1/2a or 3a (57%), followed by the serotype 4b complex (33%). Interestingly, approximately 50% of the serotype 4b isolates had the IVb‐v1 profile, associated with emerging clones of L. monocytogenes. Thus, black bears may serve as novel vehicles for L. monocytogenes, including potentially emerging clones. Our results have significant public health implications as they suggest that the ursine host may preferentially select for L. monocytogenes of clinically relevant lineages over the diverse listerial populations in the environment. These findings also help to elucidate the ecology of L. monocytogenes and highlight the public health significance of the human–wildlife interface.}, number={3}, journal={Microbial Biotechnology}, publisher={Wiley}, author={Parsons, Cameron and Niedermeyer, Jeff and Gould, Nicholas and Brown, Phillip and Strules, Jennifer and Parsons, Arielle W. and Bernardo Mesa‐Cruz, J. and Kelly, Marcella J. and Hooker, Michael J. and Chamberlain, Michael J. and et al.}, editor={Brown, PhillipEditor}, year={2020}, month={May}, pages={706–721} }
 @article{parsons_chen_niedermeyer_hernandez_kathariou_2019, title={Draft Genome Sequence of Multidrug-Resistant Listeria innocua Strain UAM003-1A, Isolated from a Wild Black Bear (Ursus americanus)}, volume={8}, ISSN={["2576-098X"]}, DOI={10.1128/MRA.01281-19}, abstractNote={There is currently limited knowledge of the genome sequences of nonpathogenic Listeria species, especially strains from wildlife. Here, we report the draft genome sequence and associated genome information of an antibiotic-resistant Listeria innocua strain, UAM003-1A, isolated from the feces of a black bear in California, USA. ABSTRACT There is currently limited knowledge of the genome sequences of nonpathogenic Listeria species, especially strains from wildlife. Here, we report the draft genome sequence and associated genome information of an antibiotic-resistant Listeria innocua strain, UAM003-1A, isolated from the feces of a black bear in California, USA.}, number={47}, journal={MICROBIOLOGY RESOURCE ANNOUNCEMENTS}, author={Parsons, Cameron and Chen, Yi and Niedermeyer, Jeffrey and Hernandez, Kevin and Kathariou, Sophia}, year={2019}, month={Nov} }
 @misc{parsons_lee_kathariou_2019, title={Heavy Metal Resistance Determinants of the Foodborne Pathogen Listeria monocytogenes}, volume={10}, ISSN={["2073-4425"]}, DOI={10.3390/genes10010011}, abstractNote={Listeria monocytogenes is ubiquitous in the environment and causes the disease listeriosis. Metal homeostasis is one of the key processes utilized by L. monocytogenes in its role as either a saprophyte or pathogen. In the environment, as well as within an animal host, L. monocytogenes needs to both acquire essential metals and mitigate toxic levels of metals. While the mechanisms associated with acquisition and detoxification of essential metals such as copper, iron, and zinc have been extensively studied and recently reviewed, a review of the mechanisms associated with non-essential heavy metals such as arsenic and cadmium is lacking. Resistance to both cadmium and arsenic is frequently encountered in L. monocytogenes, including isolates from human listeriosis. In addition, a growing body of work indicates the association of these determinants with other cellular functions such as virulence, suggesting the importance of further study in this area.}, number={1}, journal={GENES}, author={Parsons, Cameron and Lee, Sangmi and Kathariou, Sophia}, year={2019}, month={Jan} }
 @article{sai_parsons_house_kathariou_ninomiya-tsuji_2019, title={Necroptosis mediators RIPK3 and MLKL suppress intracellular Listeria replication independently of host cell killing}, volume={218}, ISSN={["1540-8140"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85067213651&partnerID=MN8TOARS}, DOI={10.1083/jcb.201810014}, abstractNote={The RIPK3-MLKL pathway protects epithelial cells from Listeria monocytogenes invasion. Sai et al. find that Listeria infection activates MLKL but does not induce its oligomerization or necroptotic cell death. Instead, Listeria-activated MLKL directly targets intracellular bacteria and suppresses their replication.}, number={6}, journal={JOURNAL OF CELL BIOLOGY}, publisher={Rockefeller University Press}, author={Sai, Kazuhito and Parsons, Cameron and House, John S. and Kathariou, Sophia and Ninomiya-Tsuji, Jun}, year={2019}, month={Jun}, pages={1994–2005} }
 @article{parsons_jahanafroozi_kathariou_2019, title={Requirement of lmo1930, a Gene in the Menaquinone Biosynthesis Operon, for Esculin Hydrolysis and Lithium Chloride Tolerance in Listeria monocytogenes}, volume={7}, ISSN={["2076-2607"]}, DOI={10.3390/microorganisms7110539}, abstractNote={Listeria monocytogenes is a foodborne pathogen that is widely distributed in nature, having been isolated from a variety of sources such as soil, water, plant matter, and animals. In addition, L. monocytogenes is often detected in the regular sampling of food and food processing environments. The most common method for detecting L. monocytogenes is the use of selective enrichments. Both lithium chloride and esculin, in combination with ferric ammonium citrate, are utilized in several of the most commonly-employed selective enrichment schemes for L. monocytogenes. Here we report that transposon-based inactivation of lmo1930, one of the genes in the menaquinone biosynthesis operon, via transposon mutagenesis severely impaired the ability of L. monocytogenes to grow in the presence of lithium chloride or hydrolyze esculin, and conferred reduced growth and colony size. All phenotypes were restored upon genetic complementation. Thus, strains of L. monocytogenes with mutations leading to inactivation of lmo1930 may evade many commonly-used selective enrichment protocols employed in the detection of L. monocytogenes.}, number={11}, journal={MICROORGANISMS}, author={Parsons, Cameron and Jahanafroozi, Midya and Kathariou, Sophia}, year={2019}, month={Nov} }
 @article{jayeola_parsons_gorski_kathariou_2019, title={Validation of an ampicillin selection protocol to enrich for mutants of Listeria monocytogenes unable to replicate on fresh produce}, volume={366}, ISSN={["1574-6968"]}, DOI={10.1093/femsle/fnz076}, abstractNote={Several outbreaks of listeriosis have implicated fresh produce but genetic factors required for growth of Listeria monocytogenes on produce remain poorly characterized. Based on the fact that β-lactam antibiotics only kill bacterial cells that are growing, we hypothesized that ampicillin selection can enrich for L. monocytogenes mutants unable to grow on produce. For validation, we examined relative recovery of L. monocytogenes strain 2011L-2858 and its cold-sensitive mutant L1E4 following inoculation of cantaloupe rind fragments with 1:1 mixture of the strains and incubation at 4°C with or without ampicillin. Listeria monocytogenes from rind fragments inoculated with the mixed cultures and incubated in the presence of ampicillin were used to inoculate fresh rind fragments for a second round of enrichment. In the presence of ampicillin, the proportion of L1E4 increased from 55% on day 0 to 78% on day 14, with higher recovery (85% after 14 days) in the second round of enrichment. These data suggested that L1E4 was enriched on cantaloupe rind fragments while growing cells of the wildtype were killed by ampicillin. Application of this protocol to transposon mutant libraries from three L. monocytogenes strains yielded several mutants unable to grow on cantaloupe. Thus, ampicillin selection can facilitate discovery of genes essential for growth of L. monocytogenes on fresh produce.}, number={7}, journal={FEMS MICROBIOLOGY LETTERS}, author={Jayeola, Victor and Parsons, C. and Gorski, L. and Kathariou, S.}, year={2019}, month={Apr} }
 @article{price_parsons_kathariou_2018, title={RNA Helicase Mediates Competitive Fitness of Listeria monocytogenes on the Surface of Cantaloupe}, volume={4}, ISSN={["2311-7524"]}, DOI={10.3390/horticulturae4040040}, abstractNote={Listeria monocytogenes is a foodborne pathogen that is implicated in numerous outbreaks of disease (listeriosis) via fresh produce. The genetic features of L. monocytogenes that allow adherence and growth on produce remain largely uncharacterized. In this study, two non-motile transposon mutants were characterized for attachment, growth, and survival on the surface of cantaloupe rind. One of the mutants, L1E4, harbored a single transposon insertion in a DEAD-box RNA helicase gene (lmo0866 homolog), while the other, M1A5, harbored an insertion in a gene from a flagellum biosynthesis and chemotaxis gene cluster (lmo0694 homolog). When inoculated alone, neither mutant was significantly impaired in growth or survival on the surface of cantaloupe at either 25 or 37 °C. However, when co-inoculated with the wildtype parental strain, the RNA helicase mutant L1E4 had a clear competitive disadvantage, while the relative fitness of M1A5 was not noticeably impacted. Genetic complementation of L1E4 with the intact RNA helicase gene restored relative fitness on cantaloupe. The findings suggest that the DEAD-box RNA helicase encoded by the lmo0866 homolog is critical for relative fitness of L. monocytogenes on cantaloupe. Mutant L1E4 was pleiotropic, being not only non-motile but also cold-sensitive and with reduced hemolytic activity, warranting further studies to elucidate the role of this helicase in the competitive fitness of L. monocytogenes on produce.}, number={4}, journal={HORTICULTURAE}, author={Price, Robert and Parsons, Cameron and Kathariou, Sophia}, year={2018}, month={Dec} }
 @article{parsons_lee_jayeola_kathariou_2017, title={Novel Cadmium Resistance Determinant in Listeria monocytogenes}, volume={83}, ISSN={["1098-5336"]}, DOI={10.1128/aem.02580-16}, abstractNote={ABSTRACT Listeria monocytogenes is a foodborne pathogen that can cause severe disease (listeriosis) in susceptible individuals. It is ubiquitous in the environment and often exhibits resistance to heavy metals. One of the determinants that enables Listeria to tolerate exposure to cadmium is the cadAC efflux system, with CadA being a P-type ATPase. Three different cadA genes (designated cadA1 to cadA3) were previously characterized in L. monocytogenes. A novel putative cadmium resistance gene (cadA4) was recently identified through whole-genome sequencing, but experimental confirmation for its involvement in cadmium resistance is lacking. In this study, we characterized cadA4 in L. monocytogenes strain F8027, a cadmium-resistant strain of serotype 4b. By screening a mariner-based transposon library of this strain, we identified a mutant with reduced tolerance to cadmium and that harbored a single transposon insertion in cadA4. The tolerance to cadmium was restored by genetic complementation with the cadmium resistance cassette (cadA4C), and enhanced cadmium tolerance was conferred to two unrelated cadmium-sensitive strains via heterologous complementation with cadA4C. Cadmium exposure induced cadA4 expression, even at noninhibitory levels. Virulence assessments in the Galleria mellonella model suggested that a functional cadA4 suppressed virulence, potentially promoting commensal colonization of the insect larvae. Biofilm assays suggested that cadA4 inactivation reduced biofilm formation. These data not only confirm cadA4 as a novel cadmium resistance determinant in L. monocytogenes but also provide evidence for roles in virulence and biofilm formation. IMPORTANCE Listeria monocytogenes is an intracellular foodborne pathogen causing the disease listeriosis, which is responsible for numerous hospitalizations and deaths every year. Among the adaptations that enable the survival of Listeria in the environment are the abilities to persist in biofilms, grow in the cold, and tolerate toxic compounds, such as heavy metals. Here, we characterized a novel determinant that was recently identified on a larger mobile genetic island through whole-genome sequencing. This gene (cadA4) was found to be responsible for cadmium detoxification and to be a divergent member of the Cad family of cadmium efflux pumps. Virulence assessments in a Galleria mellonella model suggested that cadA4 may suppress virulence. Additionally, cadA4 may be involved in the ability of Listeria to form biofilms. Beyond the role in cadmium detoxification, the involvement of cadA4 in other cellular functions potentially explains its retention and wide distribution in L. monocytogenes.}, number={5}, journal={APPLIED AND ENVIRONMENTAL MICROBIOLOGY}, author={Parsons, Cameron and Lee, Sangmi and Jayeola, Victor and Kathariou, Sophia}, year={2017}, month={Mar} }
 @article{parsons_costolo_brown_kathariou_2017, title={Penicillin-binding protein encoded by pbp4 is involved in mediating copper stress in Listeria monocytogenes}, volume={364}, ISSN={["1574-6968"]}, url={http://dx.doi.org/10.1093/femsle/fnx207}, DOI={10.1093/femsle/fnx207}, abstractNote={ABSTRACT Listeria monocytogenes raises major food safety and public health concerns due to its potential for severe foodborne disease and persistent colonization of food processing facilities. Copper is often employed to control pathogens in agriculture and is increasingly used in healthcare facilities, but mechanisms mediating tolerance of L. monocytogenes to copper remain poorly understood. A mariner‐based mutant library of L. monocytogenes 2011L‐2858, implicated in the 2011 listeriosis outbreak via whole cantaloupe, was screened for growth at sublethal levels of copper yielding mutant G2B4 with decreased copper tolerance. The transposon was localized in pbp4 (lmo2229 homolog), encoding a penicillin‐binding protein (PBP). In addition to reduced copper tolerance, G2B4 exhibited increased susceptibility to &bgr;‐lactam antibiotics, reduced biofilm formation and reduced virulence in the Galleria mellonella model. Mutant phenotypes were fully restored upon genetic complementation of G2B4 with intact pbp4. Findings provide the first evidence for the role of a PBP in copper tolerance of L. monocytogenes and suggest that pbp4 may be a suitable target to enable the use of lower levels of copper or enhance the effectiveness of levels currently in use. Given the wide distribution of PBPs and their highly conserved nature, this could have profound impacts in regard to ecology and control of L. monocytogenes and other microorganisms.}, number={20}, journal={FEMS MICROBIOLOGY LETTERS}, publisher={Oxford University Press (OUP)}, author={Parsons, Cameron and Costolo, Ben and Brown, Phillip and Kathariou, Sophia}, editor={Brown, PhillipEditor}, year={2017}, month={Oct} }
 @article{lee_ward_jima_parsons_kathariou_2017, title={The Arsenic Resistance-Associated Listeria Genomic Island LGI2 Exhibits Sequence and Integration Site Diversity and a Propensity for Three Listeria monocytogenes Clones with Enhanced Virulence}, volume={83}, ISSN={["1098-5336"]}, DOI={10.1128/aem.01189-17}, abstractNote={ABSTRACT In the foodborne pathogen Listeria monocytogenes, arsenic resistance is encountered primarily in serotype 4b clones considered to have enhanced virulence and is associated with an arsenic resistance gene cluster within a 35-kb chromosomal region, Listeria genomic island 2 (LGI2). LGI2 was first identified in strain Scott A and includes genes putatively involved in arsenic and cadmium resistance, DNA integration, conjugation, and pathogenicity. However, the genomic localization and sequence content of LGI2 remain poorly characterized. Here we investigated 85 arsenic-resistant L. monocytogenes strains, mostly of serotype 4b. All but one of the 70 serotype 4b strains belonged to clonal complex 1 (CC1), CC2, and CC4, three major clones associated with enhanced virulence. PCR analysis suggested that 53 strains (62.4%) harbored an island highly similar to LGI2 of Scott A, frequently (42/53) in the same location as Scott A (LMOf2365_2257 homolog). Random-primed PCR and whole-genome sequencing revealed seven novel insertion sites, mostly internal to chromosomal coding sequences, among strains harboring LGI2 outside the LMOf2365_2257 homolog. Interestingly, many CC1 strains harbored a noticeably diversified LGI2 (LGI2-1) in a unique location (LMOf2365_0902 homolog) and with a novel additional gene. With few exceptions, the tested LGI2 genes were not detected in arsenic-resistant strains of serogroup 1/2, which instead often harbored a Tn554-associated arsenic resistance determinant not encountered in serotype 4b. These findings indicate that in L. monocytogenes, LGI2 has a propensity for certain serotype 4b clones, exhibits content diversity, and is highly promiscuous, suggesting an ability to mobilize various accessory genes into diverse chromosomal loci. IMPORTANCE Listeria monocytogenes is widely distributed in the environment and causes listeriosis, a foodborne disease with high mortality and morbidity. Arsenic and other heavy metals can powerfully shape the populations of human pathogens with pronounced environmental lifestyles such as L. monocytogenes. Arsenic resistance is encountered primarily in certain serotype 4b clones considered to have enhanced virulence and is associated with a large chromosomal island, Listeria genomic island 2 (LGI2). LGI2 also harbors a cadmium resistance cassette and genes putatively involved in DNA integration, conjugation, and pathogenicity. Our findings indicate that LGI2 exhibits pronounced content plasticity and is capable of transferring various accessory genes into diverse chromosomal locations. LGI2 may serve as a paradigm on how exposure to a potent environmental toxicant such as arsenic may have dynamically selected for arsenic-resistant subpopulations in certain clones of L. monocytogenes which also contribute significantly to disease.}, number={21}, journal={APPLIED AND ENVIRONMENTAL MICROBIOLOGY}, author={Lee, Sangmi and Ward, Todd J. and Jima, Dereje D. and Parsons, Cameron and Kathariou, Sophia}, year={2017}, month={Nov} }
 @article{palerme_pan_parsons_kathariou_ward_jacob_2016, title={Isolation and characterization of atypical Listeria monocytogenes associated with a canine urinary tract infection}, volume={28}, ISSN={1040-6387 1943-4936}, url={http://dx.doi.org/10.1177/1040638716661381}, DOI={10.1177/1040638716661381}, abstractNote={Listeria monocytogenes, a well-described cause of encephalitis and abortion in ruminants and of food-borne illness in humans, is rarely associated with disease in companion animals. A case of urinary tract infection associated with an atypical, weakly hemolytic L. monocytogenes strain is described in a diabetic dog. The serotype of the L. monocytogenes isolate was determined to be 1/2a (3a), with the multilocus genotyping pattern 2.72_1/2a. A nucleotide substitution (Gly145Asp) was detected at residue 145 in the promoter prfA region. This residue is within the critical helix-turn-helix motif of PrfA. The source of the L. monocytogenes strain remains unknown, and the dog recovered after a 4-week course of cephalexin (30 mg/kg orally twice daily).}, number={5}, journal={Journal of Veterinary Diagnostic Investigation}, publisher={SAGE Publications}, author={Palerme, Jean-Sébastien and Pan, Po Ching and Parsons, Cameron T. and Kathariou, Sophia and Ward, Todd J. and Jacob, Megan E.}, year={2016}, month={Aug}, pages={604–607} }
 @article{pritchard_jacob_ward_parsons_kathariou_wood_2016, title={Listeria monocytogenes septicemia in an immunocompromised dog}, volume={45}, ISSN={["1939-165X"]}, DOI={10.1111/vcp.12363}, abstractNote={An 11-year-old, male castrated, Boston Terrier was presented to the North Carolina State University College of Veterinary Medicine Small Animal Emergency Service with a 2-day history of progressive ataxia, left-sided head tilt, and anorexia. The dog had previously been diagnosed with chronic lymphoid leukemia and suspected immune-mediated destruction of his bone marrow precursor cells, possibly due to therapy with immunosuppressive dosages of prednisone and azathioprine. During the physical examination, abnormal findings included an increased body temperature and horizontal nystagmus. Diagnostic investigations included a computed tomography (CT) scan, which confirmed bilateral otitis media, and a blood culture, which was positive for Listeria monocytogenes serotype 4b (epidemic clone 1). Upon treatment with ampicillin/sulbactam, enrofloxacin, and minocycline, the dog became normothermic and the neurologic signs improved. L monocytogenes serotype 4b (epidemic clone 1) has been associated with outbreaks of human listeriosis originating from food contamination. Although rare case reports of Listeria spp. infection in dogs exist, an actual infection with the epidemic clone 1 strain has never before been reported in a dog. It should be included in the differential diagnoses in immunocompromised dogs with clinical signs of septicemia.}, number={2}, journal={VETERINARY CLINICAL PATHOLOGY}, author={Pritchard, Jessica C. and Jacob, Megan E. and Ward, Todd J. and Parsons, Cameron T. and Kathariou, Sophia and Wood, Michael W.}, year={2016}, month={Jun}, pages={254–259} }