@article{martinez_osborne_jayeola_katic_kathariou_2016, title={Capacity of Listeria monocytogenes Strains from the 2011 Cantaloupe Outbreak To Adhere, Survive, and Grow on Cantaloupe}, volume={79}, ISSN={["1944-9097"]}, DOI={10.4315/0362-028x.jfp-15-498}, abstractNote={The 2011 listeriosis outbreak attributed to whole cantaloupe involved several genetically distinct strains of serotypes 1/2a and 1/2b that had not been previously reported in invasive listeriosis outbreaks. Here we investigated the potential of strains from the 2011 cantaloupe outbreak to adhere, survive, and grow on cantaloupe rind and flesh and in juice extracted from cantaloupe at different temperatures (4, 8, and 25°C). All strains were able to adhere and grow, with ∼10-fold increases after 7 days at 4 or 8°C and after 24 h at 25°C, with a propensity for more growth on rind than on flesh or in extract. No significant differences in growth potential were noted among the different strains or between them and unrelated strains from other listeriosis outbreaks involving celery, deli meats, or hot dogs. Similarly to the cantaloupe outbreak strains, these other strains exhibited greater propensity for growth on rind than on flesh or in extract. Rinsing of cantaloupe fragments in sterile water resulted in temporary reductions of the populations by 50- to 100-fold, suggesting the potential of such washing to reduce risk if the produce is promptly consumed. The absence of marked differences in adherence or growth between the cantaloupe outbreak strains and strains from other outbreaks highlights the need to further characterize the 2011 cantaloupe outbreak strains and elucidate potential biological attributes that contributed to their implication in the outbreak.}, number={5}, journal={JOURNAL OF FOOD PROTECTION}, author={Martinez, Mira Rakic and Osborne, Jason and Jayeola, Victor Oladimeji and Katic, Vera and Kathariou, Sophia}, year={2016}, month={May}, pages={757–763} } @article{dutta_elhanafi_osborne_martinez_kathariou_2014, title={Genetic Characterization of Plasmid-Associated Triphenylmethane Reductase in Listeria monocytogenes}, volume={80}, ISSN={["1098-5336"]}, DOI={10.1128/aem.01398-14}, abstractNote={ABSTRACT The enzyme triphenylmethane reductase (TMR) reduces toxic triphenylmethane dyes into colorless, nontoxic derivatives, and TMR-producing microorganisms have been proposed as bioremediation tools. Analysis of the genome of Listeria monocytogenes H7858 (1998-1999 hot dog outbreak) revealed that the plasmid (pLM80) of this strain harboring a gene cassette ( bcrABC ) conferring resistance to benzalkonium chloride (BC) and other quaternary ammonium disinfectants also harbored a gene ( tmr ) highly homologous to TMR-encoding genes from diverse Gram-negative bacteria. The pLM80-associated tmr was located two genes downstream of bcrABC as part of a putative IS 1216 composite transposon. To confirm the role of tmr in triphenylmethane dye detoxification, we introduced various tmr -harboring fragments of pLM80 in a pLM80-cured derivative of strain H7550, from the same outbreak as H7858, and assessed the resistance of the constructs to the triphenylmethane dyes crystal violet (CV) and malachite green. Transcriptional and subcloning data suggest that the regulation of TMR is complex. Constructs harboring fragments spanning bcrABC and tmr were CV resistant, and in such constructs tmr transcription was induced by sublethal levels of either BC or CV. However, constructs harboring only tmr and its upstream intergenic region could also confer resistance to CV, albeit at lower levels. Screening a panel of BC-resistant L. monocytogenes strains revealed that all those harboring bcrABC and adjacent pLM80 sequences, including tmr , were resistant to CV and decolorized this dye. The findings suggest a potential role of TMR as a previously unknown adaptive attribute for environmental persistence of L. monocytogenes . }, number={17}, journal={APPLIED AND ENVIRONMENTAL MICROBIOLOGY}, author={Dutta, Vikrant and Elhanafi, Driss and Osborne, Jason and Martinez, Mira Rakic and Kathariou, Sophia}, year={2014}, month={Sep}, pages={5379–5385} } @article{lee_rakic-martinez_graves_ward_siletzky_kathariou_2013, title={Genetic Determinants for Cadmium and Arsenic Resistance among Listeria monocytogenes Serotype 4b Isolates from Sporadic Human Listeriosis Patients}, volume={79}, ISSN={["1098-5336"]}, DOI={10.1128/aem.03551-12}, abstractNote={ABSTRACT In Listeria monocytogenes serotype 4b isolates from sporadic listeriosis, heavy metal resistance was primarily encountered in certain clonal groups (ECI, ECII, and ECIa). All arsenic-resistant isolates harbored the arsenic resistance cassette previously identified in pLI100; ECIa harbored additional arsenic resistance genes and a novel cadmium resistance determinant in a conserved chromosomal locus. }, number={7}, journal={APPLIED AND ENVIRONMENTAL MICROBIOLOGY}, author={Lee, Sangmi and Rakic-Martinez, M. and Graves, L. M. and Ward, T. J. and Siletzky, R. M. and Kathariou, S.}, year={2013}, month={Apr}, pages={2471–2476} } @article{katharios-lanwermeyer_rakic-martinez_elhanafi_ratani_tiedje_kathariou_2012, title={Coselection of Cadmium and Benzalkonium Chloride Resistance in Conjugative Transfers from Nonpathogenic Listeria spp. to Other Listeriae}, volume={78}, ISSN={["0099-2240"]}, DOI={10.1128/aem.02245-12}, abstractNote={ABSTRACT Resistance to the quaternary ammonium disinfectant benzalkonium chloride (BC) may be an important contributor to the ability of Listeria spp. to persist in the processing plant environment. Although a plasmid-borne disinfectant resistance cassette ( bcrABC ) has been identified in Listeria monocytogenes , horizontal transfer of these genes has not been characterized. Nonpathogenic Listeria spp. such as L. innocua and L. welshimeri are more common than L. monocytogenes in food processing environments and may contribute to the dissemination of disinfectant resistance genes in listeriae, including L. monocytogenes . In this study, we investigated conjugative transfer of resistance to BC and to cadmium from nonpathogenic Listeria spp. to other nonpathogenic listeriae, as well as to L. monocytogenes . BC-resistant L. welshimeri and L. innocua harboring bcrABC , along with the cadmium resistance determinant cadA2 , were able to transfer resistance to other nonpathogenic listeriae as well as to L. monocytogenes of diverse serotypes, including strains from the 2011 cantaloupe outbreak. Transfer among nonpathogenic Listeria spp. was noticeably higher at 25°C than at 37°C, whereas acquisition of resistance by L. monocytogenes was equally efficient at 25 and 37°C. When the nonpathogenic donors were resistant to both BC and cadmium, acquisition of cadmium resistance was an effective surrogate for transfer of resistance to BC, suggesting coselection between these resistance attributes. The results suggest that nonpathogenic Listeria spp. may behave as reservoirs for disinfectant and heavy metal resistance genes for other listeriae, including the pathogenic species L. monocytogenes . }, number={21}, journal={APPLIED AND ENVIRONMENTAL MICROBIOLOGY}, author={Katharios-Lanwermeyer, S. and Rakic-Martinez, M. and Elhanafi, D. and Ratani, S. and Tiedje, J. M. and Kathariou, S.}, year={2012}, month={Nov}, pages={7549–7556} } @article{rakic-martinez_drevets_dutta_katic_kathariou_2011, title={Listeria monocytogenes Strains Selected on Ciprofloxacin or the Disinfectant Benzalkonium Chloride Exhibit Reduced Susceptibility to Ciprofloxacin, Gentamicin, Benzalkonium Chloride, and Other Toxic Compounds}, volume={77}, ISSN={["1098-5336"]}, DOI={10.1128/aem.05941-11}, abstractNote={ABSTRACT Listeria monocytogenes is a leading agent for severe food-borne illness and death in the United States and other nations. Even though drug resistance has not yet threatened therapeutic interventions for listeriosis, selective pressure associated with exposure to antibiotics and disinfectants may result in reduced susceptibility to these agents. In this study, selection of several L. monocytogenes strains on either ciprofloxacin (2 μg/ml) or the quaternary ammonium disinfectant benzalkonium chloride (BC; 10 μg/ml) led to derivatives with increased MICs not only to these agents but also to several other toxic compounds, including gentamicin, the dye ethidium bromide, and the chemotherapeutic drug tetraphenylphosphonium chloride. The spectrum of compounds to which these derivatives exhibited reduced susceptibility was the same regardless of whether they were selected on ciprofloxacin or on BC. Inclusion of strains harboring the large plasmid pLM80 revealed that MICs to ciprofloxacin and gentamicin did not differ between the parental and plasmid-cured strains. However, ciprofloxacin-selected derivatives of pLM80-harboring strains had higher MICs than those derived from the plasmid-cured strains. Susceptibility to the antimicrobials was partially restored in the presence of the potent efflux inhibitor reserpine. Taken together, these data suggest that mutations in efflux systems are responsible for the multidrug resistance phenotype of strains selected on ciprofloxacin or BC. }, number={24}, journal={APPLIED AND ENVIRONMENTAL MICROBIOLOGY}, author={Rakic-Martinez, Mira and Drevets, Douglas A. and Dutta, Vikrant and Katic, Vera and Kathariou, Sophia}, year={2011}, month={Dec}, pages={8714–8721} }