@article{newman_bartz_johnston_moe_jaykus_leon_2017, title={Microbial Load of Fresh Produce and Paired Equipment Surfaces in Packing Facilities Near the US and Mexico Border}, volume={80}, ISSN={["1944-9097"]}, DOI={10.4315/0362-028x.jfp-16-365}, abstractNote={Several produce-associated outbreaks have been linked to the packing facility. Equipment surfaces may be an important source of contamination. The goal was to assess whether the microbial load of packing facility surfaces is associated with the microbial load of produce. From November 2000 to December 2003, 487 matched produce (14 types) and equipment surfaces (six production steps) were sampled from eight packing facilities in the United States near the border with Mexico and enumerated for aerobic plate counts (APC), Escherichia coli , Enterococcus, and coliforms. Bivariate correlations were assessed by Spearman's ρ, and adjusted associations were assessed by multilevel mixed linear regression models. In general, the microbial load both increased and decreased on produce (0.2 to 1.0 log CFU/g) and equipment surfaces (0.5 to 3.0 log CFU/cm2) across production steps. Equipment surface and produce microbial loads were correlated, but correlations varied from none to high depending on the equipment surface. For example, significant correlations (P < 0.01) included APC (ρ = 0.386) and Enterococcus (ρ = 0.562) with the harvest bin, E. coli (ρ = 0.372) and Enterococcus (ρ = 0.355) with the merry-go-round, Enterococcus (ρ = 0.679) with rinse cycle equipment, APC (ρ = 0.542) with the conveyer belt, and for all indicators with the packing box (ρ = 0.310 to 0.657). After controlling for crop type, sample replicate group, and sample location, there were significant positive associations between the log concentration of Enterococcus on produce and the harvest bin (β = 0.259, P < 0.01) and the rinse cycle (β = 0.010, P = 0.01), and between the log concentration of all indicators on produce and the packing box (β = 0.155 to 0.500, all P < 0.01). These statistically significant associations between microbial loads on packing facility surfaces and fresh produce confirm the importance of packing facility sanitation to protect produce quality and safety.}, number={4}, journal={JOURNAL OF FOOD PROTECTION}, author={Newman, Kira L. and Bartz, Faith E. and Johnston, Lynette and Moe, Christine L. and Jaykus, Lee-Ann and Leon, Juan S.}, year={2017}, month={Apr}, pages={582–589} }
 @article{ward_dhingra_remais_chang_johnston_jaykus_leon_2015, title={Associations between Weather and Microbial Load on Fresh Produce Prior to Harvest}, volume={78}, ISSN={["1944-9097"]}, DOI={10.4315/0362-028x.jfp-14-381}, abstractNote={Contaminated produce causes approximately 1 million cases of foodborne illness and 1 billion dollars in damages to the U.S. economy annually. The environmental conditions, especially weather, that influence the inoculation, proliferation, and dispersal of microbial load on produce are not well understood. Using a mixed models approach, we examined the relationship of temperature and precipitation to microbial indicators of contamination on fresh produce on the farm over a week-long period prior to harvest. Between 2000 and 2002, we assayed for four microbial indicators of contamination (aerobic plate count, Enterococcus, total coliforms, and Escherichia coli) on 10 produce types in 15 fields in the southern United States. The sample collection times varied, with most occurring between January and May. We collected hourly weather data for the corresponding time period and location. Our results indicated that there was a significant association between the average daily temperature (20°C) and both log aerobic plate count (e.g., an increase of 0.074 log CFU/g [standard error {SE}, 0.023] per °C increase in weekly average temperature) and log Enterococcus (e.g., an increase of 0.15 log CFU/g [SE, 0.031] per °C increase in weekly average temperature) for approximately 5 days prior to sample collection. Daily total precipitation was significantly associated with log coliforms on 2 days (∼0.11 log CFU/g [SE, 0.06] per mm of precipitation) during the week-long lag period prior to harvest. Our results suggest that microbial indicator concentrations may increase as the temperature increases. Precipitation may have a positive but complex relationship with microbial indicators, as precipitation may create moist conditions conducive to bacterial growth, spread contamination onto the field, or wash contamination off of the plant.}, number={4}, journal={JOURNAL OF FOOD PROTECTION}, author={Ward, Michelle and Dhingra, Radhika and Remais, Justin V. and Chang, Howard H. and Johnston, Lynette M. and Jaykus, Lee-Ann and Leon, Juan}, year={2015}, month={Apr}, pages={849–854} }
 @article{ailes_leon_jaykus_johnston_clayton_blanding_kleinbaum_backer_moe_2008, title={Microbial Concentrations on Fresh Produce Are Affected by Postharvest Processing, Importation, and Season}, volume={71}, ISSN={["1944-9097"]}, DOI={10.4315/0362-028X-71.12.2389}, abstractNote={In the United States, the proportion of foodborne illness outbreaks associated with consumption of contaminated domestic and imported fresh fruits and vegetables (produce) has increased over the past several decades. To address this public health concern, the goal of this work was to identify and quantify factors associated with microbial contamination of produce in pre- and postharvest phases of the farm-to-fork continuum. From 2000 to 2003, we collected 923 samples of 14 types of produce (grown in the southern United States or in the northern border states of Mexico) from 15 farms and eight packing sheds located in the southern United States. To assess microbial quality, samples were enumerated for Escherichia coli, total aerobic bacteria, total coliforms, and total Enterococcus. Most produce types had significantly higher microbial concentrations when sampled at the packing shed than when sampled at the farm. In addition, we observed seasonal differences in the microbial concentrations on samples grown in the United States, with higher mean indicator concentrations detected in the fall (September, October, and November). We developed a predictive, multivariate logistic regression model to identify and quantify factors that were associated with detectable concentrations of E. coli contamination on produce. These factors included produce type (specifically, cabbage or cantaloupe), season of collection (harvested in the fall), and packing step (bin, box, conveyor belt, or turntable). These results can be used to identify specific mechanisms of produce contamination and propose interventions that may decrease the likelihood of produce-associated illness.}, number={12}, journal={JOURNAL OF FOOD PROTECTION}, author={Ailes, Elizabeth C. and Leon, Juan S. and Jaykus, Lee-Ann and Johnston, Lynette M. and Clayton, Haley A. and Blanding, Sarah and Kleinbaum, David G. and Backer, Lorraine C. and Moe, Christine L.}, year={2008}, month={Dec}, pages={2389–2397} }
 @article{lin_yan_huang_altier_li_carrasco_suyemoto_johnston_wang_wang_et al._2007, title={Design and synthesis of boronic-acid-labeled thymidine triphosphate for incorporation into DNA}, volume={35}, DOI={10.1093/nar/gkl1091}, abstractNote={The boronic acid moiety is a versatile functional group useful in carbohydrate recognition, glycoprotein pull-down, inhibition of hydrolytic enzymes and boron neutron capture therapy. The incorporation of the boronic-acid group into DNA could lead to molecules of various biological functions. We have successfully synthesized a boronic acid-labeled thymidine triphosphate (B-TTP) linked through a 14-atom tether and effectively incorporated it into DNA by enzymatic polymerization. The synthesis was achieved using the Huisgen cycloaddition as the key reaction. We have demonstrated that DNA polymerase can effectively recognize the boronic acid-labeled DNA as the template for DNA polymerization, that allows PCR amplification of boronic acid-labeled DNA. DNA polymerase recognitions of the B-TTP as a substrate and the boronic acid-labeled DNA as a template are critical issues for the development of DNA-based lectin mimics via in vitro selection.}, number={4}, journal={Nucleic Acids Research}, author={Lin, N. and Yan, J. and Huang, Z. and Altier, C. and Li, M. Y. and Carrasco, N. and Suyemoto, M. and Johnston, L. and Wang, S. M. and Wang, Q. and et al.}, year={2007}, pages={1222–1229} }
 @article{johnston_jaykus_moll_martinez_anciso_mora_moe_2005, title={A field study of the microbiological quality of fresh produce}, volume={68}, ISSN={["1944-9097"]}, DOI={10.4315/0362-028X-68.9.1840}, abstractNote={The Centers for Disease Control and Prevention has reported that foodborne disease outbreaks associated with fruits and vegetables increased during the past decade. This study was conducted to characterize the routes of microbial contamination in produce and to identify areas of potential contamination from production through postharvest handling. We report here the levels of bacterial indicator organisms and the prevalence of selected pathogens in produce samples collected from the southern United States. A total of 398 produce samples (leafy greens, herbs, and cantaloupe) were collected through production and the packing shed and assayed by enumerative tests for total aerobic bacteria, total coliforms, total Enterococcus, and Escherichia coli. These samples also were analyzed for Salmonella, Listeria monocytogenes, and E. coli O157:H7. Microbiological methods were based on methods recommended by the U.S. Food and Drug Administration. For all leafy greens and herbs, geometric mean indicator levels ranged from 4.5 to 6.2 log CFU/g (aerobic plate count); less than 1 to 4.3 log CFU/g (coliforms and Enterococcus); and less than 1 to 1.5 log CFU/g (E. coli). In many cases, indicator levels remained relatively constant throughout the packing shed, particularly for mustard greens. However, for cilantro and parsley, total coliform levels increased during the packing process. For cantaloupe, microbial levels significantly increased from field through packing, with ranges of 6.4 to 7.0 log CFU/g (aerobic plate count); 2.1 to 4.3 log CFU/g (coliforms); 3.5 to 5.2 log CFU/g (Enterococcus); and less than 1 to 2.5 log CFU/g (E. coli). The prevalence of pathogens for all samples was 0, 0, and 0.7% (3 of 398) for L. monocytogenes, E. coli O157:H7, and Salmonella, respectively. This study demonstrates that each step from production to consumption may affect the microbial load of produce and reinforces government recommendations for ensuring a high-quality product.}, number={9}, journal={JOURNAL OF FOOD PROTECTION}, author={Johnston, LM and Jaykus, LA and Moll, D and Martinez, MC and Anciso, J and Mora, B and Moe, CL}, year={2005}, month={Sep}, pages={1840–1847} }
 @article{johnston_elhanafi_drake_jaykus_2005, title={A simple method for the direct detection of Salmonella and Escherichia coli O157 : H7 from raw alfalfa sprouts and spent irrigation water using PCR}, volume={68}, ISSN={["1944-9097"]}, DOI={10.4315/0362-028X-68.11.2256}, abstractNote={The U.S. Food and Drug Administration recognizes that raw seed sprouts are an important cause of foodborne disease and is now recommending that either spent irrigation water or final product be screened for Salmonella and Escherichia coli O157:H7 as a means of assuring the safety of product intended for consumption. In an effort to streamline such testing efforts, a simple method to preconcentrate pathogens from sprouts and spent irrigation water was investigated to facilitate the direct (without prior cultural enrichment) detection of pathogens using the PCR technique. Alfalfa sprouts and spent irrigation water were seeded with Salmonella enterica serovar Typhimurium and E. coli O157:H7 at 10(-1) to 106 CFU/g or CFU/ml, respectively. Samples were blended (sprouts only) and then centrifuged at high speed to sediment the total bacterial population. The precipitate was processed for DNA isolation, PCR amplification, and amplicon confirmation by Southern hybridization. Mean pathogen recoveries after centrifugation ranged from 96 to 99% for both pathogens in both matrices. Using primers targeting the invA gene for Salmonella Typhimurium and the stx genes of E. coli O157:H7, it was possible to detect both pathogens in alfalfa sprouts at seeding concentrations as low as 10 CFU/g. PCR detection limits for both pathogens from spent irrigation water were 10(-1) CFU/ml, the equivalent of 100 CFU/liter of water. Because spent irrigation water is constitutionally simple, it is particularly well suited for bacterial concentration by simple centrifugation steps. In this study, progress was made toward development of a rapid, inexpensive, and sensitive method for the detection of sprout-associated pathogens that is relevant to current industrial practices and needs.}, number={11}, journal={JOURNAL OF FOOD PROTECTION}, author={Johnston, LM and Elhanafi, D and Drake, M and Jaykus, LA}, year={2005}, month={Nov}, pages={2256–2263} }
 @article{johnston_jaykus_2004, title={Antimicrobial resistance of Enterococcus species isolated from produce}, volume={70}, ISSN={["1098-5336"]}, DOI={10.1128/AEM.70.5.3133-3137.2004}, abstractNote={ABSTRACT}, number={5}, journal={APPLIED AND ENVIRONMENTAL MICROBIOLOGY}, author={Johnston, LM and Jaykus, LA}, year={2004}, month={May}, pages={3133–3137} }