Biology subjects

Etter, A. J.

Publications and source records attributed to Etter, A. J..

3 recordsLinked to original sources

bioRxiv2025

Stress tolerance of multiple Salmonella enterica strains associated with foodborne outbreaks

Salmonella enterica is a foodborne pathogen commonly found in food processing environments. While control methods such as heat treatment and sanitizers are often used, S. enterica has evolved strategies for survival and persistence to overcome pathogen control. This study assessed 43 outbreak-associated (OA) and non-outbreak associated (NOA) S. enterica isolates from serovars Enteritidis, Heidelberg, Newport, Typhimurium, and monophasic Typhimurium (I 4,[5],12:i:-) for enhanced stress tolerance. Heat shock at 56{degrees} C, minimum inhibitory concentrations (MICs) for sanitizers sodium hypochlorite (NaOCl) and peracetic acid (PAA), and crystal violet microtiter assays were used to evaluate heat tolerance, sanitizer tolerance, and attachment capacity, respectively. Most isolates (n =34/43) carried at least one antimicrobial resistance gene, and nearly half (n =21/43) displayed genotypic and/or phenotypic resistance to ampicillin, ciprofloxacin, or ceftriaxone. Most isolates carried genes conferring resistance to gold (n =43/43) and arsenic (n= 41/43), and tolerance to mercury, copper, and silver was common among monophasic Typhimurium and Heidelberg isolates. Efflux pump qacEdelta1 was detected among eight Heidelberg isolates. We found enhanced stress tolerance (i.e. an unusually high ability to survive and adapt to various environmental stresses) to sanitizers and enhanced attachment capacity, indicating biofilm formation. Isolates evaluated for heat tolerance survived at least 15 min at 56{degrees} C and three survived >60 min. Overall, we found evidence of enhanced tolerance to individual stresses across both OA and NOA S. enterica. There were no strong patterns based upon serovar or OA/NOA status; however, we did find that specific enhanced stress tolerance profiles may have contributed to outbreak characteristics.

microbiology↗

bioRxiv2025

Biofilm Forming Capacity, Sanitizer Tolerance and Genetic Characterization of Persistent and Non-Persistent Listeria monocytogenes from Artisanal Cheese Processing Environments

Listeria monocytogenes is known to colonize food production environments and cross-contaminate finished foods. We investigated 30 L. monocytogenes collected from artisan cheese production facilities in Vermont from 2006-2008 for sanitizer tolerance, biofilm formation capacity, biofilm architecture, and tolerance to sanitizers of mature biofilms. Sixteen of these isolates represented a putatively persistent ribotype (DUP-1042B) found in one facility over two years. Isolates of the putatively persistent ribotype all aligned into ST191 and were 0-6 SNPs different, confirming they represented a persistent strain. We found no significant differences in sanitizer tolerance or crystal assay-based attachment capacity between persistent and non-persistent strains. However, using scanning electron microscopy, we found that isolates FML-10 and FML-19 formed substantially denser biofilms after 10 days on stainless steel. Ten-day old biofilms were highly resistant to sanitizers; neither quaternary ammonium nor sodium hypochlorite-based sanitizers achieved an EPA-recommended 6-log reduction. More EPS was found in low-nutrient biofilm conditions; thus, non-food contact surfaces in cheese environments may induce formation of biofilms with high sanitizer tolerance. Our results highlight the importance of regular environmental testing and strain typing for rapid detection of L. monocytogenes colonization attempts while they can still be removed without major renovations or equipment replacement. HighlightsO_LIIsolates from persistent ribotype DUP-1042B/ST191 were within 6 SNPs of each other C_LIO_LITwo isolates from ST191 made dense biofilms in nutrient rich conditions C_LIO_LIMore EPS was produced in nutrient-poor conditions C_LIO_LIMature biofilms of all isolates were highly resistant to QAC and SH sanitizers C_LI ImportanceThis study identifies strategies used by a set of persistently colonizing L. monocytogenes isolated from an artisanal cheese producer in Vermont, finding that some persistently colonizing isolates had high biofilm forming capacity, which may have contributed to their persistence.

microbiology↗

bioRxiv2023

Large-scale phenotypic and genomic characterization of Listeria monocytogenes susceptibility to quaternary ammonium compounds

Listeria monocytogenes is a significant concern for the food industry due to its ability to persist in the food processing environment. Decreased susceptibility to disinfectants is one of the factors that contribute to the persistence of L. monocytogenes. The objective of this study was to explore the diversity of L. monocytogenes susceptibility to quaternary ammonium compounds (QACs) using 1,671 L. monocytogenes isolates. This was used to determine the phenotype-genotype concordance and characterize genomes of the QAC sensitive and tolerant isolates for stress resistance, virulence and plasmid replicon genes. Distribution of QAC tolerance genes among 37,897 publicly available L. monocytogenes genomes were also examined. The minimum inhibitory concentration to QACs was determined by the broth microdilution method and non-sequenced isolates (n=1,244) were whole genome sequenced. Genotype-phenotype concordance was 99% for benzalkonium chloride, DDAC and a commercial QAC based sanitizer. Prevalence of QAC tolerance genes was 23% and 28% in our L. monocytogenes collection and in the global dataset, respectively. qacH was the most prevalent gene in our collection (61%), with 19% prevalence in the global dataset. Notably, bcrABC was most common (72%) globally, while 25% in our collection. Prevalence of emrC and emrE was comparable in both datasets, 7% and 2%, respectively. Replicon genes, indicative of plasmid harborage, were detected in 44% of the isolates and associated with the QAC tolerant phenotype. The presented analysis is based on the biggest L. monocytogenes collection in diversity and quantity for characterization of the L. monocytogenes QAC tolerance at both phenotypic and genomic levels. IMPORTANCEContamination of Listeria monocytogenes within the food processing environment is of concern to the food industry due to challenges in eradicating the pathogen once it becomes persistent in the environment. Genetic markers associated with increased tolerance to disinfectants have been identified, which alongside factors favor the persistence of L. monocytogenes in the production environment. By employing a comprehensive large-scale phenotypic testing and genomic analysis our study significantly enhances the understanding of the prevalence of quaternary ammonium compound (QAC) tolerant L. monocytogenes and the genetic determinants associated with the increased tolerance. Furthermore, we report on the prevalence of QAC tolerance genes among 37,897 publicly available L. monocytogenes sequences and their distribution within clonal complexes, isolation sources and geographical locations. As the propagation of QAC tolerance showed not be evenly distributed globally this highlights that understanding the development of L. monocytogenes disinfectant tolerance can be monitored using publicly available WGS data.

microbiology↗