Evidence of Metabolic Switching and Implications for Food Safety from the Phenome(s) of Salmonella enterica Serovar Typhimurium DT104 Cultured at Selected Points across the Pork Production Food Chain

Abstract

b Salmonella enterica serovar Typhimurium DT104 is a recognized food-borne pathogen that displays a multidrug-resistant phenotype and that is associated with systemic infections. At one extreme of the food chain, this bacterium can infect humans, limiting the treatment options available and thereby contributing to increased morbidity and mortality. Although the antibiotic resistance profile is well defined, little is known about other phenotypes that may be expressed by this pathogen at key points across the pork production food chain. In this study, 172 Salmonella enterica serovar Typhimurium DT104/DT104b isolated from an extensive "farm-to-fork" surveillance study, focusing on the pork food chain, were characterized in detail. Isolates were cultured from environmental, processing, retail, and clinical sources, and the study focused on phenotypes that may have contributed to persistence/survival in these different niches. Molecular subtypes, along with antibiotic resistance profiles, tolerance to biocides, motility, and biofilm formation, were determined. As a basis for human infection, acid survival and the ability to utilize a range of energy sources and to adhere to and/or invade Caco-2 cells were also studied. Comparative alterations to biocide tolerance were observed in isolates from retail. L-Tartaric acid and D-mannose-1-phosphate induced the formation of biofilms in a preselected subset of strains, independent of their origin. All clinical isolates were motile and demonstrated an enhanced ability to survive in acidic conditions. Our data report on a diverse phenotype, expressed by S. Typhimurium isolates cultured from the pork production food chain. Extending our understanding of the means by which this pathogen adapts to environmental niches along the "farm-to-fork" continuum will facilitate the protection of vulnerable consumers through targeted improvements in food safety measures.

Comparative Genotypic and Phenotypic Analysis of Cronobacter Species Cultured from Four Powdered Infant Formula Production Facilities: Indication of Pathoadaptation along the Food Chain

“…Cronobacter species are by definition a motile genus; nonetheless, few studies have explored this phenotype in a collection of isolates cultured from the PIF production environment. Salmonella Typhimurium DT104 13348 was included for comparison purposes, as it demonstrated a suitable swim and swarm phenotype (39,40). After 8 h of incubation at 37°C, 34 isolates (20.2%) were observed to have an increased swim phenotype, with 1 (0.6%) exhibiting no change in its swimming ability and 133 oth- ers (79.2%) displaying reduced swim activity compared to the reference strain ( Fig.…”

“…This was investigated by incubating bacterial cultures in M9 minimal medium at 28 and 37°C in standard microtiter plates (see Table S1 in the supplemental material). Salmonella Typhimurium ATCC 14028, a strong biofilm-forming strain (39), was included as the positive control. When incubated at 28°C, the formation of a strong biofilm was observed with 115 isolates (68.5%), whereas 35 isolates (20.8%) were defined as moderate biofilm formers and 18 isolates (10.7%) demonstrated weak biofilm formation.…”

“…The formed biofilm was then dissolved with 200 l of 33% (vol/vol) acetic acid for 30 min. The biofilm formed was then measured at an optical density of 570 nm in a microtiter plate reader (Tecan, Männedorf, Switzerland) and analyzed as described previously (39). Salmonella Typhimurium ATCC 14028, a strong biofilm-forming strain, was selected as the positive control for the biofilm formation assays.…”

“…Swim and swarm assays were performed with all 168 isolates as described previously (39). Briefly, agar plates were freshly prepared using Luria-Bertani (LB) broth (Becton Dickinson, MD, USA) supplemented with 0.3% (wt/vol) agar (Sigma-Aldrich, Gillingham, United Kingdom) for the swim assay or with 0.6% (wt/vol) agar along with 0.5% (wt/vol) glucose for the swarm assay.…”

AtypicalSalmonella entericaserovars in murine and human infection models: Is it time to reassess our approach to the study of salmonellosis?

“…The ability to survive in a low pH culture medium was assessed for all isolates as described previously 52 . Briefly, bacterial cultures were individually grown overnight (18 hours) without shaking in 5 mL buffered MH broth (MES hydrate, 2 % [w/v], pH 5) containing 0.4 % [w/v] glucose at 37 °C.…”