Plasmids contribute to food processing environment–associated stress survival in three Listeria monocytogenes ST121, ST8, and ST5 strains

Listeria monocytogenes is a food-borne pathogen responsible for the disease listeriosis and is commonly isolated from food and food production facilities. Many L. monocytogenes strains contain plasmids, though the contributions of plasmids to survival in food production environments is unknown. Three L. monocytogenes ST5, ST8, and ST121 strains containing plasmids, which harbor putative stress response genes, were cured of their plasmids. Wildtype (WT) and plasmid-cured strains were exposed to disinfectant, oxidative, heat, acid, or salt stress. After stress exposure, cells were plated for colony forming unit (CFU) counts to determine survivors. L. monocytogenes WT strains exposed to 0.01% (vol/vol) H2O2, 1% (vol/vol) lactic acid, and 15% (wt/vol) NaCl, pH 5 showed significantly higher counts of survivors compared to the plasmid-cured strains. The number of survivors for the ST5 WT strain exposed to 10 μg/mL benzalkonium chloride (BC) was significantly higher than in the plasmid-cured strain. The ST8 and ST5 strains were exposed to elevated temperature (50° and 55°C respectively); only the ST5 WT strain had significantly higher numbers of survivors than the plasmid-cured strains. Our data revealed that L. monocytogenes ST5, ST8, and ST121 plasmids contribute to tolerance against elevated temperature, salinity, acidic environments, oxidative stress and disinfectants

A Re-conceptualization of Access for 21st Century Healthcare

Many e-health technologies are available to promote virtual patient–provider communication outside the context of face-to-face clinical encounters. Current digital communication modalities include cell phones, smartphones, interactive voice response, text messages, e-mails, clinic-based interactive video, home-based web-cams, mobile smartphone two-way cameras, personal monitoring devices, kiosks, dashboards, personal health records, web-based portals, social networking sites, secure chat rooms, and on-line forums. Improvements in digital access could drastically diminish the geographical, temporal, and cultural access problems faced by many patients. Conversely, a growing digital divide could create greater access disparities for some populations. As the paradigm of healthcare delivery evolves towards greater reliance on non-encounter-based digital communications between patients and their care teams, it is critical that our theoretical conceptualization of access undergoes a concurrent paradigm shift to make it more relevant for the digital age. The traditional conceptualizations and indicators of access are not well adapted to measure access to health services that are delivered digitally outside the context of face-to-face encounters with providers. This paper provides an overview of digital “encounterless” utilization, discusses the weaknesses of traditional conceptual frameworks of access, presents a new access framework, provides recommendations for how to measure access in the new framework, and discusses future directions for research on access

A comparative analysis of Listeria monocytogenes plasmids: Presence, contribution to stress and conservation

Listeria monocytogenes is a food-borne pathogen responsible for the disease listeriosis and is commonly isolated from food products and production facilities. Some of these isolates are known to contain plasmids, though previous plasmid studies were conducted with a limited data set of 14 sequenced strains. To determine the presence of plasmids in a variety of L. monocytogenes strains and from various sequence types (ST), a large-scale analysis of 1924 L. monocytogenes genome sequences was conducted to determine the presence of plasmids in different STs, years, countries, and isolation sources. On average, 53% of all L. monocytogenes strains, and up to 92% of the strains within a ST (i.e. ST121), analyzed contained a plasmid. These plasmids ranged in size between 3 kb to 140 kb, with the majority being around 58 kb (± 1kb) and the other around 77 kb (± 1 kb). Plasmid conservation was a minimum of 91.9% nucleotide identity across all plasmids among all STs and the average similarity was 92.3% similarity. Examination of six previously identified plasmid-encoded stress-related genes indicated the genes present in L. monocytogenes plasmids are highly conserved, but their presence in plasmids is highly variable. Analysis of the dataset also identified a novel mercury-resistance operon containing seven genes involved in increasing tolerance in the presence of mercury. Understanding that plasmids often play a role in stress survival, it was necessary to determine the contribution of L. monocytogenes plasmids to stress tolerance when under such conditions. For this aim, we studied three isogenic pairs of L. monocytogenes ST5, ST8, and ST121 strains, isolated from dairy foods and production facilities, and that either contained or were cured of plasmids harboring putative stress response genes. Wildtype (wt) and plasmid-cured (pc) strains were exposed to sublethal concentrations of oxidative stress (0.01% H2O2), salinity (15% wt/vol NaCl, pH 5), acidity (1% v/v lactic acid, pH 3.4), heat stress, or disinfectant (benzalkonium chloride, BC). When exposed to H2O2, NaCl, or lactic acid, CFU counts for all wt strains were significantly higher (P Further examination of the phenotypic and functional characteristics of plasmids was required to better understand the mechanisms used by L. monocytogenes plasmids to confer tolerance to stress conditions. Therefore, a transcriptomics survey of plasmid-carrying L. monocytogenes strains 6179 and R479a was conducted under acidic and oxidative stress conditions, using the acidic and oxidative conditions of functional characterization, with an exposure time of 30 minutes at 20°C. The data showed no significant gene expression in the oxidative stress conditions for the R479a strain, and a single differentially expressed (DE) gene in the 6179 strain, a protein of unknown function. For the lactic acid conditions, pLM6179 had 35 DE genes, 16 of which were upregulated, including clpL, a gene predicted to be involved in general stress response. For pLMR479a, the most upregulated DE gene under lactic acid stress was a putative zinc riboswitch, found upstream of a zinc-transporting ATPase. Seventy percent of the transcripts of pLMR479a during lactic acid stress were mapped to this putative zinc riboswitch, indicating heavy metal riboswitches and their potentially corresponding transporters may be important for L. monocytogenes stress response.</p

Plasmids contribute to food processing environment–associated stress survival in three Listeria monocytogenes ST121, ST8, and ST5 strains

Listeria monocytogenes is a food-borne pathogen responsible for the disease listeriosis and is commonly isolated from food and food production facilities. Many L. monocytogenes strains contain plasmids, though the contributions of plasmids to survival in food production environments is unknown. Three L. monocytogenes ST5, ST8, and ST121 strains containing plasmids, which harbor putative stress response genes, were cured of their plasmids. Wildtype (WT) and plasmid-cured strains were exposed to disinfectant, oxidative, heat, acid, or salt stress. After stress exposure, cells were plated for colony forming unit (CFU) counts to determine survivors. L. monocytogenes WT strains exposed to 0.01% (vol/vol) H2O2, 1% (vol/vol) lactic acid, and 15% (wt/vol) NaCl, pH 5 showed significantly higher counts of survivors compared to the plasmid-cured strains. The number of survivors for the ST5 WT strain exposed to 10 μg/mL benzalkonium chloride (BC) was significantly higher than in the plasmid-cured strain. The ST8 and ST5 strains were exposed to elevated temperature (50° and 55°C respectively); only the ST5 WT strain had significantly higher numbers of survivors than the plasmid-cured strains. Our data revealed that L. monocytogenes ST5, ST8, and ST121 plasmids contribute to tolerance against elevated temperature, salinity, acidic environments, oxidative stress and disinfectants.This is a manuscript of an article published as Naditz, Annabel L., Monika Dzieciol, Martin Wagner, and Stephan Schmitz-Esser. "Plasmids contribute to food processing environment–associated stress survival in three Listeria monocytogenes ST121, ST8, and ST5 strains." International journal of food microbiology 299 (2019): 39-46. doi: 10.1016/j.ijfoodmicro.2019.03.016. Posted with permission. </p