No abstract

This study was designed to evaluate the viability, prophage induction, invasive ability, and relative gene expression in lysogenic Salmonella Typhimurium exposed to the simulated gastric juice (SGJ) at pH 2 (SGJ-2), 3 (SGJ-3), 4 (SGJ-4), and 5 (SGJ-5) for 30 min followed by 0.5 % bile salts for 2 h. The susceptibility of lysogenic S. Typhimurium increased with decreasing pH value and increasing bile salt concentration. The lysogenic S. Typhimurium cells were least susceptible to SGJ-4 and SGJ-5, showing <1 log reduction. The highest prophage induction was observed by 3.34 log PFU/ml in lysogenic S. Typhimurium at SGJ-3 in the presence of 0.5 % bile salts. The numbers of invading lysogenic S. Typhimurium treated at SGJ-3, SGJ-4, and SGJ-5 were 3.57, 3.73, and 4.15 log CFU/cm(2), respectively. Most genes (hilA, hilC, hilD, invA, invE, invF, and sirA) were down-regulated in lysogenic S. Typhimurium treated at SGJ-3, SGJ-4, and SGJ-5. This study provides useful information for understanding physiological changes of lysogenic S. Typhimurium in the simulated gastrointestinal conditions.

Antibiotic resistance represents one of the most pressing concerns facing public health today. While the current antibiotic resistance crisis has been driven primarily by the anthropogenic overuse of antibiotics in human and animal health, recent efforts have revealed several important environmental dimensions underlying this public health issue. Antibiotic resistant (AR) microbes, AR genes, and antibiotics have all been found widespread in natural environments, reflecting the ancient origins of this phenomenon. In addition, modern societal advancements in sanitation engineering (i.e., sewage treatment) have also contributed to the dissemination of resistance, and concerningly, may also be promoting the evolution of resistance to water treatment. This is reflected in the recent characterization of naturalized wastewater strains of Escherichia coli—strains that appear to be adapted to live in wastewater (and meat packing plants). These strains carry a plethora of stress-resistance genes against common treatment processes, such as chlorination, heat, UV light, and advanced oxidation, mechanisms which potentially facilitate their survival during sewage treatment. These strains also carry an abundance of common antibiotic resistance genes, and evidence suggests that resistance to some antibiotics is linked to resistance to treatment (e.g., tetracycline resistance and chlorine resistance). As such, these naturalized E. coli populations may be co-evolving resistance against both antibiotics and water treatment. Recently, extraintestinal pathogenic strains of E. coli (ExPEC) have also been shown to exhibit phenotypic resistance to water treatment, seemingly associated with the presence of various shared genetic elements with naturalized wastewater E. coli. Consequently, some pathogenic microbes may also be evolving resistance to the two most important public health interventions for controlling infectious disease in modern society—antibiotic therapy and water treatment.

This study was designed to evaluate the effect of bacteriophage P22 on the susceptibility, swimming motility, invasion gene expression, invasive ability, and intracellular survival of Salmonella Typhimurium exposed to the simulated intestinal conditions. S. Typhimurium cells were inoculated at 37 °C for 4 h in the simulated intestinal conditions with or without bacteriophage P22, including control (0 % bile salts, pH 7.2), SN (0 % bile salts, pH 5.0), SL (0.5 % bile salts, pH 5.0), SH (2.0 % bile salts, pH 5.0), SNp (0 % bile salts + P22, pH 5.0), SLp (0.5 % bile salts + P22, pH 5.0), and SHp (2.0 % bile salts + P22, pH 5.0). The numbers of Typhimurium cells were significantly reduced by 3.30, 3.56, and 3.75 log units, respectively, at SNp, SLp, and SHp. Considerable reduction in the swimming motility was observed at SNp (23 %), SLp (22 %), and SHp (20 %). The transcriptional regulator genes, hilA, hilC, hilD, invA, invE, and invF, were significantly down-regulated with SHp, showing 4.07-fold, 2.87-fold, 3.43-fold, 2.07-fold, 1.44-fold, and 4.83-fold, respectively. The decrease in invasive ability was most significant at SHp (45 %), followed by SLp (49 %). These results suggest that bacteriophage P22 can be used as an alternative to control Salmonella invasion of epithelial cells.

A growing body of evidence indicates that extraintestinal pathogenic E. coli (ExPEC) readily survive wastewater treatment, raising concerns about the public health risks associated with exposure to wastewater-contaminated environments. In this study, E. coli isolates recovered from chlorinated sewage or treated wastewater effluents in Canada were screened for ExPEC virulence markers. Eighty-six isolates were identified as presumptive ExPEC, clustering within major pandemic lineages including ST131, ST95, and ST73 according to multilocus sequence typing analyses. Across the whole, core, and accessory genome, 37 isolates were extremely similar to clinical bloodborne E. coli (BBEC) and neonatal meningitic E. coli (NMEC) strains, suggesting that these wastewater isolates may exhibit a similar phenotypically related pathogenic potential. Interestingly, ExPEC strains also shared accessory gene content with naturalized wastewater strains, suggesting a common genetic capacity for surviving water treatment. Collectively, these findings suggest that E. coli strains that may cause septicemia and meningitis are surviving wastewater treatment and may be transmissible through wastewater effluents.