Relating Antimicrobial Resistance and Virulence in Surface-Water E. coli.

The role of the environment in the emergence and spread of antimicrobial resistance (AMR) is being increasingly recognized, raising questions about the public health risks associated with environmental AMR. Yet, little is known about pathogenicity among resistant bacteria in environmental systems. Existing studies on the association between AMR and virulence are contradictory, as fitness costs and genetic co-occurrence can be opposing influences. Using Escherichia coli isolated from surface waters in eastern North Carolina, we compared virulence gene prevalence between isolates resistant and susceptible to antibiotics. We also compared the prevalence of isolates from sub-watersheds with or without commercial hog operations (CHOs). Isolates that had previously been evaluated for phenotypic AMR were paired by matching isolates resistant to any tested antibiotic with fully susceptible isolates from the same sample date and site, forming 87 pairs. These 174 isolates were evaluated by conventional PCR for seven virulence genes (bfp, fimH, cnf-1, STa (estA), EAST-1 (astA), eae, and hlyA). One gene, fimH, was found in 93.1% of isolates. Excluding fimH, at least one virulence gene was detected in 24.7% of isolates. Significant negative associations were found between resistance to at least one antibiotic and presence of at least one virulence gene, tetracycline resistance and presence of a virulence gene, resistance and STa presence, and tetracycline resistance and STa presence. No significant associations were found between CHO presence and virulence, though some sub-significant associations merit further study. This work builds our understanding of factors controlling AMR dissemination through the environment and potential health risks.

Susceptibility of Escherichia coli O157:H7 to Disinfectants In Vitro and in Simulated Footbaths Amended with Manure.

Escherichia coli O157:H7 is a human pathogen associated with gastrointestinal disease and hemolytic uremic syndrome. Direct contact with ruminants and their feces at agritourism or livestock interaction events is a known source of transmission. Footbath use is a pathogen reduction strategy that may decrease the transmission of E. coli O157:H7 at these interactions. The efficacy of chemical disinfectants in footbaths is not well reported. Our objective was to determine the susceptibility of E. coli O157:H7 toward commonly used disinfectants in vitro and within contaminated footbaths. The minimum inhibitory concentration and the minimum bactericidal concentration (MIC and MBC) and the time-to-kill were determined in vitro for seven E. coli O157:H7 strains using five disinfectant compounds (didecyldimethylammonium chloride [DDAC], glutaraldehyde, hydrogen peroxide, phenol, and sodium hypochlorite). Time-kill assays were performed within simulated footbaths at 22°C, 37°C, and 42°C with and without organic contamination using three commercial disinfectants with similar active ingredients (0.26% Clorox® Bleach, 0.034% Virex® II 256, and 1% Virkon™ S). The MBCs of disinfectants toward E. coli O157:H7 were 3.2, 625, 40, 5000, and 320 ppm of DDAC, glutaraldehyde, hydrogen peroxide, phenol, and sodium hypochlorite, respectively. At 2 × MIC, E. coli O157:H7 reached a 3 log10(colony-forming unit [CFU]/mL) reduction on contact with glutaraldehyde, by 20 min with DDAC and sodium hypochlorite, and by 4 h with phenol and hydrogen peroxide. In simulated footbaths, the commercial disinfectants reduced concentrations by 3 log10(CFU/mL) on contact in the absence of organic contamination, but viable E. coli O157:H7 was recovered from organically contaminated Clorox Bleach and Virex II 256 footbaths. No E. coli O157:H7 was recovered from the Virkon S footbaths after 10 min. This study highlights the ability for organic contamination to compromise the efficacy of disinfectants in footbaths and the importance of choosing an appropriate footbath disinfectant to retain the efficacy.

Efficacy of an Escherichia coli O157:H7 SRP Vaccine in Orally Challenged Goats and Strain Persistence Over Time.

Small ruminants have been implicated in outbreaks of Escherichia coli O157:H7 at livestock exhibitions throughout the United States. Additionally, goat meat or milk may serve as a reservoir for foodborne transmission of the organism. These associations highlight the public health importance of an effective strategy to reduce E. coli O157:H7 shedding in goats. We examined the efficacy of the SRP® vaccine in goats orally challenged with E. coli O157:H7. Mixed-breed goats (n = 14) were randomly allocated into vaccinated and unvaccinated treatments (n = 7 per treatment). Goats were housed with a vaccinated and unvaccinated animal in each pen. Feces were collected for 3 weeks, then at necropsy, gastrointestinal contents were collected to determine the concentration of E. coli O157:H7. Three isolates per positive sample were saved and evaluated by pulsed-field gel electrophoresis (PFGE) to assess strain persistence over time. The mean concentration of E. coli O157:H7 in the feces of goats was numerically reduced in the vaccinated treatment; however, it was not statistically significant. In addition, the total number of days goats were fecal positive for E. coli O157:H7 were not different between vaccinated and unvaccinated treatments. Pulsotypes of isolates revealed that goats initially shed two of the four challenge strains of E. coli O157:H7, after which there was a distinct shift to two different strains. Further work is needed to evaluate cost-effective intervention strategies that reliably reduce E. coli O157:H7 shedding in goats, particularly those that may reduce the risk of transmission at public events, including petting zoos and fairs.