Antibiotic-resistant indicator bacteria in irrigation water: High prevalence of extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli

PLoS One. 2018 Nov 26;13(11):e0207857. doi: 10.1371/journal.pone.0207857. eCollection 2018.

Abstract

Irrigation water is a major source of fresh produce contamination with undesired microorganisms including antibiotic-resistant bacteria (ARB), and contaminated fresh produce can transfer ARB to the consumer especially when consumed raw. Nevertheless, no legal guidelines exist so far regulating quality of irrigation water with respect to ARB. We therefore examined irrigation water from major vegetable growing areas for occurrence of antibiotic-resistant indicator bacteria Escherichia coli and Enterococcus spp., including extended-spectrum β-lactamase (ESBL)-producing E. coli and vancomycin-resistant Enterococcus spp. Occurrence of ARB strains was compared to total numbers of the respective species. We categorized water samples according to total numbers and found that categories with higher total E. coli or Enterococcus spp. numbers generally had an increased proportion of respective ARB-positive samples. We further detected high prevalence of ESBL-producing E. coli with eight positive samples of thirty-six (22%), while two presumptive vancomycin-resistant Enterococcus spp. were vancomycin-susceptible in confirmatory tests. In disk diffusion assays all ESBL-producing E. coli were multidrug-resistant (n = 21) and whole-genome sequencing of selected strains revealed a multitude of transmissible resistance genes (ARG), with blaCTX-M-1 (4 of 11) and blaCTX-M-15 (3 of 11) as the most frequent ESBL genes. Overall, the increased occurrence of indicator ARB with increased total indicator bacteria suggests that the latter might be a suitable estimate for presence of respective ARB strains. Finally, the high prevalence of ESBL-producing E. coli with transmissible ARG emphasizes the need to establish legal critical values and monitoring guidelines for ARB in irrigation water.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Agricultural Irrigation*
  • Drug Resistance, Microbial*
  • Enterococcus / drug effects
  • Enterococcus / isolation & purification*
  • Escherichia coli / drug effects
  • Escherichia coli / isolation & purification*
  • Escherichia coli / metabolism*
  • Food Microbiology
  • Phylogeny
  • Water Microbiology*
  • beta-Lactamases / biosynthesis*

Substances

  • beta-Lactamases

Grants and funding

This work was funded by the Agroscope Research Programme "Reduction and Dynamics of Antibiotic-resistant and Persistent Microorganisms along Food Chains (REDYMO)", the National Research Programme "Antimicrobial Resistance" (NRP 72) of the Swiss National Science Foundation and the COST Action CA16110 "Control of Human Pathogenic Micro-organisms in Plant Production Systems HUPLANTcontrol)". The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.