Multi-state study of Enterobacteriaceae harboring extended-spectrum beta-lactamase and carbapenemase genes in U.S. drinking water

Community-associated acquisition of extended-spectrum beta-lactamase- (ESBL) and carbapenemase-producing Enterobacteriaceae has significantly increased in recent years, necessitating greater inquiry into potential exposure routes, including food and water sources. In high-income countries, drinking water is often neglected as a possible source of community exposure to antibiotic-resistant organisms. We screened coliform-positive tap water samples (n = 483) from public and private water systems in six states of the United States for bla(CTX-M), bla(SHV), bla(TEM), bla(KPC), bla(NDM), and bla(OXA-48)-type genes by multiplex PCR. Positive samples were subcultured to isolate organisms harboring ESBL or carbapenemase genes. Thirty-one samples (6.4%) were positive for bla(CTX-M), ESBL-type bla(SHV) or bla(TEM), or bla(OXA-48)-type carbapenemase genes, including at least one positive sample from each state. ESBL and bla(OXA-48)-type Enterobacteriaceae isolates included E. coli, Kluyvera, Providencia, Klebsiella, and Citrobacter species. The bla(OXA-48)-type genes were also found in non-fermenting Gram-negative species, including Shewanella, Pseudomonas and Acinetobacter. Multiple isolates were phenotypically non-susceptible to third-generation cephalosporin or carbapenem antibiotics. These findings suggest that tap water in high income countries could serve as an important source of community exposure to ESBL and carbapenemase genes, and that these genes may be disseminated by non-Enterobacteriaceae that are not detected as part of standard microbiological water quality testing.