Enumeration and characterization of antimicrobial-resistant escherichia coli bacteria in effluent from municipal, hospital, and secondary treatment facility sources

We describe a modification of the most probable number (MPN) method for rapid enumeration of antimicrobial-resistant Escherichia coli bacteria in aqueous environmental samples. E. coli (total and antimicrobialresistant) bacteria were enumerated in effluent samples from a hospital (n = 17) and municipal sewers upstream (n = S) and downstream (n = S) from the hospital, effluent samples from throughout the treatment process (n = 4), and treated effluent samples (n = 13). Effluent downstream from the hospital contained a higher proportion of antimicrobial-resistant E. coli than that upstream from the hospital. Wastewater treatment reduced the numbers of E. coli bacteria (total and antimicrobial resistant); however, antimicrobialresistant E. coli was not eliminated, and E. coli resistant to cefotaxime (including extended-spectrum betalactamase [ESBL] producers), ciprofloxacin, and cefoxitin was present in treated effluent samples.