Occurrence of antibiotic-resistant uropathogenic Escherichia coli clonal group A in wastewater effluents

Abstract

Isolates of Escherichia coli belonging to clonal group A (CGA), a recently described disseminated cause of drug-resistant urinary tract infections in humans, were present in four of seven sewage effluents collected from geographically dispersed areas of the United States. All 15 CGA isolates (1% of the 1,484 isolates analyzed) exhibited resistance to trimethoprim-sulfamethoxazole (TMP-SMZ), accounting for 19.5% of the 77 TMP-SMZ-resistant isolates. Antimicrobial resistance patterns, virulence traits, O:H serotypes, and phylogenetic groupings were compared for CGA and selected non-CGA isolates. The CGA isolates exhibited a wider diversity of resistance profiles and somatic antigens than that found in most previous characterizations of this clonal group. This is the first report of recovery from outside a human host of E. coli CGA isolates with virulence factor and antibiotic resistance profiles typical of CGA isolates from a human source. The occurrence of "human-type" CGA in wastewater effluents demonstrates a potential mode for the dissemination of this clonal group in the environment, with possible secondary transmission to new human or animal hosts.

FIG. 1.

RAPD profiles of selected Escherichia coli isolates. Lane numbers are shown below the gel image. Lanes 4 and 17, 250-bp marker (M); lanes 1 to 3 and 5 to 16, CGA-positive sewage isolates; lanes 18 and 19, CGA positive controls (human cystitis isolates SEQ102 and UMN026, respectively); lanes 20 to 24, CGA negative controls (lanes 20 and 21, non-CGA sewage isolates [from phylogenetic groups B2 and D, respectively]; lane 22, strain CFT073 [from group B2]; and lanes 23 and 24, human-source non-CGA isolates [from groups D and B2, respectively]). Bullets above lanes indicate CGA isolates that exhibit the consensus CGA-associated virulence profile, including the F16 papA (P fimbria structural subunit) allele, and a characteristic CGA-associated RAPD profile. CGA isolates in lanes without bullets exhibit an atypical virulence profile that includes the F10 papA allele plus (except for strain 492 [lane 5]) an atypical RAPD profile that includes an extra, ∼2,000-bp band (vertical arrows; “*” for strain 492 [lane 5]). The profiles of all the CGA isolates are indistinguishable (within the reproducibility limits of RAPD analysis), except for the ∼2,000-bp band, and collectively, they are distinct from the profiles of the non-CGA isolates, each of which is unique.

FIG. 2.

XbaI PFGE profiles of selected Escherichia coli isolates. Lane numbers are shown below the gel image. Lanes 1, 10, and 18, marker (M) lanes with E. coli O157:H7 strain G5244; lanes 2 to 9 and 11 to 17, CGA-positive sewage isolates. Bullets above lanes indicate CGA isolates that exhibit the consensus CGA-associated virulence profile, including the F16 papA (P fimbria structural subunit) allele. CGA isolates in lanes without bullets exhibit an atypical virulence profile that includes the F10 papA allele and (except for strain 518 [lane 8]) exhibit a large extra band in the PFGE profile (vertical arrows; “*” for strain 518). The profiles of the CGA isolates are all unique, yet they exhibit similarities that distinguish them as a group from the E. coli O157:H7 reference strain (lanes 1, 10, and 18).