High prevalence of CTX-M β-lactamases in faecal Escherichia coli strains from healthy humans in Fuzhou, China

BACKGROUND: The community could be a reservoir of antibiotic resistance genes. The aim of this study was to investigate the prevalence and genetic environments of bla(CTX-M) among faecal Escherichia coli obtained from healthy persons in a region of China. METHODS: Bacteria in stool specimens were screened for extended-spectrum β-lactamase (ESBL) production on 2 MacConkey agars, one with cefotaxime and one with ceftazidime. bla(CTX-M) and their genetic environments, as well as phylogenetic analysis and detection of the O25b-ST131 clone of E. coli, were characterized by polymerase chain reaction and sequencing. Pulsed field gel electrophoresis and conjugation assays were performed by standard procedures. RESULTS: A surprisingly high number (50.5%, 55/109) of faecal samples showed the presence of ESBL-producing E. coli. bla(CTX-M) genes were detected in all of these strains. The CTX-M-9 group (41/55, 74.5%) was found most frequently, followed by the CTX-M-1 group (16/55, 29.1%). CTX-M-14 (n = 39) was the predominant CTX-M enzyme in this study. However, the genes for the CTX-M-2 and CTX-M-8 groups were not observed. ISEcp1 was detected in 90.9% of the strains, while IS26 was observed upstream from bla(CTX-M) in only 1 strain. Phylogenetic groups A and D were found to predominate in commensal E. coli. High clonal diversity was observed and most bla(CTX-M) genes were transferable. The O25b-ST131 clone was found in 4 strains. CONCLUSIONS: This study reveals the wide dissemination of CTX-M ESBL-producing E. coli in the gut flora of healthy individuals in China.