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.
Department of Clinical Microbiology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China.
Bin
B
Li
Jing-Yong
JY
Sun
Qing-Zhong
QZ
Liu
Li-Zhong
LZ
Han
Xin-Hong
XH
Huang
Yu-Xing
YX
Ni
D000293:Adolescent; D000328:Adult; D000368:Aged; D002681:China; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification*; D005243:Feces / Q000382:microbiology*; D005260:Female; D005838:Genotype; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests / Q000379:methods; D008875:Middle Aged; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D015995:Prevalence; D017422:Sequence Analysis, DNA; D055815:Young Adult; D001618:beta-Lactamases / Q000096:biosynthesis*
D004269:DNA, Bacterial; D001618:beta-Lactamases