Community-acquired infections caused by extended-spectrum b-lactamase (ESBL)-producing bacteria, particularly CTX-M-producing Escherichia coli, are a rising concern worldwide. There are few data from Japan on the acquisition of ESBLs in the community or the influx of these bacteria into hospitals. Therefore, we examined the prevalence of ESBL carriage in outpatients, in order to estimate the spread of ESBLs in community settings. We analysed bacterial isolates from outpatient samples at our institution over a 9-year period from 2003 to 2011, with respect to epidemiological data on ESBL-producing bacteria and their genotypic features. Out of 5137 isolates, 321 (6.3%) were ESBL producers, including E. coli, Klebsiella pneumoniae and Proteus mirabilis. The detection rates of the ESBL-producing isolates gradually increased and reached 14.3, 8.7 and 19.6% for E. coli, K. pneumoniae and P. mirabilis strains, respectively, in 2011. Genotyping analysis showed that many of the strains produced multiple b-lactamases, including TEM, SHV and CTX-M, rather than just CTX-M. The CTX-M-9 group was dominant among the CTX-M genotypes; further, the CTX-M-1 and M-2 groups were also detected (~30%). This is believed to be the first report from Japan showing a definite increase in ESBL detection in outpatients. In addition, our findings suggest the simultaneous community spread of diverse ESBL genotypes, not an expansion of particular ESBL genes.
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