High Prevalence of CTX-M Beta-Lactamases in Enterobacteriaceae from Healthy Individuals in Guangzhou, China

This study aimed to determine the prevalence of extended-spectrum beta-lactamases (ESBLs) in Enterobacteriaceae and to characterize the genetic composition of ESBL determinants among Enterobacteriaceae isolates from healthy people in Guangzhou, China. A total of 200 rectal swab samples were collected from healthy asymptomatic individuals and tested for ESBL production using ChromID ESBL agar. Phenotypic ESBL producers were screened for bla(CTX-M), bla(TEM), and bla(SHV) genes using PCR and DNA sequencing. The prevalence of ESBL-producing Enterobacteriaceae among rectal swab samples was 69.5%. All ESBL-producing isolates harbored bla(CTX-M) genes (n=138) except for one isolate that harbored bla(SHV-2a). Eleven CTX-M ESBL genes were detected. The most predominant CTX-M-type genes were bla(CTX-M-14) (n=82), followed by bla(CTX-M-55) (n=19), bla(CTX-M-65) (n=10), and bla(CTX-M-27) (n=9). Isolates carrying bla(CTX-M-38),(-3),(-15),(-14b),(-98),(-121) and (-123) were also identified. Molecular homology analysis of the selected isolates was performed by phylogenetic grouping and multilocus sequence typing and indicated that the predominant clone belonged to A-CC10. This study showed a high rate of CTX-M-type ESBL genes among Enterobacteriaceae isolates from healthy individuals in China.