Characterization of CTX-M-type extended-spectrum beta-lactamase in clinical clones of Escherichia coli in Southwest China

The rapid and widespread dissemination of CTX-M-type extended-spectrum beta-lactamases (ESBLs) Escherichia coli in most of the provinces in China has been previously characterized; however, these enzymes have been rarely reported among minority regions. A prospective study using 180 E. coli clones from three hospitals in the minority district of Dali Bai was conducted between January 2009 and June 2010 to characterize the profiles of bla(CTX-M)-producing E. coli. Overall, 87 of the isolates (48.3%) encoded the resistance phenotypes of ESBLs. Among these 87 isolates, 56 (64.4%) exconjugants were successfully obtained. The genotypes of bla(CTX-M) were evaluated by PCR and DNA sequencing. In total, 22 and 53 E. coli isolates possessed CTX-M cluster 1 and CTX-M cluster 9, respectively. Five bla(CTX-M) subtypes were detected, namely, bla(CTX-M3) (n=12), bla(CTX-M15) (n=4), bla(CTX-M22) (n=2), bla(CTX-M14) (n=41), and bla(CTX-M9) (n=8). The broth microdilution method was performed to determine the minimal inhibitory concentration of 13 antibiotics. Most CTX-M producers were multiply resistant to both -lactam and non--lactam antibiotics. Imipenem showed excellent activity, and only one isolate harboring bla(CTX-M14+CTX-M3) exhibited resistance to it. In conclusion, there seems to be great concern regarding the distribution and drug resistance of CTX-M ESBL-producing E. coli.