Detection of extended-spectrum and AmpC β-lactamases among Klebsiella pneumoniae isolates

Objective: To investigate the prevalence of extended-spectrum β-lactamases (ESBLs) and AmpC lactamases in cli-nical isolates of Klebsiella pneumoniae in China. Methods:ESBLs were detected by screening and confirmatory methods recommended by NCCLS. AmpC β-lactamases were detected by three-dimensional extract test. Isoelectric focusing analysis and PCR were performed to determine the sub-types of ESBLs and AmpC β-lactamases. Results:Of 212 strains tested, ESBLs were detected in 37 (17.5%) strains and AmpC-type β-lactamases in 2 (0.94%) strains of K. pneumoniae (these 2 strains produced ESBLs simultaneously). Among 37 ESBL-producing strains, 31 (83.8%) produced CTX-M type β-lactamases in which 20 (54.1%) and 11 (29.7%) belonged to CTX-M-1 and Toho-2 respectively, 9 (24.3%) strains produced SHV type ESBLs (both CTX-M and SHV were detected in 3 strains simultaneously). DNA sequencing results demonstrated that one strain of produced DHA-1 AmpC-type β-lactamase. Conclusions:CTX-M type ESBLs are the most common ESBLs in K. pneumoniae in China. DHA-1 AmpC-type plasmid-mediated β-lactamase can be found in K. pneumoniae.