Extended-spectrum Beta-lactamases in Bacteria: A Molecular Epidemiology Study

OBJECTIVE To investigate the resistance to 11 drugs and the prevalence of genotypes of extended-spspectrum β-lactamases in Escherichia coli and Klebsiella pneumoniae which were collected from Jan to Aug 2002 in Beijing Hospital. METHODS A total of 86 E. coli and 132 K. pneumoniae strains were tested to 11 drugs in vitro susceptibility by Etest. ESBLs were confirmed with inhibitor-potentiated test. ESBLs genotypes were analyzed by isoelectric point determination, PCR, nucleotide sequencing and conjugation experiments. RESULTS The ESBLs positive rate of E. coli was 29.1%, K. pneumoniae was 18.9%, the total ESBLs positive rate was 22.9%. The drug resistance of positive ESBLs was higher than that of negative ESBLs to most drug. ESBLs genotypes were analyzed by isoelectric point determination and PCR, then by nucleotide sequencing and conjugation experiment. In the genotypes of 50 ESBLs, TEM were 62%, all of them were TEM-1; CTX-M were 52%, they were 11 strains CTX-M-14, 9 strains CTX-M-22, 5 strains CTX-M-24 and 1 strain CTX-M-13; SHV were 44%, they were 5 strains SHV-1, 5 strains SHV-12 (transconjugation test showed that SHV-12 plasmid was located in 4 strains), 3 strains SHV-2(a) (plasmid was located in 2 strains), 2 strains SHV-2(2) (plasmid was located in 2 strains), subtypes of the other 7 strains were not identified and no SHV gene in plasmid was proved by transconjugation test. CONCLUSIONS This study shows that CTX-M-type and SHV-type are predominant genotypes of ESBLs in E. coli and K. pneumoniae in Beijing Hospital.