Molecular characterization of extended spectrum beta-lactamase among clinical isolates Escherichia coli and Klebsiella pneumoniae.

BACKGROUND

Resistance to beta-lactams has been increasing in the treatment of infections caused by Escherichia coli and Klebsiella pneumoniae. The production of extended-spectrum beta-lactamases (ESBLs), that hydrolyze extended-spectrum cephalosporins, is the major cause of beta-lactam resistance.

OBJECTIVE

To determine the prevalence and characterize of ESBLs produced by E. coli and K. pneumoniae from clinical specimens.

MATERIAL AND METHOD

ESBLs were determined by disk diffusion test, double disk synergy test, and E-test ESBLs. All ESBLs producing isolates were investigated for the presence of bla(TEM) bla(SHV), bla(CTX-M) and bla(VEB) genes by polymerase chain reaction (PCR). Nucleotide sequencing of bla(TEM) and bla(SHV) were performed E. coli and K. pneumoniae were isolated from clinical specimens of patients in King Chulalongkorn Memorial Hospital between February and May 2002. Of the 270 isolates, 212 were E. coli and 58 were K. pneumoniae.

RESULTS

ESBL roduction was detected in 17% (36/212) of E. coli and 34.5% (20/58) of K. pneumoniae isolates. Of the 20 K. pneumoniae isolates, the beta-lactamase genes were bla(SHV) (18/20, 90%), bla(TEM) (10/20, 50%), bla(VEB-like) (6/20, 30%) and bla(CTX-M-like) (3/20, 15%). Thirty-six E. coli isolates carried bla(TEM) bla(CTX-M-like) and bla(VEB-like) genes in 72.2% (26/36), 52.8% (19/36) and 16.7% (6/36), respectively Bla(SHV) was not detected in ESBL-producing E. coli, whereas it predominated in K. pneumoniae. Of the 56 ESBL producing isolates, 30 (53.6%) coharboured at least two different bla genes. All TEM identified were TEM-1B, which is not an ESBL. CTX-M ESBLs were the most common in E. coli.

CONCLUSION

The double disk diffusion test should be added routinely in the antibiotic susceptibility test for the Enterobacteriaceae. It is simple to perform, easy to interpret, and economical. The presence of bla(CTX-M) and bla(VEB) in ESBL-producing E. coli and K. pneumoniae indicates the high prevalence of these genes in Thailand.