Molecular Characterization of Extended Spectrum Beta-Lactamase among Clinical Isolates Escherichia coli and Klebsiella pneumoniae
Nibondh Udomsantisuk MSc*, Pongpun Nunthapisud MSc*, Thaweesak Tirawatanapong PhD*, Mayteera Dansuputra MSc, MBA**
Affiliation : * Department of Microbiology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand ** Inter-Department of Program in Medical Microbiology, Grauduate School, Chulalongkorn University, Bangkok, Thailand
Background : Resistance to β-lactams has been increasing in the treatment of infections caused by Escherichia coli and
Klebsiella pneumoniae. The production of extended-spectrum β-lactamases (ESBLs), that hydrolyze extended- spectrum
cephalosporins, is the major cause of β-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 blaTEM, blaSHV, blaCTX-M, and blaVEB genes by polymerase chain reaction
(PCR). Nucleotide sequencing of blaTEM and blaSHV 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 production 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 β-lactamase genes were blaSHV (18/20, 90%), blaTEM (10/20, 50%), blaVEB-like (6/20, 30%) and blaCTX-
M-like (3/20, 15%). Thirty-six E. coli isolates carried blaTEM, blaCTX-M-like and blaVEB-like genes in 72.2% (26/36), 52.8% (19/36) and
16.7% (6/36), respectively. BlaSHV 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 blaCTX-M and blaVEB in ESBL-
producing E. coli and K. pneumoniae indicates the high prevalence of these genes in Thailand.
Keywords : Extended-spectrum beta-lactamases, ESBLs, Disk diffusion test, Double disk synergy test, E-test, Polymerase chain reaction, Polymerase chain reaction, Nucleotide sequencing
