The occurrence and antimicrobial susceptibility of extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae in patients attending Siriraj Hospital in Bangkok from August 2000 to January 2001 were determined. ESBL-producing isolates were screened with four different methods: disk diffusion according to the National Committee for Clinical Laboratory Standards (NCCLS) guidelines,
Etest ESBL (CT/CTL and TZ/TZL), Oxoid combination discs and MIC Etest strip. Antimicrobial susceptibility testing were determined by a microdilution automatic method (VITEX system, bioMerieux). Of 22,178 clinical specimens, 400 (1.8%) K. pneumoniae were isolated. Of 26% (104/400) of these isolates were suspected to be ESBL-producing. Rates of detection of ESBL-producing K. pneumoniae were 18.67%, 30% and 23.78% for blood, sputum and urine samples, respectively. Susceptibility testing has revealed that all 70 tested isolates including 53 isolates from blood and sputum and 17 isolates from urine samples were susceptible to imipenem (MIC d” 4 mg/L). None of the tested isolates were susceptible to cephalosporins, cephamycin and
aztreonam. Rate of susceptibility to ciprofloxacin, levofloxacin, gentamicin and tobramycin were 60%, 64%,
28% and 9%, respectively, for isolates from blood and sputum; 71%, 71%, 18% and 6% for urinary isolates.
The present findings revealed a high occurrence rate of multi-drug resistance ESBL-producing K. pneumoniae
in patients attending the university hospital. Imipenem was highly active against ESBL-producing K. pneumoniae.

Keywords: Klebsiella pneumoniae, Extended-spectrum β-lactamase (ESBL), MIC