Extended spectrum beta-lactamase producing Klebsiella pneumoniae isolated from clinical specimen : antimicrobial susceptibility pattern and pulsotype

Abstract

One hundred ESBL producing isolates were detected from 400 K. pneumoniae isolated from sputum, urine, and blood of the patients in Siriraj Hospital using the NCCLS initial screen test and the phenotypic confirmatory test. No ESBL producing isolates could be detected from 36 K. pneumoniae isolated from the feces of 100 normal persons. Suggestive evidence from this study was that the use of positive results from all three drugs : ceftazidime, cefotaxime, and ceftriaxone in the initial screen test was necessary for the detection of suspicious ESBL producer. The results from such criterion were best correlated with those from the phenotypic confirmatory test. E-test ESBL screening test was shown to be less efficient than the NCCLS phenotypic confirmatory test. Antimicrobial susceptibility test of all ESBL producing K. pneumoniae were performed. The minimal inhibitory concentrations (MICs) of the cephalosporins included ceftazidime, cefotaxime, ceftriaxone and cefuroxime and that of the carbapenem were detected using E-test strip. According to the MICs, it was suggestive that 32 isolates produced ESBL with “broad” activity, 13 isolates produced enzyme with “ceftazidimase” activity and 55 isolates were ESBL undertermined activity. Therefore, further study on the enzymes’ characteristics should be performed performed before more definite conclusions could be made. Among the ESBL producing isolates, only 5% were susceptible to ceftazidime, while 87%, 79%, 30% 90% and 100% was susceptible to cefotaxime, ceftriaxone, cefuroxime, cefoxitin and imipenem, respectively. From the Kirby - Bauer susceptibility test, 50%, 71%, 16%, 67% and 38% of the ESBL producing isolates were susceptible to gentamicin, amikacin, tobramycin, ciprofloxacin and trimethoprime-sulfamethoxazole, respectively. There were as many as 86 different pulsotypes among all 100 ESBL producing K. pneumoniae isolated during the 6 month period of study. Thus, evidences of the endemic and epidemic strains were not demonstrated.