Epidemiological study on Extended-Spectrum β-Lactamase-Producing Klebsiella pneumoniae infections by pulsed-field gel electrophoresis

Background : Third generation cephalosporins were potent antimicrobial agents against gram-negative bacilli, however, increased resistance to these drugs has been noted recently. This study was to determine the prevalence of cefotaxime resistance and extended-spectrum β-lactamase (ESBL) in Klebsiella pneumoniae, and to determine for the existence of hospital infection by this organism. Methods : Cefotaxime resistance was tested by NCCLS disk diffusion method from 1988 to 1995 in Severance Hospital. Among the cefotaxime-intermediate or resistant strains, 118 were tested for ESBL production by double disk synergy test using cefotaxime, ceftazidime, aztreonam, and amoxicillin/clavulanic acid disks. The patterns of XbaI-digested chromosomal DNA of ESBL-producing K. pneumoniae isolates were analyzed by pulsed-field gel electrophoresis. Results : Cefotaxime-susceptible rates decreased from 78% to 46% in K. pneumoniae during the recent 8 years. The isolates from ICU patients showed higher resistance rates than those from general wards or outpatient clinics. Among the strains with intermediate or resistance to cefotaxime, 77% were isolated in the period of March to August, 1994 and 85% in October, 1995-January, 1996 were double disk synergy test-positive. ESBL-producing K. pneumoniae were grouped into 28 chromosomal DNA patterns by XbaI digestion. Type A were the most common in 1994 and type D in 1995 to 1996, and these were prevalent among the strains isolated from ICU patients. Conclusion : It is concluded that proportion of ESBL-producing K. pneumoniae strains has been increasing. They are more frequently isolated from the specimens of intensive care unit patients, and considered to be derived from a few clones. In addition, third generation cephalosporin-intermediate strains should be considered to be clinically resistant to th drugs.ope