RESUMEN
BACKGROUND: Plasmid-mediated AmpC beta-lactamases (PABL) are cephalosporinases that confer resistance to a wide variety of beta-lactam drugs and that may thereby create serious therapeutic problems. The PABL-producing organisms are a major concern in nosocomial infections and should there-fore be monitored in surveillance studies. Although reported with increasing frequency in Korea, the occurrence and genotypic distributions of PABL in Escherichia coli and Klebsiella pneumoniae remain unknown. METHODS: We tested a total of 911 consecutive, nonduplicate isolates of E. coli and K. pneumoniae at 12 university hospitals and a commercial laboratory in Korea. Antimicrobial susceptibilities were tested using the disk diffusion method. PABL production was determined by the modified Hodge test and multiplex PCR. The PCR differentiated the six PABL-specific families in E. coli and K. pneumoniae. RESULTS: Overall, 110 (12.1%) yielded cefoxitin non-susceptible isolates and that 28 (3.1%) demonstrated PABL producers by multiplex PCR. Based on the species, of 544 E. coli and 367 K. pneumoniae isolates tested, 8 (1.5%) and 20 (5.4%), respectively, demonstrated PABL producers. The genotypes of PCR amplification showed that the MOX, DHA, and CIT family were harbored by 4, 2, and 2 of 8 PABL-producing E. coli, and the DHA, MOX, and EBC family were harbored by 13, 6, and 1 of 20 PABL-producing K. pneumoniae isolates, respectively. CONCLUSIONS: These data confirm that the occurrence of PABL-producing E. coli and K. pneumoniae is relatively high and the kinds of genotypes are variously distributed in Korea.