Characterization of Extended-Spectrum-beta-Lactamase Genes from Clinical Isolates of Enterobacter species

Kim, Jeong Man; Jeong, Seok Hoon; Kim, Bit Na; Sung, Ji Hyun; Kim, Jong Chul; Jang, Hyunjung

Abstract

BACKGROUND: Among Enterobacter spp. isolates from clinical specimens in Korea, the incidence of resistance to expanded-spectrum cephalosporins is becoming an ever-increasing problem. This study was designed to determine the prevalence of expanded-spectrum cephalosporins-resistant Enterobacter spp. isolates from patients in a tertiary care hospital in Busan, Korea, and to characterize the mechanism of resistance.
MATERIALS AND METHODS
Nonduplicated clinical isolates of Enterobacter spp. were collected during the period of 1999-2000 in Kosin Medical Center, Busan, Korea. Antimicrobial susceptibilities were tested by disk diffusion method. Cefotaxime-resistant or intermediate isolates were examined for extended-spectrum beta-lactamase (ESBL)-production by double disk synergy (DDS) test. Minimal inhibitory concentrations were determined by agar dilution method. For detection of blaTEM and blaSHV genes, polymerase chain reactions (PCRs) were performed, and the DNA sequences of blaTEM and blaSHV genes were determined by using dideoxy-chain termination method.
RESULTS
From 1999 to 2000, a total of 306 Enterobacter spp. strains were isolated from patients in Kosin Medical Center. Forty one percents of Enterobacter spp. isolates were susceptible to cefotaxime. Among 90 isolates resistant or intermediate to cefotaxime, 26 isolates (29%) showed positive results in double disk synergy test. Among DDS-positive- isolates, 22 isolates contained both of blaTEM and blaSHV genes, while one isolate only contained blaTEM gene and two isolates only contained blaSHV gene. Among 64 DDS-negative isolates, 47 isolates contained blaTEM genes, and 12 isolates also contained blaSHV genes. Nucleotide sequence analysis of PCR products from 10 DDS-positive and 6 DDS-negative isolates, which contained both of blaTEM and blaSHV genes, revealed that blaTEM-1b and blaSHV-12 genes were the dominant types of beta-lactamase gene.
CONCLUSION
Expanded-spectrum cephalosporins-resistant Enterobacter spp. were wide spread in Kosin Medical Center, Busan, Korea. Some of the resistant isolates acquired resistance by production of ESBLs, and blaSHV-12 gene was the most frequent ESBL gene in cefotaxime-resistant Enterobacter spp.