Moleculoepidemiological Characteristics of Extended-Spectrum beta-Lactamase Producing Escherichia coli and Klebsiella pneumoniae Strains in Daegu

Ryoo, Nam Hee; Jeon, Dong Seok; Kim, Jae Ryong; Jeon, Chang Ho; Suh, Hun Suk

Abstract

BACKGROUND
The importance of extended-spectrum beta-lactamases (ESBL) produced in gramnegative bacilli is now well recognized, but most clinical laboratories have problems in detecting and interpreting ESBL and implicating the findings in nosocomial infections caused by ESBL producing gram-negative bacilli. The present study aims primarily to evaluate the distributions of these enzymes among Escherichia coli and Klebsiella pneumoniae, the most frequent isolates of Enterobacteriaceae producing ESBL, to differentiate the types of enzymes in theses isolates and finally to relate the clonality of specific types within a part of Daegu city. METHODS: The clinical isolates of 1, 242 E. coli and 859 K. pneumoniae were screened for ESBL production by the disk diffusion method of the National Committee of Clinical Laboratory Standard, and it was confirmed by the double-disk synergy test (DDS). Antimicrobial susceptibility test was performed by the agar dilution method. The presence of -lactamase was tested by polymerase chain reaction (PCR) and plasmid analysis. Isoelectric focusing and nucleotide sequence analysis were performed to evaluate ESBL types. Pulsed-field gel electrophoresis (PFGE) of XbaI-digested DNA fragments was carried out to determine the extend of clonality within the hospital. RESULTS: Of 34 isolates of E. coli and 31 isolates of K. pneumoniae ramdomly selected from those isolates screened for ESBL production were further tested by DDS to confirm its production: 30 (88.2%) E. coli and 29 (93.5%) K. pneumoniae were positive. TEM-52 and SHV-12 were present both in E. coli and K. pneumoniae, but SHV-2a was distributed only in K. pneumoniae. The resistance was transferable in 66.7% of E. coli and 68.9% of K. pneumoniae. Six and 5 PFGE patterns were shown by E. coli and K. pneumoniae, respectively. Among the 5 patterns of K. pneumoniae, type B was dominant, suggesting a clonal outbreak in the hospital. CONCLUSIONS: The ESBL specific enzyme types were TEM-52, SHV-2a and SHV-12. Despite many different PFGE patterns of the ESBL producing isolates, a few outbreak and edemic clones appear to be prevalent in Dongsan Medical Center.