Dissemination of ceftazidime-resistant Acinetobacter baumannii clonal complex 92 in Korea

Abstract

This study was performed to describe the epidemiological traits of ceftazidime-resistant Acinetobacter baumannii clinical isolates from Korea. Antimicrobial susceptibilities were determined by disk diffusion assay. PCR experiments were performed to detect genes encoding extended-spectrum β-lactamases and metallo-β-lactamases. Detection of ISAba1 upstream of the bla(ADC) gene was also performed by PCR amplification. The genetic organization of the bla(PER-1) gene was investigated by PCR mapping and sequencing of the regions surrounding the gene. Multilocus sequence typing was performed using seven housekeeping genes. A. baumannii isolates of clonal complex (CC) 92 exhibited a higher resistance rate (286/289, 99%) against ceftazidime compared to A. baumannii isolates of non-CC92 (7/87, 8%). Amongst 286 ceftazidime-resistant isolates of CC92, 100 (35%) isolates carried the bla(PER-1) gene, while none of the 87 isolates of non-CC92 carried the gene. The bla(ADC) gene associated with an ISAba1 element was detected in 98% (281/286) of ceftazidime-resistant isolates of CC92 and in all seven ceftazidime-resistant isolates of non-CC92. The bla(PER-1) gene was located on a transposon, Tn1213 (ISPa12-bla(PER-1) -Δgst-ISPa13), in 95 isolates and on a complex class 1 integron (orf513-bla(PER-1) -putative ABC transporter gene) in five isolates. Southern blot experiments confirmed the chromosomal location of the bla(PER-1) gene. Acinetobacter baumannii CC92 which has acquired ceftazidime resistance by the production of PER-1 extended-spectrum β-lactamases and/or the overproduction of Acinetobacter-derived cephalosporinase is widely disseminated in Korea. This study shows the mechanisms of acquiring ceftazidime resistance in A. baumannii and the epidemiological traits of ceftazidime-resistant A. baumannii isolates from Korea.