Molecular epidemiology, antimicrobial susceptibility and carbapenemase resistance determinants among Acinetobacter baumannii clinical isolates in Taiwan.

BACKGROUND: Emerging carbapenem resistance among Acinetobacter baumannii clinical isolates is a worldwide problem. Infections caused by A. baumannii are increasing and demonstrate high mortality rates. This study aimed to establish a nationwide surveillance of antimicrobial susceptibility, carbapenemase genes, and clonal relationships of A. baumannii clinical isolates in Taiwan.

METHODS: Clinical isolates of Acinetobacter calcoaceticus-A. baumannii (ACB) complex collected by the Taiwan Surveillance of Antimicrobial Resistance-V program between July 2006 and September 2006 were used in this study. Genospecies identification was verified by 16S-23S rRNA intergenic-spacer sequences. Carbapenemase genes were detected by polymerase chain reaction. Pulsed-field gel electrophoresis and multilocus sequence typing (MLST) was applied for identification of clonal relationships.

RESULTS: Among the 151 ACB-complex isolates collected, 134 (88.7%) were A. baumannii, 12 (8.0%) were A. pittii, and five (3.3%) were A. nosocomialis. A. baumannii isolates showed higher resistance rates to ciprofloxacin, amikacin, and ampicillin/sulbactam than A. pittii or A. nosocomialis (all p < 0.001). The most commonly detected carbapenemase genes were bla(OxA-51) (n = 135), followed by bla(OxA-24) (n = 4), bla(OxA-23) (n = 2), and bla(OxA-58) (n = 1). Three major A. baumannii clones were found throughout Taiwan, and showed significantly higher resistance rates to ciprofloxacin, amikacin, and ampicillin/sulbactam than the other A. baumannii isolates (100% vs. 68.7%, p < 0.001; 98.4% vs. 61.5%, p < 0.001; and 66.7% vs. 39.8%, p = 0.004; respectively). MLST showed that these major clones were sequence type 2 and belonged to international clonal complex 2.

CONCLUSION: Our results demonstrate clonal spreading of A. baumannii in Taiwan hospitals and that these clones were more resistant to many antimicrobial agents. Efforts to prevent and control A. baumannii colonization/infections and prudent use of antibiotics to reduce antimicrobial selective pressure should be emphasized.