Epidemiological characterization and distribution of carbapenem-resistant Acinetobacter baumannii clinical isolates in Italy

This study was aimed at tracing the molecular characteristics of carbapenem-resistant Acinetobacter baumannii (CRAB) clinical isolates in Italy with both pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Two hundred and two CRAB isolates were collected during 20042009, in two different surveillance periods, from 22 Italian hospitals that were representative for both distribution and infection. PFGE was performed, and the MLST scheme used was based on the gene sequence as published on the MLST Pasteur website . Representatives of the major European clones similar to I (RUH similar to 875) and II (RUH similar to 134) were used as controls. The two groups of isolates were characterized for their carbapenem resistance genes: 154 of 202 carried blaOXA-58 alone, 21 of 202 also carried blaOXA-23, and 27 of 202 carried blaOXA-23 alone. No isolates were positive for blaOXA-24. Genotype analysis of all isolates identified four distinct patterns by PFGE, which correlated with four distinct sequence types (STs) by MLST. The distribution of these four clusters in Italy confirmed the propensity of A.similar to baumannii for nosocomial cross-transmission in a vast geographical area. We observed that clones similar to A and B had similarities with European clone similar to II and I respectively. By MLST, clone similar to A was ST2, like European clone similar to II, and clone similar to B was ST1, like European clone similar to I. PFGE and MLST showed the same discriminatory power and reproducibility. In addition, the two methods were concordant in defining CRAB Italian clones and in correlating them with the two pan-European clones.