Characterization of resistance mechanisms and genetic relatedness of carbapenem-resistant Acinetobacter baumannii isolated from blood, Italy

The aim of this study was to characterize resistance mechanisms and genetic relatedness of 21 carbapenem-resistant Acinetobacter baumannii blood isolates, collected in Italy during a 1-year multicenter perspective surveillance study. Genes coding for carbapenemase production were identified by PCR and sequencing. PFGE, multiplex PCRs for group identification, and MLST were used to determine genetic relationships. Carbapenem resistance was consistently related to the production of oxacillinases, mostly the plasmid-mediated OXA-58 enzyme. Strains producing the OXA-23 enzyme (chromosomally-mediated) were also detected. Seven PFGE clones were identified, 4 of which being related to international (ICL-I, and ICL-II) or national clonal lineages. Multiplex PCRs identified 4 different groups (group 2 being dominant), further distinguishable in 6 sequence types by MLST. The heterogeneity of profiles highlights the diffusion of international and national clonal lineages in Italy. Continuous surveillance is needed for monitoring the spread of these worrisome strains equipped with multiple drug resistance mechanisms.