Molecular characterisation of colistin and carbapenem-resistant clinical isolates of Acinetobacter baumannii from Southeast Europe.

OBJECTIVES:To characterise 11 colistin- and carbapenem-resistant Acinetobacter baumannii isolates recently emerging in hospital settings. METHODS:A. baumannii isolates were collected from hospitalised patients under colistin treatment in three countries of Southeast Europe: Turkey, Croatia, and Bosnia and Herzegovina. Isolates were identified using molecular methods. RESULTS:Isolates from Turkey and Croatia belong to the sequence types ST195 or ST281 of the clone lineage 2, while the single isolate from Bosnia and Herzegovina belongs to the ST231 of clone lineage 1. All isolates turned out to be highly resistant to colistin (MIC ≥ 16 mg/L) and have point mutations in pmrCAB operon genes. The colistin-resistant isolate from Bosnia and Herzegovina had a unique P170L point mutation in the pmrB gene and the R125H point mutation in the pmrC gene. The L20S mutation in the pmrA gene was detected only in isolates from Croatia and has never been reported before in isolates from this country. CONCLUSION:Colistin resistance in A. baumannii in hospitalised patients receiving colistin treatment is a result of chromosomal mutations. The pattern of point mutations in pmrCAB genes suggests a spread of specific colistin-resistant isolates within the hospital.