Biofilm may not be Necessary for the Epidemic Spread of Acinetobacter baumannii

Biofilm is recognized as a contributing factor to the capacity of Acinetobacter baumannii to persist and prosper in medical settings, but it is still unknown whether biofilms contribute to the spread of A. baumannii. In this study, the biofilm formation of 114 clinical A. baumannii isolates and 32 non-baumannii Acinetobacter isolates was investigated using a microtiter plate assay. The clonal relationships among A. baumannii isolates were assessed using pulsed-field gel electrophoresis and multilocus sequence typing, and one major outbreak clone and 5 other epidemic clones were identified. Compared with the epidemic or outbreak A. baumannii isolates, the sporadic isolates had significantly higher biofilm formation, but no significant difference was observed between the sporadic A. baumannii isolates and the non-baumannii Acinetobacter isolates, suggesting that biofilm is not important for the epidemic spread of A. baumannii. Of the multidrug-resistant (MDR) A. baumannii isolates in this study, 95.7% were assigned to international clone 2 (IC2) and showed significantly lower biofilm formations than the other isolates, suggesting that biofilm did not contribute to the high success of IC2. These findings have increased our understanding of the potential relationship between biofilm formation and the epidemic capacity of A. baumannii.