Objectives:

To evaluate the effect of azithromycin (AZM) on biofilm formation and composition in multidrug resistant (MDR) Acinetobacter baumannii.

Material and methods:

Ninety-six A. baumannii isolates were studied. Antimicrobial susceptibility and sub-minimum inhibitory concentration (sub-MIC) were determined by the broth microdilution method. Carbapenemase genes were detected by polymerase chain reaction and clonal diversity by pulsed-field gel electrophoresis (PFGE). Biofilm formation without AZM and AZM sub-MIC were determined by crystal violet staining. AZM-free biofilm composition and AZM sub-MIC were determined by detachment assays.

Results:

The selected A. baumannii were MDR; 93.8 % were carbapenem-resistant and 24 were OXA-24-positive. PFGE showed predominance of clones A (53 %), B (34.7 %) and C (12.5 %). Biofilm production at AZM sub-MICs decreased in 53.1 %, increased in 34.7 % and showed no differences in 12.5 % of isolates, in comparison with biofilm production without AZM.

Conclusion:

AZM sub-MIC can reduce biofilm production in A. baumannii MDR isolates with decreased protein and DNA in the biofilm. Our results may be useful in synergy studies for new therapeutic alternatives.