Correlation between biofilm production and multiple drug resistance in imipenem resistant clinical isolates of Acinetobacter baumannii

Purpose: To study the qualitative and quantitative methods for the investigation of biofilm formation and to examine the correlation between biofilm and antibiotic resistance among the clinical isolates of Acinetobacter baumannii . We also verified the association between biofilm and presence of extended spectrum β-lactamases, particularly, bla PER-1 . Methods: A total of 55 isolates were subjected to susceptibility testing by disc diffusion method for 13 clinically relevant antibiotics. Screening for biofilm production was done by both qualitative and quantitative methods through tube and microtitre plate assay respectively. The presence of bla PER-1 was checked by PCR. Results: A. baumannii isolates showed very high resistance (>75%) to imipenem, cephotaxime, amikacin and ciprofloxacin. Only cefoperazone, netillin and norfloxacin were found to be effective agents. Results of microtitre and tube methods were concordant with 34 isolates (62%) showing biofilm formation. Resistance to four antibiotics such as amikacin (82% vs. 17.6%, P < 0.001), cephotaxime (88% vs. 11%, P P < 0.001), ciprofloxacin (70% vs. 29%, P =0.005) and aztreonam (38% vs. 11%, P =0.039) was comparatively higher among biofilm producers than non-biofilm producers. Microtitre assay additionally detected 14 weakly adherent isolates. Only 11 isolates had bla PER-1 gene and among these two were strong biofilm producers, while remaining were weakly adherent isolates. Conclusion: Microtitre plate method was found to be a more sensitive method for biofilm detection. This study demonstrates a high propensity among the clinical isolates of A. baumannii to form biofilm and a significant association of biofilms with multiple drug resistance. Presence of bla PER-1 appears to be more critical for cell adherence than for biofilm formation