The Correlation Between Biofilm Formation and Drug Resistance in Nosocomial Isolates of Acinetobacter baumannii

Acinetobacter baumannii has become a major cause of hospital-acquired infections due to its resistance to common antibacterial agents. Biofilm formation is a well-known pathogenic mechanism involved in A. baumannii infections. The aim of this study was to determine the association between biofilm formation and antibiotic resistance, production of AmpC and Extended-Spectrum β-lactamases (ESBL) in clinical isolates of A. baumannii collected from two hospitals of Tehran. Sixty isolates of A. baumannii were employed of which, 30 were burn and 30 were non-burn isolates. Biofilm formation was measured by the microtiter plate assay. The production of AmpC was detected by the AmpC disc test with cloxacillin, and ESBL production was determined using the double disc synergy test. Biofilm production occurred in 61.7% of the isolates among which, non-burn isolates (59.5%) produced more biofilm compared to the burn strains (40.5%). Multidrug resistance was observed in both biofilm positive and negative strains. However, the non-burn isolates were significantly more resistant to meropenem and tobramycin regardless of their potential to form biofilm. Interestingly, biofilm-producing non-burn isolates were significantly more resistant to amikacin, gentamicin, tobramycin and meropenem. Production of AmpC was also significantly higher in biofilm-producing non-burn isolates. Conversely, ESBL production was significantly higher in burn isolates. There was an association between biofilm formation and AmpC but not ESBL-production among non-burn isolates. The potential to form biofilm correlated with antibiotic resistance and AmpC production in non-burn burn isolates of A. baumannii. On the other hand, the burn strains produced significantly higher amounts of ESBL yet biofilm production was unrelated to antibiotic resistance or ESBL-production.