Screening the clinical isolates of Acinetobacter baumannii for biofilm potential/trait from a tertiary care hospital in India

Background: The multidrug resistance and biofilm potential of Acinetobacter baumannii have made it difficult for the clinicians and healthcare providers to treat and control its spread, leading to mortalities: 23% in hospitalized patients and 43% among patients in intensive care. Biofilm has become an important virulent factor for Acinetobacter baumannii as it not only protects the pathogen against the antibiotics but also enables it to evade the immune system of the host. Resistance gene transfer happens among the species and across other species in the biofilm. Knowing if the clinical isolate of A. baumannii from a patient has biofilm trait will help the clinician to make an informed, better antibiotic strategy. The relationship between biofilm trait and multidrug resistance in the clinical isolates of A. baumannii was investigated in this study. Methods: 72 clinical isolates of A. baumannii were included in this study. Antimicrobial drug sensitivity testing was performed on these isolates against two front line antibiotics: Imipenem (10µg) and Meropenem (10µg) by Kirby-Bauer disk diffusion method. Biofilm formation was monitored and estimated quantitatively in 96-well polystyrene plate. The biofilms were examined under scanning electron microscope (SEM) while some key regulatory genes of the biofilm synthetic pathway were screened by PCR to corroborate the phenotype. Results: The 72 clinical isolates were characterized for carbapenem sensitivity. They were grouped as Carbapenem Resistant (CRAB) (n=58) and Carbapenem Sensitive (CSAB) (n=14) isolates. All isolates formed biofilm in our study and based on the amount of biofilm formed they were grouped as: strong biofilm producers 83% (60/72), moderate biofilm producers 11% (08) and weak biofilm producers 6% (04). Genotyping by PCR showed certain key regulatory genes like ata, bap and csu in almost all the isolates. Morphological studies showed that the biofilms were multi-layered, closely knit and with a thick strong matrix clearly visible under SEM. Conclusions: All the isolates efficiently formed robust biofilms, 83% of which formed strong biofilms (P value < 0.05). Both CRAB and CSAB formed biofilms inferring that biofilms production is inherent trait and phenotype of these clinical isolates of A. baumannii. The genotyping confirmed the presence of certain key genes of biofilm pathway and the strong integrity of the biofilms were revealed under SEM. Our study endorses the view that biofilms constitute an inherent trait which apparently enables A. baumannii to acquire MDR phenotype.