Saipriya Kamaraju, Dr. Venkataraman Sritharan and Dr. Archana Giri
Background: The multidrug resistant nature and biofilm forming capacity of Acinetobacter baumannii have made it difficult for the clinicians and healthcare providers to treat and control its spread, leading to mortalities of 23% for hospitalized patients and 43% for patients under 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. The relationship between biofilm trait and multidrug resistance in the clinical isolates of A. baumannii was investigated in this study.
Methods: Antimicrobial drug sensitivity testing was performed on the 72 A. baumannii isolates against two front line antibiotics: Imipenem (10 µg) and Meropenem (10 µg) by Kirby-Bauer disk diffusion method. Biofilm formation was 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). Certain key regulatory genes like ata, bap and csu were detected in almost all the isolates and the biofilms were multi-layered, closely knit and clearly visible under SEM.
Conclusions: All the isolates efficiently formed robust biofilms of which 83% of the isolates 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 and apparently enable A. baumannii to acquire MDR.
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