Genotypic and Phenotypic Characterization of Clinical Isolates of Staphylococcus Aureus for Biofilm Formation Ability

摘要

The objective of the study was to characterize Staphylococcus aureus (S. aureus) isolated from human and animal clinical cases for their biofilm formation ability by genotypic and phenotypic methods. A total of 130 S. aureus strains isolated from human wound (n=20), animal wound (n=70) and animal mastitis (n=40) cases were subjected to screening for 3 different biofilm associated genes (bap, icaA and icaD) and for phenotypic assessment for biofilm formation using Congo red agar, modified Congo red agar and microtitre plate assay. PCR assays were standardized for the detection of bap, icaA and icaD genes. The results indicated that icaA gene was present in 51.15% of the isolates and bap gene was present in 8.46% isolates. None of the isolates were positive for icaD gene. Human isolates (65%) had higher occurrence of icaA gene in comparison to animal isolates (49.09%). Dog wound isolates had higher occurrence of bap gene. Of the 3 methods used for phenotypic expression of biofilm by S. aureus isolates modified Congo red agar method showed 86.92% isolates to be positive, whereas by Congo red agar method only 63.07% S. aureus were found to be biofilm producer. Microtitre plate assay showed 75.38% S. aureus isolates to be biofilm producers. A good correlation was observed between genotypic and phenotypic biofilm formation ability of the isolates. Bap gene contained isolates showed higher biofilm producing ability compare to icaA gene harbored isolates.