Phenotypic Detection of Biofilm Formation among Clinical Isolates of Staphylococci

Abstract

Summary B iofilms are communities of microorganisms which are embedded within a matrix of extracellular polymeric material.Biofilm helps the bacteria to form stable communities of protection rather than live as free planktonic cells. Biofilm is a serious threat for the patient, as it may cause therapeutic failure with regular antibacterial therapy and also evade the host immune system.High antimicrobial concentrations are required to inactivate organisms growing in biofilms and resistance may often increases thousand folds. Biofilm formation is commonly regulated by quorum sensing mechanisms. Availability of nutrients, chemotaxis,and surface adhesion influence biofilm formation in microorganisms. Among the risk factors which increase susceptibility to biofilm formation; indwelling medical devices as intravascular catheters, prior hospitalization and prior antibiotic use and prior MRSA colonization. Mechanism of biofilm formation is either PIA dependent or PIA independent. Where, PIA dependent biofilm formation is mediated by ica gene, while PIA independent is mediated by Adhesive proteins,Poly-gamma-glutamic acid and extracellular DNA. Coagulase negative Staphylococci have higher capability of biofilm production than S. aureus. Also, CONS are associated with increased antimicrobial therapeutic failure. Hence CONS cannot be neglected if isolated from the nosocomial infection samples. There are different approaches applied for the detection of biofilm formation, however, it is evident, that a method allowing a complete analysis of biofilm does not exist. Methods of detection of biofilm formation are either phenotypic or genotypic. Phenotypic methods include Staining based methods,Metabolic activity assays, Culture based methods and Microscopy based methods, While genotypic methods depend on detection of ica gene. In our study, 150 staphylococcal isolates were obtained from specimens from patients from different departments of Ain Shams University.The isolates were subjected to identification according to morphology by Gram stain, cultural characters and biochemical reactions.CONS species were identified using automated identification system (Vitek 2, bioMérieux, France). All staphylococcal isolates were tested for antibiotic susceptibility performed by Kirby Bauer disc diffusion method. All staphylococcal isolates were tested for biofilm production by three phenotypic methods; TCP, TM and CRA. Tissue culture plate method detected total positive biofilm production in 111 out of 150 isolates (74%), Strong biofilm production in 65 (43.3%) isolates of staphylococci. Moderate biofilm production was detected in 46 (30.7%) isolates of staphylococci whereas 39 (26%) isolates were biofilm non-producers. The results of our study revealed that according to TCP S. aureus was the most common biofilm producing