Effect of stress on biofilm formation by icaA positive and negative strains of methicillin resistant Staphylococcus aureus

To determine the effect of physical and chemical stress factors e.g. antibiotics, NaCI, glucose, heat shock, cold shock and sonic waves on biofilm formation by icaA positive and negative strains of Methicillin resistant Staphylococcus [S.] aureus. Experimental study. Microbiological Analytical Centre, Pakistan Council of Scientific and Industrial Research [PCSIR] Laboratories Complex, Karachi, from January to December 2010. One strain of Staphylococcus aureus labelled as FA was isolated from a food sample and the other strain labelled as CL was a clinical strain. Biofilm assays were performed in brain-heart infusion [BHI] medium and in BHI supplemented with 7% NaCI, 5% glucose, or sub-inhibitory concentrations of Vancomycin, Oxacillin, Ampicillin, Tetracycline, Erythromycin, Rifampicin and Ciprofloxacin. Polymerase chain reaction [PCR] was used for screening of the icaA and mecA genes. The FA and CL were identified as MRSA carrying mecA gene. The strain FA showed biofilm formation without any treatment and was found to carry icaA gene contrary to CL, that does not contain this gene therefore, is unable to produce biofilm under normal conditions without any stress. The use of sub-lethal doses of cell wall active antibiotics, exposure to 7% NaCI, sonication, and heat shock were found to augment biofilm quantity in FA, an icaA positive strain and induce biofilm mode of growth in CL, an icaA negative strain. Anti-protein synthesis antibiotics did not show any effect on biofilm formation process in icaA positive or negative strains. There is a role of anti-cell wall factors i.e. sonication, heat shock, NaCI and antibiotics in the induction of biofilm mode of growth in MRSA and Methicillin sensitive S. aureus. The factors which partially damage bacterial cell wall, equally, induce biofilm formation in icaA positive or negative S. aureus

Biofilm formation and isolation of Staphylococcus aureus from blood cultures of dental patients undergoing oral surgical procedures

The objective of this study was the detection and separation of S. aureus from blood cultures of patients undergoing oral surgical procedures. Antibiotic sensitivity pattern and biofilm formation of S. aureus were also performed. Total 250 patients undergoing oral surgical procedures were selected for bacteriological examination. 5ml of Blood sample was collected in blood culture bottles containing tryptone soya broth. Blood sample was incubated at 37[degree sign] C for 7 days and after incubation subculturing was done on appropriate Media. The plates were then incubated at 37[degree sign]C aerobically for 24 hours, after which isolated colonies were obtained. S.aureus was identified by Gram staining, colony morphology, pigment production, catalase, coagulase and often biochemical tests. Antibiotic susceptibility was performed by disc diffusion technique on isosensitivity agar. Strains of S.aureus were used for biofilm formation by simple tubemethod. With the help of spectrophotometer at 570 nm optical density was measured. S.aureus [ATTC2523] was analyzed for biofilm production. Bacterial isolates in descending order were S.aureus 56%, E.coli 25%, Pseudomonas spp. 13%, S.typhi 4%and Shigella spp2%. S.aureus was resistant to different antibiotics. Biofilm production of S.aureus was detected in 16.17%of the S.aureus and mostly in association with antibiotic resistant bacteria. S.aureus was the predominant group of bacteria isolated from blood cultures of dental patients. Increased antibiotic resistance of S.aureus may be due to biofilm production resulting in persistent dental infections