To determine the effect of physical and chemical stress factors e.g. antibiotics, NaCl, 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% NaCl, 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% NaCl, 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, NaCl 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.