Department of Veterinary Public Health and Epidemiology, College of Veterinary science &Animal Husbandry, Navsari Agricultural                                                                                       University, Gujarat, India

The control of microorganisms is one of the most important aspects of food preservation and its destruction ensures food safety. Prevalence of antibiotic resistance of thermo tolerant Staphylococcus aureus isolated from a variety of foods has increased. Staphylococcus aureus survive under a wide range of environmental stresses. The objective of this study was to evaluate effect of osmotic stress (2, 4, 8, 12% NaCl), pH (6, 4, 2) as well as cold (4^OC) stress on susceptibility of two laboratory isolates of Staph. aureus towards 9 different antibiotics. The susceptibility of antibiotics was tested against unstressed (control), stressed or post-stressed Staph. aureus isolates (an ATCC strain and a dairy) using the discs diffusion method. Unstressed Staph. aureus were sensitive to all tested antibiotics. In general, when Staph. aureus exposed to salt, pH and cold stress, their antibiotic resistance increased as salt concentration increased to 8 or 12%, pH reduced to pH 4 or 2, and as temperature decreased to 4^OC. Results showed that the dairy isolate and ATCC reference strain, both were resistant with Amoxycillin in stressed or post-stressed condition. The bacteria developed resistance in cold and pH stress with Streptomycin and osmotic pressure stress (4% to 12% NaCl) with Gentamicin in both isolates under stressed or post-stressed condition. The resistance against Gentamicin and Getifloxacin was revealed in acid stress condition. The both the isolates developed resistance against all four antibiotics under different stress conditions suggests that increased use of antibiotics as bacteriostatic agent, rather than bactericidal purpose in food processing and preservation systems may stimulate antibiotic resistance responses in Staphylococcus aureus.