The effect of prior heat shock on the thermotolerance of Staphylococcus aureus in broth culture and induction of heat shock proteins was investigated. S . aureus cell wall was, also, examined using Scanning Electron Microscope (SEM). Specific bacteria were grown at 37°C the optimum temperature (control), sublethally heated at 47, 52, 57 and 60°C for various times, and heat treated at 68°C were done. The estimated average of the D68-values for the control was 4.83 min while for heat shocked treatments ranged from 5.43 to 10.23 min. The current results, also, indicated that 8 - 16 new bands were induced by applying heat shock treatments with molecular weights ranged from 9 to 135 KDa. The induced heat shock proteins further confirmed the increased the thermotolerance. Moreover, selected heat shock treatments caused severe destruction in cell wall (i.e., rupture, irregular and leakage of cell contents), while heat shocked cells after incubating at 37°C for overnight in enriched medium became similar to that of the one’s normal. The enhanced heat resistance of S. aureus should be thought-about in cause of planning effective thermal processes to confirm the microbiological food safety.

Staphylococcus aureus isolates were isolated from fifty clinical samples collected from Ain Shams University Hospitals (March - July 2016) and identified using biochemical and microbiological tests. PCR was performed using specific primers to determine the isolates of Methicillin - Resistant Staphylococcus aureus (MRSA) based on the presence of mecA gene. Thirty-four isolates from total fifty isolates (68%) were identified as MRSA isolates. To study the genotoxicity for this isolates, forty-five mice were injected with these MRSA isolates and comet and micronuclei assays were performed on mice liver tissues and bone marrow respectively. These assays revealed 24% - 22% DNA damage as an indicator for chromosomal breakage by comet and micronucleus assays respectively which indicate that infection with these isolates leads to mutations. Studying these isolate furthermore will give an insight on how critical maintaining high standard hygiene in Egyptian hospitals and attention to infection control system can prevent occur of outbreaks