Comparative Study on Injury and Recovery of Staphylococcus aureus using Microwaves and Conventional Heating

Cells of Staphylococcus aureus FRI-100 were exposed to a sublethal temperature of 50°C for 30 min in 0. 1M phosphate buffer using either microwave energy or a conventional heating source. Following thermal stress, cells were allowed to recover. Injury was monitored as the difference between cell counts when an inoculum from the recovering cells was plated on TSA and TSAS. Total viable population following either heat treatment was 10⁶ cells/ml as indicated by TSA counts. When the same suspensions were plated on TSAS, a viable count of 1.7 × 10³ cells/ml resulted from conventional heating compared with 5.6 × 10² cells/ml following microwave irradiation. Greater membrane damage was sustained by the microwave-heated cells judging by the release of 260-nm absorbing intracellular substances. In addition, the microwave-heated cells regained their enterotoxin synthesis ability at a slower rate following recovery as judged by equal counts on TSA and TSAS. Microwave heating also exerted less injurious effects on S. aureus when carried out anaerobically.