Abstract:
Temperature is one of the most important preservation methods in food industry. The
objective of this study was to determine the effects of the sublethal temperature stresses
on the culturability and morphology of Staphylococcus aureus ATCC 25923. The pure
culture of S. aureus was grown in Tryptone Soya Broth before being subjected to three
different temperature stresses (20°C, 40°C and 45°C) after reaching the log phase (6
hour) and stationary phase (16 hour). The survival of the bacteria in terms of cell injury
on non-selective agar TSA and TSAS (TSA with added 4% NaCl) at these different
temperature stresses were examined. Standard growth curve at optimal temperature
(37°C) and the survival curves of S. aureus after subjected to different temperature
stresses were obtained and the percentages of cell injury were also calculated. Results
obtained showed that S. aureus is more heat resistant at 20°C during the log phase rather
than at higher temperature stresses (40°C and 45°C). The apparent of biphasic curves
were observed during the stationary phase of S. aureus. The percentage injury was
higher at log phase rather than stationary phase where the highest percentage injury
occurred after 9 hour of exposure at 20°C. The morphological changes observed under
light microscope with an imaging system showed that the occurrence of clumping
phenomenon during the stationary phase at 20°C and 45°C. The reported results
described the culturability and morphology of pathogenic Gram-positive S. aureus under
different temperature stresses.
