Inactivation and Sublethal Injury Kinetics of Staphylococcus aureus in Broth at Low Temperature Storage

Abstract

Low temperatures are widely used to ensure food quality and safety. However, sublethally injured Staphylococcus aureus is an important microbiological safety concern in low temperature food. The objective of this study was to develop predictive inactivation kinetic models for the inactivation and sublethal injury of S. aureus in broth at different temperatures (4 to -18°C) and time points. S. aureus was diluted in tryptic soy broth plus 0.6% (wt/vol) yeast extract (TSBYE) to obtain approximately 10(8) CFU/ml and was stored separately at 4, -3, -11, and -18°C. After specific time points within 96 days, survival of S. aureus was determined on TSBYE and TSBYE agar plus 10% NaCl for enumeration of the total viable and noninjured cell numbers, respectively. Linear, Weibull, and modified Gompertz models were applied to determine survival curve regression. The combination of low temperature and time resulted in S. aureus inactivation, although the cells were able to survive in this sublethal state. Storage temperature was the critical parameter in survival of S. aureus. The modified Weibull model successfully described a second model of noninjured S. aureus cell survival at different low temperatures, whereas only the linear model was able to fit the total viable cells. The predictive model may be used to estimate the level of S. aureus contamination in food at low storage temperatures and times, and it provides new insight into the sublethally injured survival state of S. aureus in low temperature food.

Effects of ZnO nanoparticle‐coated packaging film on pork meat quality during cold storage

“…In order to determine the inhibition effects of ZnO nanoparticle‐coated film on foodborne pathogens, S. aureus was selected for further study because it is a frequently detected foodborne pathogen in chilled meat samples that has shown high resistance against low temperatures . As shown in Fig.…”

“…In order to investigate the inactivation mechanism of ZnO nanoparticles on microorganisms under cold conditions, S. aureus was selected as a reference for determining changes in cell morphology, because it is an important and normally detectable foodborne pathogen in meat during cold storage, and has shown a great resistance against low temperature. 15,19 Briefly, four aliquots of late-exponential phase cells were treated with or without 2 g L −1 ZnO nanoparticles at 4 or 37 ∘ C, respectively. After 24 h treatment under aerobic conditions, 1 mL of each culture was centrifuged at 4000 × g for 5 min.…”

“…Previous studies focused on the evaluation of the inhibitory effects of ZnO nanoparticles on foodborne pathogens, but there is little information on the effects of ZnO nanoparticle‐coated packaging on the quality of pork during storage. Furthermore, it is widely known that low temperature is a stress condition for food‐derived microbiology, but the double effect of ZnO nanoparticles and low temperature on the growth of bacteria and meat quality has yet to be reported.…”

Comparative Proteomic and Morphological Change Analyses of Staphylococcus aureus During Resuscitation From Prolonged Freezing

“…Freezing is widely used to ensure the safety and quality of food. However, previous research has shown that low temperatures are sublethal to S. aureus ; at low temperatures, the S. aureus cell itself is damaged, but not dead ( Suo et al, 2014 ). The sublethally injured cells are hard to detect because of their sensitivities to selective components, such as high concentrations of sodium chloride, that are widely used in selective enrichment media ( Wu, 2008 ).…”

“…In contrast to the 4°C condition, freezing causes more damage to the cell membrane because of the formation of ice crystals ( Archer, 2004 ). Damage to the cell membrane leads to the leakage of cellular content, the disruption of membrane permeability, and the weakening of the osmoregulation ability of the cell ( Wesche et al, 2009 ; Suo et al, 2014 ). This damage also reduces the fluidity of the cell membrane and reduces the enzyme activity, according to a study on Listeria monocytogenes ( Schmid et al, 2009 ).…”