Many of the operations employed in food processing can sublethally damage staphylococci, temporarily rendering the cells incapable of growth on selective media commonly employed for their enumeration. Stressed staphylococci are, under the proper conditions, capable of recovery and subsequently normal growth, including enterotoxin production by some strains. Therefore, to ensure the safety of foods, alternative enumeration methods designed to include stressed cells should be employed. Several methods have been proposed which employ a period of preincubation in/on a non-selective medium (liquid or solid) to allow recovery before exposing the cells to selective agents. In addition, recent findings have indicated that the increased sensitivity of stressed staphylococci is at least partially due to hydrogen peroxide toxicity: based on these findings direct plating and most-probable-number techniques containing catalase to degrade peroxide have been proposed. Greatly improved enumeration of stressed cells is possible, employing these methods without the use of a preincubation period.
1University of Arizona.
2University of Illinois.