Repair of Thermal Injury of Staphylococcus aureus

Abstract

posure of Staphylococcus aureus MF 31 to sublethal temperatures produced a temporary change in the salt tolerance and growth of the organism. After sublethal heat treatment at 55 C for 15 min, more than 99% of the viable population was unable to reproduce on media containing 7.5% NaCl. The data presented demonstrate that thermal injury, in part, occurred owing to changes in the cell membrane, which allowed soluble cellular components to leak into the heating menstruum. When the cells were placed in a limiting medium, complete recovery did not occur, regardless of the incubation time. The temperature and the pH which produced the optimal rate of recovery were similar to those described previously for the multiplication of uninjured cells. However, the rate of recovery as well as the unchanging total count during recovery indicated that cell multiplication was not a factor during the recovery process. The nutrient requirements for the complete recovery of injured cells consisted of a solution containing an energy source, such as glucose, a mixture of amino acids, and phosphate. The use of the metabolic inhibitors, penicillin, cycloserine, 2,4-dinitrophenol, and chloramphenicol, did not inhibit recovery. Actinomycin D, however, completely suppressed recovery. This result implied that ribonucleic acid synthesis was particularly involved; this inference was substantiated by radio tracer experiments. The rate at which label was incorporated in the nucleic acid fraction paralleled that of recovery and the return of salt tolerance. Although an exaggerated lag phase is a cultural response to thermal injury (21, 22), it can more accurately be described as a recovery period. As defined by Harris (15), "it is the period of 'getting back' organisms from their (sublethal) environment." This is usually accomplished by incubating the treated organisms in a nutrient environment. The use of metabolites or some type of nutrient medium for post-treatment incubation of damaged cells was first reported by Heinmetz, Taylor, and Lehman (17). They demonstrated that heattreated organisms produced higher counts on minimal media if they were previously incubated in 0.2% solutions of various metabolites. Garvie (13), on the other hand, refuted these data by demonstrating that it was "virtually impossible" to purify media with respect to a nitrogen source. ' This report is from a dissertation submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree in Food Science.

Artisanal Sonoran cheese (Cocido cheese): an exploration of its production process, chemical composition and microbiological quality

“…A thermal treatment of 55 ∘ C for 15 min has been reported to negatively affect the growth of S. aureus. 42 Similar conditions were shown during the cooking of Cocido cheese (50 and 60 ∘ C for 20 min). Nevertheless, despite this reduction, we found that the final S. aureus count in dairies D1, D2, D5 and D6 surpassed the Mexican permissible limit (3 log 10 colony-forming units (CFU) mL −1 ).…”

Effects of High Hydrostatic Pressure on Heat‐Resistant and Heat‐Sensitive Strains of Salmonella

“…Apparently, the lack of available nutrients prevented recovery. Such an occurrence has been shown with heat-injured bacteria also deprived of nutrients (Iandolo and Ordal, 1966).…”

Influence of Ionic and Nonionic Materials on Thermally-nduced Ribonucleic Acid Degradation and Leakage in Staphylococcus aureus

“…Such a degradation may be responsible for thermally-induced death in this strain (1,3) and in other strains of Staph. aweus (6,7). It is, however, difficult to link this degradation with loss of viability of Staph.…”