RESUMO
Injury and recovery characteristics of Staphylococcus aureus after exposure to acetic, hydrochloric, and lactic acids were studied. Cells of S. aureus were acid-injured at 37°C for 30 min in acidic isotonic saline solutions and were enumerated on Trypticase Soy Agar (TSA) and Trypticase Soy Agar with 7% NaCl (TSAS). A difference of at least 25% between counts on the non-selective (TSA) and selective (TSAS) media was considered evidence of acid injury. The activities of coagulase and thermonuclease were reduced in injured cells. The absence of leakage of 260/280 nm absorbing material from acid-injured cells, together with the absence of change in membrane fatty acids, indicated that membrane damage was not associated with acid injury. Inhibition of RNA synthesis was observed. During recovery, renaturation and synthesis of proteins, including enzymes and ribosomal proteins, occurred which then provided the intracellular conditions for subsequent growth.
RESUMO
Staphylococcus aureus cells were injured thermally by exposure to 55°C for 15 min and allowed to recover for various lengths of time at 37°C in Trypticase Soy Broth. During recovery, thermostable nuclease (TNase) production was measured using a turbidimetric-spectrophotometric method. Production increased during recovery until approximately 2 h after injury when the amount of TNase began to decrease unexpectedly. Protease(s) was thought to be degrading the TNase, and positive results of gelatin agar diffusion tests and heat inactivation experiments supported this hypothesis. Protease inhibitor studies with ethylene diamine tetraacetate (EDTA) and phenyl methyl sulfonyl fluoride (PMSF) confirmed the involvement of protease(s) in the observed decrease in TNase activity. Implications of TNase inactivation in screening of foods for enterotoxigenic staphylococci are discussed.
