Repair of salt tolerance and recovery of lost D-alanine and magnesium following sublethal heating of Staphylococcus aureus are independent events

Abstract

Sublethal heating of Staphylococcus aureus S6 in potassium phosphate buffer caused loss of salt tolerance, D-alanine, and magnesium. During incubation in rich complex media all three of the damaged sites were repaired. Repair occurred more slowly but went to completion in a dilute synthetic medium (DSM), free of D-ala. DSM plus penicillin or D-cycloserine allowed repair of salt tolerance but recovery of normal levels of D-ala or Mg was prevented. When DSM-repaired cells were cultured into fresh rich medium they grew rapidly after a short lag. Cells which had acquired their salt tolerance in DSM plus cycloserine and were D-ala and Mg deficient grew slowly and had a lag of 3 h. We suggest that heat damage has two separate primary targets in S. aureus cells: the membrane, which is manifested by loss of salt tolerance, and a second site, possibly teichoic acids, manifested by loss of D-ala and Mg.

Importance Considering Increased Recovery of Injured Microorganisms to Attain Reproducible Sterilization Validation

“…Concerning Mg effect, our experiment indicated no effect to increase population contrary to calcium [1,4].…”

“…In SCDA, several sorts of substances such as calcium, amino acids and glucose are required to add to attain reproducible SAL and successful sterility assurance [1][2][3][4][5].…”

Reduced ribosomal thermal denaturation in Listeria monocytogenes following osmotic and heat shocks

“…Previous studies in this laboratory have shown that environmental conditions prior to and during heating can considerably affect the thermotolerance of many microorganisms including Listeria monocytogenes [1,2]. In these and other studies investigating mild temperature thermal inactivation, ribosomal damage and degradation have been implicated, either directly or indirectly, as the underlying mechanisms of inactivation [1][2][3][4][5][6][7][8][9].…”

Thermal inactivation of Listeria monocytogenes studied by differential scanning calorimetry

“…In Staphylococcus aureus, sub-lethal heating causes both release of wall magnesium and destabilization of the ribosomes (Hurst & Hughes, 1978, 1981. Hurst (1984) has argued that ribosome damage is a result of magnesium depletion, as heating in a Tris/MgC12 buffer does not result in dissociation of the ribosomes into 30s and 50s particles, whereas heating in a magnesiumchelating buffer does.…”