Temperature shock, injury and transient sensitivity to nisin in Gram negatives.
OBJECTIVE
The effect of thermal stresses on survival, injury and nisin sensitivity was investigated in Salmonella Enteritidis PT4, PT7 and Pseudomonas aeruginosa.


RESULTS
Heating at 55 degrees C, rapid chilling to 0.5 degrees C or freezing at -20 degrees C produced transient sensitivity to nisin. Cells were only sensitive if nisin was present during stress. Resistance recovered rapidly afterwards, though some cells displayed residual injury. Injury was assessed by SDS sensitivity, hydrophobicity changes, lipopolysaccharide release and NPN uptake. LPS release and hydrophobicity were not always associated with transient nisin sensitivity. Uptake of NPN correlated better but persisted longer after treatment.


CONCLUSIONS
Thermal shocks produce transient injury to the outer membrane, allowing nisin access. After treatment, the permeability barrier is rapidly restored by a process apparently involving reorganization rather than biosynthetic repair.


CONCLUSIONS
Inclusion of nisin during food treatments that impose sub-lethal stress on Gram negatives could increase process lethality, enhancing microbiological safety and stability.
Boziaris
I S
IS
School of Biomedical and Life Sciences, University of Surrey, UK.
Adams
M R
MR
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003080:Cold Temperature; D005615:Freezing; D018869:Heat-Shock Response; D006358:Hot Temperature; D009561:Nisin / Q000494:pharmacology*; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D012477:Salmonella enteritidis / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D013499:Surface Properties
D000900:Anti-Bacterial Agents; D009561:Nisin