Exposure for 20 min of stationary phase cells of Salmonella typhimurium to a combined triple stress system (TSS) treatment comprising
hypochlorite derived 5 ppm free available
chlorine in
solution acidified with 1%
succinate (pH 2.5) and at a chill
shock temperature of 5 degrees C resulted in symptoms of injury. Cells became sensitive to 40 micrograms/ml
lysozyme, 50 micrograms/ml
actinomycin D and 100 micrograms/ml
ribonuclease B, to which control cells were resistant. Metabolic injury was indicated by reduction in colony forming ability of stressed cells on minimal
salts glucose agar M9 medium. There was no detectable leakage loss of 260-280 nm-absorbing materials. This was also confirmed by assay of the cellular
RNA material components. Loss of
alkaline phosphatase activity was observed in the stressed cells. The intensity of induced cellular damage as measured by
lysozyme sensitivity was greatest in the cells exposed to the complete TSS, followed by those stressed in 1%
succinate at 5 degrees C, then 5 ppm
chlorine at 5 degrees C and the singular chill
shock stress at 5 degrees C, respectively. The magnitudes of cellular damage, however, were suggestive of synergistic interactions among the component stress factors of the TSS. The findings obtained indicated impairment of the structural integrity and functional capabilities of the permeability barriers and the inactivation of certain periplasmic
enzymes. The resultant cumulative cellular damage from the TSS exposure may therefore enhance greater sensitivity of treated cells to subsequent stress factors.