Mechanisms of triple stress-mediated damage in stationary phase cells of Salmonella typhimurium exposed to succinate-acidified hypochlorite system at 5° C

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°C resulted in symptoms of injury. Cells became sensitive to 40 μg/ml lysozyme, 50 μg/ml actinomycin D and 100 μg/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°C, then 5 ppm chlorine at 5°C and the singular chill shock stress at 5°C, respectively. The magnitudes of cellular damage, however, were suggestive of synergistic interactions among the component stress factors of the TSS.
The findings obtained indicate 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.