The Effects of Sub-Lethal Chlorine Induced Oxidative Stress on Biofilm Formation and Thermal Resistance of Salmonella
AdvisorMcDaniel, Christopher D.
Sharma, Chander Shekhar
Kiess, Aaron S.
The effect of sub-lethal chlorine stress on various strains/serotypes of Salmonella on biofilm formation and thermal resistance was studied. The effect of oxidative stress (induced by 150 ppm of chlorine in TSB) on Salmonella biofilm formation on polystyrene and stainless steel surfaces at three temperatures (4°C, 30°C, and room temperature) in nutrient rich (full strength TSB) and nutrient limited conditions (1/10th TSB) was evaluated. On polystyrene surface, chlorine stressed S. Heidelberg (strain ID 72), S. Newport (strain ID 107) and S. Typhimurium (ATCC 14028) formed stronger (P < 0.05) biofilms at 30°C. On stainless steel, the chlorine stressed S. Heidelberg (ATCC 8326) and S. Enteritidis (ATCC 4931) at room temperature formed stronger (P < 0.05) biofilms as compared to the non-stressed control cells. The thermal resistance of short-term (1h) and long-term (27d) chlorine stressed Salmonella Heidelberg and S. Typhimurium were compared with the non-stressed controls at three different temperatures (55°C, 58°C and 61°C) and two growth phases (logarithmic and stationary). The short-term stressed log phase cells (both serotypes) were found to be more sensitive (P< 0.05) to thermal inactivation in TSB. Upon long-term sub-lethal chlorine exposure, Salmonella developed a rugose morphotype on tryptic soy agar at 37°C. The rugose morphotype provided significant thermal protection (P< 0.05) against heat stress as compared to smooth morphotype. In chicken broth, at 55°C, short-term chlorine stressed stationary phase S. Typhimurium displayed a higher D55 value compared to non-stressed cells. The findings from this research reveal that some Salmonella strains have the potential to form stronger biofilms and exhibit higher thermal tolerance upon exposure to sub-lethal chlorine concentration.