Effect of Chlorine-Induced Sublethal Oxidative Stress on the Biofilm-Forming Ability of Salmonella at Different Temperatures, Nutrient Conditions, and Substrates.

The present study was conducted to evaluate the effect of chlorine-induced oxidative stress on biofilm formation by various Salmonella strains on polystyrene and stainless steel (SS) surfaces at three temperatures (30, 25 [room temperature], and 4 degrees C) in tryptic soy broth (TSB) and 1/10 TSB. Fifteen Salmonella strains (six serotypes) were exposed to a sublethal chlorine concentration (150 ppm of total chlorine) in TSB for 2 h at the predetermined temperatures. The biofilm-forming ability of the Salmonella strains was determined in 96-well polystyrene microtiter plates by using a crystal violet staining method and on SS coupons in 24-well tissue culture plates. All tested strains of Salmonella produced biofilms on both surfaces tested at room temperature and at 30 degrees C. Of the 15 strains tested, none (chlorine stressed and nonstressed) formed biofilm at 4 degrees C. At 30 degrees C, Salmonella Heidelberg (ID 72), Salmonella Newport (ID 107), and Salmonella Typhimurium (ATCC 14028) formed more biofilm than did their respective nonstressed controls on polystyrene (P <= 0.05). At room temperature, only stressed Salmonella Reading (ID 115) in 1/10 TSB had significantly more biofilm formation than did the nonstressed control cells (P <= 0.05). Salmonella strains formed more biofilm in nutrient-deficient medium (1/10 TSB) than in full-strength TSB. At 25 degrees C, chlorine-stressed Salmonella Heidelberg (ATCC 8326) and Salmonella Enteritidis (ATCC 4931) formed stronger biofilms on SS coupons (P <= 0.05) than did the nonstressed cells. These findings suggest that certain strains of Salmonella can produce significantly stronger biofilms on plastic and SS upon exposure to sublethal chlorine.