Purpose: This study aimed to determine the effects of temperature, pH, and nutrient availability on Salmonella Enteritidis biofilm formation on stainless steel coupons (SSCs) and its resistance to chlorine treatment.
Methods: Biofilm formation was investigated on SSCs using Salmonella Enteritidis ATCC 13076 (bdar morphotype) and F124 (rdar morphotype). SSCs were immersed in tryptic soy broth (TSB) or diluted TSB (1/20 TSB) at various pH conditions (pH 5.3, 7.3, and 8.3) and incubated at 4 or 25°C. Biofilm density was evaluated after 2, 4, and 7 days of incubation and the formed biofilms were subsequently exposed to 50 ppm chlorine (pH 6.8) for 1 min. Mean values were compared using ANOVA.
Results: The density of Salmonella Enteritidis biofilm and its resistance to chlorine treatment were not greatly influenced by incubation time or pH. However, biofilm formed in 1/20 TSB had a significantly (P < 0.05) higher density compared to that formed in TSB. In addition, 1/20 TSB enhanced biofilm resistance to chlorine at 25°C, especially for Salmonella Enteritidis F124 that had 0.84-log reduction in 1/20 TSB but 3.79-log reduction in TSB at pH 7.3. Due to the greater sensitivity of biofilm formed at 4°C, no significant difference (P > 0.05) in resistance to chlorine between TSB and 1/20 TSB was observed.
Significance: This study may help to design better strategies to control Salmonella biofilm formation under different stress conditions.