Biofilm Formation by Salmonella Enteritidis in a Simulated Egg Processing Environment and Its Sensitivity to Chlorine and Hot Water Treatment

Introduction: Salmonella Enteritidis outbreaks were usually associated with consumption of eggs. The ability of Salmonella Enteritidis to form biofilms on egg contact surface may serve as a source of cross-contamination, posing potential safety risks to consumers.

Purpose: This study aimed to investigate the biofilm formation by Salmonella Enteritidis in a simulated egg processing environment and its resistance to chlorine and hot water treatment.

Methods: Three Salmonella Enteritidis strains (ATCC 13076, 124 and 125) were individually inoculated into 0.1% peptone water (PW), 10% whole eggs (WE), 10% egg yolks (EY) and 10% egg whites (EW). Stainless steel coupons were immersed in the inoculated media and incubated at 25°C under a static condition. Biofilm densities were evaluated after 2, 4, and 7 days of incubation, and biofilms at day 2 or day 7 were treated by 200 ppm chlorine (pH 6.8) for 5 min or by hot water at 71.1°C for 30 s. Mean values were compared using ANOVA.

Results: Densities of Salmonella Enteritidis biofilms and their resistance to chlorine and hot water were affected by growth medium but not by strains and incubation time. Salmonella Enteritidis formed significantly (P < 0.05) denser biofilms in PW and EW (6.28 CFU/cm²) than WE and EY (4.94 CFU/cm²). However, biofilms formed in PW were less resistant to chlorine treatment than those formed in WE, EY, and EW, with average log reductions of 6.41, 2.28, 0.63 and 0.95 CFU/cm², respectively. All biofilm cells were very sensitive to hot water treatment, which reduced the cell populations by 4.30-6.39 log. 

Significance: The study provides information on the biofilm forming abilities of S. Enteritidis in a simulated egg processing environment and the effectiveness of chlorine and hot water treatment against Salmonella Enteritidis biofilms, which may aid in the development of better sanitation strategies.