Bactericidal Efficacy of Sodium Hypochlorite on Eggshells Contaminated with Three Salmonella Serovars

Eggs are nutrient-dense yet recognized vehicles for Salmonella transmission. Because eggshells are easily contaminated during production and handling, washing is critical to reduce microbial load. Here, we evaluated the bactericidal efficacy of 150 ppm sodium hypochlorite (NaOCl) against Salmonella enterica subsp. enterica serovar Enteritidis (S. Enteritidis), serovar Typhimurium (S. Typhimurium), and serovar Thompson (S. Thompson) across washing temperatures and exposure times. Eggs were inoculated by immersion in 100 mL of a Salmonella suspensions (approximately 8 log CFU/mL) prepared separately for each serovar, air-dried for 1 h, and subsequently washed in 150 ppm NaOCl for 35, 40, 45, or 50 °C. Following washing, eggs were transferred to buffered peptone water, homogenized, and plated on xylose lysine deoxycholate agar to quantify the residual Salmonella populations on the eggshells. Washing with 150 ppm NaOCl significantly reduced counts (3-5 log) under all conditions versus unwashed eggs (p < 0.001). Maximum inactivation for S. Enteritidis occurred at 35 °C for 45 s (4.95 log), whereas S. Typhimurium was greatest at 45 °C for 45 s (5.48 log). In contrast, S. Thompson showed a nonmonotonic, time-dependent pattern, with maximum inactivation occurring at 40 °C for 45 s (5.17 log). Overall, 150 ppm NaOCl effectively reduced S. Enteritidis, S. Typhimurium, and S. Thompson on eggshells. Efficacy appeared to be serovar dependent, with maximal reduction occurring at different temperatures for each serovar. These findings support standardized egg-washing guidelines to minimize Salmonella transmission across the food supply chain.