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

Eggs are nutrient-dense yet recognized vehicles for <i>Salmonella</i> 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 <i>Salmonella enterica</i> subsp. <i>enterica</i> serovar Enteritidis (<i>S.</i> Enteritidis), serovar Typhimurium (<i>S.</i> Typhimurium), and serovar Thompson (<i>S.</i> Thompson) across washing temperatures and exposure times. Eggs were inoculated by immersion in 100 mL of a <i>Salmonella</i> 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 <i>Salmonella</i> populations on the eggshells. Washing with 150 ppm NaOCl significantly reduced counts (3-5 log) under all conditions versus unwashed eggs (<i>p</i> < 0.001). Maximum inactivation for <i>S.</i> Enteritidis occurred at 35 °C for 45 s (4.95 log), whereas <i>S.</i> Typhimurium was greatest at 45 °C for 45 s (5.48 log). In contrast, <i>S.</i> 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 <i>S.</i> Enteritidis, <i>S.</i> Typhimurium, and <i>S.</i> 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 <i>Salmonella</i> transmission across the food supply chain.