Comparison of different preenrichment broths, egg:preenrichment broth ratios, and surface disinfection for the detection of Salmonella enterica ssp. enterica serovar Enteritidis in shell eggs

Salmonella enterica ssp. enterica serovar Enteritidis is the leading reported cause of Salmonella infections. Most Salmonella Enteritidis infections are associated with whole shell eggs and egg products. This project attempted to lay the foundation for improving the Food and Drug Administration’s current Bacteriological Analytical Manual method for the detection of Salmonella Enteritidis in shell eggs. Two Salmonella Enteritidis isolates were used for comparisons among different preenrichment and enrichment media and for the evaluation of egg:preenrichment broth ratios for the detection of Salmonella Enteritidis in shell eggs. The effect of surface disinfection on the detection of Salmonella Enteritidis in shell eggs was also investigated. The results indicated that tryptic soy broth (TSB) was similar to TSB plus ferrous sulfate, but significantly (α = 0.05) better than nutrient broth, Universal Preenrichment broth, and buffered peptone water when used for preenrichment of Salmonella in shell eggs. Salmonella Enteritidis populations after enrichment with Rappaport-Vassiliadis broth were 0.40 to 1.11 log cfu/mL of culture lower than those in preenrichment cultures. The reduction was statistically significant (α = 0.05). Egg:broth ratios at 1:9 and 1:2 produced significantly (α = 0.05) higher Salmonella Enteritidis populations after preenrichment with TSB with inoculum levels at 4 cfu/100 g of eggs and 40 cfu/1,000 g of eggs than the ratio at 1:1. Salmonella Enteritidis populations in TSB preenrichment cultures of shell eggs surface-disinfected with 70% alcohol:iodine/potassium iodide solution and untreated control were 9.11 ± 0.11 and 9.18 ± 0.05 log cfu/mL, respectively, for SE 13-2, and 9.20 ± 0.04 and 9.16 ± 0.05 log cfu/mL, respectively, for SE CDC_2010K_1543. Surface disinfection of eggs did not reduce the sensitivity of detection of Salmonella Enteritidis in liquid eggs. These results could improve the Food and Drug Administration’s current Bacteriological Analytical Manual method for the detection of Salmonella in shell eggs by simplifying the preenrichment medium and changing the sample handling before enrichment.