Purpose: The objective of this project is to provide the scientific bases for how to improve the conventional detection method for SE in shell eggs in FDA’s BAM.
Methods: Two SE isolates (2 phage types) were used for comparison of five different preenrichment broths, and evaluation of egg:preenrichment broth ratios for the detection of SE in shell eggs. The effect of surface disinfection on the detection of SE in shell eggs was also investigated. The experiment was conducted in three replications.
Results: The results indicated that tryptic soy broth (TSB) was similar to TSB plus ferrous sulfate (FeSO4); but significantly (α = 0.05) better than nutrient broth, universal pre-enrichment broth, and buffered peptone water when used for preenrichment of SE in eggs. Egg:broth ratios at 1:9 and 1:2 produced significantly (α = 0.05) higher SE populations after preenrichment with TSB with inoculum levels at 4 CFU SE/100 g eggs and 40 CFU SE/1,000 g eggs than the ratio at 1:1. SE 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 for SE 13-2, respectively; 9.20 ± 0.04 and 9.16 ± 0.05 log CFU/ml for SE CDC_2010K_1543, respectively.
Significance: In conclusion, preenrichment with TSB was as effective as with TSB plus FeSO4. Surface disinfection of eggs had no effect on SE populations in the preenrichment culture. These discoveries can substantially reduce the workload and shorten the detection time for SE in shell eggs and eventually improve the current FDA’s BAM method for detection of SE in shell eggs.