P3-170 Evaluation of Growth Kinetics of Diverse Salmonella in Modified Bam Preenrichment for Shell Eggs

Wednesday, July 12, 2017
Exhibit Hall (Tampa Convention Center)
Melanie Butler , U.S. Food and Drug Administration , College Park , MD
Anna Laasri , U.S. Food and Drug Administration , College Park , MD
Thomas Hammack , U.S. Food and Drug Administration , College Park , MD
Gina Ryan , U.S. Food and Drug Administration , College Park , MD
Introduction: The FDA BAM method for detection of Salmonellain shell eggs uses a more concentrated preenrichment medium (1:2 egg:TSB) than 1:9 sample:broth ratio found in the BAM for other foods. Evidence shows strain differences and contamination levels may reduce outgrowth levels in 24-hour preenrichment cultures. The sensitivity of the current culture method permits detection of a single organism through multiple enrichment steps; however typical qPCR assays require higher cell concentrations (above 4-log). Factors affecting qPCR sensitivity and performance that may lead to false negative results include differences in genetic diversity (e.g., divergent alleles in target sequence), strain biology and cell injury incurred from prior exposure to specific egg factors (e.g., yolk or albumen).

Purpose: The purpose of this study was to evaluate factors affecting Salmonella growth dynamics in concentrated shell egg preenrichment, such as cell history, genetically diverse strains, and contamination ratio.

Methods: Homogenized albumen and whole egg aliquots were contaminated with eight egg and clinical Salmonella strains, representing seven serotypes, at two concentration levels. Preenrichment samples were inoculated with cold-adapted samples per BAM protocol. Salmonella growth was determined by plate count methods. Growth parameters were analyzed by the Baranyi model.

Results: Overall, growth rates in concentrated BAM shell egg preenrichment were similar for all strains evaluated. Lag phase duration was significantly different (p < 0.001) for serotype, contamination level, and prior exposure to albumen or whole egg at low temperature. However, maximum growth in preenrichment cultures exceeded 7-log cell concentration for all samples tested.

Significance: Our study provides evidence the revised Salmonella BAM shell egg preenrichment medium supports recovery of diverse and injured Salmonella cells to sufficient levels for detection by a rapid screening qPCR assay.