Detection of Salmonella Typhimurium from Environmental Cellulose and Polyurethane Sponge Swab Rinsates as Compared to Direct Sponge Enrichment
Wednesday, August 3, 2022 – Poster Session 3. 9:00 a.m. – 11:00 a.m. Board Assignment P3-42.
Ryan Zimmerman, Laurie Post, LeAnne Hahn, Brian Farina, Charles Deibel
Introduction: Environmental testing for pathogens is a vital component of a food safety program. Testing of multiple pathogens from a single swabbing site requires the collection of a sponge swab for each pathogen target. Each entire sponge is enriched for direct detection. A sponge rinsing procedure with incubation of the rinsate was investigated as an alternative to direct sponge enrichment which could allow the detection of multiple pathogens from one sponge.
Purpose: To assess whether detection of Salmonella from cellulose and polyurethane sponge swab rinsates is equivalent to detection from direct sponge enrichments.
Methods: Cellulose sponges with DE neutralizing broth and polyurethane sponges with HiCap™ broth were inoculated with S. Typhimurium at 0.25CFU (n=10), 2.5CFU (n=10), 25CFU (n=5) and uninoculated (n=3); coinoculated with Citrobacter freundii (competitor) at 10X the pathogen inoculation level. Sponges were refrigerated 40h to simulate shipping conditions prior to enrichment.
Using an FDA BAM sponge procedure, lactose broth was added to one set of reference sponges (direct enrichment) and incubated. Fifty mL BPW was added to another sponge set and homogenized for 5 or 30 seconds manually or by stomacher. The rinsate from each was transferred to lactose broth and incubated. All incubated enrichments were streaked to XLD and chromogenic agars, and the plates examined for typical colonies.
Results: An unpaired statistical analysis compared rinsates to reference method sponges (Mantel-Haenszel Chi Square and relative sensitivity rate). A statistically significant difference was determined by Chi Square values of >3.84 between the reference method and the rinsate methods regardless of sponge type, homogenization time or procedure. At a 2.5CFU contamination level, a statistically lower recovery rate for rinsates was observed for 75% of the treatments. Significance: Sponge rinsates result in a lower Salmonella recovery rate and are not comparable to a standard direct enrichment (FDA BAM) for the detection of Salmonella from environmental sponges.