P1-38 Detection and Isolation of Salmonella from Naturally Contaminated Pine Nuts Using Several Different Preenrichment Media

Monday, July 23, 2012
Exhibit Hall (Rhode Island Convention Center)
Hua Wang, U.S. Food and Drug Administration, College Park, MD
Introduction:   A multistate outbreak of Salmonella Enteritidis infections, linked to Turkish pine nuts purchased from bulk bins at grocery store chain, located in the Mid-Atlantic States, was reported by CDC from October to November 2011. A total of 43 individuals from 5 states were infected with the outbreak strain of Salmonella Enteritidis.

Purpose:   To determine the relative efficacies of five preenrichment media for the detection of Salmonellafrom naturally contaminated pine nuts: lactose broth (LB), buffered peptone water (BPW), modified BPW (mBPW), universal preenrichment (UP) broth, and BAX broth.

Methods:   Twenty-five g pine nut test portions were soaked in 225 ml portions of LB, BPW, mBPW, UP and BAX broths. The preenrichments were incubated for 24 h at 35°C. The Bacteriological Analytical Method (BAM) Salmonella culture method was followed thereafter. The contamination level was determined with the most probable number method. Two real-time PCR (qPCR) analyses were performed on 24 h-incubated preenrichment media on ABI Fast 7500.  qPCR1 is a singleplex PCR assay developed by FDA to detect the invA gene (unique to Salmonella) and is currently deployed by FDA’s mobile lab.  qPCR2 is a multiplex qPCR assay recently developed by FDA to detect Salmonella by targeting invA and ttr genes to enhance the reliability of detection results.

Results:   The BAM culture results showed no significant differences (> 0.05) among the five different preenrichment media for the detection of Salmonella from pine nuts. However, both qPCR procedures  had significantly (< 0.05) higher false negative rates when used with LB, the current BAM Salmonellapreenrichment medium for pine nuts, as compared to the other four media. qPCR results, from both qPCR procedures, corresponded perfectly with culture results from mBPW, UP and BAX media (100% sensitivity).

Significance:   This study addressed a need to improve current BAM Salmonella culture method for the detection of Salmonella from pine nuts when using real-time PCR as screening method.