Evaluation of rapid screening techniques for detection of Salmonella spp. from produce samples after pre-enrichment according to FDA BAM and a short secondary enrichment

Abstract

Conventional detection of Salmonella from foods involves enrichment and isolation on selective media which can significantly lengthen time to result. The objective of this study was to evaluate the utility of an accelerated plating procedure and the use of rapid screening devices for Salmonella detection. Fresh produce was inoculated with Salmonella at ~2·5, ~7·5 and ~25 CFU sample(-1) . After 24 h pre-enrichment, subcultures were made into TT and RV broths and further incubated at 42°C for an additional 7 and 24 h. Enrichments were streaked for isolation of Salmonella as well as tested by rapid screening methods. The 7-h accelerated plating procedure worked well from 4/6 to 6/6 in all produce samples inoculated at the lowest level. Both the RapidChek and Neogen Reveal tests worked as well as the VIDAS-SLM after 24 h secondary enrichment, but failed to detect the pathogen after 7 h selective enrichment in romaine lettuce and tomatoes, while fractional detection was observed in cilantro and jalapenos. Both devices detected Salmonella on cantaloupe at the lowest level of inoculation. An abbreviated selective enrichment procedure worked well to accelerate the isolation of colonies of Salmonella from contaminated samples providing isolates for further characterization 1 day earlier than standard analysis.

Significance and impact of the study: In the event of a foodborne disease outbreak, rapid identification and characterization of the pathogen is essential to prevent the spread of disease and reduce the number of illnesses. This study reports the utility of an abbreviated secondary enrichment for the isolation of Salmonella in artificially contaminated fresh produce at very low levels. In addition, incorporation of rapid, easy-to-use lateral flow devices to screen enrichments can provide a low cost (equipment and highly trained personnel), high return (rapid identification of contaminated food) investment in the timely pathogen screening of fresh produce.

Keywords: Salmonella; VIDAS; lateral flow device; produce; rapid screening.