S. M. Madson1 , E. W. Laster1 , M. Z. Thomas1 , K. A. Watts1 , J. N. Sofos2 , 1FDA Denver District Laboratory, Denver, CO 80225, 2Colorado State University, Fort Collins, CO 80523
Shigella is a pathogen of concern due to its presence in produce, and because a low dose can cause infections. Detection of this organism in produce by FDA laboratories uses a PCR procedure and a cultural method involving aerobic incubation (FDA Domestic and Import Produce Assignments). While PCR detection is quite sensitive, it is extremely difficult to isolate a culture from samples that are positive for the ipaH gene, possibly due to background flora overgrowth. Pathatrix is a new technology patented by Matrix Microscience for the concentration of cells of various food pathogens through the use of immunomagnetic capture beads. Cationically charged beads for the capture ofcells from foods are also available. Since no immunomagnetic beads specific for Shigella were available, in this study, we evaluated the cationic beads for potential use in the detection of Shigella in cantaloupe rinses. A S. sonnei culture containing a green fluorescent protein (GFP) gene was used to inoculate cantaloupe rinses at various levels. The Pathatrix concentration step with or without pre-enrichment was followed by cultural detection after aerobic or anaerobic enrichment. The results of this preliminary testing indicated that the cationic beads used were able to capture Shigella, but since they are not specific for Shigella, they also captured and concentrated other background microorganisms which outgrew Shigella during enrichment. Use of specific Shigella immunomagnetic capture beads in combination with anaerobic pre-enrichment and/or enrichment should enhance detection of the pathogen.