Development of a Liquid Crystal-based Salmonella Detection Assay

Introduction: Salmonella is the most common causative agent of foodborne illness in meat. The CDC estimates that 1.2 million cases of salmonellosis occur annually in the United States, resulting in 400 deaths per year. Because elimination of Salmonella from food is nearly impossible, detection of the organism before it reaches the consumer is essential. Crystal Diagnostics (CDx) has developed a liquid crystal technology that detects microsphere aggregates formed when specific antibody coated microspheres interact with their target pathogen.

Purpose: This study evaluates anti-Salmonella magnetic microspheres in a rapid pathogen detection system.

Methods: Anti-Salmonella magnetic microspheres were assayed against 32 Salmonella enterica subsp. enterica serovars representative of serogroups A-F. Salmonella serovars were grown overnight in TSB; 6.75 x 10⁶ CFU were assayed using the anti-Salmonella magnetic microspheres via immunomagnetic separation and detected using the liquid crystal technology. In addition, 21 non-Salmonella species were grown overnight in TSB or BHI and assayed undiluted. Finally, 50 ground beef samples from an institutional processing plant, along with appropriate controls, were enriched overnight in mTSB + novobiocin and assayed for Salmonella.

Results: When Salmonella serovars were grown in non-selective media, and processed through the existing CDx methodology, 30 of 32 serovars (94%) were detected. When 21 non-Salmonella species were assayed after overnight growth in non-selective media, two species (9.5%) were identified as Salmonella. After comparing CDx methods with culture-based methods, all 50 samples from the beef processing plant were correctly identified.

Significance: These preliminary data suggest that integration of commercially available anti-Salmonella antibody-coated microspheres into the liquid crystal based immunoassay will permit broad-based detection of Salmonella. Such an assay would permit rapid detection of this important foodborne pathogen.