Evaluation of Stabilized Bismuth Sulfite Agar for Detection of Salmonella in Foods

Abstract

The combination of a new manufacturing process, packaging, and media engineering has all contributed to the development of extended shelf-life (stabilized)-plated media (DuraPak™). One of the first products stabilized by this process was bismuth sulfite agar plates (BSA). Stabilized BSA were stored 3-4 months at 35°C and then were inoculated in parallel with lab-prepared BSA following overnight aging at room temperature. Several strains of Salmonella were tested in pure cultures and in foods, including raw ground turkey, chicken, and nonfat dry milk. Also, two naturally contaminated raw ground turkey and chicken samples were tested. Both lab-prepared and stabilized BSA detected all positive samples after 24 h incubation at 35°C. Recovery, colony size, and amount of sheen produced by Salmonella were generally equivalent on both types of BSA, but stabilized BSA often yielded enhanced blackening of colonies and of the surrounding medium. Results were dependent upon strain of Salmonella used, type of food, and type of enrichment broth streaked onto the plates. Stabilized BSA were generally more inhibitory to nonsalmonellae than lab-prepared BSA, as demonstrated with pure cultures and food samples. Overall , the performance of stabilized BSA was equivalent to that of lab-prepared BSA.