Description

Intended Use:

 Shigella Broth is a selective enrichment broth for the isolation of Shigella species from food.

Summary and Explanation:

Shigella was first recognized as the etiologic agent of bacillary dysentery or shigellosis in the 1890s.¹

Humans are the only natural reservoir. No natural food products harbor endogenous Shigella species, but a wide variety of foods may be contaminated.¹

Shigellosis can manifest itself as a waterborne or foodborne disease. It is usually spread among people by food handlers with poor personal hygiene. Foods most often incriminated in the transmission of the disease have been potato salad, shellfish, raw vegetables, and Mexican food.²

The infectivity dose is extremely low. As few as ten S. dysentery bacilli can cause clinical disease, whereas 100-200 bacilli are needed for S. sonnei or S. flexneri infection.¹ One possible reason for this low-dose response may be that virulent Shigellae can withstand the low pH of gastric juice.¹ Shigella species are gram-negative, nonmotile, facultatively anaerobic, and non-spore-forming rods. They utilize glucose and other carbohydrates, producing acid but not gas. They do not decarboxylate lysine or ferment lactose. Shigella organisms may be difficult to distinguish biochemically from E. coli. The genus Shigella consists of four species: S. dysenteriae, S. flexneri, S. boydii, and S. sonnei.

Common contaminating bacteria found in food sources could mask the presence of any Shigella that could be present in the sample. Identification of Shigella is based on the successful isolation of the organism, biochemical characterization, and serological confirmation. Shigella Broth is based on the formula developed by Mehlman, Romero, and Wentz.2 Selectivity of the medium is achieved by the addition of novobiocin to the completed medium. Shigella Broth is recommended in standard test methods for use as a selective enrichment when isolating Shigella sp. from food samples^.3-6