Shigella Broth 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
User Quality Control
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 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
Principles of the Procedure
Identity Specifications
Solution:
3.1% solution, soluble in purified water. Solution is pale to light amber, clear to slightly opalescent.
Prepared Appearance:
Pale to light amber, clear to slightly opalescent.
Tryptone is a source of carbon, nitrogen, vitamins and minerals. Phosphates are the buffering agents in the solution. Sodium chloride maintains the osmotic balance. Glucose is the carbohydrate source. Polysorbate 80 neutralizes preservatives in food products, allowing bacteria to grow. Novobiocin suppresses the growth of nuisance organisms commonly found in foods.
Reaction of 3.1% Solution at 25°C:
pH 7.0 ± 0.2
Formula
Difco™ Shigella Broth Dehydrated Appearance: Off-white to light tan, free-flowing, may appear moist, free of extraneous material.
Difco™ Shigella Broth
Cultural Response
Approximate Formula* Per Liter Tryptone.................................................................... 20.0 Dipotassium Phosphate................................................ 2.0 Monopotassium Phosphate.......................................... 2.0 Sodium Chloride.......................................................... 5.0 Glucose........................................................................ 1.0 Polysorbate 80............................................................. 1.5
Difco™ Shigella Broth Prepare the medium per label directions. Inoculate and incubate under anaerobic conditions at 40-44°C for 18-24 hours. ORGANISM
ATCC™
INOCULUM CFU
RECOVERY
Escherichia coli
25922
100
Good
Shigella flexneri
12022
100
Good
Shigella sonnei
25931
100
Good
Directions for Preparation from Dehydrated Product
Shigellosis can manifest itself as a waterborne or a 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. dysenteriae 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, non-sporeforming 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.
*Adjusted and/or supplemented as required to meet performance criteria
1. Dissolve 31.5 g of the powder in 1 L of purified water. Mix thoroughly. 2. Autoclave at 121°C for 15 minutes. Cool to 45-50°C. 3. Prepare novobiocin solution by weighing 50 mg of novobiocin into 1 L of purified water. Sterilize by filtration using a 0.45μ filter. 4. Add 2.5 mL of sterile novobiocin solution from Step 3 to 225 mL of Shigella Broth. 5. Test samples of the finished product for performance using stable, typical control cultures.
Procedure For food samples, follow appropriate standard methods for details on sample collection and preparation according to sample type and geographic location.3-6 Consult appropriate standard references for details on test methods using Shigella Broth.3-6
Expected Results Growth is evident by the appearance of turbidity.
Difco™ & BBL™ Manual, 2nd Edition
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References 1. Sureshbabu, Poothirikovil, Abuhammour, and Burny. 2008. Shigella infection. . 2. Mehlman, Romero and Wentz. 1985. J. Assoc. Off. Anal. Chem. 68:552. 3. U.S. Food and Drug Administration. 2001. Bacteriological analytical manual, online. AOAC International, Gaithersburg, Md. 4. Health Canada. The compendium of analytical methods, online. Food Directorate, Health Products and food Branch, Health Canada, Ottawa, Ontario Canada. 5. International Organization for Standardization. 2004 Microbiology of food and animal feeding stuffs – horizontal method for the detection of Shigella spp. ISO 21567, 2004-11-01. International Organization for Standardization, Geneva, Switzerland. 6. Downes and Ito (ed.). 2001. Compendium of methods for the microbiological examination of foods, 4th ed. American Public Health Association, Washington. D.C.
Availability Difco™ Shigella Broth BAM CCAM COMPF ISO
Cat. No. 214915 Dehydrated – 500 g
Difco™ & BBL™ Manual, 2nd Edition
