Clostridium perfringens food poisoning is one of the most common types of human food borne illness (1). The foods usually involved are cooked meat or poultry products containing large numbers of viable cells. A heat- labile enterotoxin produced only by sporulating cells (2) induces the major symptoms of diarrhea in perfringens poisoning.
Egg Yolk Agar Base, Modified is based on McClung and Toabe Agar Base (3) for isolation and detection of C. perfringens. In Egg Yolk Agar Base, Modified, CDC Anaerobe Agar is used as a base to prepare the medium. CDC Anaerobe Agar is a nonselective, highly enriched medium for the cultivation of obligate anaerobes, developed by Center for Disease Control (CDC) (4). The medium is made suitable for detection of lipase and lecithinase activity by the addition of egg yolk emulsion (5-7).
Casein enzymic hydrolysate and papaic digest of soyabean meal provide the essential nutrients along with carbonaceous and nitrogenous substances. Yeast extract supplies B-complex nutrients. Ssdium chloride maintains the osmotic equilibrium. Lcystine is an amino acid which also acts as a reducing agent. Vitamin K1 and hemin help to enhance the growth of anaerobic organisms. Organisms producing lecithinase break down lecithin present in the egg yolk emulsion producing an insoluble opaque precipitate around the colonies. Lipase-producing organisms break down free fatty acids (in the egg yolk emulsion) forming an iridescent sheen on the surface of the colonies. Lipase activity may be delayed, therefore plates should not be discarded as negative before incubation for a week. Proteolytic activity is seen as clear zones around the colonies (6). The media should be directly inoculated with the test specimen. Prior to inoculation, the media plates should be reduced by placing in an anaerobic jar for 18-24 hours.
An enrichment broth should be simultaneously inoculated with the test sample to detect small number of anaerobic organisms. Standard procedures for the isolation of organism should be referred. Incubation should be carried out for 18-48 hours and continued for 7 days.
Storage and Shelf-life:
Store below 30°C in tightly closed container and use the prepared medium as fresh as possible. Use before expiry date on the label.
References:
1. Labbe R., 1989, Clostridium perfringens, In Foodborne Bacterial Pathogens Ed., Doyle M. P., P.191, Marcel Dekker, New York , N.Y.
2. Duncan C. L., 1973, A. J. Bacteriol., 113:932
3. McClung and Toabe, 1947, J. Bacteriol., 53:139
4. Dowell, Lombard, Thompson and Armfield, 1977, Media for Isolation, Characterization and Identification of Obligately Anaerobic Bacteria, CDC Laboratory Manual, Center for Disease Control, Atlanta, Ga.
5. Dowell and Hawkins, 1987, Laboratory Methods in Anaerobic Bacteriology, CDC Laboratory Manual, HHS Publication No. (CDC) 87-8272, Centers for Disease Control, Atlanta, Ga.
6. Murray P. R., Baron J. H., Pfaller M. A., Jorgensen J. H. and Yolken R. H., (Ed.), 2003, Manual of Clinical Microbiology, 8th Ed., American Society for Microbiology, Washington, D.C.
7. Baron E. J., Peterson and Finegold S. M., Bailey & Scotts Diagnostic Microbiology, 9th Ed., 1994, Mosby-Year Book, Inc., St. Louis Mosby Co., St. Louis.