Vogel-Johnson Agar Medium, 500G

Vogel-Johnson Agar Medium is prepared according to the formula of Vogel and Johnson (1) and is recommended for the microbial limit test (pharmaceutical testing) in USP (2). Originally it was developed by Zebovitz (3) as a Tellurite Glycine Agar, a selective medium for the detection of coagulase positive Staphylococci. This medium is used to detect Staphylococcus in pharmaceutical and cosmetics products (4). Staphylococcus in prevalent pathogen in food borne poisoning due to its enterotoxin production. It is commensal found on skin and scalp of human body. Vogel-Johnson modified the medium by adding phenol red as a pH indicator and increased the mannitol quantity. Tryptone and yeast extract provide nitrogenous and carbonaceous compounds, long chain amino acids, vitamin B complex and other growth nutrients. Dibasic potassium phosphate gives buffering capacity to the medium. During first 24 hours of incubation, contaminating organisms are almost inhibited by tellurite, lithium chloride and high glycine content. Staphylococcus aureus may be inhibited by these inhibitors but get compensated by mannitol and glycine. Coagulase-positive Staphylococci reduce potassium tellurite to metallic free tellurium and thus produce black colonies surrounded by yellow zones. This yellow color is due to phenol red indicator, which turns yellow in acidic condition by the fermentation of mannitol. Prolonged incubation may result in the growth of black coagulase negative colonies. Application: For Selective Isolation of Coagulase Positive, Mannitol Fermenting Staphylococcus Aureus from Heavily Contaminated Food and Clinical Specimens in Accordance with Us Pharmacopoeia