Vogel-Johnson Agar Medium , 250g

Description: 

Vogel-Johnson Agar, by selecting and identifying coagulase positive and mannitol-fermenting strains, permits the early detection of Staphylococcus aureus from heavily contaminated foods and clinical specimens. It corresponds to the specification of the United States Pharmacopoeia1 in terms of its formula. 

Vogel and Johnson2 modified the Tellurite Glycine Agar formula of Zebovitz et al.3 by doubling the mannitol concentration to 1% (w/v) and adding Phenol Red as a pH indicator. The enhanced fermentation reaction which occurs as a result of the increase in mannitol content is clearly indicated by the development of yellow zones surrounding the colonies. 

Staphylococcus aureus is able to reduce tellurite to metallic tellurium resulting in growth as black colonies. 

During the first 24 hours of incubation contaminating organisms are almost completely inhibited by tellurite, lithium chloride and the high glycine concentration. Virtually all the organisms that grow in this time are coagulase positive. 

Organisms that grow as black colonies surrounded by a yellow zone after incubation at 35-37°C for 24 hours may be presumed to be Staphylococcus aureus. 

Prolonged incubation may result in the growth of black coagulase -negative colonies and if these organisms also ferment mannitol they may be falsely identified from their appearance as Staphylococcus aureus. In these circumstances further tests of identity should be carried out before concluding that the organism is Staphylococcusaureus. 

Specification: 

250g