COAGULASE MANNITOL AGAR BASE

The genus Staphylococcus comprises 28 accepted or proposed species, 14 of which may be encountered in human clinical specimens. Staphylococci are generally found on the skin and mucous membranes of humans and other animals. Some of the pathogenic staphylococci in both humans and animals produce an enzyme called coagulase and detection of this enzyme is used in the laboratory to identify these organisms.
These media are used for the isolation of Staphylococcus aureus from clinical specimens and for differentiation of S.aureus from other species on the basis of coagulase production and mannitol fermentation. Chapman for the first time introduced a medium for selective isolation and differentiation of Staphylococci. Tellurite-glycine media were designed by Zebovitz et al and Marwin for selectively isolating coagulase-positive Staphylococcal species. Present medium is based on Esber and Faulconer formulation. Mutant or old cultures of S.aureus may be weak coagulase producers. They should be freshly sub cultured and rechecked. Escherichia coli ferments mannitol and may be weakly coagulase positive. Coagulase production is dependent on the presence of a fermentable sugar like mannitol in this case. It is also dependent on the presence of a protein factor in the HI infusion and blood plasma. When mannitol is fermented, the pH of the medium surrounding the coagulase positive colonies drops. This drop in pH is indicated by the change in colour of the bromocresol purple indicator, which turns yellow and exhibits yellow zones around the colonies.
An opaque area of coagulated plasma forms around the colonies of coagulase positive organisms. Staphylococcus epidermidis is coagulase negative and mannitol non-fermenting species, which does not change the colour of the medium. Coagulase negative species may ferment mannitol and produce a yellow zone around the colonies but an opaque zone will not be formed

for isolation and di?erentiation of pathogenic staphylococci from clinical specimens