CHAPMAN STONE MEDIUM

A selective medium for the isolation and presumptive identification of Staphylococci.

Code: CB1/3002

Typical formula g/l

Tryptone	10.0
Yeast extract	2.0
Gelatin	30.0
D-Mannitol	10.0
Sodium chloride	55.0
Ammonium sulphate	75.0
Dipotassium phosphate	5.0
Agar	15.0

pH 7.0 +/- 0.2

Directions

Suspend 202g in 1000 ml of cold distilled water: heat to boiling heat with frequent agitation and autoclave at 121^{_{°C for 15 minutes.}}

Description and Method

_{Chapman Stone Medium is a selective medium, prepared according to the original formula of Chapman, for the isolation and presumptive identification of Staphylococci.}

_{Inoculate the medium by streaking the specimen onto the surface and incubate at 37°C for 24-48 hours. Chapman Stone Medium is used for gelatin hydrolysis and mannitol fermentation tests. The selectivity of the medium is due to the high content of NaCl (5,5%) that allows a good growth of Staphylococcus aureus. For this reason Chapman Stone Medium is used for the isolation of staphylococci from foods suspected of being the cause of food poisoning. S. epidermidis also grows on Chapman Stone Medium even though it has different characteristics (white or non-pigmented colonies, with or without a clear zone) from S. aureus. Streptococcus faecalis is partially inhibited while Gram-negative bacteria are completely inhibited. The inoculated medium is opaque and whitish in colour, owing to precipitates that form between the gelatin and ammonium sulphate. The medium appears clear around the colonies of microorganisms that have liquefied the gelatin.}

_{Mannitol is present in the medium as a fermentable carbohydrate. S. aureus ferments the mannitol producing acidification of the medium around the colonies. To determine this acidification, typical colonies are removed and a drop of Bromocresol purple is added to the area. To confirm the identification of S. aureus, carry out the coagulase test and/or thermonuclease test.}

_{User quality assurance (37°C-48 hrs)}

_{Productivity Control}

_{S. aureus ATCC 25923: growth}

_{S. epidermidis ATCC 12228 growth}

_{Selectivity control}

_{P. mirabilis ATCC 12453: partially inhibited}

_Storage

_{Dehydrated medium: 15-30°C}

_{User prepared plates: 1 month at 2-8°C}

_Reference

_{Chapman (1948) - Food Research; 13 100}