Thermo Scientific™ Crossley Milk Medium (Dehydrated)

Description

• Carry out routine examination of canned food samples for anaerobes with Thermo Scientific™ Oxoid™ Crossley Milk Medium (Dehydrated)
• The medium gives rapid growth without the use of special anaerobic apparatus while allowing the detected bacteria to be provisionally identified by their reactions upon the medium
• Canned foods are more often prone to flat sour spoilage due to contamination by either mesophilic or thermophilic anaerobic spore formers
• Crossley milk medium is recommended, in the second edition of Tanner’s `The Microbiology of Foods’ 1 , for the examination of meat, meat products, and canned foods for sporing anaerobes
• Organism Diagnostic reaction Organism indicated 1 Neutral or alkaline pH (purple colour), gas production,soft curd followed by rapid digestion of casein, often to clear brown liquid, formation of black sediment accompanied by typical foul odor Cl
• putrificum Cl
• sporogenes Cl
• flabelliferum Cl oedematiens Cl
• histolyticum 2 No initial change of pH, formation of soft curd within 2-3 days, slight gas formation
• Complete digestion later with alkaline reaction, no odor Cl
• centrosporogenes 3 Slight acidity (pale yellow colour), formation of soft curd, and whey
• Slight gas production Cl
• sphenoides 4 Acid (bright yellow colour), formation of firm clot and gas
• Bleaching of the indicator may sometimes occur Cl
• butyricum 5 (a) Acid, formation of ’stormy’ clot
• (b) Acid and ’stormy’ clot but with less gas and cloudy whey (a) Cl
• perfingens (b) Usually Cl
• tertium 6 Strong alkaline pH, with peptonization commencing at the surface and spreading downwards
• Digestion not complete, no blackening, no odor, no gas production B
• subtilis B
• vulgaris 7 Acid and clot, or slightly acid only
• Peptonization in some cases B
• cereus B
• coagulans B
• silvaticus and various cocci (more detailed tests required) Crossley 2 modified his medium, by the addition of 20% (w/v) of autoclaved meat or fish paste, so that it was suitable for the examination of vegetable and dairy products
• The medium recommended by Jepsen 3 in `Meat Hygiene’ published by the World Health Organization, is Crossley Milk Medium modified by the addition of 20% (w/v) of cooked fish; it is suitable for the examination of meat products for clostridia, and gives diagnostic reactions essentially similar to those outlined above
• Riemann 4 modified Crossley Milk Medium by the addition of 0.08% of cysteine hydrochloride, before autoclaving, or by the addition of 1mL of a sterile 10% sodium thioglycollate solution just before use
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