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Material Safety Data Sheet

Organisms

Organisms this product works with:

Dehydrated Culture Media

CROSSLEY MILK MEDIUM

Code: CM0213

This medium is suitable for use where Litmus Milk was previously specified.

Typical Formula*

gm/litre

Skim milk powder

100.0

Peptone

10.0

Bromocresol purple

0.1

pH 6.8 ± 0.2 @ 25°C

 
* Adjusted as required to meet performance standards

Directions
Cream 110g of the powder with a little distilled water and gradually dilute to 1 litre with continuous mixing. Tube in 10ml quantities and autoclave at 121°C for 5 minutes.

Description
A simple medium originally described by Crossley1 for the routine examination of canned food samples for anaerobic bacteria, this medium has evolved as the result of comparative trials carried out by Crossley with several standard media. It is capable of giving rapid growth without the use of special anaerobic apparatus, yet the bacteria detected may be provisionally identified by their reactions upon the medium.

Crossley milk medium is recommended, in the second edition of Tanner’s `The Microbiology of Foods’ 2, for the examination of meat, meat products, and canned foods for sporing anaerobes.

Technique
The following method of examination is suggested: Inoculate 10ml of Oxoid Crossley Milk Medium with 1.5 to 2.0g of the sample. Incubate for 3 to 4 days at 37°C and examine for the following striking and characteristic reactions.

  Organism 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 odour 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 odour 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 peptonisation commencing at the surface and spreading downwards. Digestion not complete, no blackening, no odour, no gas production B. subtilis
B. vulgaris
7 Acid and clot, or slightly acid only. Peptonisation in some cases B. cereus
B. coagulans

B. silvaticus and various cocci (more detailed tests required)


Crossley1 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 Jepsen3 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. Riemann4 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.

Any of the above additions may be used to supplement Oxoid Crossley Milk Medium.

Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the prepared medium at 2-8°C.

Appearance
Dehydrated medium: Pale blue coloured, free-flowing powder
Prepared medium: Pale blue coloured solution

Quality control

Positive controls:

Expected results

Clostridium sporogenes ATCC® 19404 *

Purple colour, gas production, soft curd (see table)

Bacillus cereus ATCC 10876 *

Yellow colour, acid and clot (see table)

Salmonella typhimurium ATCC14028 * Alkaline reaction (either green/blue or blue colour of milk)

Negative control:

 
Uninoculated media No change
* This organism is available as a Culti-Loop®

References
1. Crossley E.L. (1941) J. Soc. Chem. Ind. 60, 131-136.
2. Tanner F.W. (1944) `The Microbiology of Foods’ 2nd ed., Garrard Press, London, pp. 893, 1001-1002.
3. Jepsen A. and Albertsen V.E. et al. (1957) `Meat Hygiene’, World Health Organization, Geneva, pp. 424-426, 439.
4. Riemann H. (1959) Personal communication.

 
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