| 麦康凯琼脂 MacConkey Agar
用途:鉴别培养基，用于分离水、乳制品和生物学标本中的的大肠菌群和肠道致病菌
500g可以配制9.6 升培养基
2.5kg可以配制48.0 升培养基
Directions
Suspend 52g in 1 litre of distilled water. Bring to the boil to dissolve completely. Sterilise by autoclaving at 121°C for 15 minutes. Dry the surface of the gel before inoculation.
Description
A differential medium for the detection, isolation and enumeration of coliforms and intestinal pathogens in water, dairy products and biological specimens. MacConkey Agar corresponds to the medium recommended by the World Health Organization1, the Dept. of Health2 and by Windle Taylor3 for the bacteriological examination of water.
Although principally used for coliforms, this medium may also be employed for the differentiation of other enteric bacteria (including pathogens) and is suitable for the differentiation of Pasteurella species4.
Technique
Pathological specimens
Due to its ability to support the growth of pathogenic Gram-positive cocci (e.g. staphylococci and enterococci) as well as Enterobacteriaceae, MacConkey Agar is particularly recommended for the cultivation of pathogens which may be present in a variety of specimens such as urine, faeces and wound swabs. Whilst it is selective it does not suppress a mixed bacterial flora to the same extent as other inhibitory media (including other MacConkey agars). It provides a number of other diagnostic indications in addition to bile tolerance, such as colony morphology and chromogenesis. MacConkey Agar should be used in parallel with other selective indicator media such as Desoxycholate Citrate Agar, Bismuth Sulphite Agar, Brilliant Green Agar and Brilliant Green Bile (2%) Broth, and a non-selective medium such as Blood Agar.
Water Examination2,3
The medium may be used for the direct count of coli-aerogenes bacteria, using pour-plates prepared from known volumes of the water sample, but a more exact role for the medium is for the differentiation of organisms producing acid and gas in MacConkey Broth at 35°C: all positive broth tubes are plated on MacConkey Agar, the plates are incubated for 24 hours at 35°C and examined for typical colonies (see below). Colonies composed of Gram-negative non-sporing rods are subcultured for further identification.
The presence of enterococci in azide or tellurite media may be confirmed by subculture on MacConkey Agar. See below for colonial morphology.
Yersinia and Pasteurella differentiation
MacConkey Agar can be used to differentiate Yersinia species from Pasteurella species4. Yersinia pestis, Yersinia pseudotuberculosis and Yersinia enterocolitica will show growth on MacConkey Agar after 24 hours incubation at 35°C5.
Pasteurella species (including Pasteurella multocida) will not grow on MacConkey Agar.
Pectinolytic Organisms (Stewart6)
Stewart used Oxoid MacConkey Agar as the basis of a selective-diagnostic medium for pectinolytic organisms, in order to isolate soft-rot Erwinia species from specimens containing other Enterobacteriaceae.
MacConkey Agar-calcium chloride plates (5.2g CM0007 powder, 0.4g CaCl2, 75ml distilled water) overlaid with a pectate-EDTA layer (0.1% EDTA containing 2% sodium polypectate) are inoculated and incubated for 48 hours at 25°C. Lactose fermenting Erwinia produce red colonies in shallow pits formed by pectate liquefaction.
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 plates of medium at 2-8°C.
Appearance
Dehydrated Medium: Straw pink c |
