Macconkey agar

EHEC belonging to serotype 0157 H7 characteristically do not ferment sorbitol, whereas more than 70% of intestinal floral f. coli do. To properly screen EHEC strains in cases of diarrhea, stool should be placed on special sorbitol-MacConkey agar. Colonies of f. coli 0157 H7, which do not ferment the sorbitol, can be identified readily and confirmed by serotyping with specific antisera. In addition, stool should be tested directly for the presence of Stx I and II by enzyme immunoassay (EIA). 

To detect low levels of bacteria that might be missed with the quantitative technique, 5 pL of a biological fluid is inoculated into 5 mL of trypticase-soy broth and incubated overnight at 37°C. If bacterial growth is identified, the colonies are seeded onto a tryptic soy blood-MacConkey agar plate for further identification. 

These included nutrient agar (Oxoid), Mueller-Hinton Agar (Oxoid), Desoxy-cholate Citrate Agar (Oxoid), and MacConkey Agar (Oxoid). 

First, we obtained three E. coli mutant strains and each strain contained a mutation in one of the three genes encoding the synthesis of the three enzymes required for metabolism of L-Arabinose in E. coli. As a results, these three mutant strains could only produce white colonies but not red colonies on MacConkey agar plates [32]. If a functional gene had been cloned into each of these mutants and could complement the specific mutation of the mutant strains, the recombinant strains should then produce red colonies on the MacConkey plates. 

Other sorbitol-non-fermenting bacterial species tested. This agar was tested on cattle rectal swabs and has increased the rate of STEC 0157 isolation. Cefixime Tellurite Sorbitol MacConkey Agar (CT-SMAC) is now the media of choice in the ISO standard protocol (ISO 16654) for E. coli 0157 although this medium has been reported to fail to isolate two sorbitol-fermenting STEC 0157 H- on HUS patients (Karch et al. 1996). 

Okrend AJG, Rose BE, Lattuda (1990) C.P. 5-bromo-4-chloro-3-indoxyl- -D-glucuronide in sorbitol MacConkey agar to aid in the isolation of Escherichia coli 0157 H7 from ground beef. J Food Protect 53 941-943... 

MacConkey agar containing appropriate test product neutralizers for use in selectively culturing the E. coli. 

Differential media these distinguish colonies of specific microbes from others. When a culture medium containing certain substances helps to distinguish the differing properties of different bacteria, it is called differential media, e.g., MacConkey agar. It is also an indicator medium. It contains peptone, agar, lactose, sodium taurocholate and nentral red. The lactose fermenters form pink colonies while non-lactose fermenters produce colourless or pale colonies. Blood agar it serves both as an enriched as well as an indicator medium and shows different types of haemolysis. 

Selective-differential media some media have both properties, e.g., MacConkey agar. It is selective as it contains crystal violet and bile salts which inhibit the growth of bacteria other than coliforms. It is differential as it contains neutral red and lactose, which is degraded by coliforms to acid and is detected due to a change in pH. At acidic pH, colourless neutral red becomes red and the colonies develop a red colour. Shigella and Salmonella colonies remain colourless and therefore can be easily distinguished [9,11]. 

Entero- bacteriaceae 1. MacConkey agar/broth 2. UBA agar 1. PCR 2. Automated ribo typing Jespersen and Jakobsen (1996), Maugueret and Walker (2002) and Koivula et al. (2006). 

Colonies on MacConkey Agar are yellow or yellowish-pink color. 

MacConkey agar 35°C-37°C + 0.5°C for 18-24 h Red colonies surrounded by an opaque zone of precipitated bile [2]... 

Prepare MacConkey agar plus galactose according to manufacturer s instructions (Difeo). After autoclaving and cooling to 50°C, to 1L add 500 pi chloramphenicol (final cone. 12.5 pg/ml), and pour the plates, 25-40 plates/L. 

Following a similar principle but using different chromogenic substrates, recombinants can be screened by their respective colors (i) lactose (0.4%)—MacConkey agar (Lac" red, Lac white), (ii) lactose—tetrazolium agar (Lac" white, Lac red) (4), and (iii) lactose-EMB (eosin—methylene blue) agar (Lac purple, Lac white or pink) (6). 

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