Selective Growth Media for Differentiation and Detection of Escherichia Coli and Other Coliforms

By: Jvo Siegrist, AnalytiX Volume 8 Article 4

E. coli and other coliforms are important indicator organisms for the presence of pathogens in food, occupational and environmental safety applications, some of the most important areas of analytical microbiology.

Jvo Siegrist, Product Manager Microbiology ivo.siegrist@sial.com

E. coli: Indicator organism for fecal contamination

Normal constituents of the intestinal flora of animals, coliforms are rod-shaped, Gram-negative, non-spore forming facultative anaerobes. They ferment lactose with the production of acid and gas when incubated at 35–37°C. Although commonly found in lakes, rivers, swimming pools and soil from faecal sources, in most cases coliforms do not cause illness. However, they are used as indicators for other pathogenic organisms of faecal origin. The most common genera of coliforms are Citrobacter, Enterobacter, Escherichia, Klebsiella and Serratia.

Escherichia coli (Figure 1) is the best-known coliform and an important indicator of faecal contamination because it is found almost exclusively in faeces. Occasional outbreaks of food poisoning have been linked to certain gastroenteritis-causing E. coli strains, such as serotype O157:H7. E coli are rod-shaped bacteria, distinguished from most other coliforms by their ability to ferment lactose at 44°C, and by their growth characteristics on certain media. Easy to culture, E. coli is often used in molecular biology.


Figure 1 Escherichia coli

Figure 1 Escherichia coli


Selective growth media for E. coli

Microbiological media is used not only to grow microorganisms, but also to select or identify a particular type of microorganism based on some unique or distinctive aspect of its biochemistry. Most of this so-called “selective growth” media contain a protein source, often a hydrolysate of casein, and a fermentable sugar, like lactose or glucose. Occasionally an indicator, like neutral red or bromo cresol purple, is added to detect the acid produced by the fermentation process.

A new generation of selective media is available from Sigma-Aldrich that employs chromogenic and fluorogenic substrates (Figure 2). These media indicate E. coli by the presence of β-D-glucuronidase (GUD) and other coliforms by the presence of β-D-galactosidase. GUD catalyses the hydrolysis of β-D-glucopyranosiduronic acid into the corresponding aglycones and D-glucuronic acid. GUD is present in 94–96 % of E. coli strains, but is also found in some Salmonella, Shigella and Yersinia spp. (1-3). There is a wide range of media available that use different substrates for the detection of E. coli and coliforms (Table 1). The media are also supplemented with agents like bile salts, brilliant green, sodium lauryl sulphate and other substances to enhance their selectivity.


Figure 2 HiCrome™ M-TEC Agar for differentiation and enumeration of thermotolerant E.coli from water by membrane filtration technique.

Figure 2 HiCrome™ M-TEC Agar for differentiation and enumeration of thermotolerant E.coli from water by membrane filtration technique. E.coli colonies appear blue because the chromogen, X-glucuronide, is cleaved by the enzyme β-glucuronidase.


For a complete list of our growth and selective media, and our other products and resources for microbiology, please visit our website www.sigma-aldrich.com/ microbiology


Media System Part No.   Name
Non-selective media used for identification A0715 Andrade Peptone Water
  28943 Andrade peptone water, Vegitone
  70133 Blood Agar (Base)
  36408 Bromcresol Purple Broth
  22520 China Blue Lactose Agar
  27048 Christensen’s Urea Agar
  55420 CLED Agar
  D2935 Decarboxylase Broth Base, Moeller
  31436 DEV Lactose Broth
  31437 DEV Lactose Peptone Broth
  31406 DEV Tryptophan Broth
  16447 Glucose Bromcresol Purple Agar
  73009 HiCrome™ ECC Agar
  00563 HiCrome™ MM Agar
  16636 HiCrome™ UTI Agar, modified
  60787 Kligler Agar
  94792 Lactose Broth
  70142 Lactose Broth
  19057 Lactose Broth, Vegitone
  62915 Lysine Iron Agar
  M8802 Malonate Broth
  39484 Methyl Red Voges Proskauer Broth
  69150 Methyl Red Voges Proskauer Saline Broth
  17171 Mineral-modified Glutamate Broth (Base)
  M1053 Motility Test Medium
  17178 Mucate Broth
  17165 MUG Tryptone Soya Agar
  72548 Nitrate Broth
  75315 OF Test Nutrient Agar
  51413 Plate Count MUG Agar
  85463 Simmons Citrate Agar
  44940 Triple Sugar Iron Agar
  93657 Tryptone Medium
  07507 Tryptone Water
  39964 Tryptone Water, Vegitone
  51463 Urea Broth
Selective media for differentiation 16016 BRILA MUG Broth
  31432 DEV ENDO Agar
  44657 ECD MUG Agar
  70186 EMB Agar
  E5399 Endo Agar
  70137 ENDO Agar (Base)
  48716 Gassner Agar
  81938 HiCrome™ Coliform Agar
  70722 HiCrome™ E. coli Agar B
  85927 HiCrome™ ECC Selective Agar
  09142 HiCrome™ ECD Agar with MUG
Selective media for differentiation 83339 HiCrome™ Mac Conkey Sorbitol Agar
  90924 HiCrome™ M-TEC Agar
  51489 HiCrome™ Rapid Coliform Broth
  54232 Lactose TTC Agar with Tergitol®-7
  62087 Levine EMB Agar
  62634 LST-MUG Broth
  70143 Mac Conkey Agar No. 1
  19352 Mac Conkey Agar No. 1, Vegitone
  94216 MacConkey Agar with Crystal Violet, Sodium Chloride and 0.15 % Bile Salts
  M8302 MacConkey Agar with Crystal Violet, Sodium Chloride and 0.15 % Bile Salts
  70144 MacConkey Broth
  75717 MacConkey Broth purple
  16377 MacConkey Broth purple
  63014 MacConkey MUG Agar
  51405 MacConkey-Agar (without salt)
  88902 MacConkey-Sorbitol Agar
  39734 Membrane Lactose Glucuronide Agar
  85766 m-Endo Agar LES
  96961 M-FC Agar
  19958 m-FC Agar Plates (55 mm diameter)
  43291 M-FC Agar, Vegitone
  07348 M-Lauryl Sulphate Broth
  M1678 MUG EC Broth
  92435 TBX Agar
  86455 Tergitol®-7 Agar
  70188 Violet Red Bile Agar
  42376 Violet Red Bile Agar, Vegitone
  79873 Violet Red Bile Glucose Agar
  70189 Violet Red Bile Glucose Agar
  17213 Violet Red Bile Glucose Agar without Lactose
  53605 Violet Red Bile Glucose Agar without Lactose, Vegitone
  41270 Violet Red Bile Lactose Dextrose Agar
  95273 VRB MUG Agar
  17215 WL Differential Agar
  76721 XLT4 Agar (Base)
Selective media 17112 A1 Broth
  16025 Brilliant Green Bile Lactose Broth
  44653 EC Broth
  44655 ECD Agar
  61749 Lauryl sulphate Broth
  17349 Lauryl sulphate Broth
  17162 M Endo Broth
  17184 M HD Endo Broth with Brilliant Green
  49522 M-Lauryl Sulphate Broth, Vegitone
  69965 Mossel Broth

Table 1 Specific media for the detection, enumeration and identification of coliforms and E. coli

Key: red = chromogenic media; blue = fluorescent media; violet = chromogenic and fluorogenic media

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Materials

     

References

  1. Frampton, E. W.; Restaino, L. Methods for E. coli identification in food, water and clinical samples based on beta-glucuronidase detection. J. Appl. Bacteriol. 1993, 74, 223–233.
  2. Hartman, P. A. The MUG glucuronidase test for E. coli in food and water. In Rapid Methods and Automation in Microbiology and Immunology; Turano, A. Ed.; Brixia Academic Press: Brescia, Italy, 1989; 290–308.
  3. Manafi, M. Fluorogenic and chromogenic enzyme substrates in culture media and identification tests. Int. J. Food. Microbiol. 1996, 31, 45–58.

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