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

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.

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.

escherichia

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 us 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.

HiCrome™ M-TEC Agar for differentiation

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.

Media SystemProduct No.Name
Non-selective media used for identificationA0715Andrade Peptone Water
 28943Andrade peptone water, Vegitone
 70133Blood Agar (Base)
 36408Bromcresol Purple Broth
 22520China Blue Lactose Agar
 27048Christensen’s Urea Agar
 55420CLED Agar
 D2935Decarboxylase Broth Base, Moeller
 31436DEV Lactose Broth
 31437DEV Lactose Peptone Broth
 31406DEV Tryptophan Broth
 16447Glucose Bromcresol Purple Agar
 73009HiCrome™ ECC Agar
 00563HiCrome™ MM Agar
 16636HiCrome™ UTI Agar, modified
 60787Kligler Agar
 94792Lactose Broth
 70142Lactose Broth
 19057Lactose Broth, Vegitone
 62915Lysine Iron Agar
 M8802Malonate Broth
 39484Methyl Red Voges Proskauer Broth
 69150Methyl Red Voges Proskauer Saline Broth
 17171Mineral-modified Glutamate Broth (Base)
 M1053Motility Test Medium
 17178Mucate Broth
 17165MUG Tryptone Soya Agar
 72548Nitrate Broth
 75315OF Test Nutrient Agar
 51413Plate Count MUG Agar
 85463Simmons Citrate Agar
 44940Triple Sugar Iron Agar
 93657Tryptone Medium
 07507Tryptone Water
 39964Tryptone Water, Vegitone
 51463Urea Broth
Selective media for differentiation16016BRILA MUG Broth
 31432DEV ENDO Agar
 44657ECD MUG Agar
 70186EMB Agar
 E5399Endo Agar
 70137ENDO Agar (Base)
 48716Gassner Agar
 81938HiCrome™ Coliform Agar
 70722HiCrome™ E. coli Agar B
 85927HiCrome™ ECC Selective Agar
 09142HiCrome™ ECD Agar with MUG
Selective media for differentiation83339HiCrome™ Mac Conkey Sorbitol Agar
 90924HiCrome™ M-TEC Agar
 51489HiCrome™ Rapid Coliform Broth
 54232Lactose TTC Agar with Tergitol®-7
 62087Levine EMB Agar
 62634LST-MUG Broth
 70143Mac Conkey Agar No. 1
 19352Mac Conkey Agar No. 1, Vegitone
 94216MacConkey Agar with Crystal Violet, Sodium Chloride and 0.15 % Bile Salts
 M8302MacConkey Agar with Crystal Violet, Sodium Chloride and 0.15 % Bile Salts
 70144MacConkey Broth
 75717MacConkey Broth purple
 16377MacConkey Broth purple
 63014MacConkey MUG Agar
 51405MacConkey-Agar (without salt)
 88902MacConkey-Sorbitol Agar
 39734Membrane Lactose Glucuronide Agar
 85766m-Endo Agar LES
 96961M-FC Agar
 19958m-FC Agar Plates (55 mm diameter)
 43291M-FC Agar, Vegitone
 07348M-Lauryl Sulphate Broth
 M1678MUG EC Broth
 92435TBX Agar
 86455Tergitol®-7 Agar
 70188Violet Red Bile Agar
 42376Violet Red Bile Agar, Vegitone
 79873Violet Red Bile Glucose Agar
 70189Violet Red Bile Glucose Agar
 17213Violet Red Bile Glucose Agar without Lactose
 53605Violet Red Bile Glucose Agar without Lactose, Vegitone
 41270Violet Red Bile Lactose Dextrose Agar
 95273VRB MUG Agar
 17215WL Differential Agar
 76721XLT4 Agar (Base)
Selective media17112A1 Broth
 16025Brilliant Green Bile Lactose Broth
 44653EC Broth
 44655ECD Agar
 61749Lauryl sulphate Broth
 17349Lauryl sulphate Broth
 17162M Endo Broth
 17184M HD Endo Broth with Brilliant Green
 49522M-Lauryl Sulphate Broth, Vegitone
 69965Mossel Broth
Table 1Specific media for the detection, enumeration and identification of coliforms and E. coli
Materials
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References

1.
Frampton E, Restaino L. 1993. Methods for Escherichia coli identification in food, water and clinical samples based on beta-glucuronidase detection. 74(3):223-233. https://doi.org/10.1111/j.1365-2672.1993.tb03019.x
2.
Hartman P. 1989. The MUG glucuronidase test for E. coli in food and water.. Brescia, Italy: Brixia Academic Press.
3.
Manafi M. 1996. Fluorogenic and chromogenic enzyme substrates in culture media and identification tests. International Journal of Food Microbiology. 31(1-3):45-58. https://doi.org/10.1016/0168-1605(96)00963-4
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