Thermotolerant coliforms

Chen H, Shu W, Chang X et al (2010) The profile of antibiotics resistance and integrons of extended-spectrum beta-lactamase producing thermotolerant coliforms isolated from the Yangtze River basin in Chongqing. Environ Pollut 158(7) 2459-2464... 

There are a number of reactions used in identification for which the temperature is critical, e.g. the growth of thermotolerant coliforms at 44 °C in various media is used as a diagnostic test, especially in water samples. Other species in which temperature is important are those which can grow at low temperatures in refrigerators, thus causing problems such as spoilage and food poisoning, e.g. Listeria. 

The characteristic features of the coliforms are non-sporing, Gram-negative rods, which are bile tolerant and able to ferment lactose at 37 °C producing acid and gas within 48 hours. The term faecal coliform was used to describe coliforms capable of fermenting lactose to acid and gas within 24 hours at 44 °C. The term thermotolerant coliforms is now used more commonly in the UK, although the term faecal coliform is still widely used elsewhere. It should be pointed out that not all thermotolerant coliforms are faecal in origin. 

The differential tests make use of the positive samples obtained in the presumptive tests. These differential tests are intended to differentiate E. coli from non-thermotolerant coliforms, and coliforms in general from non-coliforms. Samples from each of the positive presumptive tubes are inoculated into each of the four following media ... 

Tube (a) is examined for the production of acid and gas within 24 hours. A positive result is given by E. coli and a negative result by non-thermotolerant coliforms. 

International Standard, ISO 9308-2 (1990). Water Quality—Detection and enumeration of coliform organisms, thermotolerant coliform organisms and presumptive Escherichia coli— Part 2 Multiple tube (most probable number) method. International Organization for Standardization, Geneva, Switzerland. 

In the test for fecal coliform bacteria, a sample of water is incubated at 112°F (44.5°C) for about 24 hours. Ifbacteria are present, the person conducting the test counts the number of colonies formed or looks for carbon dioxide gas in the incubation tube. This test is specific for fecal coliforms because they are members of a group of coliform bacteria known as thermotolerant that survive at temperatures of 112°F (44.5°C) or more other types of coliforms do not. 

The traditional method for detection of waterborne microbes is direct plating. Samples may also be filtered either on- or off-line and filters placed directly on the surface of an agar plate. A range of media for the detection of coliforms is available (Table 13.3) and confirmation of thermotolerant E. coli is possible by incubation at 44 C. 

Caplenas, N.R. and Kanarek, M.S. (1984). Thermotolerant non-fecal source Klebsiella pneumoniae validity of the fecal coliform test in recreational waters. Am. J. Public Health. 74 1273-1275. 

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