Oxoid Limited has extended their range of products for testing the microbiological quality of water with the addition of new m-CP Medium - a selective, chromogenic medium for the rapid identification and enumeration of Clostridium perfringens in water samples. Compared to traditional methods, m-CP Medium provides faster results with increased selectivity and specificity.

Clostridium perfringens spores are resistant to environmental stress and can survive in water for longer than vegetative bacteria, including E. coli. This makes Cl. perfringens an important indicator of water pollution and a useful marker to alert water companies to the possible presence of other stress-resistant pathogens, such as viruses and protozoal cysts. In addition, its resistance to chlorination is useful in testing the effectiveness of water treatment processes.

Levels of Cl. perfringens in raw water are monitored to detect increases in contamination. Furthermore, the presence of Cl. perfringens in drinking water is considered significant and warrants immediate investigation.

The new Oxoid m-CP Medium is designed to improve the differentiation of Cl. perfringens from other clostridial species and background flora.

Chromogenic compounds within m-CP Medium cause Cl. perfringens colonies to turn yellow (based on their ability to ferment sucrose), thus differentiating them from other Clostridium species, whilst colonies of contaminating organisms turn purple (based on their ability, unlike Cl. perfringens, to hydrolyse indoxyl-b-D-glucoside). Additional confirmation is provided by exposing the culture plate to ammonium hydroxide. This highly specific reaction causes acid phosphatase-producing Cl. perfringens colonies to turn a distinctive dark pink.

The addition of D-cycloserine and polymixin B, and an incubation temperature of 44°C, improve selectivity by inhibiting the growth of Gram-negative bacteria and staphylococci.

The chromogenic agar substrates in m-CP Medium are so specific that further verification steps are not required. This allows results to be obtained in a day instead of the 3-4 days required by traditional methods. In a comparative evaluation, m-CP Medium demonstrated increased sensitivity and specificity compared to TSC Agar, with a decrease of 48 hours in the time taken to obtain a result¹.

The European Council Directive 98/83/EC recommends m-CP Medium for testing water intended for human consumption².

References:

1: Oxoid Limited, data on file.
2: E.U. (1998) 98/83/EC of Council of 3rd November 1998 on the quality of water intended for human consumption. Off. J. Eur. Commun., L330, 32-54.

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