Published: 23/08/22 13:18 Categories: Microbiology


Summer is here, and with it a sharp increase in water consumption as the main source of hydration to avoid dangerous heat stroke. It is therefore of vital importance for the population to have access to drinking water that is contaminant-free in order to avoid gastrointestinal or systemic diseases. 


Pathogens analyzed in drinking water 


The main pathogens associated with water are bacteria such as Legionella, Salmonella, Escherichia coli and several viruses and protozoa. Most of these contaminants originate from fecal matter, although it is true that some are specific to the source and/or the environment. 


Due to the wide variety of microorganisms that may be present, it is complicated to perform individual analyses of each one, especially when the great majority are eliminated by purification/cleaning systems. For this reason, drinking water is monitored using certain microbial indicators to ensure their quality. 


The indicator groups used are fecal indicators such as coliform bacteria. Directive 2020/2184 currently sets out the parameters to be analyzed in the EU: 


Microbiological parameters, indicators and operational parameters 

Parameter value 

(CFU/100 ml or 250 ml1) 

Escherichia coli 




2Clostridium perfringens (including spores) 


Colony count at 22ºC  

No abnormal changes 

Coliform bacteria 


3Somatic Coliphages 


1For bottled water  

2If the risk assessment indicates it is appropriate to do so 

3Untreated water 


E. coli-coliforms, Enterococci and Legionella are parameters that are commonly found in drinking water analysis. However, what about Clostridium perfringens? 


Clostridium perfringens: opportunistic pathogen 


This microorganism is of particular interest, as it commonly inhabits in the form of vegetative cells and spores that are resistant, meaning they can survive for long periods, even longer than other fecal indicators, in bodies of contaminated waters. And, like other indicators, their existence warns of the possible existence of other microorganisms such as Cryptosporidium. 


These spores are structures that are difficult to remove completely with standard disinfection processes, which is partly why they have become valuable bacteria in the assessment of drinking water treatments.  


Culture media for the analysis of Clostridium perfringens 


TSC Agar: colonies from black C. perfringens


The analysis of this pathogen in accordance with standard ISO 14189:2013 begins with a thermal pre-treatment prior to membrane filtration to retain the spores present in the sample. The media to be used are TSC, a selective medium with cycloserine, which is responsible for inhibiting accompanying flora such as Bacillus and other facultative anaerobes that may interfere. 


Similarly, C. perfringens will react with hydrogen sulfide indicators to produce the typical coloration of black, greyish or brownish colonies. 


Columbia Agar and the acid phosphatase test are used to confirm suspicious colonies. 


If you have any questions concerning Clostridium perfringens in water sample analyses, do not hesitate to contact us. 

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