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ATP testing: A predictive indicator of bacteriological non-compliance in water

HPC (Heterophoric Plate Count) culture mediums such as YEA, PCA or R2A, frequently used for environmental bacteria counting, detect less than 1% of the total flora (WHO, 2003). Indeed, a large proportion of bacteria cannot multiply on those mediums. For example, there are:

  • Anaerobic organisms (tolerant or obligate): oxygen presence slows down or inhibits their growth.
  • Bacteria requiring a specific temperature to grow such as psychrophile (low temperature) or thermophile (high temperature).
  • Germs requiring a specific environment such as acidophiles (high acidic conditions) or halophiles (high salinity).
  • Germs requiring specific elements such as rare amino acids, complex sugars, vitamins, cations…
  • Non-culturable bacteria whose culture is impossible using traditional methods.
Total bacterial flora

Diagram of total bacterial flora

  • VBNC bacteria (viable but non-culturable) which have momentarily lost their growing capacities as a response to stress. The use of biocides, physical treatments (ex: UV) or the environmental parameter modifications (temperature, pH…) can cause that change of state.

Furthermore, the bacteria needs to form a colony to be detected by the technicians’ eye. Which means growing from one to several billions within the allocated time period. That implies a short lag phase and a fast growth. Those parameters partly depend on the incubating temperature and the type of medium used.

 

In the end, we only detect aerobic mesophilic flora able to grow between 20°C (68°F) and 45°C (113°F) in the given time and for which the nutrients are adequate.
Why you should not speak of “total flora” with culture method?

Each culture medium will only detect a part of the bacteria depending on chosen conditions.
Thus, to be thorough, we should speak of “culturable flora” indicating the medium, temperature and incubation time chosen.

Diagram ATP vs cultural method

Example of bacterial growth monitored by culture and ATP-metry

As for ATP testing, it detects the whole living bacterial flora, even non culturable bacteria. For all these reasons, it is often observed an increase of total flora by ATP testing long before the appearance of the first colonies on the culture medium.

ATP-metry is an early indicator of microbiological contamination.

Research project: development of a detection kit for somatic coliphages

By Estelle Alaume

In Europe, water intended for human consumption is highly regulated by the Drinking Water Directive. Water intended for human consumption includes distribution systems, drinking water in bottles or containers and water used in the food-processing industry. Recently, the revision of the Drinking Water Directive (n°98/83/CE) adds new parameters to the list of criteria determining water safety, such as control of somatic coliphages. These viruses are used as indicator organisms for faecal contamination. Its control represents an important step towards a high quality of drinking water.

Somatic coliphages, new faecal contamination indicatorContinue Reading