Payment, P. (1995) Health Significance of Bacterial Regrowth
in Drinking Water: Free Opinion. Rev. Sci. Eau 8 (3) : 301-314. [bilingual]
Simultaneously published in french under the title: Effets sur la santé de
la recroissance bactérienne dans les eaux de consommation: Tribune
Communication presented at the International Symposium Matière
Organique Biodégradable, École Polytechnique de Montréal,
The presence of heterotrophic bacteria in drinking water (tap,
point-of use treated or bottled) poses a difficult problem because we do not
clearly know if they are really innocuous. Two points of views are presented:
they could be totally unimportant whatever their number or they can be opportunistic
pathogens and even frank pathogens if they are allowed to multiply in large
numbers. These bacteria are not of faecal origin and are not indicators of
faecal pollution even if occasionally some can be described as coliforms. Studies
in the United States on families drinking water from domestic filtration units
did not observe any significant health effects while other researchers have
observed an inhibitory effect of these heterotrophic bacteria on coliforms
and some pathogenic bacteria. On the other band, recent Canadian studies have
observed that high bacterial counts in the water produced by reverse-osmosis
units were correlated to gastrointestinal illnesses and that bacteria of potential
virulence were present in tap water. All these observations have brought back
the question of the potential health effects of heterotrophic bacteria. At
the same time, the ability of current water quality indicators to protect public
health is questioned and we must find other methods for the surveillance of
waterborne diseases. Within these new guidelines or regulations, will probably
have to set a limit on the acceptable number of heterotrophic bacteria in water.
What this level will be remains to be determined, but until then we must assume
that it is prudent to test drinking water in such a way, that it will not promote
or permit the uncontrolled multiplication of bacteria of which we know so little.
We are discovering new pathogens each year and we cannot assume that they are
not present in treated waters. There are two approaches that can be used to
limit potential health risks. The first is to limit the total population of
heterotrophic bacteria by limiting available nutrients and using appropriate
enumeration methods (heterotrophic plate count or epifluorescence viable counts).
The second is to use or develop an indicator of health risk based on the virulence
of bacteria (i.e., detection of virulence factors). There are still long discussions
and researches ahead, but the driving force will be probably directed at limiting
the nutrient available to heterotrophic bacteria and preventing significant
growth in water distribution systems.
P. Payment, Institut Armand Frappier, Université du
Quebec, 531 Boul.
des Prairies, Laval (Québec), H7N 4Z3 CANADA