When exposed to oxidation, algae release dissolved organic matter with significant carbohydrate (52%) and biodegradable (55 to 74%) fractions. This study examined whether algal organic matter (AOM) added in drinking water can compromise water biological stability by supporting bacterial survival. Escherichia coli (1.3 ؋ 10 5 cells ml ؊1 ) was inoculated in sterile dechlorinated tap water supplemented with various qualities of organic substrate, such as the organic matter coming from chlorinated algae, ozonated algae, and acetate (model molecule) to add 0.2 ؎ 0.1 mg of biodegradable dissolved organic carbon (BDOC) liter ؊1 . Despite equivalent levels of BDOC, E. coli behavior depended on the source of the added organic matter. The addition of AOM from chlorinated algae led to an E. coli growth equivalent to that in nonsupplemented tap water; the addition of AOM from ozonated algae allowed a 4-to 12-fold increase in E. coli proliferation compared to nonsupplemented tap water. Under our experimental conditions, 0.1 mg of algal BDOC was sufficient to support E. coli growth, whereas the 0.7 mg of BDOC liter ؊1 initially present in drinking water and an additional 0.2 mg of BDOC acetate liter ؊1 were not sufficient. Better maintenance of E. coli cultivability was also observed when AOM was added; cultivability was even increased after addition of AOM from ozonated algae. AOM, likely to be present in treatment plants during algal blooms, and thus potentially in the treated water may compromise water biological stability.In spite of the disinfection processes, bacterial proliferation can be observed in drinking water distribution network systems (20,26,37,42) proving that certain bacterial populations are able to adapt, transiently or permanently, to the oligotrophic conditions of distribution networks (16,17). This phenomenon has been described for fecal indicators such as coliform bacteria, particularly Escherichia coli (16), and poses the problem of compliance with water quality health regulations.Although multiple factors certainly affect microbial growth phenomena, organic matter in treated waters, mainly the biodegradable fraction, has a determining effect since it provides a carbon and energy source essential to the growth of heterotrophic bacteria, including coliforms (16,19,25,38,39,42). Atypical events (algal bloom, swelling, rainfall, etc.) capable of modifying the quality of the organic matter in raw and treated waters have been suggested to be a catalyst for coliform growth (3, 18, 23). Lake et al. (15) showed that there is a strong link between the end of the algal bloom and the presence of coliforms in the distribution system, leading to a situation incompatible with health standards. Algal products in the treated water were suspected of providing a good nutritional source for bacterial regrowth in the distribution system. In addition to the natural capacity of algae to secrete organic compounds, massive contamination at the inlet of a treatment plant using preoxidation can lead to algal cell lysis and re...
Legionella pneumophila is a pathogenic bacterium commonly found in water and responsible for severe pneumonia. Free-living amoebae are protozoa also found in water, which feed on bacteria by phagocytosis. Under favorable conditions, some L. pneumophila are able to resist phagocytic digestion and even multiply within amoebae. However, it is not clear whether L. pneumophila could infect at a same rate a large range of amoebae or if there is some selectivity towards specific amoebal genera or strains. Also, most studies have been performed using collection strains and not with freshly isolated strains. In our study, we assess the permissiveness of freshly isolated environmental strains of amoebae, belonging to three common genera (i.e. Acanthamoeba, Naegleria and Vermamoeba), for growth of L. pneumophila at three different temperatures. Our results indicated that all the tested strains of amoebae were permissive to L. pneumophila Lens and that there was no significant difference between the strains. Intracellular proliferation was more efficient at a temperature of 40°C. In conclusion, our work suggests that, under favorable conditions, virulent strains of L. pneumophila could equally infect a large number of isolates of common freshwater amoeba genera.
This study was undertaken after a report of drinking water industries which suggested the existence of a relation between algal proliferation (algal bloom) in resource water and coliform non-conformity in distribution networks. Our objective was thus to estimate if algal organic matter (AOM) could be used as a substrate by E. coli and explain its resuscitation in drinking water. For this purpose, E. coli was inoculated in sterile dechlorinated drinking water supplemented with organic matter of various origins in order to reach +0.2 (±0.1) mg BDOC L−1 (AOM, glucose or acetate). The results showed that the addition of AOM (naturally secreted by algae or released after a chlorine or ozone stress) in drinking water can represent a risk for water biological stability: indeed, AOM allowed either a higher cellular production, or a better maintenance of cultivability of E. coli than those observed in non-supplemented sterile drinking water, glucose or acetate solutions (in spite of equivalent additions of BDOC). Growth of E. coli was even up to 10 times higher in the presence of AOM coming from ozonated algae.
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