No abstract

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...

This work assessed the risks associated with the virological quality of tapwater using a molecular analytical tool manageable in a field survey. It combined a daily epidemiological follow-up of digestive morbidity among a panel of volunteers and a microbiological surveillance of drinking water. RT-PCR was used for detection of enterovirus, rotavirus and astrovirus. 712 cases of acute digestive conditions occurred in the 544 volunteers. 38% (9/24) raw water and 23% (10/44) tap water samples were positive for at least one virus marker with 9/10 positive tap water samples complying with bacterial criteria. No statistically significant association was found between the presence of viral markers and observed incidence of digestive morbidity. However, when an outbreak occurred, enterovirus and rotavirus RNA was detected in the corresponding stored tap water samples. Sequencing of the amplified fragments showed that the rotavirus detected was of bovine origin. This work demonstrated that enteric virus markers were common in tapwater of the study communities (characterised by a vulnerable raw water) despite absence of bacterial indicators. Tangential ultrafiltration coupled to RT-PCR allowed a simultaneous and fast detection of the study viruses from environmental samples. This process is a promising tool usable for virological water surveillance, in as much the corresponding know-how is transferred to the field professionals.

The ability of Mycobacterium xenopi to colonize an experimental drinking water distribution system (a Propella reactor) was investigated. M. xenopi was present in the biofilm within an hour following its introduction. After 9 weeks, it was always present in the outlet water (1 to 10 CFU 100 ml ؊1 ) and inside the biofilm (10 2 to 10 3 CFU cm ؊2 ). Biofilms may be considered reservoirs for the survival of M. xenopi.Mycobacteria have no usual adherence factors such as pili, fimbriae, and slime, but the hydrophobic properties of the cell wall appear to contribute to the adherence process. The glycopeptidolipids present in the outermost layer of the cell walls of mycobacteria play an important role in surface colonization and biofilm formation (3,7,10). The biofilms represent an important risk of contamination for water distribution systems (8,9,12,13). Lately, a nosocomial outbreak of vertebral osteomyelitis due to Mycobacterium xenopi (5) has been reported by a French surgical center (2). These infections were associated with invasive medical procedures and related to the presence of M. xenopi in the tap water distribution network. However, the role of M. xenopi in the biofilm formation process has not yet been investigated. The aim of this study was to evaluate the ability of M. xenopi to colonize an experimental water supply system.A model biofilm reactor, the Propella reactor (with a distribution pipe 90 mm in diameter and 500 mm long), was used to simulate a drinking water distribution system (1). The inner surface of the pipe was covered with high-density polyethylene (HDPE), which is commonly used in drinking water pipes. The reactor had a volume of 2,080 ml and an HDPE pipe surface of 1,413 cm 2 . It was continuously supplied with tap water (from a local drinking water network) at a flow rate of 83.5 ml h Ϫ1 . The water velocity (0.2 m s Ϫ1 ) was controlled with a marine propeller, which pulsed the water through an inner pipe, giving a flux parallel to the pipe wall. The formation of a biofilm on the pipe wall and the concentration of embedded bacterial cells could be studied by using 20 coupons (1.7 cm 2 ) inserted into the inner surface of the pipe. A special device allowed the removal of the coupons without any flow interruption.M. xenopi (CIP 104035) was subcultured on LowensteinJensen medium at 40°C (optimal growth temperature). A suspension was prepared in sterile distilled water and centrifuged (4,300 ϫ g for 30 min at 20°C). The pellet was washed twice in sterile distilled water to limit carbon contamination from culture media and suspended in sterile distilled water. The suspension was calibrated to a density equivalent to a McFarland standard of 1 and serially diluted (10 Ϫ1 to 10 Ϫ9 ) in sterile distilled water; for the enumeration of mycobacteria, 0.2 ml of each dilution was plated on Lowenstein-Jensen medium (catalog no. 55246; Bio-Rad). Media were incubated at 40°C. Five weeks later, the colonies were counted.The investigation was performed in duplicate with two similar Propella reactors (A an...

Background: Dose-response parameters based on clinical challenges are frequently used to assess the health impact of protozoa in drinking water. We compare the risk estimates associated with Giardia in drinking water derived from the dose-response parameter published in the literature and the incidence of acute digestive conditions (ADC) measured in the framework of an epidemiological study in a general population.