Detection of Escherichia coli in Biofilms from Pipe Samples and Coupons in Drinking Water Distribution Networks

Abstract

Fluorescence in situ hybridization (FISH) was used for direct detection of Escherichia coli on pipe surfaces and coupons in drinking water distribution networks. Old cast iron main pipes were removed from water distribution networks in France, England, Portugal, and Latvia, and E. coli was analyzed in the biofilm. In addition, 44 flat coupons made of cast iron, polyvinyl chloride, or stainless steel were placed into and continuously exposed to water on 15 locations of 6 distribution networks in France and Latvia and examined after 1 to 6 months exposure to the drinking water. In order to increase the signal intensity, a peptide nucleic acid (PNA) 15-mer probe was used in the FISH screening for the presence or absence of E. coli on the surface of pipes and coupons, thus reducing occasional problems of autofluorescence and low fluorescence of the labeled bacteria. For comparison, cells were removed from the surfaces and examined with culture-based or enzymatic (detection of ␤-D-glucuronidase) methods. An additional verification was made by using PCR. Culture method indicated presence of E. coli in one of five pipes, whereas all pipes were positive with the FISH methods. E. coli was detected in 56% of the coupons using PNA FISH, but no E. coli was detected using culture or enzymatic methods. PCR analyses confirmed the presence of E. coli in samples that were negative according to culture-based and enzymatic methods. The viability of E. coli cells in the samples was demonstrated by the cell elongation after resuscitation in low-nutrient medium supplemented with pipemidic acid, suggesting that the cells were present in an active but nonculturable state, unable to grow on agar media. E. coli contributed to ca. 0.001 to 0.1% of the total bacterial number in the samples. The presence and number of E. coli did not correlate with any of physical and/or chemical characteristic of the drinking water (e.g., temperature, chlorine, or biodegradable organic matter concentration). We show here that E. coli is present in the biofilms of drinking water networks in Europe. Some of the cells are metabolically active but are often not detected due to limitations of traditionally used culture-based methods, indicating that biofilm should be considered as a reservoir that must be investigated further in order to evaluate the risk for human health.The drinking water supplier has to provide the consumer potable water of a quality identical to that leaving the treatment plant. However, it has been well documented that water that reaches the consumer's tap is often of worse microbiological quality than that which left the plant (29). Therefore, the analyses used for monitoring the hygiene of potable water must be rapid to perform and able to detect the major microbial groups of concern. Escherichia coli is still used as the principle indicator for drinking water pollution monitoring (39) and is even considered a superior indicator (11), since enterotoxic and enterohemorrhagic forms are one of the major causes of water-related outbreaks (29...

Evaluating the Growth Potential of Pathogenic Bacteria in Water

“…Additionally, a multilevel concept that integrates the results from the bioassay into the bigger framework of pathogen growth in water is discussed. The proposed approach provides a first step for including pathogen growth into microbial risk assessment.Pathogenic bacteria can survive and also grow in lownutrient aquatic environments, such as surface waters or man-made water treatment systems (2,17,30). Studies on pathogen survival and/or die-off (including disinfection) in water are common, but little is known about the fundamental factors governing their growth in the environment (34,35).…”

Effect of Flow Velocity on Chlorine Decay in Water Distribution Network:A Pilot Loop Study

“…Past studies have reported an increase in the rate of biofilm growth when water distribution network is subjected to flow/non-flow conditions 2,3 . Few studies have also suggested that the biofilm in addition to consuming residual chlorine in water also shields harmful bacteria from chlorine oxidation 4,5 . Chlorine decay in distribution network depends on the reaction that occurs both within the bulk water and biofilm attached to the pipe 6 .…”

Le réseau de distribution d’eau potable : un écosystème complexe lié à des enjeux de santé publique

“…Par ailleurs, les biofilms constituent également une microniche pour les microorganismes pathogènes. Plusieurs études ont montré que des pathogènes (tels que des virus ou des bactéries) peuvent persister (BRAGANçA et al, 2007;JUHNA et al, 2007;SzEwzyK et al, 2000), ou sont capables de s'accumuler et de survivre au sein des biofilms formés en réseau d'eau potable (AzEvEDO et al, 2006;LANGMARK et al, 2005;LEHTOLA et al, 2007;PARIS et al, 2009;qUIGNON et al, 1997).…”