Dissolved organic matter in water of Daugava river

Application of Fluorescent Technologies to Identify Viable Pathogens inDrinking WaterM.Linda 1 , T.Juhna* 11 Department of Water Engineering and Technology, Riga Technical University, Riga, Latvia.e-mail: Linda.mezule@rtu.lvWhen subjected to unfavourable environmental conditions or nutrient limitation manymicroorganisms (including pathogenic ones) can attain a state of non-cultivability (viablebut not cultivable, VBNC) where they are unable to form visible colonies on traditionalculture media 1 . In environmental studies Fluorescent in situ hybridization (FISH) withfluorescent oligonucleotide or peptide nucleic acid probes have become an important toolin monitoring and identification of certain bacterial species or groups. However, studieshave shown that FISH alone is not a direct marker of cell viability. To monitor cellmembrane integrity, metabolic activity, enzymatic activity or ability to divide as such,different molecular assays have been developed. Our studies have shown that many ofthese assays can be combined with specific identification of viable target species e.g. ableto divide Escherichia coli, in their natural environments, e.g. biofilm of drinking waterdistribution system. During the years analyses on occurrence of Legionella species in hotwater systems and enumeration of pathogenic protozoa in distribution systems have beenperformed with fluorescence microscopy. However, most studies have been performed onthe assessment of faecal indicator E. coli in drinking water distribution systems whichmeet current microbiological standards and potential inactivation techniques for theseorganisms.The results have shown that in low numbers able to divide E. coli can be detected even inthe biofilm of freshly treated water. On average around 53 % of all detected E. coli hadthe ability to divide and the concentration increased with water residence time in thenetwork. At the same time no colonies were isolated on culture media. Monitoring of E.coli concentration dynamics in drinking water distribution system and pilot scale reactorsshowed that after the application of disinfectant (chemical or mechanical) cells first losttheir cultivability (formation of colonies), then ability to divide (limited amount of time)and only then the metabolic activity (respiratory activity), indicating on possibleunderestimation of pathogen concentration when traditional techniques have been used,thus, posing the risk for the consumer.1. Oliver JD. Recent findings on the viable but nonculturable state in pathogenic bacteria. FEMSMicrobiol Rev. 2010, vol. 34, p. 415–425.- 28 -