SURVIVAL OF CRYPTOSPORIDIUM-PARVUM, ESCHERICHIA-COLI, FECAL ENTEROCOCCI AND CLOSTRIDIUM-PERFRINGENS IN RIVER WATER - INFLUENCE OF TEMPERATURE AND AUTOCHTHONOUS MICROORGANISMS

Oocysts of Cryprosporidium parvum can survive for several months in su rface water, one of the main factors determining their success in envi ronmental transmission and thus their health hazard via water. Several factors in the environment, e.g. temperature, presence of predators a nd exo-enzymes will probably influence oocyst survival. ?he high persi stence of oocysts may also limit the value of traditional faecal indic ator bacteria. The aim of this study was to determine the rate at whic h C parvum oocysts, E coil, faecal enterococci and C perfringens spore s die in surface water and the influence of temperature and the presen ce of autochthonous (micro)organisms on the die-off rate. Microcosms w ith autoclaved river water were inoculated with the organisms. Microco sms with untreated river water were inoculated with concentrated prima ry effluent containing the bacteria and with C parvum oocysts. Microco sms were incubated at 5 degrees C or 15 degrees C at 100rpm. Viability of oocysts was monitored by in vitro excystation and dye-exclusion; v iability of the bacteria was determined on appropriate selective media . When pseudo first-order die-off kinetics were assumed, the die-off r ate of oocysts at 5 degrees C was 0.010 log(10)/d and at 15 degrees C, 0.006-0.024 log(10)/d. These rates underestimate die-off since oocyst disintegration wits not accounted for. Incubation in autoclaved or un treated water did influence the die-off rate of oocysts at 15 degrees C but not at 5 degrees C. The die-off rate of E coli and enterococci w as faster in the non-sterile river water than in autoclaved water at b oth temperatures. At 15 degrees C, E coli (and possibly E. faecium) ev en multiplied in autoclaved water. In untreated river water, the die-o ff of E coli and enterococci was approximately 10x faster than die-off of oocysts but die-off rates of C perfringens were lower than those o f oocysts. As for oocysts, die-off of the bacteria and spores was fast er at 15 degrees C than at 5 degrees C. Oocysts are very persistent in river water: the time required for a 10x reduction in viability being 40-160d at 15 degrees C and 100d at 5 degrees C. Biological/biochemic al activity influenced oocyst survival at 15 degrees C and survival of both vegetative bacteria at 5 and 15 degrees C. The rapid die-off of E coil and enterococci makes them less suitable as indicators of oocys t presence in water. As C perfringens survived longer in untreated riv er water than oocysts, it may prove useful as an indicator of the pres ence of C parvum. (C) 1997 IAWQ. Published by Elsevier Science Ltd.