Isolement de bacteries pathogenes contaminant une eau a l'aide d'immunoadsorbants

Abstract

The potability of water is indicated by the presence or the absence of bacteria from faecal origin. According to the World Health Organization, water is not considered dangerous in the absence of such bacteria. However, only a water free of true pathogenic bacteria is clearly drinkable. In our laboratory, we have elaborated a method allowing direct isolation from water of the main pathogenic bacteria which are common faecal contaminants. These bacteria include Salmonella typhi-murium, Escherichia coli K 88 and K 99 and Vibrio cholerae of the El Tor biotype. Our method consists of filtering contaminated water through small immunoabsorbant columns packed with polyacrylamide-agarose beads coupled to specific antibodies against bacterial antigenic structures. Antisera were obtained from rabbits immunized with antigenic fractions of the bacterial walls, known as Ch 1 + 2 ( V. cholerae) Tm 1 + 2 ( S. typhi-murium), Ec 1 + 2 K 88 and K 99 ( E. coli K 88 and K 99). Antibodies were then isolated and coupled to glutaraldehyde-activated 3% polyacrylamide 4% agarose beads (AcA 34). 500 ml of contaminated water was filtered through the columns. The water consisted either of artificially contaminated samples from the Oise river (France) or of similarly contaminated saline. After filtration, the beads were recovered from the columns, diluted in hypersaline peptone water ( V. cholerae) or saline ( S. typhi-murium, E. coli K 88 and K 99) and incubated overnight at 37°C. The growth from the hypersaline peptone or saline broth was then removed, placed onto Petri dishes and the colonies were counted. Water samples containing a mixture of 10 3 of each of the four bacteria were filtered through beads coated with the different antibodies. Bacteria retained on the beads were only those against which antibodies were directed (Table 1). On the other hand, we have analysed column effluent waters after passing 10 3 bacteria through the relevant columns. No bacteria were detected after filtration, which suggest that most of the bacteria were retained on the beads. Bacteria were found in column effluent waters when the water samples contained more than 10 5 bacteria. This technique is highly specific and allows the filtration of relatively large quantities of water. We believe the method may prove useful for collecting pathogenic bacteria from water directly, without the need for the usual isolation steps.