A 4-YEAR STUDY OF THE DIVERSITY AND PERSISTENCE OF COLIFORMS AND AEROMONAS IN THE WATER OF A SWEDISH DRINKING-WATER WELL

Coliforms and Aeromonas, isolated over a sampling period of 4 years fr om a Swedish drinking water well, were analysed for their phenotypical diversity and for their ability to persist in the well water. From ea ch of the 40 water samples collected from the well, 32 bacterial isola tes were subjected to typing by the PhenePlate (PhP) biochemical finge rprinting system. Strains able to persist in the well water were furth er characterized using the API 20E system, gas-liquid chromatographic cellular fatty acid analysis, and the DNA fingerprinting technique AFL P. Using the PhP system, a total of 170 different phenotypes were iden tified among 1143 studied isolates. Most phenotypes were only represen ted by a few isolates and (or) were restricted to one or two sampling occasions. However, one particular phenotype (RV-C01), identified as A eromonas hydrophila using the API 20E system and fatty acid analysis, reoccurred in 28 samples distributed over the whole study period and o ften dominated the bacterial population in the well water. AFLP analys is revealed that the RV-C01 isolates displayed basically identical fin gerprints. Our results thus suggest that a genetically stable Aeromona s clone resided in the well water over the whole 4-year study, whereas other bacterial strains studied were only transient inhabitants of th e well.