Escherichia coli: diversidad de fenotipos bioquímicos en ambientes acuáticos (Santa Fe, Argentina) / Escherichia coli: diversity of biochemical phenotypes in aquatic environments (Santa, Fe, Argentina)

ABSTRACT

During certain environmental conditions, the floating aquatic vegetation, mainly represented by Eichhornia crassipes (water hyacinth) invade and even cover water courses assigned to recreational activities or to the supply of drinkable water. The rhizosphere of these plants constitutes an unknown biotope of bacteria of sanitary interest, possibly different from waters without vegetation and of the sediment of the same aquatic system. To verify such possibility, 206 isolated strains in MacConkey Agar (Difco) were typified and identified (78 from water, 65 from sediment and 63 from rhizosphere) using the API 20 E system (v. 4.0) and Apilab plus software (v 3.3.3), both of bioMÚrieux (Marcy-l'Etoile, France, 1998). Nineteen different biochemical phenotypes from E. coli were found. The 79 of the population belonged to only 7 phenotypes; the 21 remaining, to the other 12 phenotypes. Twelve phenotypes did not share the biotopes, while only 4 were in the three. These results (and those obtained by other authors who used the API 20 E system in other biotopes) suggest that it would be possible to characterize the rhizosphere using those phenotypes that are found in smaller proportion. The greatest index of diversity (H) and evenness (E) were found in the rhizosphere (H = 2.903; E = 0.874). The dendrogram (average distances and UPGMA method) reaffirms the dissimilarity in biochemical phenotypes of E. coli populations of the rhizosphere with regard to the other biotopes. The most abundant bacterial species in the three biotopes were E. coli, Klebsiella terrigena and K. pneumoniae, corresponding to 75.2 of the community. The rhizosphere differed from Serratia odorifera and from Klebsiella spp. because of its higher rate of isolation.