Antimicrobial resistance of heterotrophic bacteria in sewage-contaminated rivers

Sewage-contaminated rivers are ecosystems deeply disturbed by human activity due to the release of heavy metals, organic pollutants and pharmaceuticals as well as faecal and pathogenic micro-organisms, which coexist with the autochthonous microbial population. In this study, we compared the percentage of resistance in faecal and heterotrophic bacteria in rivers with different degrees of sewage pollution. As a matter of fact, no correlation was found neither between the degree of sewage pollution and the percentage of antimicrobial resistant heterotrophic bacteria nor between the number of resistant faecal bacteria and that of resistant heterotrophic bacteria. Most of the resistant isolates from the Zenne river downstream Brussels were multi-resistant and the resistance patterns were similar among the strains of each phylogenetic group. The total microbial community in this polluted river (as evaluated through a 16S rRNA gene clone library analysis) appeared to be dominated by the phyla Proteobacteria and Bacteroidetes while the phylum TM7 was the third most represented.