Isolation of Salmonella serotypes in wastewater and effluent: Effect of treatment and potential risk.

The characteristics of strains of Salmonella isolated in wastewater were compared before and after treatment with activated sludge (conventional sewage treatment). Of the 21 strains studied, 11 came from raw wastewater and 10 from treated water. Our objective was to determine if the treatment affected all serotypes to the same extent, and whether it had an effect on the plasmidic composition and selection of resistances to antibiotics and disinfectants. The serotypes of all strains were identified, and we also determined the sensitivity to antibiotics, the minimal bactericidal concentration of three disinfectants (peracetic acid, glutaraldehyde, and sodium hypochlorite), and plasmidic content. Results showed no significant differences in the isolated strains before versus after treatment, thus indicating that the conventional treatment of sewage does not constitute a risk factor in the selection of Salmonella strains with a greater pathogenic potential.