Characterisation of pathogenic bacteria in a UASB-polishing pond system using molecular techniques

Molecular techniques have been commonly used to detect and quantify pathogenic bacteria in food, clinical and environmental samples, but in wastewater treatment plants few studies have been carried out. This work applied PCR with a specific set of primers to investigate pathogenic bacteria in a wastewater plant comprised of a UASB reactor followed by polishing ponds. In addition, in-situ hybridisation technique (FISH) was used to estimate the abundance of Escherichia coli in the system. According to the PCR results it was observed that Escherichia coli and Salmonella enterica subsp. enterica were not completely removed in the system, since they were detected either in the raw sewage or UASB and pond effluents. Shigella dysenteriae and Enterococcus spp. were detected in raw sewage and UASB, but not in the pond effluent. In contrast Staphylococcus aureus and Helicobacter pylori were not detected in any samples. The quantification of E. coli using FISH revealed values in the range of 107 cells/100 mL for raw sewage and 106 cells/100 mL for pond effluent, slightly higher than values obtained by traditional techniques. Finally the results show the applicability of PCR method for monitoring pathogenic bacteria in wastewater systems; however, more samples need to be analysed in order to certify the applicability of FISH to estimate pathogenic bacteria in WWT effluents.