ISOLATION AND TYPING OF SALMONELLA SPECIES AND SCREENING FOR SALMONELLA-PHAGES IN THE WASTEWATER TREATMENT PLANT, UNIVERSITY OF NIGERIA, NSUKKA
Wastewater may contain high number of potentially pathogenic organisms. Despite large advances in water and wastewater treatment, waterborne diseases still poses a major worldwide threat to public health. Salmonella species are widely distributed in nature and are also found in wastewater. They are the etiological agents of a wide range of diseases, thus contamination of the environment, including food and water with Salmonella, poses a serious public health concern to wildlife and human health. The occurrence and identity of Salmonella serovars present in the University of Nigeria, Nsukka (UNN) wastewater treatment plant were examined. Salmonella serovars present in the wastewater were detected, isolated and characterized. Traditional and molecular typing methods were employed in the identification and characterization of Salmonella species isolated. Forty wastewater samples were collected from four (4) different units of the treatment plant (Imhoff inlet, Imhoff outlet, Waste Stabilization Ponds A and B). A total of 100 suspected Salmonella colonies on selective media (Salmonella-Shigella agar and MacConkey Agar) were subjected to biochemical testing. Twelve biochemically typical Salmonella isolates were identified and further characterized. Serotyping analysis of our isolates identified 3 outr of 12 (25%) of our Salmonella isolates as Salmonella enterica serovar Limete with antigenic formula Salmonella I 4,12: b:1,5. Phage typing also revealed non-susceptibility to lysis of the Salmonella spp isolated from wastewater. Salmonella specific PCR assay (16S rRNA) validated the result obtained by serotyping. Two of the Salmonella enterica serovar Limete isolates showed an amplification of 244 bp fragment of Salmonella invA gene indicating the presence of Salmonella invA virulence gene. Random amplified polymorphic DNA (RAPD-PCR) analysis revealed the genetic relatedness of the Salmonella serovars isolated from wastewater. Primers 787 and RAPD2 identified 4 RAPD-binding patterns, while primer 1254 did not give any discriminatory pattern. This investigation shows a low occurrence of Salmonella species in the University of Nigeria, Nsukka’s wastewater treatment plant and the presence of Salmonella enterica serovar Limete (a rare serovar). Furthermore, it revealed the precision and sensitivity of molecular typing methods to conventional culture methods in identifying and characterizing Salmonella from wastewater.