Serotyping and molecular typing of Salmonella species isolated from wastewater in Nsukka, Nigeria

The objective of this investigation was to isolate and identify Salmonella serovars present in wastewater from the University of Nigeria, Nsukka (UNN) wastewater treatment plant and to evaluate the sensitivity and precision of different microbial typing methods (conventional and molecular), in identifying and characterizing Salmonella species. A total of 100 suspected Salmonella colonies on selective media (Salmonella-Shigella agar and MacConkey Agar) were subjected to biochemical testing. A total of 12 biochemically typical Salmonella isolates were identified and further characterized. Serotyping analysis further identified 3 (25%) of the isolates as Salmonella enterica serovar Limete. Salmonella specific (16S) polymerase chain reaction (PCR) assay validated the result obtained by serotyping, although 2 of the isolates could not be serotyped and were identified as rough strains. PCR assay produced positive amplifications of 574 bp of the 16S rRNA gene specific for Salmonella, while non-Salmonella serovars were negative (100%). Random amplified polymorphic DNA (RAPD-PCR) analysis revealed the genetic relatedness of Salmonella serovars isolated from wastewater. Primers 787 and RAPD2 identified 4 RAPD-binding patterns, while primer 1254 did not give any discriminatory pattern. Molecular analyses (16S PCR and RAPD) showed discriminatory power, reproducibility, easy interpretation and performance. It is therefore a promising alternative method for typing Salmonella species. Key words: Wastewater, Salmonella, serovars, serotyping, polymerase chain reaction (PCR), 16S rRNA, random amplified polymorphic DNA.