Molecular and biochemical diagnosis of Salmonella in wastewater

Abstract

This study aimed to employ biochemical and molecular assays to detect and diagnose Salmonella in wastewater. For this reason, two water samples were collected from Alexandria wastewater treatment plant (S1) and septic tank of a hospital at Alexandria governorate (S2). Selective culture media specific for Salmonella were used to grow and purify a number of isolates from water samples. Direct plate count revealed a high frequency of Salmonella cells in sample S2 than S1. As a confirmatory, species-specific PCR assay was performed for 17 randomly selected bacterial isolates from both water samples. Positive-PCR Salmonella isolates (5 from S1 and 4 from S2) were subjected for identification using API 20E biochemical identification kit. Among various examined antibiotics, rifamycine was the most effective antimicrobial agent on Salmonella isolates.
Subsequently, PCR-RFLP of 16S and 23S rDNA genes, Rep-PCR fingerprinting and plasmid profile were employed to recognize among isolates. Out of nine examined restriction endonucleases, HinfI, HincII and HaeIII were the most discriminative enzymes which allowed clear differentiation among isolates, while PCR-RFLP of 23S rDNA was most discriminative than 16S rDNA. Higher levels of polymorphism and specificity were achieved by reproducible genomic fingerprints of Rep-PCR. However, poor discrimination results were achieved by employing plasmid profile assay.