Detection of non typhoidal salmonella isolated from food products and clinical cases by PCR and conventional methods: a comparative study

ABSTRACT

Non typhoidal Salmonella [NTS] are important food-borne pathogens. Infection with NTS may not lead to fatal disease, hut it may remain localized in the gastrointestinal tract resulting in gastroenteritis or may take a septicemic form that can affect several organs systems causing gastroenteritis, bacteremia and subsequent focal infection. To compare PCR with different conventional methods for identification of non-typhoidal Salmonella species, and to determine the virulence of the Salmonella serovars obtained from human and animal sources by investigating the presence of virulence gene, InvA in the chromosomal DNA. A total of 480 clinical samples were collected. These included 120 milk, 115 eggs and 125 fresh slaughtered chicken from farms, slaughterhouses, markets, in addition to 120 stool samples from Assiut Children University Hospital. They were subjected to conventional methods for bacteriological and biochemical examination. Conventional cultural examination, API 20 E system and PCR amplification assay of virulence gene invA were investigated in animal and human isolates. By comparing the results of PCR using SI 39 and SI 41 primers and those of culture examination, it was found that PCR had similar results to culture examination. PCR could detect 50 positive cultures of Salmonella species, while API 20 E could detect only 47 of these positive cultures. PCR amplification assay has the ability to detect a wide range of Salmonella species depending on the design of primers targeted to invasion gene operon [InvA gene] of salmonella. PCR technique may provide a valuable, rapid, specific and sensitive laboratory diagnostic test for detection of salmonella DNA in cultures