Bacteriological negative bacteria like Salmonella grow as red
Preparation of Samples:
Each sample was placed in a separate clean sterile plastic bag. Samples were transported to the lab. Immediately after collection one hour in an ice box and tested upon arrival. Samples were prepared according to the technique that recommended by the (ICMSF) (17) as follows: From each shawarma sample 25 g was aseptically weighed and macerated and adds 225 ml of sterile water was added. Sterile dilution was carried out using sterile distilled water as diluents. From each dilution 1 ml was plated using the pour plate methods of (18).
Isolation of Bacteria:
Samples were cultivated on different media. The inoculated media were cultured at different temperatures. Pure cultures of the microorganisms were identified using the standard procedures of (19). The test employed for the identification of isolates was the gram stain, biochemical test, pigments and colony morphology. The streak plate method for the recovery of the various bacteria species. The culture media used were Nutrient agar medium was used for total bacterial count, MaConkey agar medium is a differential and low selectivity medium used to distinguish lactose fermenting (e.g, Klebsiellaand Eshericia Coli) from non-lactose fermenting bacteria (Salmonella Species, Pseudomonas aeroginosa and Proteus mirabilis), Salmonella-Shigella agar medium was used for isolation of salmonella and shigella and incubation at 35oCfor 24-48hours, MaConkey agar and Nutrient Agar was used for isolation Escherichia coli, Mannitol salt agar & Sheep blood agar is a differential and selective plate medium used to isolate Staphylococcus aureus. Mannitol is fermented by Staphylococcus aureus (yellow in medium), Brilliant Green Agar is selective agent. It is indicative principle is based on the ability to ferment lactose and sucrose. Phenol red is pH indicator, which changes from yellow to red at –pH 6.8-8.4. Therefore, lactose negative and sucrose negative bacteria like Salmonella grow as red –pink, white opaque colonies surrounded by brilliant red zones in the agar.