Salmonella shigella agar

The reference strain S. Typhi (ATCC 6539) used in the present study was purchased from American Type Culture Collection (ATCC). Clinical isolates, S. Enteritidis, S. Typhi, S. Typhimurium, and S. Choleraesuis, were provided by “Centre Pasteur du Cameroun.” All bacterial strains were plated from cultures, which were stored at − 80°C onto Salmonella-Shigella agar (SSA) (Condalab) for 18–24 h at 37°C. Cultures were subsequently subcultured and maintained on Muller Hinton agar (MHA Sigma-Aldrich) plates at 4°C until needed for further bioassay.

To isolate Salmonella and Shigella, a loopful of each stool sample was cultured in Selenite F Broth at 37°C for 24h followed by subculturing onto Salmonella-Shigella agar (Condalab, Spain) at 37°C for 24h. On Salmonella-Shigella agar, Salmonella spp. colonies appeared colorless with a black center, while Shigella spp. colonies were colorless. Antisera from the Salmonella seroquick ID kit (SSI Diagnostica, Denmark) were used for further serotyping of Salmonella typhimurium and enteritidis. Campylobacter spp. were isolated for 48h at 42°C in microaerophilic conditions generated by Campygen sachets (Oxoid, UK) on Karmali agar medium enriched with selective Karmali supplement (Condalab, Spain). Catalase, hippurate hydrolysis, the H₂S test, and gram stain were used to identify and differentiate C. jejuni and C. coli colonies grown on Karmali agar.

Tree culture media were used in this work namely Salmonella-Shigella agar (Conda, Madrid, Spain), Mueller Hinton agar (Conda, Madrid, Spain) and Mueller-Hinton broth (MHB) (Conda). The bacterial cell suspensions were prepared at 1.5 × 10⁸ colony-forming units/mL (CFU/ml) following McFarland turbidity standard N° 0.5. For this purpose, 18 h old overnight bacterial cultures were prepared on Mueller-Hinton agar, and few bacteria colonies were collected aseptically with a sterile loop and introduced into 10 ml of sterile 0.90% saline distilled water and homogenised.