Salmonella agar plates

Since Salmonella Typhimurium infection induced acute outbreaks exhibiting clinical disease mainly in chicks younger than 2 weeks old, infection was self-limiting and resulted in asymptomatic intestinal infections in elder chickens, so the shedding levels of Salmonella was determined by culturing method. From each cloacal sample, 0.2 g of the mixed feces was taken and emulsified in 1 mL of sterile saline, decimal dilutions were then steaked onto CHROMagar Salmonella agar plates (CHROMagar, France). Salmonella appearing typical purple colonies were enumerated after incubation at 37°C for 24 h.

Blood cultures were performed by aseptically introducing 8 mL of blood into biphasic blood culture bottles. The cultures were incubated for 14 days at 37 °C. On day 3 and day 7, subcultures were plated on CHROMagar Salmonella agar plates (CHROMagar, Paris, France). Suspected Salmonella isolates were identified using API 20E test strips (bioMérieux, Marcy-l'Étoile, France).
Salmonella isolates were plated on Columbia nutrient agar plates (Oxoid, Basingstoke, UK) and cultured overnight (16–18 h) at 37 °C. The isolates were characterized by agglutination of the O antigen, H1 phase antigen, and H2 phase antigen; normal saline was used as a self-agglutination control. Antigenic properties were confirmed in accordance with the Kauffmann–White serotyping table.
Total genomic DNA was extracted from the supernatants of 7-day and 14-day blood cultures and screened for the presence of Salmonella by using real-time PCR detection kits (Liferiver, Shanghai, China).