Observations on brilliant green agar with H2S indicator

Area of Science:

• Microbiology
• Clinical Diagnostics

Background:

• Brilliant green agar is a selective culture medium used for isolating Salmonella species.
• Accurate differentiation of Salmonella from other enteric bacteria is crucial for public health.

Purpose of the Study:

• To evaluate and optimize formulations of brilliant green agar supplemented with an H2S indicator for improved Salmonella detection.
• To compare the efficacy of the optimized brilliant green agar with existing selective media like Hektoen agar.

Main Methods:

• Several brilliant green agar formulations were tested with varying concentrations of key ingredients including lactose, sucrose, phenol red, sulfanilamide, ferric ammonium citrate, sodium thiosulfate pentahydrate, and brilliant green dye.
• The growth and colony characteristics of 39 Salmonella strains and other common enteric bacteria were assessed on the optimized media.
• Differentiation capabilities were evaluated based on colony color, presence of black centers (indicating H2S production), and growth inhibition of non-target organisms.

Main Results:

• An optimal formulation was identified, supporting good growth of all tested Salmonella strains.
• Salmonella colonies typically appeared pink with black centers, while H2S-negative strains showed pink colonies without black centers.
• The optimized medium effectively inhibited most non-Salmonella bacteria, with only Enterobacter, Klebsiella, and some Citrobacter strains showing significant growth.
• Addition of xylose and L-lysine hydrochloride further enhanced differentiation and the intensity of blackening in Salmonella colonies.
• The brilliant green agar formulations demonstrated superior differentiation of Salmonella compared to Hektoen agar with novobiocin.

Conclusions:

• Optimized brilliant green agar formulations with an H2S indicator significantly improve the identification of Salmonella species.
• The enhanced medium offers better selectivity and differentiation compared to conventional methods, aiding in clinical and research settings.