How can you tell the difference between Salmonella and Shigella SS Agar?

How can you tell the difference between Salmonella and Shigella SS Agar?

Result Interpretation on Salmonella Shigella Agar Salmonella will not ferment lactose, but produce hydrogen sulfide (H2S) gas. The resulting bacterial colonies will appear colorless with black centers. Shigella do not ferment lactose or produce hydrogen sulfide gas, so the resulting colonies will be colorless.

What color is Shigella on SS Agar?

Result Interpretation of SS Agar

Organisms Result
Shigella Clear, colorless, transparent
Escherichia coli Small, pink to red
Enterobacter, Klebsiella Larger than E.coli, mucoid, pale, opaque cream to pink
Salmonella Colorless, transparent, with a black center if H2S is produced

What color is Salmonella on SS Agar?

On SS Agar, colonies of Salmonella or Shigella are smooth and opaque or colorless. Strains of Salmonella which produce H2S will form black-centered colonies. Lactose-fermenters are pink to rose-red in color and may have a precipitate.

How is Salmonella Shigella Agar selective?

SS Agar is a moderately selective medium in which gram-positive bacteria are inhibited by bile salts, brilliant green and sodium citrate. Sodium thiosulphate is reduced by certain species of enteric organisms to sulphite and H2S gas and this reductive enzyme process is attributed by thiosulphate reductase.

When to use SS agar or Shigella agar?

SS Agar and Salmonella Shigella Agar are moderately selective and differential media for the isolation of pathogenic enteric bacilli, especially those belonging to the genus Salmonella. This formula- tion is not recommended for the primary isolation of Shigella. Summary and Explanation

What are the results of Salmonella-Shigella agar?

Results Lactose fermenter: If lactose fermentation occurs, the medium will turn red due to the acidic pH. e.g. Escherichia coli, Klebsiella pneumoniae gives red colonies. Non-Lactose fermenter: Salmonella, Shigella, and other non-lactose fermenters appear as transparent or translucent colorless colonies.

What makes SS agar a moderately selective media?

Principles of the Procedure SS Agar and Salmonella Shigella Agar are designated as moderately selective media based upon the degree of inhibition of gram-positive microorganisms that they inhibit due to their content of bile salts, brilliant green and citrates.

What to do with Salmonella Shigella Culture Media?

Suspend 60 g of the medium in one liter of deionized or distilled water. Mix well. Heat with frequent agitation and boil for one minute. Do not autoclave the media. Pour into plates. Let the agar solidify and store in the refrigerator (avoid freezing).