SALMONELLA SHIGELLA AGAR
SS Agar
Formula in grams per liter
Lactose............................ ................................... 10,00 Bile salts mixture............................ ........................... 8,50
Sodium Citrate............................ ..........................8,50 Sodium Thiosulphate....................... ........................... 8,50
Beef Extract............................ ..............................5,00 Peptone Mixture............................ ............................. 5,00
Ferric Citrate............................ .............................1,00 Neutral Red…............................... ............................ 0,025
Brilliant Green.............................. ...................0,330mg Bacteriological Agar............................... .................. 13,50
Final pH 7,0 ± 0,2 at 25ºC
· SS agar is a selective and differential medium widely used
In sanitary bacteriology to isolate Salmonella and Shigella.
· From feces, urine, and fresh and canned foods. Inhibition
Of Gram-positive microorganisms is obtained by the bile
salts mixture. Due to its strong inhibitory power
· Non-lactose fermenting bacteria (supposed pathogens)
produce clear colonies, transparent or colourless, while
coliforms are sufficiently inhibited, and form small colonies
that vary from rose to red in color.
· The H2S producing bacteria produce colonies with black
centers and a clear halo such as Proteus and other
species of Salmonella. The plates of the medium can be kept for at least a week in refrigeration
Principles of the Procedure
· The 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.
· Differentiation of enteric organisms is achieved by the incorporation of lactose in the medium.
· Organisms that ferment lactose produce acid
which, in the presence of the neutral red indicator, results in
the formation of red colonies. Lactose nonfermenters form
colorless colonies.
The latter group contains the majority of the intestinal pathogens, including Salmonella and Shigella.
The sodium thiosulfate and ferric citrate enable the detection of hydrogen sulfide production as evidenced by colonies with
black centers
ملف مرفق 2175
A. Klebsiella pneumoniae
B. Escherichia coli
Klebsiella pneumoniae & Escherichia coli are positive for acid production from fermentation of the carbohydrate(s) present.
C: Salmonella sp.
D: Proteus mirabilis
Both Salmonella sp. & Proteus mirabilis product hydrogen sulfide.
E: Pseudomona aeruginosa
The Pseudomonas colonies are nearly colorless.
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