Mode of Action
The selection of suitable nutrients and vitamins (peptones, yeast extract) allow optimal growth of salmonellae. At the same time the surfactant NIAPROOF-4 (formerly Tergitol-4/Sodiumtetradecylsulfate) largely inhibits the accompanying flora. Salmonellae, due to H2S-formation (thiosulfate and iron(III)- ions), can be easily detected as black colonies on a red-violet background and differentiated from the residual accompanying flora. E. coli, in contrast, will show yellow colonies on a yellow background due to acidification of the medium (pH-indicator:
phenol-red). Other accompanying organisms, like Shigella, due to a missing H2S-formation and acidification, will grow colourless on a red background.
Typical Composition (g/litre)
Proteose peptone No. 3 1,6; yeast extract 3.0; L-lysine 5.0; xylose 3.75; lactose 7.5; sucrose 7.5; ammonium-iron(III) citrate 0.8; sodium thiosulfate 6.8; sodium chloride 5.0; phenol-red 0.08; agar-agar 18.0.
Suspend 59 g in 1 litre of demin. water, add 4.6 ml XLT4 Agar
Supplement solution and heat the medium in a boiling waterbatch (not on a heating-plate!). Cool to approx. 50°C and pour plates.
Do not overheat, do not autoclave.
The medium should not be kept longer than 45 minutes at 50 °C
to avoid possible precipitates.
pH: 7.4 ± 0.2 at 25 °C.
The plates are clear and red
Spread sample material from an enrichment on the surface of the culture medium.
Incubation: 18-24 hours at 35 °C aerobically. If this will neither result in black colonies nor in visible growth continue incubation up to 48 hours.
Black or black centred colonies on a red-violet background indicate the presence of H2S-positive salmonellae. Further tests should be performed in order to identify the colonies