CHROMOSENSE SALMONELLA AGAR BASE
A chromogenic medium, with selective supplements for the isolation and identification of Salmonella spp. including S.typhi.
Code: CB1/105
Typical formula g/l
| Peptone | 10.0 |
| Selective compounds | 12.0 |
| Chromogenic mixture | 0.9 |
| Agar | 15.0 |
Add: Salmonella Selective Supplement Vial A (each vial sufficient for 500 ml of medium) Code: CBS/5125A
Emulsifying agents - 5.7ml
Add: Salmonella Selective Supplement Vial B (each vial sufficient for 500 ml of medium) Code: CBS/5125B
Cefsulodin - 2.5mg
Final pH 7.2 ± 0.2
Directions
Suspend 19g in 500 ml of cold distilled water; add the contents of one vial of Salmonella Selective Supplement Vial A, heat to boiling and sterilise by autoclaving at 121°C for 15 minutes. Cool to 50°C and add the contents of one vial of Salmonella Selective Supplement Vial B reconstituted with 2ml of sterile distilled water. Mix well and pour into sterile petri dishes.
Description
Chromogenic Salmonella Agar is a selective and diagnostic medium useful for the isolation and identification of Salmonella spp. from clinical specimens, foodstuff and environmental samples. The selectivity of the medium is improved by a cephalosporin which inhibits the growth of Pseudomonas, by sodium deoxycholate which suppress the growth of Gram-positive and some Gram-negative bacteria and by Tergitol 4 which is active mainly against the growth of Proteus spp. The differentiation between the salmonella and non-salmonella colonies is achieved by a chromogenic substrate for a specific esterase enzyme of Salmonella that is split with the liberation of an insoluble magenta-red dye. A chromogenic glucopyranoside derivative, which is split by beta-glucosidase due to the formation of an insoluble blue-green dye.
The chromogenic and selective compounds of the medium allow the detection also of the rare lactose positive Salmonella strains. Chromogenic Salmonella Agar is useful also for the detection of Salmonella typhi.
Method
Chromogenic Salmonella Agar can be used according to the normal laboratory practices for Salmonella isolation with direct plating or after the enrichment in non-selective and selective liquid media. Incubate the inoculated plates at 37°C for 18-24 hours and observe for the presence of typical magenta-red colonies. The growth characteristics of different species are summarised in the following table:
Microorganism Growth characteristics
Salmonella spp. Good growth, magenta-red colonies
Salmonella spp. lac+ good growth, magenta-red colonies
Salmonella typhi good growth, magenta-red colonies
E.coli poor growth with colourless colonies
Enterobacter spp. growth with blue-green colonies
Klebsiella spp. poor growth with blue-green colonies
Pseudomonas spp. inhibited
Proteus spp. poor growth with pale brown or green colonies
Gram-positive bacteria inhibited
The sensitivity of Salmonella detection with Chromogenic Salmonella Agar is very high, thus all the plates without typical colonies can be rejected with no further identification tests. The plates with typical (magenta-red) growth must be retained and the colonies submitted to biochemical and/or serological confirmation. Sometimes rare strains of Pseudomonas and Aeromonas can cultivate with magenta-red colonies. These strains can be easy differentiated with a simple oxidase test.
User quality assurance (24 h-37°C)
Productivity control
S. typhimurium ATCC 14028: growth, magenta-red colonies
Specificity control
E. aerogenes ATCC 13048: poor growth, blue colonies
Selectivity control
P. aeruginosa ATCC 27853: inhibited
Storage
Dehydrated medium: 2-8°C
User prepared plates: 7 days at 2-8°C