SALMONELLA CHROMOGENIC AGAR BASE

CODE: CM1007

Salmonella Chromogenic Medium is a selective and differential agar base the identification of Salmonella species from other organisms in the family Enterobacteriaceae.

Typical Formula*	gm/litre
Special Peptone	10.0
Chromogenic mix	28.0
Agar	12.0
pH 7.2 ± 0.2 @ 25°C

* Adjusted as required to meet performance standards 

SALMONELLA SELECTIVE SUPPLEMENT

Code: SR0194

Vial contents (each vial is sufficient for 500ml of medium)	per vial	per litre
Cefsulodin	6.0mg	12.0mg
Novobiocin	2.5mg	5.0mg

Directions
Suspend 25g in 500ml of distilled water and add the contents of one vial of Salmonella Selective Supplement (SR0194) reconstituted as directed. Mix well and bring to the boil with frequent agitation. DO NOT AUTOCLAVE. DO NOT HOLD AT BOILING TEMPERATURE. Cool to 50°C, mix well and pour into sterile Petri dishes.

Description
Salmonella Chromogenic Medium is designed to identify Salmonella species based on their utilisation of one chromogenic substrate. Their inability to utilise another chromogenic substrate, that most other members of the family Enterobacteriaceae can utilise, enables rapid and reliable identification of Salmonella species.

There are in excess of 2000 known species of Salmonella, some of which differ from the typical rod-shaped, Gram-negative motile bacterium. In the U.S. alone there are between 800,000 and 4 million reported cases of salmonellosis per year resulting in 500 deaths. Infections due to Salmonella are of particular concern in the very young, the elderly and in the severely immunosuppressed where salmonellosis is recognised as an AIDS defining condition. Incidence continues to rise and infections due to Salmonella remain a principal health issue¹. The widespread occurrence means there is a need for the rapid detection and identification of Salmonella in food and water to aid in the prevention and control of outbreaks².

Traditionally, media used to differentiate Salmonella species from other members of the family Enterobacteriaceae depend upon the ability of Salmonella species to produce hydrogen sulphide coupled with their inability to ferment lactose^2,3. These are, however, essentially inadequate methods, with a significant number of the 2000 plus species not exhibiting these characteristics. In recent times chromogenic media have been developed for the rapid and more reliable identification of Salmonella.

Salmonella Chromogenic Agar Base combines two chromogens for the detection of Salmonella sp., 5-Bromo-6-Chloro-3-Indolyl caprylate (Magenta-caprylate) and 5-Bromo-4-Chloro-3-Indolyl b-D galactopyranoside (X-gal). X-gal is a substrate for the enzyme b-D-galactosidase. Hydrolysis of the chromogen, Mag-caprylate, by lactose negative Salmonella species results in magenta colonies.

The medium contains bile salts to inhibit the growth of Gram-positive organisms and the addition of the Salmonella Selective Supplement SR0194 is recommended to increase the selectivity of the medium. This uses novobiocin to inhibit Proteus growth and cefsulodin to inhibit growth of Pseudomonads.

Technique
Inoculate the plates with a food or clinical sample to produce single colonies. A Salmonella enrichment broth may be used prior to streaking out, e.g. Rappaport-Vassiliadis Enrichment Broth CM0669, Selenite Broth CM0395 & LP0121 or Tetrathionate Broth Base CM0029. Incubate for 18-24 hours at 37°C. Examine the plates for coloured colonies.

On Salmonella Chromogenic Medium CM1007 & SR0194, typical colonies will be coloured as follows:

Species	Colony Colour	Colony Diameter	Colony Morphology
Salmonella spp.	Magenta	1.0mm	Raised, smooth
Salmonella typhi	Magenta	1.0mm	Raised, smooth
Salmonella paratyphi	Magenta	1.0mm	Raised, smooth
Salmonella arizonae	Magenta / blue †	1.5mm	Raised, smooth
Salmonella gallinarum	Magenta	0.75mm	Raised, smooth
Salmonella indiana	Blue †	1.0mm	Raised, smooth
Escherichia coli	Blue	1.0mm	Raised, smooth
Enterobacter spp.	Blue	1.5mm	Raised, smooth
Klebsiella spp.	Blue	3.0mm	Raised, mucoid
Citrobacter spp.	Blue	1.5mm	Raised, mucoid
Proteus spp.	No growth / straw	0.25mm	-
Pseudomonas spp.	No growth	-	-
Shigella sonnei	Blue	4.0mm	Undulate
Shigella dysenteriae	Magenta	1.0mm	Raised