DIASALM Medium Base

EMD Cat. No. 1.09803.0500
500 g
Product available March 2005


Diasalm is a diagnostic semi-solid selective motility agar to be used for the isolation of Salmonella spp. in food and environmental samples.




Mode of Action Preparation
Experimental Procedure and Evaluation Quality Control
Typical Composition (g/liter) Literature
Picture/Image  


Mode of Action
 DIASALM combines the characteristics of semi-solid indole motility agar (SIM Agar) and Rappaport-Vasilliadis (RVS Broth). The selective system exploits the resistance of Salmonella spp. as compared to other Enterobacteriaceae to high osmolarity (MgCl2) and low pH (5.5). The combination of novobiocin and malachite green suppresses the growth of Gram-positive bacteria and most, but not all Gram-negative bacteria. The semi-solid approach simultaneously enriches salmonellae and separates motile salmonellae from most competitive organisms resistant to the selective system. As a result of this on plating agars, salmonellae are rarely overgrown by non salmonellae. Sometimes salmonellae occur mixed with Proteus, Hafnia or Enterobacter spp. as interfering motile Enterobacteriaceae. A diagnostic system consisting of saccharose, lactose and bromocresol purple differentiates salmonellae from lactose and many lactose and saccharose dissimilating organisms. Non motile salmonellae growing at the inoculum spot(s) may produce a grey blackish center.
Typical Composition (g/liter)
 Peptone from casein 13.5; peptone from meat 13.5; saccharose 7.5; lactose 0.5; ammonium iron(II) sulfate 0.2; sodium thiosulfate 0.8; potassium dihydrogen phosphate 1.47; magnesium chloride-6-H2O 23.3; malachite green 0.037; bromocresol purple 0.08, agar-agar 2.7.

Preparation
 Suspend 64 g in 1 liter of purified water by heating in a boiling water bath or in a flowing steam until the medium is completely dissolved. Do not autoclave / do not overheat! Dissolve the

lyophilisate of 1 vial MSRV Selective Supplement (Cat. No. 1.09874.) by adding 1 ml sterile distilled water and add the solution to the medium cooled to 45-47 °C. Mix gently and pour plates.
pH: 5.5 ± 0.2 at 25 °C.
 The prepared medium is clear and dark green. Prepared plates can be stored for up to 1 week at +2 to +8°C.
 The plates must be well dried before use (minimum: 1 h at room temperature).

Experimental Procedure
1)
 		Enrich the sample material in Buffered Peptone Water (incubation: 16-20 h at 35°C).

2)
 		Inoculate with either 3 drops (3 x 0.03 ml) or 1 drop of 0.1 ml of the pre-enrichment culture in the center of DIASALM medium plates.
3)
 		Incubate the plates aerobically in an upright position at 42°C for 12-18 h, but not longer than 24 h.

Evaluation
 Motile salmonellae show a purple halo of growth originating from the inoculation spot. Against a white background the purple halo can be surrounded by a light brown black zone. A grey-blackish centre may suggest the presence of non-motile salmonellae, Citrobacter freundii or Proteus spp. On the edge of a typical migration zone a loopful is taken for  subculture on plating agars e.g. Rambach agar, Brilliant Green Phenol Red Lactose Agar, mod. XLD agar. For the confirmation of Salmonella spp. further biochemical serological tests are recommended.

Quality control

Test strains
 Growth (swarming)
 		Motility zone (color)
Salmonella typhimurium ATCC 14028
 		+
 		grey-violet, dark circle
Salmonella abony NCTC 6017
 		+
 		grey-violet, dark circle
Salmonella dublin ATCC 15480
 		+
 		grey-white, violet, dark circle
Salmonella enteritidis ATCC 13076
 		+
 		grey-white, violet, dark circle
Citrobacter freundii ATCC 8090
 		20 mm
Pseudomonas aeruginosa ATCC 9027
 		20 mm
Enterobacter cloacae ATCC 13047
 		20 mm
Hafnia alvei ATCC 29926
 		20 mm


Additives


EMD Cat. No. Product Pack Size
1.07228.0500 Buffered Peptone Water 500 g
1.07228.5000 Buffered Peptone Water 5 kg
1.09874.0001 MSRV Selective-Supplement 1 x 16 vials


Literature

CURTIS, G.D.W., a. BAIRD, R.M. (eds): Pharmacopoeia of culture media for Food Microbiology: Additional Monographs (II). - Int. J. of Food Microbiology Vol 17; 230-233 (1993)
 VAN DER ZEE, H.: Conventional methods for the detection and isolation of salmonella enteritidis. - Int. J. Food Microbiol., 21; 41-46 (1994).
 PUZICKOVA, V., KARPIKOVA, R., a. PAKROVA, E.: Use of semi-solid medium for the isolation of Salmonella enteritidis. - Vet. Med. Praha Vol 41 (9); 283-288 (1996).
 VAN DER ZEE, H., a. VAN NETTEN, P.: Diagnostic selective semi-solid media based on Rappaport-Vassiliadis broth for detection of salmonella spp. and Salmonella enteritidis in foods. - Proc. Symp. "Salmonella and Salmonellosis" Ploufragen.; 69-77 (1992).


Salmonella typhimurium


© 2002 Merck KGaA, Darmstadt, Germany