Semisolid IMRV Medium Base

Semisolid IMRV Medium Base is used for the simultaneous enrichment as well as isolation of motile Salmonella from other competitive organisms

Composition**

Final pH (at 25°C): 5.5±0.2

**Formula adjusted, standardized to suit performance parameters

Directions

Suspend 51.2 grams in 1000 ml distilled water. Heat with stirring to boiling to dissolve the medium completely. DO NOT AUTOCLAVE / DO NOT OVERHEAT. Cool to 45°C and aseptically add rehydrated contents of 1 vial of IMRV/RV Selective Supplement (FD193). Mix well and pour into sterile Petri plates.

Note: The motility of Salmonellas can be drastically reduced when the agar surface becomes too dry. Hence the plates should be well dried before use. If visible moisture occurs on the lid of the plates or the surface of agar, it must be removed. While incubation, incubate the plates aerobically in an upright position for no longer than 24 hours at 42°C.

Principle And Interpretation

Semisolid IMRV Medium Base is used for simultaneous enrichment and isolation of motile Salmonella from food and environmental samples. It is diagnostic medium distinguishing motile Salmonella from non motile forms (1, 2). Also Salmonella can be identified from a mixed culture of different gram negative organisms. These media detects more Salmonella positive samples than the routinely used enrichment procedures (3,4,5). Addition of Novobiocin as a supplement and malachite green in the medium selectively inhibits most gram positive organisms. Salmonella generally survives a little high osmotic pressure (due to MgCl2 in the medium), grows at slightly low pH and are resistant to malachite green compared to other bacteria. Saccharose, lactose and bromocresol purple differentiates Salmonella from lactose and sucrose fermenting organisms. Ammonium ferric sulphate and sodium thiosulphate are indicators of H2S production. Thiosulphate is reduced to hydrogen sulphide by several species of bacteria and H2S combines with ferric ions to produce the insoluble black precipitate of ferrous sulphide as indicated by formation of grayish black colour at the centre of the colony.

Casein enzymic hydrolysate and peptic digest of animal tissue, provide the nitrogenous and carbonaceous substances and other essential growth nutrients. Phosphate gives good buffering capacity to the medium. Addition of novobiocin as a supplement (FD193) and malachite green in the medium selectively inhibits most gram-positive organisms. Sodium chloride maintains the osmotic equilibrium of the media. All these factors make the medium selective for the isolation of Salmonella. This medium enriches Salmonella and the semi-solid nature of the medium helps to differentiate the motile Salmonella from non-motile ones.

Quality Control

Appearance: Light yellow to blue homogeneous free flowing powder

Gelling: Semisolid, comparable with 0.27% Agar gel.

Colour and Clarity of prepared medium: Dark green coloured clear semisolid gel forms in Petri plates

Reaction: Reaction of 5.12% w/v aqueous solution at 25°C. pH : 5.5±0.2

pH: 5.30-5.70

Cultural Response

M1427: Cultural characteristics observed after an incubation at 42-43°C for 18-24 hours with added IMRV/RV Selective Supplement (FD193), when one drop of culture is inoculated in the centre of the medium plate.(Motility is checked by inoculating a drop of culture in the centre of the medium plate).

Storage and Shelf Life

Store below 30°C in tightly closed container and the prepared medium at 2-8°C. Use before expiry date on the label.

Reference

1. Vander Zee H, and Van Netten P. 1992 Proc. Symp. "Salmonella and Salmonellosis". Ploufragan ; 69.
2. Ruzickova, V; Karpiskova, R. and Pakrova, E. 1996. Vet Med. Praha. 41 (9): 283-288.
3. DeSmedt J. M., Bolderjik R. F., 1987, J. Food Prot.; 50: 658-661.
4. DeZutte et al, 1991, Int. J. Food Microbiol., 13:11
5. DeSmedt J. M. et al, 1991, Int. J. Food Microbiol. 13:301