RAPPAPORT-VASSILIADIS SOYA PEPTONE BROTH (RVS BROTH)

Code: CM0866

A selective enrichment broth for the isolation of salmonellae.

Typical Formula*	gm/litre
Soya peptone	4.5
Sodium chloride	7.2
Potassium dihydrogen phosphate	1.26
Di-potassium hydrogen phosphate	0.18
Magnesium chloride (anhydrous)	13.58
Malachite green	0.036
pH 5.2 ± 0.2 @ 25°C

* Adjusted as required to meet performance standards

Directions
Suspend 26.75g in 1 litre of distilled water and heat gently to dissolve. Dispense 10ml volumes into screw-capped bottles or tubes and sterilise by autoclaving at 115°C for 15 minutes.

Description
Rappaport-Vassiliadis Soya Peptone Broth (RSV Broth) is recommended as a selective enrichment medium for the isolation of salmonellae from food and environmental specimens. It shares with the original formulation¹, the ability to exploit the full characteristics of Salmonella species when compared with other Enterobacteriaceae. These are:
1. The ability to survive at relatively high osmotic pressure.
2. To multiply at relatively low pH values.
3. To be relatively more resistant to malachite green.
4. To have relatively less demanding nutritional requirements.

RVS Broth is based on the revised formulation described by van Schothorst et al.², and is recommended as the selective enrichment medium for the isolation of salmonellae from food and environmental specimens. It can also be used to isolate salmonellae from human faeces without the need for pre-enrichment. It is a modification of the Rappaport Vassiliadis (RV) Enrichment Broth described earlier by van Schothorst and Renauld³. The modifications to their earlier formula are:
1. The addition of di-potassium hydrogen phosphate to buffer the medium so that the pH is maintained during storage of the prepared broth.
2. Clarifying the optimum concentration of magnesium chloride 6H₂O.

The two modifications are said to enhance the reliability of the enrichment broth¹. Peterz et al.⁴ have also highlighted the importance of the concentration of magnesium chloride in the final medium.

Technique
Food and environmental specimens.
1. Prepare Buffered Peptone Water CM0509 or Buffered Peptone Water (ISO) CM1049 as instructed on the label in volumes of 225ml.
2. Prepare RVS Broth as instructed.
3. Add 25g or 25ml of the test sample to 225ml of Buffered Peptone Water and incubate at 37°C for 16-20 hours. Transfer 0.1ml of the pre-enrichment peptone water culture to 10ml of RVS Broth and incubate at 42 ± 1°C for 24 hours.
4. Subculture the enrichment broth by streaking onto plates of MLCB Agar CM0783 and Brilliant Green Agar (Modified) CM0329. Incubate at 35°C for 18-24 hours. Colonies suspected as salmonellae should be confirmed by biochemical or serological methods. Refer to standard methods such as ISO 6579:2002 +A1:2007⁵.

Faecal specimens
no pre-enrichment needed. Add one or two 3mm loopfuls of liquid faeces (or an emulsion of faeces in saline) to 10ml of RVS Broth pre-warmed to 42°C. Incubate at 42 ± 1°C for 24 hours, and then streak onto selective agars of choice.

Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the prepared medium at 2-8°C.

Appearance
Dehydrated medium: Straw/green coloured, free-flowing coarse powder
Prepared medium: Blue coloured solution

Quality control

Positive control:	Expected results
Salmonella Typhimurium ATCC® 14028*	Good growth
Negative control:
Escherichia coli ATCC® 25922 *	Inhibited