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VRE BROTH BASE

Code: CM0984

Selective media for the isolation of Vancomycin Resistant Enterococci (VRE) and High Level Aminoglycoside Resistant Enterococci (HLARE) from clinical samples.

VRE AGAR BASE

Code: CM0985

MEROPENEM SUPPLEMENT

Code: SR0184

GENTAMICIN SUPPLEMENT

Code: SR0185

VANCOMYCIN SUPPLEMENT

Code: SR0186

Directions
VRE Broth
Suspend 37.0g of VRE Broth Base in 1 litre of distilled water. Warm to dissolve completely, sterilise by autoclaving at 121°C for 15 minutes and cool to 50°C. Supplement the medium as shown in the table below. Then mix well and distribute into final sterile containers.
VRE Agar
Suspend 42.6g of VRE Agar Base in 1 litre of distilled water. Warm to dissolve completely, sterilise by autoclaving at 121° C for 15 minutes and cool to 50°C. Supplement the medium as shown in the table below. Then Mix agar well and distribute into sterile Petri dishes.

Description
Selective media for the isolation of Vancomycin Resistant Enterococci (VRE) and High Level Aminoglycoside Resistant Enterococci (HLARE) from clinical samples. NB Enterococci containing the Van C genes will not be isolated on this medium.

The proliferation of enterococci, resistant to many commonly used antimicrobials is on the increase¹. The recent emergence of VRE is of great concern as enterococci can cause bacteraemia, endocarditis and urinary tract infections. The use of VRE Broth Base and VRE Agar Base complies with recommendations from the Centre for Disease Control and Prevention (CDC) to detect VRE infection in its early stages².

Resistant enterococci can be isolated either directly by inoculation of the clinical sample onto supplemented VRE Agar, or indirectly isolated with a selective enrichment through VRE Broth followed by inoculation onto supplemented VRE Agar. VRE Agar Base contains an indicator system to detect the growth of aesculin-hydrolysing organisms. Enterococci produce black zones around the colonies from the formation of black iron phenolic compounds derived from aesculin-hydrolyis products and ferrous iron.

Oxoid has developed three antibiotic supplements to selectively isolate antibiotic resistant populations amongst pathogenic Enterococci:
Meropenem Supplement SR0184 is used at 2mg/l in VRE Broth Base , and 1mg/l in VRE Agar Base for the suppression of contaminating flora, particularly Gram-negatives and Enterococcus gallinarum. It has been reported that some Enterococcus faecalis can be sensitive to meropenem. To isolate these strains the level of meropenem may need to be reduced, or the supplement omitted from the formulation.
Gentamicin Supplement SR0185 is used at 512mg/l⁴ in VRE Agar Base for the selective isolation of HLARE.
Vancomycin Supplement SR0186 is used at 6mg/l in VRE Agar Base for the selective isolation of VRE.

Technique
Broth
Add ‘pea sized’ amounts of faecal samples directly to the supplemented VRE Broth and vortex to ensure emulsification. Incubate at 37°C for a minimum of 18 hours and subculture onto VRE Agar.
Agar
Inoculate faecal samples or VRE Broth culture onto supplemented VRE Agar plates with a sterile swab and spread with a loop using the diminishing sweep technique. Incubate at 37°C for 48 hours and examine at 24 hours. Re-incubate negative plates for a further 24 hours.
Enterococci appear as round grey / pale brown colonies about 1mm in diameter surrounded by black zones.

Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Meropenem Supplement SR0184, Gentamicin Supplement SR0185 and Vancomycin Supplement SR0186 should be stored in the dark at 2-8°C.
Prepared medium may be stored for up to two weeks at 2-8°C in the dark.

Appearance
Dehydrated medium: Broth: Cream coloured, free-flowing powder. Agar: Cream coloured, free-flowing powder.
Prepared medium: Broth: Straw coloured solution. Agar: Straw-green coloured gel with blue hue.

Quality control
VRE Broth

* This organism is available as a Culti-loop®

VRE Agar

* This organism is available as a Culti-loop®

HLARE Agar

* This organism is available as a Culti-loop®

Precautions
Warning: Sodium azide is harmful if swallowed, please take all necessary precautions.

References
1. King, W. K. (1996) Bug Bytes Vol. 2 No. 19.
2. CDC Preventing the spread of vancomycin resistance: a report from the Hospital Infection Control Practices Advisory Committee (1994). Fed Regist. May 17.
3. Gold, H. S. & Moellering R.C. Jr. (1996) N. Engl. J. Med.; 335(19): 1445-53.
4. Weinbren, M. J., Johnson, A.P. & Woodford, N. (2000) J. Antimicrobial Chemotherapy; 45 :404-405.