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ROGOSA AGAR

Code: CM0627

A medium for the selective isolation and enumeration of lactobacilli.

Directions
Suspend 82g in 1 litre of distilled water and bring to the boil to dissolve completely. Add 1.32ml glacial acetic acid and mix thoroughly. Heat to 90-100°C for 2-3 minutes with frequent agitation. Distribute into sterile tubes, Petri dishes or bottles.
DO NOT AUTOCLAVE.

Description
Rogosa Agar, a modification of the medium described by Rogosa et al.¹, is a selective medium for the isolation and enumeration of lactobacilli. The medium has given excellent results when used in quantitative and qualitative studies of lactobacilli in faeces, saliva and mouth rinses, and in dairy products. It is an effective, selective medium for lactobacilli but the high acetate concentration and low pH suppresses many strains of other lactic acid bacteria.

If the pH of the medium is adjusted to 6.2 without adding acetic acid then the selectivity of the medium is altered to include the whole group of lactic acid bacteria^2,3.

Technique
For the isolation of lactobacilli, Sharpe⁴ recommends that Rogosa Agar plates should be incubated for 3 days at 35°C or for 5 days at 30°C. Lactobacilli prefer a microaerophilic atmosphere, however, if a suitable container is not available, overlay the inoculated plate with a second layer of Rogosa Agar, before incubation.

Thermophilic lactic acid bacteria are incubated at 42°C for 48 hours and suspected psychrotrophic organisms can be incubated at 30°C for 2 days and at 22°C for a further day. Leuconostocs from meat are incubated at 25°C for 3 days.

After incubation all well grown colonies may be considered as lactic acid bacteria although enterococci and pediococci show a reduced growth rate. Some leuconostocsfrom meat show slime production at 25°C.

Colony characteristics
Small greyish-white, flat or raised, smooth, rough or intermediate

Size
Lactobacilli and other lactic acid bacteria 0.5-2.5mm diameter; enterococci 0.5-1.0mm diameter; non-lactic acid bacteria >2.5mm after prolonged incubation at room temperature

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 coloured, free-flowing powder
Prepared medium: Straw coloured gel

Quality control

* This organism is available as a Culti-Loop®

Precautions
Lactobacillus carnis does not grow on this medium.
All colonies must be tested by Gram stain and catalase test before carrying out further identification tests.

References
1. Rogosa M., Mitchell J. A. and Wiseman R. F. (1951) J. Bact. 62. 132-133.
2. Reuter G. (1985) Int. J. Food Microbiol. 2. 55-68.
3. ISO/TC34/SC6/WG15. (1984) Enumeration of Lactobacteriaceae in meat and meat products.
4. Sharpe M. Elizabeth (1960) Lab. Practice 9. 223-227.