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Material Safety Data Sheet

Organisms

Organisms this product works with:

Dehydrated Culture Media

SALMONELLA SHIGELLA AGAR (SS AGAR MODIFIED)

Code: CM0533

An improved formulation which gives better growth of shigellae and better colony characteristics for salmonellae.

Typical Formula*

gm/litre

`Lab-Lemco’ powder

5.0

Peptone

5.0

Lactose

10.0

Bile salts

5.5

Sodium citrate

10.0

Sodium thiosulphate

8.5

Ferric citrate

1.0

Brilliant green

0.00033

Neutral red

0.025

Agar

12.0

pH 7.3 ± 0.2 @ 25°C

 

* Adjusted as required to meet performance standards 

Directions
Suspend 57g in 1 litre of distilled water. Bring to the boil with frequent agitation, and allow to simmer gently to dissolve the agar. DO NOT AUTOCLAVE. Cool to about 50°C mix well and pour into sterile Petri dishes.

Description
Although widely used, SS Agar has been criticised because of excessive inhibition of Shigella species.

Investigation has shown that modification to the formulation by alterations to the bile salt mixture, peptone and pH value considerably improve its performance in the growth of shigellae without too much increased growth of commensal organisms.

Salmonella colonies are also larger with improved blackening at the centre. The change in formulation has reduced the number of g/litre from 63g to 57g.

Technique
Inoculate the medium heavily with the specimen, spreading a portion of the original inoculum in order to obtain well separated colonies on some part of the plate. Incubate for 18-24 hours at 35°C; non-lactose fermenters form colourless colonies. Occasional resistant coliforms and other lactose fermenters produce pink or red colonies.

In addition to the SS Agar (Modified) plate, inoculate a tube of Selenite Broth Enrichment Medium, CM0395. Incubate it for 12 hours at 35°C, and sub-culture on to another SS Agar (Modified) plate.

Colonial Characteristics
Non-Lactose Fermenting Organisms

Salmonella species

Transparent colonies usually with black centres

Shigella species

Transparent colonies

Proteus species Citrobacter species

Transparent colonies grey-black centres

Late-lactose fermenting organisms will develop colonies with pink centres after 48 hours incubation.

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: Pink-red coloured, free-flowing powder
Prepared medium: Pink-red coloured gel

Quality control

Positive controls:

Expected results

Salmonella enteritidis ATCC® 13076 *

Good growth; straw coloured colonies with black centre

Shigella sonnei ATCC® 25931 *

Good growth; straw coloured colonies

Negative control:

 
Enterococcus faecalis ATCC® 29212 *

No growth

* This organism is available as a Culti-Loop®

References
See SS Agar CM0099 as well.

 
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