SS Agar (Salmonella Shigella Agar)
Intended Use:
Recommended for the isolation of Salmonella and some Shigella species from pathological specimens, suspected
foodstuffs etc.
Composition**
Ingredients Gms / Litre
Peptone 5.000
HM peptone B # 5.000
Lactose 10.000
Bile salts mixture 8.500
Sodium citrate 10.000
Sodium thiosulphate 8.500
Ferric citrate 1.000
Brilliant green 0.00033
Neutral red 0.025
Agar 15.000
Final pH ( at 25°C) 7.0±0.2
**Formula adjusted, standardized to suit performance parameters
Directions
Suspend 63.02 grams in 1000 ml purified /distilled water. Boil with frequent agitation to dissolve the medium completely.
DO NOT AUTOCLAVE OR OVERHEAT. Overheating may destroy selectivity of the medium. Cool to about 50°C. Mix and
pour into sterile Petri plates.
Principle And Interpretation
SS Agar medium is recommended as differential and selective medium for the isolation of Salmonella and Shigella species
from pathological specimens (1) and suspected foodstuffs (2,3,4,5) and for microbial limit test (6). SS Agar is a moderately
selective medium in which gram-positive bacteria are inhibited by bile salts, brilliant green and sodium citrate.
Peptone, HM peptone B provides nitrogen and carbon source, long chain amino acids, vitamins and essential growth
nutrients. Lactose is the fermentable carbohydrate. Brilliant green, bile salts and thiosulphate selectively inhibit gram-positive
and coliform organisms. Sodium thiosulphate is reduced by certain species of enteric organisms to sulphite and H2S gas and
this reductive enzyme process is attributed by thiosulphate reductase. Production of H2S gas is detected as an insoluble black
precipitate of ferrous sulphide, formed upon reaction of H2S with ferric ions or ferric citrate, indicated in the center of the
colonies.
The high selectivity of Salmonella Shigella Agar allows the use of large inocula directly from faeces, rectal swabs or other
materials suspected of containing pathogenic enteric bacilli. On fermentation of lactose by few lactose-fermenting normal
intestinal flora, acid is produced which is indicated by change of colour from yellow to red by the pH indicator-neutral red.
Thus these organisms grow as red pigmented colonies. Lactose non-fermenting organisms grow as translucent colourless
colonies with or without black centers. Growth of Salmonella species appears as colourless colonies with black centers
resulting from H2S production. Shigella species also grow as colourless colonies which do not produce H2S.
Type of specimen
Clinical: faeces, rectal swabs; Suspected food stuffs.
Specimen Collection and Handling
For clinical samples follow appropriate techniques for handling specimens as per established guidelines (8,9).
For food and dairy samples, follow appropriate techniques for sample collection and processing as per guidelines (2,3,4,5).
After use, contaminated materials must be sterilized by autoclaving before discarding.
Warning and Precautions
In Vitro diagnostic use. For professional use only. Read the label before opening the container. Wear protective gloves/
protective clothing/eye protection/face protection. Follow good microbiological lab practices while handling specimens and
culture. Standard precautions as per established guidelines should be followed while handling clinical specimens. Safety
guidelines may be referred in individual safety data sheets
Limitations
1.The medium is highly selective and may be toxic to certain Salmonella or Shigella species. Hence it is recommended
to use to inoculate plates of less inhibitory media parallel to SS Agar, such as Hektoen Enteric Agar (M467) or Deoxycholate
Citrate Agar (M065) for easier isolation of Shigella species (9).
Performance and Evaluation
Performance of the medium is expected when used as per the direction on the label within the expiry period when stored at
recommended temperature.
Quality Control
Appearance
Light yellow to pink homogeneous free flowing powder
Gelling
Firm, comparable with 1.5% Agar gel
Colour and Clarity of prepared medium
Reddish orange coloured clear to slightly opalescent gel forms in Petri plates
Reaction
Reaction of 6.3% w/v aqueous solution at 25°C. pH : 7.0±0.2
pH
6.80-7.20
Cultural Response
Cultural characteristics observed after an incubation at 35-37°C for 18-24 hours.
Organism Inoculum Growth
(CFU)
Recovery Colour of
colony
# Klebsiella aerogenes 50-100 fair 20-30% cream pink
ATCC 13048 (00175*)
Escherichia coli 50-100 fair 20-30% pink with bile
precipitate ATCC 25922 (00013*)
Salmonella Choleraesuis
ATCC 12011 =50% colourless with
black centre
Salmonella Typhi
ATCC 6539
50-100 good-luxuriant
50-100 good-luxuriant =50% colourless with
black centre
Enterococcus faecalis
ATCC 29212 (00087*)
50-100 none-poor =10% colourless
Proteus mirabilis
ATCC 25933
50-100 fair-good 30-40% colourless, may
have black centre
Shigella flexneri
ATCC 12022 (00126*)
50-100 good 40-50% colourless
Salmonella Typhimurium
ATCC 14028 (00031*)
=50% colourless with
black centre
Salmonella Enteritidis
ATCC 13076 (00030*)
50-100 good-luxuriant
50-100 good-luxuriant =50% colourless with
black centre
Key : *Corresponding WDCM numbers.
# Formerly known as Enterobacter aerogenes
Storage and Shelf Life
Store between 10-30°C in a tightly closed container and the prepared medium at 20-30°C. Use before expiry date on the label.
On opening, product should be properly stored dry, after tightly capping the bottle in order to prevent lump formation due to
the hygroscopic nature of the product. Improper storage of the product may lead to lump formation. Store in dry ventilated
area protected from extremes of temperature and sources of ignition Seal the container tightly after use. Product performance
is best if used within stated expiry period.
Disposal
User must ensure safe disposal by autoclaving and/or incineration of used or unusable preparations of this product. Follow
established laboratory procedures in disposing of infectious materials and material that comes into contact with clinical sample
must be decontaminated and disposed of in accordance with current laboratory techniques (8,9).
