SALMONELLA SHIGELLA (SS) AGAR
INTENDED USE
Remel Salmonella Shigella (SS) Agar is a solid medium recommended for use in qualitative procedures for selective and differential isolation
of Salmonella and, to a lesser degree, Shigella.
SUMMARY AND EXPLANATION
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SS Agar is a modification of Desoxycholate-Citrate Agar described by Leifson which was used for the detection of enteric pathogens. The
modified medium contains a bile salts mixture to inhibit the growth of gram-positive organisms. SS Agar is recommended for isolation and
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differentiation of pathogenic enteric bacilli, especially Salmonella and Shigella from clinical specimens, including feces, and food samples.
PRINCIPLE
Differentiation of gram-negative bacilli on SS Agar is based on the fermentation of lactose and subsequent absorption of neutral red; gram-
negative bacilli which ferment lactose produce pink to red colonies. Lactose-nonfermenters, such as Salmonella and Shigella, form
transparent, colorless colonies. Bile salts, brilliant green, and citrates are selective agents which inhibit gram-positive bacteria and coliforms.
Sodium thiosulfate, a sulfur source, and ferric ammonium citrate, an indicator, are added to enable organisms which produce H2S to form
black-centered colonies, including some strains of Salmonella.
REAGENTS (CLASSICAL FORMULA)*
Lactose............................................................................ 10.0 g Meat Peptone ................................................................... 2.5 g
Bile Salts ........................................................................... 8.5 g Ferric Citrate..................................................................... 1.0 g
Sodium Citrate .................................................................. 8.5 g Neutral Red .................................................................... 25.0 mg
Sodium Thiosulfate ........................................................... 8.5 g Brilliant Green................................................................. 0.33 mg
Beef Extract....................................................................... 5.0 g Agar ................................................................................ 13.5 g
Casein Peptone................................................................. 2.5 g Demineralized Water .................................................. 1000.0 ml
pH 7.0 ± 0.2 @ 25°C
*Adjusted as required to meet performance standards.
PROCEDURE
1. Inoculate and streak the specimen as soon as possible after it is received in the laboratory. Selective and nonselective media should be
inoculated to increase the potential for isolation of enteric pathogens.
2. If material is being cultured directly from a swab, roll the swab over a small area of the agar surface. Streak the plate for isolation using a
sterile inoculating loop.
3. Incubate the plates in ambient air at 33-37°C for 18-24 hours.
4. Examine plate for growth and typical colony morphology. On SS Agar, colonies of Salmonella or Shigella are smooth and opaque or
colorless. Strains of Salmonella which produce H2S will form black-centered colonies. Lactose-fermenters are pink to rose-red in color
and may have a precipitate.
QUALITY CONTROL
All lot numbers of Salmonella Shigella Agar have been tested using the following quality control organisms and have been found to be
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acceptable. This quality control testing meets or exceeds CLSI standards. Testing of control organisms should be performed in accordance
with established laboratory quality control procedures. If aberrant quality control results are noted, patient results should not be reported.
CONTROL INCUBATION RESULTS
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*Salmonella enterica serovar Typhimurium ATCC 14028 Ambient, 18-24 h @ 33-37°C Growth, clear colonies w/ black centers
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*Shigella flexneri ATCC 12022 Ambient, 18-24 h @ 33-37°C Growth, clear colonies
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*Enterococcus faecalis ATCC 29212 Ambient, 18-24 h @ 33-37°C Inhibition (partial to complete)
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*Escherichia coli ATCC 25922 Ambient, 18-24 h @ 33-37°C Inhibition (partial); colonies pink to rose-red w/
precipitate
*CLSI recommended organism
LIMITATIONS
1. Organisms other than Salmonella and Shigella which grow on this medium may be differentiated by their ability to ferment lactose and
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form pink or red colonies.
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2. SS Agar is not recommended for primary isolation of Shigella spp. because it is highly selective and may inhibit some strains.
BIBLIOGRAPHY
1. Leifson, E., 1935. J. Pathol. Bacteriol. 40:581.
2. MacFaddin, J.F. 1985. Media for Isolation-Cultivation-Identification-Maintenance of Medical Bacteria. Vol. 1. Williams & Wilkins, Baltimore, MD.
3. Clinical and Laboratory Standards Institute (CLSI). 2004. Quality Control for Commercially Prepared Microbiological Culture Media; Approved
Standard, 3rd ed. M22-A3. CLSI, Wayne, PA.
Refer to the front of Remel Technical Manual of Microbiological Media for General Information regarding precautions, product storage and
deterioration, specimen collection, storage and transportation, materials required, quality control, and limitations.
ATCC® is a registered trademark of American Type Culture Collection.
IFU 1840, Revised September 28, 2010 Printed in U.S.A.
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