Salmonella Shigella Agar (SS Agar)
- Salmonella Shigella (SS) Agar can be moderately specific and a differing medium used for the cultivation, isolation as well as differentiation Salmonella spp. ...
- The SS Agar is a variation of Deoxycholate Citrate Agar.
- It is recommended to test the clinical specimens and food samples to detect evidence of Salmonella Spp. ...
What is Salmonella Shigella agar?
Salmonella Shigella (SS) Agar is moderately selective and differential medium for the isolation, cultivation and differentiation of Salmonella spp. and some strains of Shigella spp. SS Agar is a modification of the Desoxycholate Citrate Agar.
How do you isolate Salmonella Shigella from a specimen?
Take Salmonella-Shigella (SS) Agar plates. Heavily inoculate and streak the specimen as soon as possible after collection. If the specimen to be cultured is on a swab, roll the swab over a small area of the agar surface. Streak for isolation with a sterile loop.
What is the pH of Salmonella Shigella?
Final pH 7.0 +/- 0.2 at 25ºC. Salmonella Shigella agar comprises bile salts, sodium citrate, brilliant green, an enzymatic digest of casein, beef extract, an enzymatic digest of animal tissue, thiosulphate, ferric citrate, neutral red, and agar.
What is the purpose of SSSS agar?
SS agar was also developed to aid in the differentiation of lactose and non-lactose-fermenters from clinical specimens, suspected foodstuffs, and other such specimens.
What does Salmonella Shigella Agar choose?
Salmonella Shigella (SS) Agar is highly selective for Salmonella species but is inhibitory to some strains of Shigella. It was developed to aid in the differentiation of lactose and non-lactose-fermenters from clinical specimens, suspected foods, and other such samples.
What organisms grow on Salmonella Shigella Agar?
Principle of Salmonella-Shigella (SS) Agar The inclusion of bile salts, sodium citrate, and brilliant green serve to inhibit gram-positive and coliform organisms. Salmonella, Shigella, and other non-lactose-fermenting organisms appear as transparent or translucent colorless colonies on SS Agar.
Is Salmonella Shigella Agar selective or differential?
Salmonella-Shigella agar or SS agar is a selective and differential medium for the isolation of pathogenic enteric bacilli, particularly Salmonella and Shigella, from stool, food and clinical material.
What color are Salmonella colonies on Salmonella Shigella Agar?
colorlessOn 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.
What is the difference between Salmonella and Shigella?
Salmonella is a genus of bacteria that causes salmonellosis in humans, while Shigella is a genus of bacteria that causes shigellosis in humans. Thus, this is the key difference between Salmonella and Shigella. Furthermore, Salmonella bacterial species are rod-shaped while Shigella bacterial species are slender shaped.
Is Shigella Gram positive or negative?
Nonetheless, Shigella species are Gram-negative, facultatively anaerobic, nonsporulating, nonmotile rods in the family Enterobacteriaceae. They do not decarboxylate lysine or ferment lactose within 2 days.
Which test can differentiate between Salmonella and Shigella?
6-25 The urea agar is one of the most useful of these screening media, which readily differentiates the lactose- negative Salmonella and Shigella isolates, which are urease- negative, from many of the lactose-negative normal enteric flora that produce urease, such as Proteus, Providencia, and Morganella.
Which media is used for culturing Salmonella?
BS agar is the medium of choice for the isolation of Salmonella enterica serovar Typhi, and it is used for the isolation of atypical salmonellae, such as those which ferment lactose (7).
Is Salmonella Gram positive or negative?
Salmonella is a gram negative rods genus belonging to the Enterobacteriaceae family. Within 2 species, Salmonella bongori and Salmonella enterica, over 2500 different serotypes or serovars have been identified to date.
What can grow on SS Agar?
Salmonella Shigella (SS) Agar is moderately selective and differential medium for the isolation, cultivation and differentiation of Salmonella spp. and some strains of Shigella spp....Composition of Salmonella Shigella Agar.IngredientsGms / LitreBrilliant Green0.00033Neutral Red0.025Agar13.508 more rows•Aug 10, 2022
Does Salmonella grow on nutrient agar?
Media used for Salmonella identification are those used for identification of all Enterobacteriaceae. Most Salmonella strains are motile with peritrichous flagella, however, nonmotile variants may occur occasionally. Most strains grow on nutrient agar as smooth colonies, 2-4 mm in diameter.
What is XLD agar used for?
XLD Agar (Xylose Lysine Deoxycholate Agar) is a moderately selective differential medium used for the isolation and differentiation of enteric gram-negative pathogens, particularly salmonella and shigella in clinical, environmental and food samples.
Does Proteus grow on SS Agar?
Proteus vulgaris and Proteus mirabilis do not invade S.S. agar. All manufactured reagents are prepared according to our Quality System, starting from reception of raw material to the final commercialization of the product.
What is Shigella medium used for?
It is used as a selective and differential medium for the isolation of Salmonella and some Shigella species from clinical and non-clinical specimens. This medium is not recommended for the primary isolation of Shigella. It was also developed to aid in the differentiation of lactose and non-lactose-fermenters from clinical specimens, ...
What are the nutrients in Shigella agar?
Salmonella Shigella agar comprises of bile salts, sodium citrate, brilliant green, enzymatic digest of casein, be ef extract, enzymatic digest of animal tissue, thiosulphate, ferric citrate, neutral red and agar. The inclusion of Bile Salts, Sodium Citrate and Brilliant Green serve to inhibit gram-positive, coliform organisms and inhibit swarming Proteus spp., while allowing Salmonella spp. to grow. Beef Extract, Enzymatic Digest of Casein, and Enzymatic Digest of Animal Tissue provide sources of nitrogen, carbon, and vitamins required for organism growth. Lactose serves as a carbohydrate source in Salmonella Shigella Agar. Differentiation of enteric organisms is achieved by the incorporation of lactose in the medium. Organisms which ferment lactose produce acid which, in the presence of the neutral red indicator, results in the formation of red/pink colonies. Lactose non-fermenters form colorless colonies. Sodium thiosulfate and Ferric Citrate permit detection of hydrogen sulfide by the production of colonies with black centers. Neutral red turns red in the presence of an acidic pH, thus showing fermentation has occurred.
What is SS agar?
Salmonella Shigella (SS) Agar is moderately selective and differential medium for the isolation, cultivation and differentiation of Salmonella spp. and some strains of Shigella spp. SS Agar is a modification of the Deoxycholate Citrate Agar.
How long can you keep agar culture?
Do not autoclave the media. Pour into plates. Let the agar solidify and store in the refrigerator (avoid freezing). Prepared culture media can be kept for at least a week in refrigeration.
How to make SS agar?
Preparation of SS Agar 1 Suspend 60 g of the medium in one liter of deionized or distilled water. 2 Mix well. 3 Heat with frequent agitation and boil for one minute. 4 Do not autoclave the media. 5 Pour into plates. 6 Let the agar solidify and store in the refrigerator (avoid freezing). Prepared culture media can be kept for at least a week in refrigeration.
What tests are performed on colonies from pure culture?
It is recommended that biochemical, immunological, molecular, or mass spectrometry testing be performed on colonies from pure culture for complete identification.
Is SS agar selective?
and some Shigella spp. SS Agar is a moderately selective medium in which gram-positive bacteria are inhibited by bile salts, brilliant green and sodium citrate. Salmonella Shigella (SS) Agar is highly selective for Salmonella species, ...
Why is SS agar not recommended for Shigella?
This medium is not recommended for the primary isolation of Shigella because of inhibitory to most strains. SS agar was also developed to aid in the differentiation of lactose and non-lactose-fermenters from clinical specimens, suspected foodstuffs, and other such specimens.
What is SS agar?
Salmonella-Shigella (SS) Agar is recommended for use as a selective and differential medium for the isolation of Salmonella and some Shigella species from clinical and non-clinical specimens ( suspected foodstuffs).
What is the basis for differentiation on SS agar?
The basis for differentiation on Salmonella-Shigella (SS) agar depends on the fermentation of lactose and the absorption of neutral red as the bile salts precipitate in the acidic condition. Neutral red turns red in the presence of an acidic pH, thus showing fermentation has occurred. The inclusion of bile salts, sodium citrate, and brilliant green serve to inhibit gram-positive and coliform organisms. Salmonella, Shigella, and other non-lactose-fermenting organisms appear as transparent or translucent colorless colonies on SS Agar. Sodium thiosulfate is added to the medium as a hydrogen sulfide source, and ferric citrate is added as an indicator for hydrogen sulfide production.
How long does it take for Shigella to ferment?
Some strains of Shigella, such as Shigella sonnei and Shigella dysenteriae serovar 1, may ferment lactose relatively slowly, and colonies change to lactose-fermenting after cultivation for 2 or more days.
What is the organism that came under serogroup B?
According to serotyping- Came under serogroup-B, which is why the organism is Shigella flexneri.
How to dissolve agar powder?
Mix thoroughly and heat with frequent agitation and boil for 1 minute to completely dissolve the powder. Avoid overheating and do not autoclave. Leave for cooling to 45-50°C. Mix well before dispensing. Pour into each plate and leave plates on the sterile surface until the agar has solidified.
What is the color of salmonella?
Salmonella (good-luxuriant growth): Colorless, usually with a black center
How to detect Shigella in stool?
To optimize detection of Shigellain stool, samples should be plated on MacConkey and either xylose-lysine-deoxycholate, Hektoen enteric, or deoxycholate citrate agar. Colonies are bluish-green on Hektoen agar and do not have the black center seen with Salmonella, as Shigellado not produce H2S. Shigellado not ferment lactose and xylose and are relatively inert biochemically. Some strains of S. sonneiare exceptions and may ferment lactose. Most isolates do not produce gas, except some S. flexneri.6, 75Appropriate colonies can be characterized further using Kligler iron or triple sugar iron agar. Lysine decarboxylase tests are typically negative for Shigella. Groups A, B, and C have similar biochemical characteristics, but S. sonneihas ornithine decarboxylase activity and beta-galactosidase activity.75
What is Shigella pathogenesis?
Shigellapathogenesis involves translocation through ileal and colonic M cells, uptake by macrophages, basolateral invasion of epithelial cells, and dissemination within the mucosa. 98, 99Shigellahas a large virulence plasmid, encoding a Type III-secretion system and a set of secreted proteins. The system results in the injection of virulence factors into host colonic epithelial cells, leading to damage to the epithelial lining, as well as proteins that antagonize the adaptive and innate immune response.98, 100Shigellavirulence is enhanced by the presence of enterotoxins, which is separate from the Shiga toxin produced in limited strains.101The genes encoding the Shiga toxin genes are located in the genome of heterogeneous lambdoid prophages. These are highly mobile genetic elements that play a role in horizontal gene transfer and genome diversification.102Shiga toxin is made by the Shigella dysenteriaetype I strains and E. coliO157:H7 among other E. colishiga toxin-producing strains. Shiga-like toxin II, also seen in some E. colistrains is 56% homologous with Shiga toxin (or Shiga-like toxin I).103
What are the diseases caused by salmonella?
Salmonella, Shigella, and Yersiniacause a well-characterized spectrum of disease in humans, ranging from asymptomatic carriage to hemorrhagic colitis and fatal typhoidal fever. These pathogens are responsible for millions of cases of food-borne illness in the U.S. each year, with substantial costs measured in hospitalizations and lost productivity. In the developing world, illness caused by these pathogens is not only more prevalent, but is also associated with a greater case-fatality rate. Classical methods for identification rely on selective media and serology, but newer methods based on mass spectrometry and PCR show great promise for routine clinical testing.
How to identify Salmonella?
Once Salmonellahas been isolated in culture, there are a variety of methods available for identification and classification.6Definitive identification ordinarily relies on a combination of phenotypic and serologic methods. The widely-used Kauffmann-White serologic typing scheme is based on the LPS O antigen, the H1 and H2 flagellar antigens, and the Vi antigen.21While the O and H1 antigens are detectable in almost all strains of Salmonella, the H2 antigens are present only in certain strains and the Vi antigen is found predominantly in typhoidal strains.6It should be noted that Vi, though useful for detection of serovar Typhi, may also be expressed in Citrobactersp. and therefore the Vi antigen alone cannot be used for definitive identification.6
What is the best method to identify enteric bacteria?
Molecular methods, including mass spectrometry and PCR-based multiplex panels have been developed for the detection of enteric bacteria, and some laboratories are beginning to incorporate these techniques. These newer methods have the potential to improve our ability to provide rapid and accurate bacterial identification, but they have limitations that are important to understand. Commercial matrix assisted laser desorption ionization – time of flight mass spectrometry (MALDI-TOF MS) instruments can provide rapid identifications of Salmonellaand Yersinia, and limited identification of Shigella.31, 32Both the Bruker Biotyper and Biomerieux Vitek MS MALDI-TOF MS systems are FDA approved for in vitrodiagnostic use to identify cultured isolates of Y. enterocoliticaand Y. pseudotuberculosis(species level identification) and Salmonella(genus level identification), but not Shigella. The Biomerieux Vitex MS system carries a manufacturer’s note that confirmatory testing is recommended when identifications of Salmonellaare made. Neither system is FDA approved for species-level or serovar-level classifications of Salmonella. However, recent literature suggests that MALDI-TOF mass spectrometry-based systems may have the power to distinguish among subspecies and some Salmonellaserovars.33As this technology is new and experience is still relatively limited, caution is appropriate, as illustrated by a recent report of a patient with both bacteremia and gastrointestinal symptoms for whom an isolate of Y. pseudotuberculosiswas misidentified as Y. pestisusing a MALDI-TOF MS method. This highlights the need for comprehensive MALDI-TOF MS spectral databases in combination with careful validations and appropriate additional confirmatory testing for this group of less commonly seen bacteria.34
How many cases of shigellosis are there worldwide?
The worldwide incidence of shigellosis has been reported to be approximately 165 million cases, but the mortality has decreased substantially over the past three decades.59–61Though the causes of this decrease in shigellosis-associated mortality are likely to be multifactorial, it has occurred along with a decrease in prevalence of S. dysenteriaetype 1.61Infection with S. dysenteriaetype 1 carries relatively high mortality in the developing world, as demonstrated by the case fatality rate of 5–15% in Africa and Central America. There are an estimated 500,000 cases of shigellosis per year in the U.S. with 38 deaths.62
When was the Enterobacteriaceae manual published?
Based on Edwards and Ewing’s identification of Enterobacteriaceae, 4thedition, 1986 and/or Cowan and Steel’s manual for the identification of medical bacteria, 3rdedition, 1993.
Ⅰ. Overview
- ◈ La Salmonella Shigella Agar is a modification of deoxycholate-citrate agar described by Einar Leifsonin 1935.
Ⅱ. Preparation / Composition
- Suspend the components, dehydrated powder, in water (63 grams in 1000 ml of purified/distilled water). Boil, stirring frequently to completely dissolve the medium. Do not autoclave or overheat: Overheating can destroy the selectivity of the medium. Cool to 50°C and pour into Petri dishes.
Ⅲ. Principle of Salmonella-Shigella (SS) Agar
- Note : - SS agar can inhibit some species of Shigella such as S. sonnei and S. dysenteriae - Lactose late fermenters may require 48 hours of incubation to develop and produce a color reaction on SS agar
Ⅳ. Reading / Interpretation
- ◈ After 24 hours at 37°C aerobically, in general : Lactose-negative colonies are colorless. Lactose-positive colonies are pink to red. Colonies producing H2S have a black center..