Salmonella Typhi (black colony) and Shigella growth on xylose lysine deoxycholate (XLD) agar Shigella flexneri biochemical reactions and growth on SS agar, sorbitol MacConkey medium, and XLD agarįig. Shigella boydii in XLD agar Salmonella Typhi (black colony) and Shigella growth on xylose lysine deoxycholate (XLD) agar Fig. Enterobacter and Klebsiella species: Mucoid, yellow colonies.Proteus species: Red to Yellow colonies. ![]() Shigella species and Salmonella H 2S negative: Red colonies.Salmonella: H 2S positive Red colonies with black centers.for 18-24 hours.Ĭolony Characteristics of various organisms in XLD Agar Incubate plates aerobically at 35-37✬.Streak for isolation with a sterile loop.If the specimen to be cultured is on a swab, roll the swab over a small area of the agar surface.Inoculate and streak the specimen as soon as possible after collection.Allow the plates to warm at 37☌ or to room temperature, and the agar surface to dry before inoculating.Test procedure (specimen/organism inoculation) Control strains ( Salmonella enterica ATCC 14028 and Escherichia coli ATCC 25922).Type of specimen -As may be clinical ( blood, feces) or non-clinical specimens like food samples and water.The product is light and temperature-sensitive protects from light, excessive heat, moisture, and freezing.Media should not be used if there are any signs of deterioration (shrinking, cracking, or discoloration), or contamination.Store at 2-8✬ and away from direct light.It is advisable not to prepare large volumes that will require prolonged heating, thereby producing precipitate.After cooling, pour into sterile Petri plates.Transfer immediately to a water bath at 50☌.Heat with frequent agitation until the medium boils.Oxoid says 53 gm in 1 liter while Hardy Diagnostics 56.93 and Himedia 56.68. Suspend 56.68 grams of dehydrated powder XLD agar in 1000 ml distilled or deionized or purified water. Note: The amount of XLD agar varies from manufacturer to manufacturer e.g.The final pH should be 7.4 +/- 0.2 at 25✬. Escherichia coli, Citrobacter, and Proteus species. Organisms that ferment xylose, are lysine decarboxylase-negative and do not ferment lactose or sucrose cause an acid pH in the medium, and form yellow colonies e.g. The addition of sodium thiosulfate and ferric ammonium citrate as a sulfur source and indicator, respectively, allows hydrogen sulfide (H 2S) forming organisms to produce colonies with black centers, under alkaline conditions. Medium is an indicator due to having two indicators, one pH indicator (phenol red) and another hydrogen sulfide indicator(ferric ammonium citrate). To avoid this reversal to a Shigella reaction, lactose and sucrose are added in excess. Lysine decarboxylation reverts the pH of the medium to an alkaline condition. A second differential mechanism for Salmonella is employed by the addition of lysine. Xylose is fermented by most enterics except for Shigella species, and these colonies appear red on this medium as a result. Xylose, lysine, lactose, and sucrose act as both differential as well as carbohydrate source ingredients. The selective agent is sodium deoxycholate, which inhibits the growth of gram-positive organisms. ![]() Xylose lysine deoxycholate (XLD) agar is a selective, differential, and indicator medium. Paratyphi: Only red colonies no black center Salmonella Typhi: Red colonies with a black center Salmonella and Shigella species colony characteristics on XLD agar – It has also been found to be an excellent medium for isolating Salmonellaspecies as well. It was specially designed to allow the growth of Shigella species and is a proven medium for the isolation of this organism. It also supports the growth of more fastidious enteric organisms. XLD agar is a selective, differential, and indicator medium for the isolation of enteric pathogens. XLD stands for xylose lysine deoxycholate. Shigella flexneri biochemical reactions and growth on SS agar, sorbitol MacConkey medium, and XLD agar. ![]()
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