Shigella xld agar12/26/2023 Colony characteristics in Deoxycholate Citrate Agar (DCA) If organisms are late developers or if no non-lactose fermenters are observed, incubate for a further 24 hours.Inoculate the medium heavily with feces or rectal swabs, spreading part of the original inoculum in order to obtain well-separated colonies on some portion of the plate.Prepared medium: Pink colored gel Inoculation of the prepared medium.Dehydrated medium: Straw/pink colored, free-flowing powder.Shelf life is up to 6 weeks providing there is no change in the appearance of the medium to suggest contamination or an alteration of pH. Store the prepared agar plates at 2-8☌.Store the dehydrated medium at 10-30☌ and use it before the expiry date on the label.Store the plates at 2☌ – 8☌, preferably in sealed plastic bags to prevent loss of moisture. Date the medium and give it a batch number. As soon as the medium has cooled to 50☌ -55☌ mix well and dispense aseptically in sterile Petri dishes.(If autoclaved the agar becomes soft and almost impossible to streak) Heat with great care to dissolve the medium completely.Suspend 52g of dehydrated medium (supplied by the manufacturer) in 1 liter of distilled water.Prepare the medium as instructed by the manufacturer. The reduction of ferric ammonium citrate to iron sulfide is indicated by the formation of black iron sulfide. If the bacteria produce H2S, the colonies will have black centers.Ĭoliform bacteria and gram-positive bacteria are inhibited or greatly suppressed due to sodiumdeoxycholate, sodium citrate, and ferric ammonium citrate. The fermentation of lactose causes acidification and the pH indicator neutral red changes color to red. Lactose-fermenting colonies may have a turbid zone of precipitation around them caused by the precipitation of deoxycholate in the acidic environment. Lactose helps in differentiating enteric bacilli (lactose fermenters produce red/pink colonies while lactose non-fermenters produce colorless colonies). It will enhance the growth of many bacteria and it is incorporated into a wide range of culture media as a solid foundation material as it enhances the growth of many bacteria.ĭipotassium phosphate buffers the medium. Lab-Lemco is a meat extract made from specially selected raw materials, adjusted to neutrality, and dried to a fine powder. Peptone provides carbon, nitrogen, vitamins, and minerals. Colony characteristics in Deoxycholate Citrate Agar (DCA) Composition of Deoxycholate Citrate Agar (DCA) Ingredients Gm/litre Peptone 5.0 Lab-Lemco powder 5.0 Lactose 10.0 Sodium citrate 8.5 Sodium thiosulphate 5.4 Ferric ammonium citrate 1.0 Sodium deoxycholate 5.0 Neutral red 0.02 Agar 12.0 pH 7.3 ± 0.2 25☌.
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