XLD Agar (Xylose Lysine Deoxycholate Agar)

Biology Professor (Twitter: @DrWhitneyHolden) teaches you about XLD Agar (Xylose Lysine Deoxycholate Agar), its components/ingredients, and how it is used to distinguish Salmonella and Shigella with a hydrogen sulfide (H2S) indicator system.

[WhyNot-sipj]

Thank you so much Dr.Holden for the lecture !

6:50 You mentioned that the black dots present in the salmonella colonies grown on the (XLD) agar are due to the production of hydrogen sulfide " H2S " .

Actually hydrogen sulfide " H2S " is a colorless gas with an odor of " rotten eggs " ; which does NOT give that characteristic black dot appearance to the salmonella colonies .

That black dot appearance of the colonies is rather due to the precipitation of ferrous sulfide salt " FeS " & that is produced by the reaction between (ferric ammonium citrate) & (sodium thiosulfate ) in what is called " H2S indicator system " .

The switch in pH levels ; from acidic pH due to lactic acid production from xylose fermentation to basic pH due to cadaverine production from lysine decarboxylation catalyzes the reactions of the " H2S indicator system " ===> FeS production .

8:00 Finally coliform bacteria favor lactose & sucrose on xylose NOT lysine as an energy source to produce lactic acid as a byproduct .

[GodswillFriday-dqrp]

Dr Joshua Remedy right now that l have my PHD in biophysics, l can agree with him that seamoss has all the essential elements needed by the humau body, a perfect balance 💕💕

[najibgetahun]

Clear and understanding video thanks keep it up

[colummccrudden]

Hot professor strikes again with a super video!
I used XLD as a basic trainee biomed without fully knowing the ins and outs of it.
Be great to have a whole set of videos based on the agar plates and their uses if at all possible?

[demsewbekele]

Thank you, Dear Holden, for your nice explanation on XLD agar. please would you mind if i ask one question? well! my question is that: how can I count salmonella bacteria colony per gram of culturing on XLD agar from ergot sample? thank you!!

[meghasharma]

Pls make videos on brilliance salmonella agar base

[JahanaraImam-ww]

Smith Sarah Miller David Thomas Angela

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Lopez Joseph Anderson John Thompson Laura