Loading...

[Microbiology] Xylose Lysine Desoxycholate Agar

Isolation Techniques and Selective Media, A Photographic Atlas for the Microbiology Laboratory, Xylose Lysine Desoxycholate Agar



Purpose
Xylose Lysine Desoxycholate (XLD) Agar is a selective and differential medium used to isolate and identify Shigella and Providencia from stool samples.

Principle
XLD Agar is a selective and differential medium containing sodium desoxycholate, xylose, L-lysine, and ferric ammonium citrate. Desoxycholate is a Gram-positive inhibitor, xylose is a fermentable carbohydrate, L-lysine is an amino acid provided for decarboxylation (See Decarboxylation, page 67), and ferric ammonium citrate is an indicator to mark the presence of hydrogen sulfide gas (H2S) from sulfur reduction. Phenol red, which is yellow when acidic and red or pink when alkaline, is added as a pH indicator. Organisms that ferment xylose will acidify the medium and produce yellow colonies. Organisms able to remove the carboxyl group from (decarboxylate) L-lysine will release alkaline products and produce red colonies. Organisms able to reduce sulfur will produce a black precipitate in the growth due to the reaction of ferric ammonium citrate with H2S.
Shigella and Providencia, which do not ferment xylose but decarboxylate lysine, appear red on the medium. Salmonella species, which ferment xylose but then decarboxylate the lysine also appear as red colonies but with black centers due to the reduction of sulfur to H2S. Other enterics that would ordinarily revert to decarboxylationafter exhausting the sugar and alkalinize the medium are prevented from doing so by the high sugar content and the short incubation time. These organisms appear yellow on the medium (Figure 2-31). 

XYLOSE LYSINE DESOXYCHOLATE AGAR
2-31 XYLOSE LYSINE DESOXYCHOLATE AGARXLD agar inoculated with (clockwise from top): Proteus
mirabilis
(positive for sulfur reduction), Salmonella
typhimurium
(atypically negative for sulfur reduction),
and
Escherichia coli (positive for lactose fermentation).  

Suggested Reading
- Michael J. Leboffe & Burton E. Pierce. A Photographic Atlas for the Microbiology Laboratory 4th edition 2011

COMMENTS

Loading...
QC5
Loading...
Name

CLINICAL ATLAS,118,DERMATOLOGY ATLAS,11,EMERGENCY ATLAS,44,HAEMATOLOGY ATLAS,23,HUMAN ANATOMY,1,MICROBIOLOGY ATLAS,66,PARASITOLOGY ATLAS,4,PATHOLOGY ATLAS,22,PEDIATRIC ATLAS,41,STDs,19,SUBCLINICAL ATLAS,116,
ltr
item
Free Medical Atlas: [Microbiology] Xylose Lysine Desoxycholate Agar
[Microbiology] Xylose Lysine Desoxycholate Agar
Isolation Techniques and Selective Media, A Photographic Atlas for the Microbiology Laboratory, Xylose Lysine Desoxycholate Agar
https://3.bp.blogspot.com/-b3cPu5dfO_4/WoTkOAUj2BI/AAAAAAAAFRw/cv7JOjxHJ6sTZyQgyMBmTNZf8XhlreHPACLcBGAs/s320/vs2.31.jpg
https://3.bp.blogspot.com/-b3cPu5dfO_4/WoTkOAUj2BI/AAAAAAAAFRw/cv7JOjxHJ6sTZyQgyMBmTNZf8XhlreHPACLcBGAs/s72-c/vs2.31.jpg
Free Medical Atlas
https://www.tuyenlab.net/2018/02/microbiology-xylose-lysine.html
https://www.tuyenlab.net/
https://www.tuyenlab.net/
https://www.tuyenlab.net/2018/02/microbiology-xylose-lysine.html
true
3150612095398522649
UTF-8
Loaded All Posts Not found any posts VIEW ALL Readmore Reply Cancel reply Delete By Home PAGES POSTS View All RECOMMENDED FOR YOU LABEL ARCHIVE SEARCH ALL POSTS Not found any post match with your request Back Home Sunday Monday Tuesday Wednesday Thursday Friday Saturday Sun Mon Tue Wed Thu Fri Sat January February March April May June July August September October November December Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec just now 1 minute ago $$1$$ minutes ago 1 hour ago $$1$$ hours ago Yesterday $$1$$ days ago $$1$$ weeks ago more than 5 weeks ago Followers Follow THIS PREMIUM CONTENT IS LOCKED STEP 1: Share. STEP 2: Click the link you shared to unlock Copy All Code Select All Code All codes were copied to your clipboard Can not copy the codes / texts, please press [CTRL]+[C] (or CMD+C with Mac) to copy