Xylose Lysine Deoxycholate Agar Plate
For the selection of Salmonella in accordance with the harmonized method of USP/EP/BP/JP/IP.
Composition**
Ingredients Gms / Litre
Xylose 3.500
L-lysine 5.000
Lactose monohydrate 7.500
Sucrose 7.500
Sodium chloride 5.000
Yeast extract 3.000
Sodium deoxycholate 2.500
Sodium thiosulphate 6.800
Ferric ammonium citrate 0.800
Phenol red 0.080
Agar 13.500
**Formula adjusted, standardized to suit performance parameters
Directions
Either streak, inoculate or surface spread the test inoculum (50-100 CFU) aseptically on the plate.
Principle And Interpretation
Enterobacteriaceae is a family of gram-negative, non-spore-forming bacilli that contains more than 100 species of bacteria
that normally inhabit the intestines of humans and animals. Members forming part of the normal intestinal microflora are
referred to as coliforms. The clinically significant genera of Enterobacteriaceae include Cedecea, Citrobacter, Edwardsiella,
Enterobacter, Escherichia, Ewingella, Hafnia, Klebsiella, Kluyvera, Proteus, Salmonella, Shigella and Yersinia (1).
The Salmonellae are the most complex of all the Enterobacteriaceae . Human Salmonella infections are most commonly
caused by ingestion of food, water or milk, contaminated by human or animal excreta (2). A large number of media have been
developed for the selective isolation and identification of enteric bacilli including Salmonella @.
Xylose Lysine Deoxycholate Agar is a selective as well as differential medium formulated by Taylor (3-7) for the isolation and
identification of enteric pathogens especially Shigellae from stool samples. It is also used for pharmaceutical testing and nonsterile product testing for the detection (or absence) of Salmonella after enrichment in Rappaport Vassiliadis Salmonella
Enrichment Broth (MH1491) in accordance with the harmonized method of USP/EP/BP/JP (8-11).
Deoxycholate, ferric ammonium citrate and sodium thiosulphate are selective agents that inhibit gram-positive microorganisms.
Essential nutrients, growth factors for growth of microorganism are provided by yeast extract. Xylose, sucrose and lactose are
the fermentable sugars in this medium. Xylose is fermented by almost all the enteric bacteria except Shigellae , which enable
the differentiation of Shigellae from Salmonellae.Salmonellae metabolize the xylose and decarboxylate lysine and thus change
the pH to alkaline and mimic Shigellae reaction. However to prevent this reaction by lysine positive coliforms, lactose and
sucrose are added in excess to produce acid and hence nonpathogenic H2S producers do not decarboxylate lysine. Sodium
thiosulphate helps in reactivation of sulphur containing compounds and prevents the desication of these compounds during
storage. It also forms the substrate for enzyme thiosulphate reductase, which breaks it to form H2S. Thiosulphate and ferric
ammonium citrate are the H2S indicators in the medium. Sodium thiosulphate is also inactivator of halogens, mercurial and
aldehyde and can minimize its toxicity in the testing sample, if any during microbial limit tests. Sodium chloride maintains the
osmotic equilibrium in this medium. Phenol red is the pH indicator.
Degradation of fermentable sugars proceed concurrently and generates acids, which cause pH indicator to give various shades
of colour, causing a color change in the colonies and in the medium from red to yellow on prolonged incubation. Hydrogensulfide production results in colonies with black centers under alkaline conditions, which can be inhibited by acid production
by carbohydrate fermentation. Alkaline condition causes the color of the medium to change back to red. This medium is an
ideal medium for screening samples containing mixed flora of enteric pathogens as recovery of Salmonellae and Shigellae is
not conspicuous by even profuse growth of other species (12,13).
Quality Control
Appearance
Sterile Xylose Lysine Deoxycholate Agar in 55mm disposable plate.
Colour
Red coloured medium
Quantity of Medium
20ml of medium in scored plate.
Reaction
7.20- 7.60
Cultural Response
Growth Promotion is carried out in accordance with the harmonized method of USP/EP/BP/JP. Cultural response was
observed after an incubation at 30-35°C for specified time. Recovery rate is considered as 100% for bacteria growth on
Soyabean Casein Digest Agar.
Growth promoting properties
Growth of microorganism comparable to that previously obtained with previously tested and approved lot of medium occurs
at the specified temperature for not more than the shortest period of time specified inoculating =100 cfu(at 30-35°C for 18
hours).
Indicative properties
Colonies are comparable in appearance and indication reaction to those previously obtained with previously tested and
approved lot of medium occurs for the specified temperature for a period of time within the range specified inoculating
=100cfu (at 30-35°C for 18-72 hours).
Inhibitory properties
No growth of the test microorganism occurs for the specified temp for not less than longest period of time specified
inoculating = 10³(at 30-35°C for = 72 hours).
Sterility test
Passes release criteria.
Sterility Test
Passes release criteria
Cultural Response
MPH031: Cultural characteristics observed after incubation at 30-35 °C for 18-48 hours. Recovery rate is considered as
100% for bacteria growth on Soyabean Casein Digest Agar.
Organism Inoculum Growth Recovery
(CFU)
Colour of
Colony
Incubation
temperature
Incubation
period
Growth Promoting +
Indicative
Salmonella Typhimurium
ATCC 14028
50 -100 luxuriant =50 % red with black
centres
30 -35 °C 25 -100
Salmonella Abony NCTC
6017
50 -100 good-luxuriant =50 % red with black
centres
30 -35 °C 25 -100
Indicative
Escherichia coli ATCC 8739 50 -100 fair 20 -30 % yellow 30 -35 °C 10 -30
Additional Microbiological
testing
Staphylococcus aureus
ATCC 25923
0% inhibited =10³ - 30 -35 °C =72 hrs
Enterococcus faecalis ATCC
29212
0% inhibited =10³ - 30 -35 °C =72 hrs
Staphylococcus aureus
ATCC 6538
0% inhibited =10³ - 30 -35 °C =72 hrs
Escherichia coli ATCC
25922
50 -100 fair 20 -30 % yellow 30 -35 °C 10 -30
Escherichia coli NCTC 9002 50 -100 fair 20 -30 % yellow 30 -35 °C 10 -30
Proteus vulgaris ATCC
13315
50 -100 good-luxuriant =50 % grey with black
centres
30 -35 °C 25 -100
Salmonella Paratyphi A
ATCC 9150
50 -100 good-luxuriant =50 % red 30 -35 °C 25 -100
Salmonella Paratyphi B
ATCC 8759
50 -100 good-luxuriant =50 % red with black
centres
30 -35 °C 25 -100
Salmonella Enteritidis ATCC
13076
50 -100 good-luxuriant =50 % red with black
centres
30 -35 °C 25 -100
Salmonella Typhi ATCC
6539
50 -100 good-luxuriant =50 % red with black
centres
30 -35 °C 25 -100
Shigella flexneri ATCC
12002
50 -100 fair-good 30 -40 % red 30 -35 °C 15 -40
Shigella dysenteriae ATCC
13313
50 -100 good-luxuriant =50 % red 30 -35 °C 25 -100
Shigella sonnei ATCC 25931 50 -100 fair-good 30 -40 % red 30 -35 °C 15 -40
Enterobacter aerogenes
ATCC 13048
50 -100 fair 20 -30 % yellow 30 -35 °C 10 -30
Enterobacter cloacae ATCC
13047
50 -100 fair 20 -30 % yellow 30 -35 °C 10 -30
Storage and Shelf Life
Store between 20-30°C. Use before expiry date on the label
