V4 – 12/08/11

XLD/Agar 356-9124 (Xylose--Desoxycholate) 354-1751

DEFINITION THEORETICAL FORMULA Medium used for the detection and enumeration Yeast extract 3 g of Enterobacteria , and especially , in L-lysine hydrochloride 5 g the analysis of food products and for testing Saccharose 7.5 g contamination of non-sterile pharmaceutical Lactose 7.5 g products. Xylose 3.75 g Sodium desoxycholate 1 g STANDARDS Sodium chloride 5 g FOOD Sodium thiosulfate 6.8 g • NF EN ISO 6579 (December 2002): Food Ferric ammonium citrate 800 mg microbiology - Horizontal method for the Phenol red 80 mg detection of Salmonella spp. Agar 13.5 g Distilled water 1,000 ml WATER Final pH (25°C) = 7.4 ± 0.2 • EN ISO 19250 (July 2010): Water quality - Detection and enumeration of Salmonella OTHER PRODUCTS REQUIRED (NOT SUPPLIED) • NF T90-461/A2 (May 2007) : Water quality - • Distilled water Microbiology - Quality control for culture media EQUIPMENT REQUIRED (NOT SUPPLIED) (non-exhaustive) PRINCIPLE • Scales Several differentiation reactions are revealed in • Sterile weighing bags this medium: • Grinder - attack by lactose, xylose and/or saccharose; • Hotplate the resulting acidity turns phenol red to • Mixer-homogenizer yellow. • Sterile Petri dishes (Ø = 90 mm) - production of H 2S: thiosulfate serves as a • Sterile pipettes (code 355-0751) or inoculating reaction component and ferric salts as loop indicators through the formation of iron • Water-bath precise to ±1°C sulfide, which blackens the colonies. • Thermostatically-controlled incubator or - decarboxylation of the lysine in cadaverin: the incubation room, precise to ±1°C alkalinization resulting from the amine • All usual laboratory equipment produced turns the area around LDC-positive colonies red. PREPARATION OF DEHYDRATED MEDIUM PRESENTATION Always shake before use. • Pre-poured Dissolve 55 g of powder in 1 liter of distilled 90 mm x 20 plates code 354-1751 water. Mix until a homogenous suspension is obtained. Heat gently stirring frequently, then • Dehydrated bring to boiling point until completely dissolved. 500g code 356-9124 Do not prolong heating. Pour into Petri dishes and leave to dry. STORAGE • Pre-poured: +2-8°C Reconstitution ratio: 55 g/l • Dehydrated: +15-25°C, in carefully-sealed 500 g of powder makes 9 liters of medium. bottles in a cool, dry place • Expiration date and batch number are shown PROTOCOL on the package. • Preparation of samples According to the standards applicable to the product concerned.

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V4 – 12/08/11 XLD/Agar (Xylose-Lysine-Desoxycholate)

• Enrichment QUALITY CONTROL OF MANUFACTURER According to the standards applicable to the Every product manufactured and marketed by product concerned. Bio-Rad is subject to a quality-assurance procedure at all stages, from the reception of • Inoculation and incubation raw materials to the marketing of the end- Inoculate the XLD medium in streaks or by product. Each batch of finished product spreading. Incubate at 37°C ± 1°C for 24-48 undergoes quality control and is marketed only hours. if it satisfies the acceptability criteria.

READING AND INTERPRETATION Documentation relative to the production and Salmonella forms well-developed, red colonies, control of each batch is kept on file. with or without a black center. The following table can be used to interpret the KEY WORDS reading: XLD/Salmonella /Food products/Detection/Enumeration/Lactose/Xylos RESULTS OBSERVED STRAINS e/Saccharose/H 2S/Decarboxylation/Phenol Red Medium

Escherichia coli BIBLIOGRAPHY Opaque yellow colonies Enterobacter (Fermentation of at least 2 Klebsiella TAYLOR, W.J. (1965): Isolation of . I. sugars or of LDC(-), Citrobacter Xylose lysine agars, new media for isolation of sometimes H 2S(+)) Proteus enteric pathogens. American Journal of Clinical Serratia Pathology 44: 471-475

Red colonies Shigella (Fermentation or not of Providencia xylose or Salmonella H 2S LDC(+))

Salmonella (H 2S+) Red colonies with black Edwardsiella center (H 2S+) Arizona

PRECAUTION Comply with Good Laboratory Practice.

PERFORMANCES/QUALITY CONTROL OF THE TEST The growth performances of the media are verified with the following strains:

Results after STRAINS 24–48 hr culture at 37°C

Salmonella Typhimurium Red colonies ATCC 14028 with a black center

Salmonella enteridis Red colonies ATCC 13076 with a black center

Escherichia coli Yellow colonies ATCC 25922 Partial inhibition

Enterococcus faecalis Total inhibition ATCC 19433 within 48 hours

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