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Material Safety Data Sheet

Organisms

Organisms in the Clinical sector this product works with:

Dehydrated Culture Media

Sector: Clinical

DERMASEL AGAR BASE

Code: CM0539

A selective medium for dermatophyte fungi recommended for the examination of hair, skin scrapings, nails, etc.

Typical Formula*

gm/litre

Mycological peptone

10.0

Glucose

20.0

Agar

14.5

pH 6.9 ± 0.2 @ 25°C

 
* Adjusted as required to meet performance standards

DERMASEL SELECTIVE SUPPLEMENT

Code: SR0075

Vial contents
per vial
per litre
Cycloheximide

200mg

400mg

Chloramphenicol

25.0mg

50.0mg


Directions
Suspend 44.5g in 1 litre of distilled water and heat gently to dissolve completely. Add the contents of 1 vial of Dermasel Selective Supplement SR0075, reconstituted as directed in the product insert, to each 500ml of medium to give a level of cycloheximide 0.4g/l and chloramphenicol 0.05g/l. Mix gently and sterilise by autoclaving at 121°C for 10 minutes. Avoid overheating at any time.

Description
Oxoid Dermasel Agar is used for the primary isolation and identification of dermatophyte fungi from hair, nails or skin scrapings.

Emmons1 suggested that media for growth of dermatophytes should have a pH of 6.8-7.0 rather than pH 5.6 as is often recommended. A near neutral pH is better for the growth of some fungi and the acid pH used to suppress bacterial contaminants can be replaced by antibiotics.

The addition to the medium of Dermasel Selective Supplement SR0075 to give a level of cycloheximide 0.4g/l and chloramphenicol 0.05g/l renders the medium selective for dermatophytes, inhibiting the growth of saprophytic fungi, yeasts and bacterial skin flora2.

The chloramphenicol and cycloheximide supplement SR0075 reduces the potential risk to health from these antibiotics. To include them in the powder mix could allow them to be scattered as dust whilst weighing the medium. It also ensures a fixed, accurate dose of antibiotic that has been protected from degradation on storage.

The addition of cycloheximide and an anti-bacterial agent has been reported to improve considerably the isolation of dermatophytes, especially when the inoculum, such as horse hair was heavily contaminated3,4. The presence of staphylococci, which may grow in the absence of the antibiotic has been shown to prevent the in-vitro growth of Trichophyton rubrum5.

The presence of cycloheximide in the medium inhibits the growth of Trichosporon cutaneum, Candida parasilosis, Candida krusei, Aspergillus, Penicillium, Fusarium and Cephalosporium species which have been associated with diseased nails6,7.

The incorporation of griseofulvin at a level of 20µg/ml into one of paired tubes of selective media has been recommended as an additional aid in the diagnosis of dermatophytosis8. The absence of growth, on the medium containing griseofulvin provides presumptive identification of a dermatophyte fungus.

Dermatophyte fungi cultured on Oxoid Dermasel Agar show characteristic colonial morphology with typical pigmentation. Macroconidia and microconidia are typical for the species when studied microscopically.

Technique
Oxoid Dermasel Agar may be prepared as slopes in test tubes with loose caps to ensure adequate aeration, or in vented Petri dishes.
Small, pin head sized samples of the test material are stabbed into the surface of the agar. A number of samples may be inoculated on to the same surface.

The medium is incubated at 22-30°C and examined at regular intervals for two to four weeks.

Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the prepared agar plates at 2-8°C.

Appearance
Dehydrated medium: Straw coloured, free-flowing powder
Prepared medium: Straw coloured gel

Quality control

Positive controls:

Expected results

Trichophyton rubrum ATCC® 28191 White mycelium, buff spores

Candida albicans ATCC® 10231*

Good growth;cream coloured colonies

Negative controls:

 
Aspergillus brasiliensis ATCC® 16404* Inhibited or no growth

Escherichia coli ATCC® 25922*

No growth

* This organism is available as a Culti-Loop®

Precautions
This medium should not be used if agents causing systemic mycoses are being sought9. If such agents are suspected e.g. cryptococcus, histoplasma etc., either Dermasel Agar Base without antibiotic supplement must be used in parallel or Brain Heart Infusion Agar CM0375.
If the fungal agent sought is suspected to be nutritionally fastidious, the use of Brain Heart Infusion Agar is particularly helpful.
Dermasel Selective Supplement SR0075 contains a toxic concentration of cycloheximide. Note the precautions to be taken under HAZARDS.

References
1. Emmons C. W., Binford C. H. and Utz J. P. (1963) Medical Mycology. Henry Kimpton.
2. Georg L. K., Ajello L. and Papageorge C. (1954) J. Lab. Clin. Med. 44. 422.
3. Quaife R. A. (1968) J. Med. Lab. Technol. 25. 227-232.
4. Merz W. G., Berger C. L. and Silva-Huntar M. (1970) Arch. Derm. 102. 545-547.
5. Silva M., Kesten B. M. and Benham R. W. (1955) J. Invest. Derm. 25. 311-328.
6. Zaias N. (1966) Sabouraudia 5. 99-103.
7. Rosenthal S. A., Stritzler R. and Villafane J. (1968) Arch. Derm. 97. 685-687.
8. Blank H. and Rebell G. (1965) Arch. Derm. 92. 319-322.
9. McDonough E. S., Georg L. K., Ajello L. and Brinkman S. (1960) Mycopath et Mycol. Appl. 13. 113-115.

 
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