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Letters to the Editor

Is inclusion of Sabouraud dextrose agar essential for the laboratory diagnosis of fungal keratitis?

Kaliamurthy, Jayaraman; Thomas, Philip A

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Indian Journal of Ophthalmology: May–Jun 2011 - Volume 59 - Issue 3 - p 263-264
doi: 10.4103/0301-4738.81037
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Dear Editor,

We read with great interest the article by Das et al.[1] describing the status of inclusion of Sabouraud dextrose agar for laboratory diagnosis of fungal keratitis. The authors performed the study on 26 patients with culture-proven fungal keratitis. The authors have provided compelling evidence for the use of blood agar (BA) and chocolate agar (CA) for diagnosis of both bacterial and fungal keratitis in situations where resources are limited. We also agree with the points discussed by the authors. However, we have concerns regarding the statement related to estimated savings if only BA/CA are used, the saving being Rs. 600 per patient. The cost of 500 g of various types of dehydrated Sabouraud dextrose agar (SDA) ranges from Rs. 1406 to Rs. 1943 (Catalogue 2009–10, HiMedia, Mumbai, India). The quantity of the ready-made mixture used for the preparation of a 1000-ml medium is only 45–80 g (depends upon the type of SDA). We can prepare 40–50 plates (approximately 20 ml/plate) from the 1000-ml medium. The disposable petriplate costs around Rs. 12 per plate. We would very much like to know how the estimated saving for excluding SDA alone is Rs. 600. If so, the estimate for the whole process for the corneal scrapes per case sounds very high.

The authors have included potassium hydroxide with calcofluor white stains as part of the standard protocol. The safe-life of an ultraviolet (UV) lamp is only 200 h. The cost of one UV bulb will be Rs. 40,000. The working cost of this set-up may be higher than one SDA plate per case. Hence, one perfect Gram-stained smear reviewed by more than one person with adequate experience in ocular microbiology is perhaps sufficient to diagnose mycotic and bacterial keratitis. The authors did not mention about the exclusion of potassium hydroxide with calcofluor white stains to reduce the working cost.

1. Das S, Sharma S, Kar S, Sahu SK, Samal B, Mallick A. Is inclusion of Sabouraud dextrose agar essential for the laboratory diagnosis of fungal keratitis? Indian J Ophthalmolo. 2010;58:281–5
© 2011 Indian Journal of Ophthalmology | Published by Wolters Kluwer – Medknow