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Indian Journal of Medical Microbiology, Vol. 23, No. 2, April-June, 2005, pp. 145 Letter To Editor Evaluation of Crystal Violet Blood Agar for Primary Isolation and Identification of Group A-beta haemolytic streptococci Menon T., Malathy B. Department of Microbiology, Dr. AL Mudaliar Postgraduate Institute of Basic Medical Sciences, Taramani, Chennai Correspondence Address:Department of Microbiology, Dr. AL Mudaliar Postgraduate Institute of Basic Medical Sciences, Taramani, Chennai - 600 113, Tamil Nadu, thangam16@rediffmail.com Code Number: mb05043 Dear Editor, We read the article in your Journal, vol.22 (3); 2004 page 201, entitled "Evaluation of crystal violet blood agar for primary isolation and identification of Group A-beta haemolytic Streptococcus" by K. Chawla and P. S. Rao. We wish to bring to your notice, that the concentration of crytal violet they have used 1: 5 x 104 units is too high and would inhibit also, many strains of group A - β haemolytic Streptococci. The reference, they have quoted, for this concentration, is the book on District Laboratory Practice in Tropical Countries, Part 2, by Monica Cheesbrough, page 160. However, page 387, of the same book[1] has given the crystal violet concentration as 1: 5x105. We have rechecked both these concentrations in our laboratory and found that concentration of 1:5x 105 is appropriate i.e. supports the growth of β haemolytic Streptococci, whereas the concentration quoted by the authors is actually inhibitory to the isolates of β haemolytic Streptococci. Hence it is probable, that the concentration of 1:5x104 crystal violet quoted on page 160 in Monica Cheesbrough′s book is probably a printing error, since the same book has mentioned the concentration as 1:5x105 on page 387. Recommended concentrations of crystal violet in crystal violet blood agar are actually even lower (1: 10,00,000 and 1: 5,00,000) in standard publications.[2],[3] References
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