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Year : 2003  |  Volume : 21  |  Issue : 3  |  Page : 220-

Author's reply

MJ Bharathi 
 Department of Microbiology, Aravind Eye Care System, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Tirunelveli - 627 001, Tamil Nadu, India

Correspondence Address:
M J Bharathi
Department of Microbiology, Aravind Eye Care System, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Tirunelveli - 627 001, Tamil Nadu

How to cite this article:
Bharathi M J. Author's reply.Indian J Med Microbiol 2003;21:220-220

How to cite this URL:
Bharathi M J. Author's reply. Indian J Med Microbiol [serial online] 2003 [cited 2020 Apr 9 ];21:220-220
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Full Text

Dear Editor,

We thank Dr.Prema Bhat for her interest in our article. We would like to submit the following reply.

As per recommended procedure for corneal scraping cultures,[1] the inoculated Sabouraud dextrose agar was incubated at 270C, examined daily, and discarded at 3 weeks if no growth was seen. The plates of sheep blood agar and chocolate agar and tubes of thioglycollate broth and brain heart infusion broth were incubated at 370C, examined daily, and discarded at 7 days if growth was not seen. In a case of suspected Nocardia keratitis, all inoculated media were incubated for upto 30 days. I do agree with Dr.Bhat's suggestion regarding the need for holding the plates for longer period of time at room temperature, taking care to minimize the drying up of the plates.

In culture, Nocardia organisms are not fastidious and grow aerobically. However, they tend to grow slowly. Dry colonies, usually tiny, grow in 48-72 hours on sheep blood agar. On further incubation, they may appear as dry, chalky, rough, folded, irregular and powdery. The colour of the colony may be creamy, yellow or orange, pink or red. In our study, out of 31 culture positive Nocardia keratitis, Nocardia growth was visible in corneal scrapings of 28 cases between 2-7 days after incubation and in remaining 3 cases the growth was found between 8-10 days after incubation. Although, the growth usually appears within 10 days, the culture should be incubated for at least 3 weeks to 30 days.

In our study, corneal scrapings obtained from all 2184 cases were studied by 10% KOH wet mount preparation and Gram-staining technique. In a suspected cases of Nocardia keratitis Kinyoun's acid-fast staining technique was performed. The sensitivity of 10% KOH smear, Gram-stained smear and Kinyoun's acid-fast smear for the detection of Nocardia filaments were 100%, 90.32% and 90.32% respectively. A high index of clinical suspicion, very good corneal scraping (deep scraping) using a blade no.15 on Bard Parker handle, and thorough and accurate microscopic examination of direct smears yielded 100% sensitivity of 10% KOH smear. In addition, in our study most of the patients used traditional eye medicines (48.39%) and majority (83.87%) had previous medical treatment before presenting at our institute. 26(83.87%) patients reported at our institute between 4-35 days after onset of illness. Traditional eye medicines may cause corneal damage, aiding the growth of microorganisms, and finally lead to increase in the size of an ulcer. We believe that these large sized ulcers provide adequate material for smear and easy detection of the Nocardia filaments in KOH smear.


1Sharma S, Athmanathan S. Diagnostic procedures in infectious keratitis. In: Nema HV, Nema N, Eds. Diagnostic Procedures in Ophthalmology. (Jaypee Brothers Medical Publishers, New Delhi) 2002:232-253.