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| Year : 2003 | Volume
: 21
| Issue : 3 | Page : 219-220 |
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Nocardia asteroides keratitis in South India
P Bhat
Department of Microbiology, Sri Sathya Sai Institute of Higher Medical Sciences, Prashanthigram - 515 134, Puttaparthi, Andhra Pradesh, India
Correspondence Address:
Department of Microbiology, Sri Sathya Sai Institute of Higher Medical Sciences, Prashanthigram - 515 134, Puttaparthi, Andhra Pradesh, India
How to cite this article:
Bhat P. Nocardia asteroides keratitis in South India. Indian J Med Microbiol 2003;21:219-20 |
Dear Editor,
This is regarding the article entitled “Nocardia asteroides keratitis in South India”, by Bharathi et al which appeared in the Indian Journal of Medical Microbiology, 2003; 21(1):31-36. I wish to congratulate the authors for highlighting the problems of corneal ulcers in southern Indian population with special reference to Nocardia keratitis. They have rightly stated that, “a high index of suspicion of Nocardia infection should exist in patients with a history of trauma to eye by soil or sand”. In this context, I wish to make a few comments:
While Nocardia spp. are non fastidious, growing on all the routinely used culture media like sheep blood agar (SBA), one should remember that they are often slow-growing. Growth on the ordinary culture media may be visible from 3 - 4 days to 6 weeks - 30 days. That being the case, when routine microbiology culture reports on clinical samples are ready usually by 48 hours following the receipt of the samples, growth of Nocardia will not be often apparent. Hence, there is need to hold the routine plates for longer period of time at room-temperature, taking care to minimize drying up of the plates, so as not to miss the growth of the slow - growing Nocardia, whenever Nocardia infection is suspected.
Though the authors have stated how long they held the Sabouraud dextrose agar (SDA), no where have they mentioned for how long they held the other culture media like SBA, following inoculation. Under discussion, the authors mention that the minimum time taken for the growth of Nocardia to be visible is 48-72 hours, but the maximum time taken for its growth to be apparent is not mentioned. After how many days following inoculation, did the colonies of the 31 isolates of N.asteroides  appear? Figure 1 shows growth of Nocardia on SBA following 5 days of incubation. Did all the isolates grow after 5 days of incubation?
Though the current study showed 100% correlation between microscopic examination and culture, such correlation is reported only in one third of the cases.[1] Even in the earlier reports[2],[3] on Nocardia keratitis from southern India, such correlation was not seen. Therefore, in a routine clinical microbiology laboratory, the laboratory staff should be alerted whenever Nocardiosis is suspected clinically so that the routinely used culture plates are not discarded after 48 hours. In a mixed culture from clinical material like respiratory secretions, rapidly growing commensal bacteria may obscure the tiny Nocardia colonies and it is only by holding the cultures for a longer period of time like 2-4 weeks that the typical colonies of Nocardia are visualized.[1] This is particularly important in immunocompromised patients as in renal transplant recipients. Often it may be only the clinical suspicion with or without any clue in the microscopic examination when it is important to hold the culture plates for longer periods, as renal transplant recipients are often prone to infection by opportunistic pathogens like Nocardia.
In my own experience (unpublished data), the few times I was successful in isolating N.asteriodes, were from specimens of pus and sputum received from immunocompromised patients from SBA, chocolate agar and MacConkey agar by holding the plates longer and on LJ slants because of the acid-fast nature of Nocardia and its ability to resist digestion. Growth was apparent after 3 days or as late as 2-3 weeks. In conclusion, I wish to reemphasize the importance of holding routine culture plates for a longer period after 48 hours.
| ~ References | |  |
| 1. | Lerner PI. Nocardia species. Chapter 234, Vol.2. In : Mandell, Douglas, Bennett's Principles and Practice of Infectious Diseases. 4th ed. Mandell GL, Bennett JE, Dolin R, Eds. (Churchill Livingstone, London) 1995:2273-2280.  |
| 2. | Sridhar MS, Sharma S, Reddy M.K,Mrutyunjay P, Rao GN. Clinicomicrobiological review of Nocardia keratits. Cornea 1998;17:17-22. |
| 3. | Rao SR, Madhavan HN, Sitalakshmi G, Padmanabhan P. Nocardia asteroides keratitis: report of seven patients and literature review. Indian J Ophthalmol 2000;48:217-221. |
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