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ORIGINAL ARTICLE
Year : 2002  |  Volume : 20  |  Issue : 1  |  Page : 19-24
 

Aetiological diagnosis of microbial keratitis in South India - A study of 1618 cases


Department of Microbiology, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Tirunelveli - 627 001, India

Correspondence Address:
Department of Microbiology, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Tirunelveli - 627 001, India

 ~ Abstract 

PURPOSE: To identify the specific microbial pathogens responsible for corneal ulceration in South India and compare these profiles with other series. METHODS: All patients with infectious keratitis who presented between 20th September 1999 and 31st March 2001 were evaluated. They were examined by slit-lamp biomicroscopy and corneal scrapings were performed for cultures and smears by using standard protocols. RESULTS: In the 18 months period, 1618 patients with corneal ulcerations were evaluated. Corneal cultures were found to be positive in 1126(69.59%) patients. Of the 1618 patients, 566(34.98%) had bacterial growth, 522(32.26%) had fungal growth, 30(1.85%) had mixed bacterial and fungal growth, 8(0.49%) had Acanthamoeba species growth and the remaining 492(30.41%) were found to be culture negative. The predominant bacterial pathogen isolated was Streptococcus pneumoniae representing 41.85%, followed by Pseudomonas aeruginosa 21.25%. The predominant fungal pathogens isolated were Fusarium species (45.85%) followed by Aspergillus species (24.37%). CONCLUSIONS: Bacterial and fungal infections occurred almost with equal frequency, the predominant bacterial and fungal species isolated being Streptococcus pneumoniae and Fusarium species respectively. The findings of our study show that there is a region wise variation in the predominance of corneal pathogens. This has an important public health implication for the initiation of therapy.

How to cite this article:
Bharathi M J, Ramakrishnan R, Vasu S, Meenakshi, Palaniappan R. Aetiological diagnosis of microbial keratitis in South India - A study of 1618 cases. Indian J Med Microbiol 2002;20:19-24


How to cite this URL:
Bharathi M J, Ramakrishnan R, Vasu S, Meenakshi, Palaniappan R. Aetiological diagnosis of microbial keratitis in South India - A study of 1618 cases. Indian J Med Microbiol [serial online] 2002 [cited 2019 Oct 19];20:19-24. Available from: http://www.ijmm.org/text.asp?2002/20/1/19/8333


Corneal infection is a leading cause of ocular morbidity and blindness worldwide.[1],[2],[3],[4],[5],[6] Corneal ulceration is a major cause of monocular blindness in developing countries. Surveys in Africa and Asia have confirmed these findings,[1],[2],[3],[4],[5],[6] and a recent report on the causes of blindness world wide consistently lists corneal scarring second only to cataract as the major aetiology of blindness and visual disability in many of the developing nations in Asia, Africa and the Middle East.[7]
Almost any microorganism can invade the corneal stroma if the normal corneal defence mechanisms, i.e. lids, tear film and corneal epithelium are compromised.[8] A wide spectrum of microbial organisms can produce corneal infections and consequently the therapeutic strategies may be variable.[9] One of the key elements in this effort is a proper understanding of the microbiological and clinical characteristics of this disease entity which will enable the ophthalmologist to initiate appropriate antimicrobial therapy.[9]
Considering the importance of corneal ulceration as a world wide cause of visual loss, there are surprisingly few studies evaluating the aetiological factors predisposing a population to corneal infection.[10],[11],[12] The majority of bacteria cultured from infections of the cornea are of the same species that normally are present in the conjunctival sac, on the lids or periocular skin, and in the adjacent nasal passages. Their incidence may vary geographically.[13],[14],[15]
The purpose of this study was to evaluate the current microbial pathogens of all infectious corneal ulcers seen at a tertiary referral centre in south India, during a period of 18 months and compare these profiles with other series.

 ~ Materials and Methods Top

Clinical Procedures
All patients underwent thorough slit-lamp biomicroscopic examination by an ophthalmologist. After a detailed ocular examination corneal scrapings were collected under aseptic conditions from each ulcer by an ophthalmologist after instillation of 4% lignocaine(lidocaine) without preservative using a sterile Bard Parker blade (No 15).[9] The procedure was performed under magnification of slit-lamp or operating microscope. The scraping material obtained from leading edge and base of each ulcer was initially directly inoculated onto the surface of solid media such as sheep's blood agar, chocolate agar and Sabouraud dextrose agar in a row of C- shaped streaks and also deep inoculation in the liquid media such as brain heart infusion broth without gentamicin sulphate and thioglycollate medium.10,16 The material obtained by the next scraping was spread onto labeled slides in a thin, even manner for 10 % potassium hydroxide (KOH) wet mount, Gram staining and Giemsa staining. In cases of suspected actinomycetes keratitis Kinyoun's method of acid fast staining was performed. When KOH smears were positive for Acanthamoeba cysts further corneal scrapings were performed and the materials were inoculated onto non-nutrient agar. Meticulous care was taken in the collection of material and transferring it to the appropriate culture media aseptically.[10],[16]
Laboratory procedures
All inoculated media were incubated aerobically. The inoculated media - blood agar, chocolate agar, thioglycollate broth and brain heart infusion broth were incubated at 37C and were evaluated at 24 hours and at 48 hours and later discarded if there was no growth. The inoculated fungal media-Sabouraud dextrose agar were incubated at 27C, examined daily, and discarded at 3 weeks if no growth was seen. The inoculated non-nutrient agar plates were incubated at 37C after overlaying with  Escherichia More Details coli broth culture and were examined daily for the presence of Acanthamoeba species and discarded at 1 week, if there were no signs of growth. All laboratory methods followed standard protocols.[10],[16] Microbial cultures were considered positive only if at least one of the following criteria were met.[9]
a. The growth of the same organism was demonstrated on two or more solid media on the C-streak; or there was semiconfluent growth at the site of inoculation on one solid medium,
b. The same organism was grown from repeated scraping ,
c. It was consistent with clinical signs,
d. Smear results were consistent with cultures.
Cultures for Staphylococcus epidermidis and Corynebacterium spp. were considered positive only if there was moderate growth on atleast two solid media. Liquid media were found to be so easily contaminated that they could not be relied upon for accurately identifying organisms. The specific identification of bacterial pathogens was based on microscopic morphology, staining characteristics, and biochemical properties using standard laboratory criteria.[16]

 ~ Results Top

From 20th September 1999 to 31st March 2001 there were 1618 patients with the clinical diagnosis of corneal ulceration that were evaluated. Out of 1618 corneal ulcers cultured, 566(34.98%) were found to be bacteria, 522(32.26%) were found to be fungi, 30(1.85%) were found to be mixed with bacteria and fungi, 8(0.49%) were found to be Acanthamoeba species and the remaining 492(30.41%) were found to be culture negative [Table - 1].
A total of 626 bacterial pathogens were isolated from 596 corneal ulcers [Table - 2]. Of the 626 isolates, 411(65.65%) were gram positive cocci, 26(4.15%) were gram positive bacilli, 8(1.27%) were gram negative cocci and coccobacilli, 160(25.56%) were gram negative bacilli and 21(3.35%) were found to be aerobic actinomycetes (Nocardia species). The most commonly isolated organism was  Streptococcus pneumoniae  262(41.85%) followed by  Pseudomonas aeruginosa  i>133(21.24%) and Staphylococcus epidermidis 105(16.77%). Nocardia asteroides were found in 21(3.35%) and alpha haemolytic Streptococci (S.viridans) were found in 18(2.88%). The gram negative cocci and coccobacilli,  Moraxella More Details species and  Neisseria More Details species were infrequently found. Enterobacter species was found in 12(1.92%) whereas other gram negative bacilli like Proteus species, Klebsiella species, Haemophilus species and  Escherichia More Details coli were isolated only rarely. Of the 626 positive bacterial cultures from corneal ulcer patients, 536(85.62%) were pure isolates, 60(9.58%) were mixed with another species of bacteria, and 30(4.79%) were mixed with a single fungal species.
A total of 554 fungal pathogens were isolated from 552 corneal ulcers [Table - 3]. Of the 554 total isolates, 254(45.85%) were found to be of Fusarium species, 135(24.37%) were of Aspergillus species, 27(4.87%) were of Cladosporium species, 21(3.79%) were of Curvularia species, 14(2.53%) were of Bipolaris species and 13(2.35%) were of Exserohilum species. Botryodiplodia thaeobromae, Alternaria species, Mucor species, Rhizopus species and Penicillium species were isolated in decreasing frequency. 24 unidentified hyaline fungal species and 35 unidentified dematiaceous fungal species were isolated. Of all the fungal pathogens isolated from patients with corneal ulcers, 520(93.86%) were pure isolates, 4(0.72%) were mixed with another fungal species and 30(5.41%) were mixed with a single species of bacteria.
Among the 1618 corneal ulcers cultured only 8(0.49%) patients were found to be culture positive for Acanthamoeba species.
Of the 1618 patients, 1311(81.03%) had sought previous medical help before initial examination at our institute. Out of 1618 patients, 475(29.36%) had already been examined and treated by local ophthalmologists, 130(8.03%) by general physicians, 526(32.51%) by chemists or pharmacists and 130(8.03%) by various medical practitioners. It is of great interest to note that 50(3.09%) patients had used some old medications which were given to them by their neighbours and relatives.
A total of 554 fungal pathogens were isolated from 552 corneal ulcers [Table - 3]. Of the 554 total isolates, 254(45.85%) were found to be of Fusarium species, 135(24.37%) were of Aspergillus species, 27(4.87%) were of Cladosporium species, 21(3.79%) were of Curvularia species, 14(2.53%) were of Bipolaris species and 13(2.35%) were of Exserohilum species. Botryodiplodia thaeobromae, Alternaria species, Mucor species, Rhizopus species and Penicillium species were isolated in decreasing frequency. 24 unidentified hyaline fungal species and 35 unidentified dematiaceous fungal species were isolated. Of all the fungal pathogens isolated from patients with corneal ulcers, 520(93.86%) were pure isolates, 4(0.72%) were mixed with another fungal species and 30(5.41%) were mixed with a single species of bacteria.
Among the 1618 corneal ulcers cultured only 8(0.49%) patients were found to be culture positive for Acanthamoeba species.
Of the 1618 patients, 1311(81.03%) had sought previous medical help before initial examination at our institute. Out of 1618 patients, 475(29.36%) had already been examined and treated by local ophthalmologists, 130(8.03%) by general physicians, 526(32.51%) by chemists or pharmacists and 130(8.03%) by various medical practitioners. It is of great interest to note that 50(3.09%) patients had used some old medications which were given to them by their neighbours and relatives. 

 ~ References Top

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