Organism isolation in corneal ulcer: utility of different techniques

Various techniques are available for isolation of microorganism in cases of microbial keratitis including conventional methods of scraping, re-scraping inoculation in different media and corneal biopsy.

This was a cross sectional descriptive study conducted from February 2002 to July 2003. A total of 161 eyes of corneal ulcers were evaluated with scraping inoculation. Re-scraping and corneal biopsy were performed in those cases which did not grow any organism in the first scraping or which did not respond to initial treatment.

Microorganisms were isolated in 116 patients (72.04%) after first scraping. S pneumoniae was seen in 50(42%), Fusarium in 21(18%) and Aspergillus in 16(14%) cases. Re-scraping was done in 22 culture negative and non improving cases of which 14 (63.63%) showed isolation of organisms. After re-scraping, Fusarium and Aspergillus were isolated in four patients each (18% each) followed by S. pneumoniae in 3 (14%), S. aureus in 2 (9%), and Penicillium in 1(5%) case. Corneal biopsy was done in 10 cases with isolation of microbial agents in 7 (70%) with Aspergillus and S. aureus in three each, and S. epidermidis in 1(10%).

Apart from conventional scraping, other isolation techniques should be considered in the treatment of non-responding and culture negative cases of corneal ulcers. Compared to bacteria, fungi are difficult to isolate in the first scraping and requires more frequent repeat scraping and corneal biopsy.