Comparison of techniques for culturing corneal ulcers

All consecutive cases of presumed microbial keratitis were cultured with both a platinum spatula and calcium alginate swab moistened with trypticase soy broth. Ten (77%) of the 13 culture-proven ulcers in this series showed a greater number of colonies and more confluent growth on the agar plates inoculated with a moistened swab compared with a much lower yield obtained using a platinum spatula. All culture-positive bacterial ulcers showed growth when cultured with a swab. Two ulcers that were partially treated before culturing yielded very light growth from those rows inoculated with a swab and no growth from those rows inoculated with a spatula. Two ulcers showed equal growth between the two methods. One ulcer (Actinomycetes-Streptomyces/Nocardia) had greater growth obtained with a spatula compared with a swab. This series demonstrated a significantly greater retrieval of organisms from bacterial keratitis when a calcium alginate swab moistened with trypticase soy broth was used to rub the ulcer and directly inoculate the solid agar media. The single case of filamentous bacteria suggests that a spatula may yield better organism retrieval from ulcers caused by filamentous organisms.