Experience with a broth culture technique for diagnosis of bacterial keratitis

To determine if a broth culture technique is a practical means for bacteriological investigation of keratitis.

Twenty-seven eyes of 27 patients with a clinical diagnosis of bacterial keratitis were included in a prospective and non-comparative study at a Danish referral hospital. A corneal scrape was inoculated directly into broth medium which was transferred to the diagnostic laboratory for incubation and subculture.

Culture was negative in 4 patients, and 19 of the remaining 23 patients had a pure growth of either Pseudomonas aeruginosa (n = 8), Staphylococcus aureus (n = 2), Streptococcus pneumoniae (n = 2), Haemophilus influenzae biotype III (n = 1), Moraxella species (n = 1), Corynebacterium species (n = 1), or coagulase-negative staphylococci (n = 4). In 4 patients there was a mixed gram-positive growth. There was no association between microbiological findings and previous topical antibiotic therapy. Contamination and lack of quantitative assessment of growth proved not to be a problem.

By broth culture technique we identified a definite pathogen (P. aeruginosa, S. aureus or S. pneumoniae) in 44% of patients (95% binomial confidence limits: 25-65%). The technique may replace the standard technique of direct plate culture under circumstances where it is difficult to keep a supply of fresh media or transport inoculated plates.