Limulus lysate assay for early detection of certain Gram-negative corneal infections

R. W. Wolters, J. H. Jorgensen, E. Calzada and R. H. Poirier

The limulus endotoxin assay has been previously demonstrated to be the most sensitive method available for detection of bacterial endotoxin. A commercially available form of limulus amoebocyte lysate was used in this study for detection of Gram-negative corneal infections in both experimental animals and in a group of nine patients. The limulus assay enabled rapid detection of Gram-negative infections in both the experimentally induced ulcers in rabbits and in the patients studied. False-positive reactions did not occur in corneal infections due to either Gram-positive bacteria, fungi, or herpes simplex keratitis. The limulus test proved to be more sensitive than examination of Gram-stained smears of corneal scrapings and became positive earlier than bacterial cultures. The limulus test was helpful in the diagnosis of partially antibiotic-treated corneal infections but could not be used to assess the response to antimicrobial therapy, since endotoxin persisted in the corneal scrapings for some time after initiation of therapy.