Platinum spatula versus mini-tip culturette in culturing bacterial keratitis

Purpose. To compare the traditional method of culturing bacterial keratitis (platinum spatula) with the use of a commercially available Mini- tip Culturette (Becton-Dickinson, Cockeysville, MD, U.S.A.). Methods. An experimental model of bacterial keratitis was created in rabbit corneas by intrastromal injection of bacteria. Cultures were taken of rabbit corneas with both the Mini-tip Culturette and the platinum spatula. Culture results were compared with corneal colony counts. Humans with community-acquired presumed bacterial keratitis were cultured with both the Mini-tip Culturette and the platinum spatula. The sensitivity and specificity of the Mini-tip Culturette method was determined and compared with the platinum-spatula technique. Results. Rabbit keratitis model: 100% of corneas had established infections by colony count. Each ulcer was culture positive with platinum spatula, moist Mini-tip Culturette, and dry Mini-tip Culturette. Human keratitis: Seven patients had culture-negative keratitis with both the Mini- tip Culturette and the platinum spatula. Five patients were culture positive with both the Mini-tip Culturette and the platinum spatula. One of the positive cultures had growth of multiple organisms by using the platinum spatula but not with the Mini-tip Culturette. The sensitivity of the Mini- tip Culturette was 83.3%. The specificity of the Mini-tip Culturette was 100%. Detected organisms included group A β-hemolytic Streptococcus, S. aureus, coagulase-negative Staphylococcus, Serratia marcescens, and Pseudomonas aeruginosa. Conclusion. The Mini-tip Culturette is a highly specific and moderately sensitive method for culturing bacterial keratitis.