Fluorescent Gram stain in the microbiologic diagnosis of infectious keratitis and endophthalmitis

Purpose. To verify the sensitivity of a recently described technique of fluorescent Gram stain (FGS) and evaluate its role in direct microscopic examination of clinical ocular samples. Methods. In the first part of the study, culture suspensions of 10 bacterial isolates were stained, using FGS and conventional Gram stain (CGS), and were assessed for morphology and Gram sign. In the second part, 39 corneal scrapings and 18 vitreous biopsy materials were stained and observed by both methods. Results. Gram reaction and morphology of the bacteria, using CGS and FGS, were compared against culture. In both parts of the study, the sensitivity of CGS was significantly higher than FGS in the detection of Gram positive reaction (p = 0.01, 0.02). The specificities and predictive values of CGS and FGS were comparable in the evaluation of clinical samples. The bacterial morphology was demonstrated better (p = 0.01) with CGS. Significant quenching of fluorescence and change in Gram reaction with time were noted in FGS. Conclusions. The low sensitivity, quenching of fluorescence and change in Gram reaction presently preclude the usage of FGS as a diagnostic tool in ocular infections.