Use of gram stain to predict vitreous fluid infection.

To determine whether vitreous fluid Gram stains can successfully predict and indicate the nature of intraocular bacterial infection while awaiting culture results, a retrospective study of Gram stain and culture results on 12 endophthalmitis cases over the last two years was conducted. Out of ten culture-positive vitreous fluids, seven demonstrated bacteria on direct Gram stain and three had negative Gram stain results. Vitreous fluid artifacts resembling bacteria were seen in two other Gram stains and are described. When organisms are present in the vitreous fluid, they are frequently visible on a Gram-stained smear. The microbiologist must be able to differentiate the Gram stain appearance of normal vitreous fluid, probable artifacts, and infected vitreous fluid. Experience and diligence of the microbiologist are essential to correctly evaluate the vitreous fluid Gram stains.