Antibiotic resistance pattern and visual outcome in experimentally-induced Staphylococcus epidermidis endophthalmitis in a rabbit model

To study whether the clinical outcome of Staphylococcus epidermidis-induced endophthalmitis in rabbits is related to the antibiotic resistance pattern of the infecting strain. Experimental animal study. The right eyes of 36 New Zealand white albino rabbits were inoculated with strains of S. epidermidis that displayed various patterns of antibiotic resistance. There were 12 rabbits in each of three study groups: fully antibiotic susceptible (FS), partially antibiotic resistant (PR), and multiresistant (MR). Five days after inoculation, the eyes were enucleated and prepared for histologic studies. Comparisons among the three groups were made based on electroretinographic (ERG) findings, histologic evaluation by a masked observer, and clinical examination. Electroretinographic findings on all rabbits were made by an unmasked observer. At 30 hours after inoculation, the ERG was diminished to 65% of normal for group FS, compared with a flat ERG waveform for groups PR ( P < 0.05) and MR ( P < 0.05). The ERG waveform was flat for all three groups at 72 hours after inoculation. Histologic evaluation by use of a histologic score revealed that the degree of inflammation and destruction of the retina was less for group FS (n = 10) compared with groups PR (n = 8) and MR (n = 8). Clinical examination revealed that there was a trend of less ocular inflammation for group FS compared with groups PR and MR. In a rabbit model of S. epidermidis-induced endophthalmitis, antibiotic-susceptible strains caused less inflammation and destruction of the infected retina than did antibiotic-resistant strains.