To report a case of endogenous endophthalmitis due to Streptococcus mitis in a patient with Staphylococcus aureus sepsis.

A 77-year-old male complained of sudden visual loss and ocular pain in his right eye and was treated with intravenous antibiotics for Staphylococcus aureus sepsis. With a diagnosis of endogenous endophthalmitis, the patient received pars plana vitrectomy and intravitreal injection of antibiotics. Vitreous fluid was obtained before surgery, and the organism was identified as Streptococcus mitis . Twenty-one days after the surgery, intraocular inflammation was stabilized, and visual acuity was improved from light perception to 20/60.

Appropriate sampling and culture of vitreous fluid are important for the diagnosis of endogenous endophthalmitis. The possibility that the causative organism of endogenous endophthalmitis may be different from the result of blood culture should be considered.