We report a rare case of Kocuria koreensis keratitis complicated with a shield ulcer in an AKC patient. In cases of opportunistic corneal infection complicating AKC, we should consider the possibility of Kocuria spp., in addition to Staphylococcus aureus and Fungus as causative organisms [7–9], because these species are also considered one of the resident skin flora.
Patients with atopic dermatitis are susceptible to developing skin infections due to alterations in the normal flora, compromised host immunological mechanisms caused by atopic diathesis, and immunosuppression due to administration of certain medications such as steroids and immunosuppressive agents [1, 10]. Staphylococcus aureus populations in the resident flora of the skin increase in patients with atopic dermatitis due to reduced antimicrobial peptides, such as human beta-defensin-2 [1, 11, 12]. In chronic AKC patients, Staphylococcus aureus colonization of the lid margins may exacerbate the allergic inflammatory reactions in the conjunctiva and cornea, thereby facilitating the development of infectious keratitis. In addition, the use of steroid or other immunosuppressive ophthalmic medications in these patients may predispose them to the development of opportunistic infection. Recognized types of infectious keratitis in AKC patients include staphylococcal keratitis and fungal keratitis [7–9].
The characteristic clinical finding in Kocuria keratitis is an echinulate white corneal opacity. Hence, we described the cornea as having a “coral-like appearance” in this case. A case of Kocuria keratitis reported by Mattem et al. [5] exhibited corneal opacity with a coral-like appearance, similar to our case. Therefore, this coral-like appearance may be considered a useful diagnostic sign.
In this case, microbiological diagnosis was performed using MALDI-TOF/MS. Identification of Kocuria spp. has been performed previously using an automated instrument for identification and antibiotic susceptibility testing (VITEK® 2 system) [13] or 16S ribosomal DNA sequencing [5]. In our diagnostic method for bacterial keratitis, an abrasion sample of infected cornea is applied directly to chocolate agar and cultured, and species of isolated bacteria are identified using MALDI-TOF/MS. Since diagnosis of the bacterial strain and antimicrobial susceptibility testing can be provided simultaneously, these combination of diagnostic method are considered useful for the rapid diagnosis of rare bacterial keratitis cases. Furthermore, The 16S rRNA gene sequence analysis was performed using isolated Kocria strain from the patient. The obtained DNA sequence showed 99% homology with Kocuria koreensis. Kocuria koreensis is a rare species in causative organism of infectious disease by Kocuria spp. A phylogenetic analysis based on the 16S rRNA gene sequence indicated that Kocuria koreensis P31T was most closely related to Kocuria kristinae DSM 20031T, with 96.9% similarity, and these two strains clustered together in constructed phylogenetic trees [14]. To the best of our knowledge, this is a first report of Kocuria koreensis keratitis.
The Kocuria koreensis isolated from the corneal shield ulcer in this case showed susceptibility to penicillin and a first-generation cephalosporin antimicrobial agent. Therefore, in this case, the combination therapy of corneal scraping and instillation of the cefmenoxime antibiotic ophthalmic solution was considered effective for Kocuria keratitis. However, further investigation on the selection of antibiotics for Kocuria spp. isolated from corneal ulcer is needed.