Boston Type 1 Keratoprosthesis: Microbial Colonization and Antibacterial Resistance

Abstract

Purpose: : Eyes with Boston Keratoprosthesis type 1 (KPro) have a life-long risk of severe ocular infections such as bacterial keratitis and endophthalmitis. The chronic use of topical antibiotics may also promote the growth of aggressive and resistant organisms. The purpose of this study is to characterize the bacterial and fungal flora colonizing the ocular surface of patients with a KPro and to determine the prevalence of resistance to antibiotics.

Methods: : 25 eyes with KPro were recruited from the Centre Hospitalier de l’Université de Montréal (CHUM) cornea subspecialty clinic. 25 eyes with PKP and 25 normal eyes were included as age-matched controls. After stopping topical antibiotics for 24 hours, the inferior conjunctiva was sampled using calcium alginate swabs. Cultures on blood, chocolate, MacConkey and Sabouraud agar as well as thioglyocalate broth were performed. Colonies were identified by subculture and antibiograms were obtained. Patients also completed a questionnaire to assess observance to antibiotic prophylaxis.

Results: : Bacterial cultures were positive in 65% (95% confidence interval [CI] 41-84%) of KPro eyes, 88% (CI 47-99%) of PKP eyes and 82% (CI 56-95%) of normal eyes (Χ²=0.33). Fungal cultures were negative in all cases. The most common isolates were Staphylococcus epidermidis, other coagulase-negative Staphylococci and Corynebacterium species. S. epidermidis was found in 60% of KPro eyes, 38% of PKP eyes and 59% of normals (Χ²=0.53). Other coagulase-negative Staphylococci specieswere found in 30% of KPro eyes, 63% of PKP eyes and 41% of normals (Χ²=0.28). Corynebacterium species were found in 5% of KPro eyes, 13% of PKP eyes and 12% of normal eyes (Χ²=0.71). S. aureus (12%) and Streptococcus viridans were found in 12% (Χ²=0.28) and 6% (Χ²=0.43) of normal eyes. Coagulase-negative Staphylococci resistant to fourth generation fluoroquinolones (FQ) were found in 50% (CI 30-70%) of eyes with KPro, 13% (CI 1-53%) of eyes with PKP and 12% (CI 2-38%) of normal eyes (Χ²=0.02).

Conclusions: : Eyes with KPro were as likely to yield positive cultures than eyes with PKP or normal eyes. Eyes with KPro were more likely to be colonized with FQ-resistant coagulase-negative Staphylococci. Chronic prophylaxis with low-dose FQ is likely responsible for this increased antibiotic resistance. Modifications in the prophylaxis regimen may be helpful in preventing further emergence of resistant pathogens.

Keywords: keratoprostheses