Microbial colonization and antibacterial resistance patterns after Boston type 1 keratoprosthesis

To characterize the bacterial and fungal flora colonizing the ocular surface of eyes with Boston type 1 keratoprosthesis (KPro) and to determine the prevalence of resistance to antibiotics. Culture positivity and antibiotic resistance rates in eyes with KPro are compared with those of eyes after penetrating keratoplasty (PKP) as well as control eyes.

Cross-sectional, case-control study.

A total of 75 eyes of 75 patients (25 KPro eyes, 25 PKP eyes, and 25 control eyes) were recruited from the Centre Hospitalier de l'Université de Montréal (Université de Montréal, Montréal, Canada) Ophthalmology Department.

The inferior bulbar conjunctiva was sampled using calcium alginate swabs. Standard culture media and protocols were used to identify colonizing bacteria and fungi. Extensive antibiotic susceptibility testing was performed on every isolate. Patients completed a validated questionnaire evaluating adherence to antibiotic prophylaxis. Hospital charts were reviewed to identify risk factors for bacterial resistance.

Culture positivity rates and prevalence of resistance to fourth-generation fluoroquinolones (FQ).

Bacterial cultures were positive in 64% of KPro eyes, 76% of PKP eyes, and 80% of control eyes (chi-square test; P = 0.41). Fungal cultures were negative in all but 1 eye with PKP. The most common isolates were Staphylococcus epidermidis, other coagulase-negative Staphylococci, and Corynebacterium species. At least 1 bacterial isolate resistant to fourth-generation FQ was found in 44% of eyes with KPro, 24% of eyes with PKP, and 8% of control eyes (chi-square test; P = 0.01). Patient adherence to antibiotic prophylaxis did not alter microbial susceptibility to fourth-generation FQ (odds ratio, 0.83; 95% confidence interval, 0.2-4.1).

Culture positivity rates and bacterial species composition were similar in KPro, PKP, and control eyes. Eyes with KPro were more likely to be colonized with FQ-resistant bacteria. Chronic prophylaxis with low-dose FQ is likely responsible for this increased antibiotic resistance. Modifications to the current prophylaxis regimen may be helpful in preventing further emergence of resistant pathogens.

The authors have no proprietary or commercial interest in any of the materials discussed in this article.