Till Örebro universitet

First, to describe the microbial spectrum in infectious keratitis by both a culture and a targeted sequencing approach; second, to describe the clinical and genetic characteristics of Corynebacterium macginleyi; and third, to study different aspects of the corneal culture process by comparing two instruments used for sampling and two sampling and inoculation strategies. 

The five studies in this thesis made use of two retrospective study populations and one prospective study population.

In the retrospective population the microbial spectrum by corneal culture was explored, Gram-positive bacteria, mainly coagulase-negative staphylococci, Staphylococcus aureus, and Corynebacterium spp. were commonly isolated. In the prospective study population, culture detected 13 different bacterial genera, while targeted sequencing identified a total of 168 different bacterial genera, with individual samples having a median of 13 (7–28) genera. Culture and sequencing showed an 82% agreement on the bacterial genera detected by culture. Genome sequencing and analysis of C. macginleyi revealed two different clades of which the minor clade (n=7), not previously described, exhibited a more complicated disease course. Cotton tipped applicators generated a significantly higher rate (44%) of positive corneal cultures on solid media than knife blades (31%). Direct transferal of multiple corneal samples to culture media generated a significantly higher rate of positive corneal cultures (61%) than indirect transferal through a single transport medium (44%).

In conclusion, the microbial spectrum in a Swedish population is similar to previously described in Europe, and C. macginleyi may be considered a corneal pathogen. Targeted sequencing may gain clinical application if further developed. The findings of this thesis indicate that a cotton tipped applicator may be sufficient for corneal sampling for direct inoculation, and the corneal culture procedure can be simplified from seven samplings on four different media to three samplings on two media.