Shotgun metagenomic sequencing in culture negative microbial keratitis

Purpose To evaluate the microbiota of culture negative Corneal Impression Membrane (CIM) microbial keratitis samples with the use of shotgun metagenomics analysis. Methods DNA of microbial keratitis samples were collected with CIM and extracted using the MasterPure™ Complete DNA and RNA Purification Kit (Epicentre). DNA was fragmented by sonication into fragments of 300 to 400 base pairs (bp) using Bioruptor® (Diagenode, Belgium) and then used as a template for library preparation. DNA libraries were sequenced on Illumina® HiSeq2500. The resulting reads were quality controlled, trimmed and mapped against the human reference genome. The unmapped reads were taxonomically classified using the Kraken software. Results 18 microbial keratitis samples were included in the study. Brevundimonas diminuta was found in 5 samples while 6 samples showed the presence of viral infections. Cutibacterium acnes, Staphylococcus aureus, Moraxella lacunata and Pseudomonas alcaligenes were also identified as the presumed putative cause of the infection in 7 samples. Conclusions Shotgun sequencing can be used as a diagnostic tool in microbial keratitis samples. This diagnostic method expands the available tests to diagnose eye infections and could be clinically significant in culture negative samples.