Eye-catching microbes – Polyphasic analysis of the microbiota on microscope oculars verifies their role as fomites
Regularly touched surfaces usually represent fomites, particularly if touched by different persons. This also applies for microscopes, widely used in clinical or biological laboratories. Previous, cultivation-based studies suggested that direct contact with microscope eye-pieces significantly increases the risk of eye infections. In order to obtain a comprehensive view of the microbial community profile and its hygienic relevance, we performed cultivation-based and molecular analyses of the ocular microbiota. We swab-sampled oculars of 10 recently used microscopes from a university laboratory. Samples of the left oculars were used for quantification and MALDI-biotyping of representative isolates, following protocols previously established for spectacles. Samples from the right oculars were used for a 16S rRNA gene sequencing approach. After sampling, all oculars were carefully cleaned with isopropanol, re-sampled and analyzed again.While fungi were not detected, all investigated oculars were contaminated with bacteria, with a maximum load of 1.7 x 103 CFU cm-². 114 morphologically different isolates were assigned to 11 genera and 8 species, mainly Cutibacterium (total 68%), Staphylococcus (total 14%) and Brevibacterium (10%), with the most abundant species being Cutibacterium acnes (13%) and Staphylococcus capitis (6%). Cleaning reduced the microbial load up to 2 log scales, leaving mainly cutibacteria. 15 samples yielded good sequencing results. 1667 ASVs OTUs were assigned to 10 phyla and 267 genera. The dominant genera before cleaning were Cutibacterium (78%), Paracoccus (13%), Pseudomonas (2%) and Acinetobacter (1%). The bacteriota composition on cleaned oculars was similar, however, probably largely representing dead bacteria. We report the first comprehensive insight into the microscope bacteriota. Used oculars were notably contaminated with skin and environmental bacteria, including potential pathogens. Clearly, regular cleaning after use is highly recommendable to prevent eye and skin infections.