"For once we wanted to use our microscopes, not to help us observe microorganisms, but to examine more closely their role as potential vectors of infectious pathogens. Very little was known about this until now," explains the head of the study, Prof. Dr. Markus Egert, a lecturer in microbiology and hygiene at Furtwangen University. The focus was on the microscope eyepieces because of the intense contact with users' hands and eyes.
Microorganisms such as bacteria and fungi are so small that they are invisible to the naked eye. To see them you need a light microscope which magnifies the cells 1000 times. Because microorganisms are so important for the environment, well-being and health of humans, such microscopes are commonly found in scientific laboratories.
For the study, the oculars of ten microscopes from a university laboratory were tested immediately after a practical class. Bacteria and fungi from all left eyepieces and eye cups were cultivated on various culture media, while all right eyepieces and eye cups underwent comprehensive molecular biological analysis. The tests were carried out before and after they were cleaned with 70% isopropanol for 30 seconds.
"We were able to obtain excellent values from up to 1700 living bacteria per cm2, above all from typical skin bacteria such as cutibacteria and staphylococci, but also from environment and water bacteria such as paracocci. We did not find any fungi," said Prof. Egert. The molecular biological tests generally confirmed these findings; in total, 262 different types of bacteria were identified on the oculars tested. With staphylococcus epidermidis, paracoccus yeei, cutibacterium acnes and brevibacterium casei, four potentially pathogenic bacteria were isolated from the eyepieces. These can cause eye conditions such as keratitis or inflamation of the eyelid in sensitive people.
"So microscope oculars definitely have the potential to act as carriers of infectious pathogens. The good news: cleaning with isopropanol reduces the number of germs significantly by 99%. This should be carried out regularly, particularly if different people use the same microscope," concludes Prof. Egert.