Antimicrobial Coating for Educational Microscopes

A Contribution to Laboratory Hygiene

March 01, 2012

Bacteria are part of our world. There are countless numbers of them in the human body and they are completely harmless. But in people with a weak immune system or at the wrong place they can cause serious illness. Educational microscopes that pass through many hands are potential breeding grounds for germs. To solve this problem, Leica Microsystems and SANITIZED AG in Burgdorf, Switzerland have designed AgTreatTM – an antimicrobial coating technique using the active substance silver for the Leica educational microscopes. Christoph Fankhauser, Customer Support of SANITIZED AG, is responsible for the initialization and coordination of the antimicrobial inspection of customer samples. He reports on the benefits of AgTreatTM.

Why are plastic surfaces like those of microscopes a particularly good breeding ground for germs and fungus?

To be able to spread, germs need a source of carbon to feed on. Many plastics provide such a source. Another major factor, though, are the people working at the microscope, who contaminate the surfaces with an ultra thin film of dead skin flakes, saliva or perspiration. Particles of dust that settle on microscope surfaces can also help bacteria to spread. Regular disinfection is important. If a cleaning cycle cannot be carried out occasionally, or between two cleaning cycles, an antimicrobial coating with AgTreatTM helps keep germ growth in check.

Why are silver ions so effective against microbial surface pollution?

Silver has long been known as an active substance. Even the Romans were hygiene pioneers in that they used silver cutlery to prevent germs. Silver tablets are used to disinfect groundwater wells in Africa, for example. Silver is highly active, particularly in relation to germs, unicellular organisms and microbes, although this property also has undesirable effects such as staining. The crucial point is: How can this reaction be controlled? To do this, we have incorporated silver particles in a glass ceramic container. This releases the silver particles exactly when they are needed – i.e. at body temperature and high humidity, which are ideal conditions for microbial growth. The positively charged silver then reacts with the negatively charged bacteria. This destabilizes the cell membrane of the unicellular organism, preventing cell division and thus inhibiting bacterial growth.


Fig. 1: Antimicrobial function of silver ions

What harmful bacteria does the coating protect against?

Fig. 2: SANITIZED carries out around 20’000 microbiological tests every year in accordance with standardized methods.

The AgTreatTM coating protects users from a large number of bacteria types. We examine the particularly relevant germs in our laboratory. Some of them are hospital germs like the methicillin-resistant Staphylococcus aureus (MRSA), which is resistant to certain antibiotics and is a particular risk for antibiotic patients whose own immune system is incapacitated. A temperature of about 37 °C is ideal for MRSA to multiply and eventually paralyze the complete organism. However, we’re also talking about food-relevant germs such as Escherichia coli bacteria which mainly populate the intestinal tract but can lead to dangerous infections elsewhere. Food can also often contain salmonella, which cause serious diarrhoeal diseases.

How do you test the efficacy of the coating on microscopes?

Fig. 3: The set of dilution is stroked out with the micro pipette for determining the exact germ count.

The surface we are testing is seeded, i.e. brought into contact with, a liquid containing bacteria. The liquid is covered with a film to create an evenly distributed layer. This is then incubated for a day under ideal growth conditions for bacteria at 37 °C storage temperature and at least 90 per cent relative humidity. After 24 hours, the counting procedure is begun to see how many of the original number of about 100,000 germs have survived this test.

On an untreated sample there are about a million germs after a 24-hour incubation period. On a treated sample, we ideally only find a fraction of the germs that were put there. In the case of the Leica DM500 und DM750 with the AgTreatTM coating, we found that germs had been reduced by between 90 and 99.9 per cent.

How high do you rate the importance of the antimicrobial coating for school and university microscopes?

Being young and active, students are usually in contact with a large number of people – not only at university, but also in their free time. This means that any germs they encounter could multiply very rapidly. The danger is when germs are passed on to people whose immune system is temporarily or permanently weakened in some way. Large groups of people with different physical conditions and hygienic requirements are always a potential risk in this respect.

Practical application

Fig. 4: Students of the University of Buffalo, NY, work with the Leica DM750.

Eileen Sylves supervises the General and Developmental Biology student laboratories at the University of Buffalo, NY. There, the students examine various types of cells under the microscope. She explains why the faculty deliberately chose the Leica DM750: “Besides their excellent optics and illumination, we liked the fact that the educational microscopes of Leica Microsystems are easy to pack and to move from one laboratory to another. However, the key deciding factor was the AgTreatTM coating. We have up to twelve different people using each microscope. The silver ion coating protects our students from the germs they would otherwise be exposed to, particularly in the winter months.”