Viruses are different - and so medicines against viruses should also be different than against bacteria. However, this only applies as long as you concentrate on fine details: if clumsy violence is the order of the day, the difference between viruses and bacteria quickly becomes negligibly small. Antibiotics are double-edged swords. At first they seem all the more helpful, the deadlier they are for all sorts of contagious things. But the more deadly, the faster what happens reliably, what has happened in the millennia of human weapon technology: The hand with the sharp sword exaggerates, and the ancient mechanisms of selection promptly ensure that among those fought only those with particularly good, impenetrable armor can be found. Medical professionals call the armor "resistance," referring to the sudden success of some new biochemical pathway by which the biologically-weaponized germs have learned to detoxify.
And this is how the armament spiral turns: A new weapon against bacteria has to replace an old antibiotic that used to be highly effective and is now useless. Unfortunately, it seems that in this competition, the germs are often quicker than the antibiotics innovators are resourceful. Alexander Klibanov from the Massachusetts Institute of Technology and his colleagues found time for completely new approaches: away from the sophisticated chemical-biological club and towards the good, old, sturdy arsenal of slotting, piercing and cutting. For some time now, Klibanov and Co have been trying to put an end to attacking bacteria with a kind of pitfall with a deadly bed of nails at the bottom.
The art, according to the researchers, is actually only to make the nails sufficiently small, pointed and also really dangerous in the micro-world of bacteria. Fortunately, nature also provides a sufficient range of potentially unpleasantly prickly molecules in the chemical hardware store - for example in the "Polyethyleneimine" drawer.
Klibanov and his comrades-in-arms used it a year ago. Roughly speaking, the PEIs investigated are elongated, partly branched chains of water-repellent components and a positively charged area. Various versions of this can be knitted together - and depending on the type of chains, side chains and charge of the appendages, they are actually harmless to deadly for various bacteria, the chemists determined. Many germs - both harmless intestinal dwellers such as E. coli and dangerous, multi-resistant germs such as Staphylococcus aureus - that Klibanov's team dropped onto a hydrophobic and polycationically coated glass surface were doomed as a result.
The reason for this was not just to be found in the chemistry of the PEI, but in the dimensions of the coating: the chains are only lethal from a certain molecular size. PEI do not act as a contact poison, the scientists explain, but if they are long enough, they literally pierce the membrane envelopes and cell walls of the bacteria. The ruptured germs then lose control of their internal environment through the leak and finally burst.
Which gave the researchers another idea. Spearheads, according to their calculations, shouldn't really care what they drill their way through. And so the PEI chains could not only penetrate bacteria, but also, for example, influenza viruses with their typical, not necessarily more stable envelope of membrane-enclosed proteins. They tested the idea on influenza viruses, which they dropped onto a PEI-coated surface and then tried to multiply.
Impressive result: Almost none of the obviously damaged viruses were still infectious afterwards. A second type of virus was then shown to be deadly impressed – just like previously different gram-positive and -negative bacteria, whose shells are structurally very different. The scientists report after further meticulous serial investigations that the recipe for the antimicrobial coating depends in particular on the length and the positive net charge of the molecular chains. Ideally, the antiviral and bactericidal Totstech argument PEI works within just five minutes.
The only question that remains is the everyday use of the antibiotic coating. In theory, applied to all kinds of surfaces, it could be really useful to stop the spread of viruses and bacteria, the scientists hope optimistically. It is also more than unlikely that new armor will soon be found in the medical arsenal against the new spear: the entire outer shell should be completely rebuilt to make it impenetrable for hydrophobic penetrators - which an average pathogen rarely encounters in nature - should also be done difficult for the most innovative virus and bacterium. Then the only question that remains is the price. The research pioneers worked with branched polyethylenimines, 100 grams of which can be purchased for just under 40 euros. Maybe mass production for the all-over germicidal paint will be cheaper.