Staphylococcus aureus causes many diseases, from skin rashes and boils to serious and life-threatening inflammatory conditions in the heart and bones. However, existing antibiotics can have severe side-effects and are not always effective. Now researchers have used bacteriophages – viruses that kill bacteria – as inspiration to design a novel enzyme that is effective in killing Staphylococcus aureus. In addition, the enzyme does not cause side-effects or multidrug resistance.
Staphylococcus aureus hides in microscopic cracks in the skin of people with cutaneous T-cell lymphoma. Theycolonise the skin and fuel disease activity in the skin cancer that has helped them to hide by chemically bolstering the cancer. In the most severe cases, Staphylococcus aureus infection is a major cause of death, and attempts to fight the bacteria often fail when Staphylococcus aureus has become resistant to antibiotics. Now, results based on a new principle look extremely promising.
“Bacteriophages naturally kill bacteria. They produce enzymes – endolysins – that make small pore-shaped holes in the cell wall so that the bacteria die. Our collaborators have designed and developed novel artificial enzymes that selectively kill Staphylococcus aureus. We have now tested one of these enzymes and determined that it specifically targets Staphylococcus aureus, which causes considerable pain and is potentially the reason why people with advanced stages of the skin lymphoma die. Everything so far indicates that Staphylococcus aureus does not develop resistance to the endolysins,” explains a main author, Niels Ødum, Professor, LEO Foundation Skin Immunology Research Center, University of Copenhagen.
Splitting a layer of sugar and amino acids
Staphylococcus aureus is the villain in many disease situations, both inside and on the surface of the body, and is strongly suspected of increasing disease activity, including in diseases such as atopic dermatitis and cutaneous T-cell lymphoma.
“Staphylococcus aureus secretes a toxin – enterotoxin – that makes the cancer cells divide faster and thus become more malignant. So the bacteria fuel the cancer, making it worse. In the past, aggressive antibiotic treatment has been used, but it is not really suitable in the long term because of potential side-effects but also because multidrug-resistant Staphylococcus aureus can develop,” says Niels Ødum.
Bacterial attacks can ultimately kill the people affected, and researchers have therefore searched intensively for alternative ways to eliminate the bacteria. Such an opportunity occurred to Niels Ødum, who attended a conference and heard about Staphefekt, a recombinant type of endolysin, that Micreos Pharmaceuticals had developed as a drug to treat staphylococcal infections.
“I therefore wrote to them and quickly got a positive response, including about a new and even more potent compound (XZ.700) that we decided to test,” he explains.
XZ.700 represents a promising new class of recombinant antibacterial proteins that were designed based on knowledge from bacteriophages. They kill bacteria by splitting the layer of sugar and amino acids – peptidoglycans – that forms a membrane around especially gram-positive bacteria, including Staphylococcus aureus.
“We have shown in laboratory experiments that endolysin strongly inhibits the growth of Staphylococcus aureus isolated from lesional skin. We then performed tests on some skin samples – also in the laboratory. The skin was suspended in a liquid culture so that it was nourished from below, just as in the body. When we tested this on both healthy and cancerous skin, we found that the endolysins strongly inhibited the growth of the bacteria,” explains another main author, Emil M.H. Pallesen, Postdoctoral Fellow, LEO Foundation Skin Immunology Research Center, University of Copenhagen.
Little chance of resistance
The experiments suggest that endolysins can keep healthy skin free of Staphylococcus aureus and can remove it from cancerous skin. The researchers had doubts about the latter. Cancerous skin is strongly affected by cytokines, signalling compounds that normally activate the immune system. The cytokines also influence skin cells to both lose water and downregulate the production of multifunctional skin-protective proteins called filaggrin.
“The cracks in the skin are therefore perfect for hiding the Staphylococcus aureus, but XZ.700 inhibits both the number of bacteria on the skin and the bacteria’s potential tumour-promoting effects, so it seems to be a really effective remedy,” says Emil M.H. Pallesen.
Since artificially produced endolysins have only existed for a few years, it is not known whether Staphylococcus aureus may eventually develop resistance. However, laboratory studies show that Staphylococcus aureus has not yet developed resistance to endolysin – even in bacterial cultures that have been cultivated for a long time.
“Bacteria may become resistant to the bacteriophages from which the endolysins originate, but this has only affected other parts of the bacteriophages’ arsenal. However, resistance to designer endolysins is less likely because they do not have to enter the cell, which means that many of the bacteria’s resistance mechanisms are never activated,” explains Emil M.H. Pallesen.
Important clinical trials ahead
In addition, the structure of the peptidoglycans the endolysins attack is so well preserved through many years of evolution that envisioning that the bacteria could change the peptidoglycans without fatal consequences is difficult. Finally, XZ.700 has been very effective against multidrug-resistant staphylococci in biofilms, which are normally highly resistant to antibiotics.
“Endolysins such as XZ.700 have great potential for eradicating various subtypes of Staphylococcus aureus. Another equally important feature, however, is that XZ.700 does not seem to be active against the “good” bacteria in our skin,” says Niels Ødum.
The useful skin bacteria, such as Staphylococcus epidermidis, normally live in large colonies and protect us from harmful bacteria. However, whether the targeted eradication of Staphylococcus aureus by endolysin can actually make life easier for other beneficial bacteria is too early to say.
“Experiments in the laboratory are one thing. The important clinical trials involving humans lie ahead. But if the endolysin works against staphylococci in connection with skin cancer, there is reason to believe that it should also work against other skin diseases involving Staphylococcus aureus, such as atopic dermatitis and diabetic skin ulcers,” concludes Niels Ødum.
“Endolysin inhibits skin colonization by patient-derived Staphylococcus aureus and malignant T cell activation in cutaneous T cell lymphoma” has been published in NN. In 2021, the Novo Nordisk Foundation awarded a Tandem Programme grant to Niels Ødum and Lars Iversen for the project Staphylococcus aureus and Skin Barrier Defects are Novel Therapeutic Targets in Cutaneous T-cell Lymphoma.