What causes recurring staph infections

Why Infected Wounds Don't Heal - The Tricks of Bacteria

The skin is our protective coat. It protects us from external environmental influences, from allergens and pathogens. If the skin is injured, however, pathogens can enter the body. One of these “culprits” is the bacterium Staphylococcus aureus. "It is quite natural for such staphylococci to settle on our skin," says Professor Dr. Mathias Herrmann, infection medicine specialist at the Saarland University Hospital. They can cause skin infections, such as hair follicle infections. However, these are mostly harmless and self-healing. “It only becomes problematic when staphylococci enter the body. There they can lead to inflammation of wounds, severe suppuration and even blood poisoning, ”describes Herrmann. Another problem is: Staphylococci are very adaptable and often resistant to antibiotics. The methicillin-resistant Staphylococcus aureus, the hospital germ MRSA, is particularly notorious. For the research association SkinStaph - a funding measure of the Federal Ministry of Education and Research - reasons enough to research the disease mechanisms of Staphylococcus aureus infections in more detail.

More than just a door opener: the protein Eap

For Herrmann, the key to understanding staphylococcal infections is a protein that the bacteria carry on their surface: the extracellular adhesive protein, Eap for short. “Up to now, we assumed that Eap only helped the bacteria to attach themselves to the skin cells of their host, for example to human skin cells,” explains Herrmann. But obviously its disease-causing significance goes well beyond this originally known effect. Together with his institute colleague, Privatdozent Dr. Markus Bischoff, the Giessen biochemist Professor Klaus Preissner, as well as scientists from the Utrecht University Hospital led by Professor Suzan Rooijakkers and the University of Missouri led by Professor Brian Geisbrecht, the research alliance has found that Eap creates optimal conditions for bacteria for an infection through various mechanisms.

First, Eap opens the “door” to various human cells, such as skin cells, for the staphylococci. With the help of the surface protein Eap, the bacteria get inside the cells. "In this protected environment, the staphylococci can then multiply - undetected by the body's defense reactions," describes Herrmann. But that's not all: If the staphylococci settle in a wound, Eap specifically inhibits the formation of new skin cells and tiny blood vessels there. “But it is precisely these newly formed skin cells and blood vessels that are crucial for wound healing,” explains Herrmann. "So Eap is the reason why infected skin wounds heal poorly!"

The immune system is actively influenced

The latest results from the SkinStaph group show that Eap is also able to directly and actively weaken the host's defense mechanisms. "Until now, it was assumed that Staphylococcus aureus pathogens damage the infected organism directly through tissue enzymes and toxins," says Herrmann. Bischoff adds: "We have now discovered a previously unknown interaction between the Eap proteins of the staphylococci and certain protein-splitting enzymes in white blood cells, the neutrophil proteases." Neutrophil proteases play a decisive role in the immune defense: They can kill bacteria directly, but also inactivate pathogenic bacterial factors and influence the immune response. However, as a result of the interaction with Eap, the proteases lose their ability to break down proteins - and thus their function in the immune system. “As part of this cooperation project, we were able to describe Eap molecules for the first time as a new class of protease inhibitors that are responsible for the 'intelligent' inhibition of host defense,” explains Herrmann. As harmful as Eap can be for the healing of chronic wounds, for example, the protein's abilities could be helpful for diseases in which there is an excessive immune reaction. Preissner formulates the outlook for this work: “Eap proteins could represent a new class of substances against chronic immunological diseases. We will continue to take a close look at proteins in the future. "

Literature: Stapels DAC, Ramyar KX, Bischoff M, von Köckritz-Blickwede M, Milder FJ, Ruyken M, Eisenbeis J, McWhorter WJ, Herrmann M, van Kessel KPM, Geisbrecht BJ, Rooijakkers SH. Staphylococcus aureus secretes a unique class of neutrophil serine protease inhibitors. Proc Natl Acad Sci USA 2014; 111: 13187-92

Contact Person:
Prof. Dr. Mathias Herrmann
PD Dr. Markus Bischoff
Institute for Medical Microbiology and Hygiene
Saarland University Hospital
Kirrberger Strasse
66421 Homburg / Saar
06841 16-23900
06841 16-23985
[email protected]