University of Dundee

The secret war of Staphylococcus aureus revealed

10 Oct 2016

Staphylococcus aureus, a bacterium that colonises approximately 30% of the human population at any one time, has now been shown to attack other bacteria, according to ground-breaking research from the University of Dundee.

The bacterium which often inhabits the skin of humans and animals can cause a wide range of illnesses including minor skin infections to pneumonia, sepsis and toxic shock syndrome.

Staphylococcus aureus is also one of the world’s most common causes of hospital-acquired infections.

The research, led by Professor Tracy Palmer, Head of the Division of Molecular Microbiology in the School of Life Sciences at the University, suggests that whilst Staphylococcus can live commensally on their human hosts, it possesses a dark side - secreting the toxin EsaD through its type VII secretion system to target competing strains.

Victorious strains of Staphylococcus have been shown to contain both multiple variants of EsaD toxins as well as EsaG-like proteins which neutralise EasD and protect them from the toxic activity of competitors.

Professor Palmer said, “During our work we found that Staphylococcus secretes a large toxin which we think doesn’t target human cells but rather targets and kills other strains of Staphylococcus. This is exciting because it means they purposefully use their secretion system to compete with other strains, most likely for dominance in the human host.

“Colonising our bodies is the first step in the ability of Staphylococcus to cause disease. We believe this finding is just the tip of the iceberg, and we are now looking to find the entire toxin armoury and ultimately how it uses these toxins to colonize the body.”

Recent analysis of over a thousand strains of Staphylococcus suggests that the toxins used in this ‘germ’ warfare were only present in half of them, yet all of those sequenced proved to contain the antitoxin, EsaG, which has now been shown to neutralise the aggressive toxin - EsaD.

This suggests that the strains are actively producing these proteins to target their rivals whilst also producing antitoxins to try and protect themselves. One strain had recently gained 11 copies of the antitoxin, suggesting that Staphylococcus is in a molecular arms race, probably to get a foothold on our bodies.

The research has been funded by the Wellcome Trust, the Medical Research Council (MRC) and the Biotechnology and Biological Sciences Research Council (BBSRC) will be published by the journal Nature Microbiology on Monday, 10th October.

The study is part of wider research developed to help contribute to the fight against antimicrobial resistance, one of the major health problems facing the world today. 

The University of Dundee is the top ranked University in the UK for biological sciences, according to the 2014 Research Excellence Framework, the major survey of research quality in the UK.