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Silver lining to staph discovery

Silver lining to staph discovery

Scientists from a pioneering Northern Territory-based research project have uncovered two new species of the bacteria Staphylococcus.

Several years ago Menzies researchers began to notice a ‘strange’ golden staph (Staphylococcus aureus) bacteria causing skin infections in Aboriginal children.

Investigations in 2014 determined that the bacterium was not golden staph, but rather a strain of ‘silver staph’. The scientific community has since formally recognised this as a new species of staph – Staphylococcus argenteus.

Menzies senior research fellow, Associate Professor Steven Tong explains that for both S. argenteus and S. schweitzeri, distinguishing these species from golden staph (Staphyococcus aureus) using standard laboratory techniques can be difficult.

Golden staph continues to cause a heavy burden of disease across the world, especially in the NT where it is the most commonly isolated bacteria in the Royal Darwin Hospital.

“The discovery is important because it deepens our understanding of the whole group of Staphylococci which are a major cause of human disease,” Assoc Prof Tong said.

The research group, led by Associate Professor Philip Giffard, has spent the past 10 years looking into the genetic sequences of golden staph recovered from NT communities.

Assoc Prof Giffard explains the differentiation between the silver and golden staph species.

“It is called ‘silver staph’ because it cannot make the golden pigment that is a defining characteristic of S. aureus (golden staph), and appears a brilliant silvery white on agar a plates.”

Senior scientist, Dr Deborah Holt said the research team engaged in further investigations after certain strains appeared different with regards to their DNA sequence.

“We came across some unusual results while investigating the genetic sequences of golden staph from the NT and across the world,” she said.

“During this process we noticed some strains isolated from monkeys in Africa also looked unusual so we decided to combine efforts with collaborators in Munich, Germany who had collected these monkey strains. Further investigations showed us we were dealing with three entirely separate species.”

Menzies have been using the latest DNA sequencing technology in collaboration with the Wellcome Trust Sanger Institute in Cambridge, UK to definitively show that there is sufficient genetic distance between S. argenteus, S. schweitzeri and S. aureus for them to be formally recognised as different species.

“While initially concerning more recent studies have shown that silver staph causes less severe disease,” Assoc Prof Tong said.

“However, the silver staph strain has demonstrated an ability to become resistant to penicillin like antibiotics just like golden staph which has become methicillin-resistant Staphylococcus aureus (MRSA). In fact, these different species can swap genes with each other – a bit like bacteria having sex.”

Assoc Prof Tong said the findings would be of great significance to the international scientific community.

“Researchers and doctors all over the world are now able to look more specifically at the kinds of disease that these new species cause. It is likely that infections due to the different species can be treated differently,” he said.

To put these findings in a different context, Assoc Prof Tong points to the importance of differentiating certain species of reptiles such as crocodiles.

“Knowing that there are different species of crocodiles is important as some are more dangerous than others. We don’t lump all crocodiles together, but rather treat freshwater and saltwater crocodiles differently,” he said.

“Similarly, we should not be lumping these different species of staphylococci together. Additionally, the scientific community can now look at what sets S. aureus apart from the other two species and understand why it is better able to cause disease.”

This research has been funded by Australian National Health and Medical Research Council, the Wellcome Trust through core funding for the Sanger Institute Pathogen Variation Group, and by the Deutsche Forschungsgemeinschaft, Germany Research Foundation.

View the article on the International Journal of Systematic and Evolutionary Microbiology website

To learn more about Menzies research into tropical and infectious disease visit the Menzies website.