Researchers Discover New Way to Attack Staphylococcus aureus
A team of researchers at Imperial College London (ICL), UK, has found a ‘salty way’ to attack Staphylococcus aureus , an important opportunistic human pathogen.
This electron micrograph shows clumps of methicillin-resistant Staphylococcus aureus . Image credit: Janice Haney Carr / Jeff Hageman / USCDCP.
Staphylococcus aureus is a common bacterium that can normally be found in the nose, on the skin or in the lower intestine of any person.
This germ is the leading cause of recurrent infections in humans that include pneumonia, bacteremia, osteomyelitis, arthritis, endocarditis, and toxic shock syndrome.
A ‘superbug’ form of Staphylococcus aureus , called MRSA, has also developed resistance to the antibiotic methicillin.
Staphylococcus aureus can also trigger food poisoning, commonly through contaminated meat products, sandwiches, salads and dairy products.
In a new study published in the journal Science Signaling , Prof. Angelika Gründling of ICL’s Department of Medicine and co-authors have discovered how Staphylococcus aureus regulates its salt intake.
Disrupting this mechanism means the bacterium either absorbs too much salt from its environment, or loses too much water – causing it to dehydrate and die.
“With this research we now have a better understanding of how Staphylococcus aureus copes with salt stress,” Prof. Gründling said.
“Although this research is at an early stage, we hope this knowledge will someday help us to prevent food borne staphylococcal infections, as well as open new possibilities for a type of treatment that may work alongside antibiotics.”
Prof. Gründling’s team looked at MRSA cells in the lab and found that a signaling molecule called cyclic di-AMP is critical for the process through which the bacteria regulate their salt levels.
Staphylococcus aureus is notoriously resistant to high-salt concentrations, although up until now scientists have been unclear why.
Prof. Gründling and her colleagues revealed that when the signaling molecule detects the bacterium is in a high-salt environment, the molecule latches onto several ‘transporter’ proteins to signal to them to respond and protect the cell.
High salt concentrations act to pull water out of a cell – which is why we feel thirsty after eating salty foods.
Therefore to prevent water loss, the transporter protein pulls into the cell a type of a molecule that acts like a miniature sponge. It soaks up the water, locking it in the cell and preventing it from escaping. By stopping water loss, the miniature sponges also prevent salt from moving into the cell.
The team was able to disrupt this salt mechanism, and found that by increasing the signal to the transporter protein, the number of these miniature sponges was significantly reduced.
Inhibiting these salt protection mechanisms renders MRSA cells more sensitive to salt – which could ultimately lead to the destruction of the bacterial cells.
Experiments from other teams have revealed a similar mechanism is present in Listeria bacteria, which are also a common source of food poisoning.
The scientists are now further exploring this mechanism, in the hope of finding the exact way the signaling molecule regulates the transporter protein.
They are also investigating what other types of molecular sponges are involved in this process.