Polymerized Peptide SNAPPS May Be An Alternative To Antibiotics

The polymer has protein chains in star shapes with 16 or 32 arms that are about 10 nanometres in diameter, much larger than other antimicrobial peptides.

A star-shaped polymerised peptide – which is a large repeated chain of proteins has been designed by Shu Lam and her team from the Melbourne University School of Engineering.

Bacteria are increasingly resistant to antibiotics, evolving into feared "superbugs" that threaten to kill millions of people a year.

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‘SNAPPS can kill bacteria more effectively and selectively than other peptides without damaging the surrounding cells.’

In the US, the Food Drug Administration is pulling anti-bacterial soaps off the market for fear that they are exacerbating antibiotic resistance in some bacteria. "Our project is to build better alternatives to antibiotics. It kills bacteria in multiple ways. We designed it to break the cell wall apart but we also found it can trigger the cell to kill itself," Lam said.

Lam and the team called their polymers SNAPPs: structurally nanoengineered antimicrobial peptide polymers.

A peptide is a short chain of amino acids. Scientists have experimented previously with antimicrobial peptides but have found that while they kill bacteria, they are also hugely toxic to the hosts.

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Lam has designed her protein chains in star shapes with 16 or 32 arms that are about 10 nanometres in diameter, much larger than other antimicrobial peptides.

Professor Greg Qiao is Ms Lam's supervisor. He said that what is novel in her design is that their relatively large size means it doesn't seem to affect the healthy cells around the bacteria.

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"With this polymerised peptide we are talking the difference in scale between a mouse and an elephant," he said. "The large peptide molecules can't enter the [healthy] cells." Lam and her team tested six different superbugs in vitro and found that the star-shaped peptide polymer killed the bacteria and did not damage red-blood cells in the in vitro environment.

They also tested the efficacy of the polymer in vivo, inside mice, against Acinetobacter baumannii, and the researchers "did not observe any resistance acquisition by A. baumannii".

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Associate Professor Cyrille Boyer, at the University of NSW, said it was very promising research but warned its use was still a long way from clinical application.

"The main advantage seems to be they can kill bacteria more effectively and selectively" than other peptides, said Associate Professor Boyer, who is not associated with the research.

Professor Qiao said one of the next steps is to look at how different shapes, such as rings, will work against the superbugs. He also said there will need to be a lot more in vivo research to explore the limits of their toxicity.

Source-Medindia