An antimicrobial protein found in the blood of an Australian oyster could help in the fight against superbugs, new research suggests.
Australian scientists have discovered that a protein found in the haemolymph – the equivalent of blood – of the Sydney rock oyster, Saccostrea glomerata, can kill bacteria itself and increase the effectiveness of some conventional antibiotics.
Antimicrobial resistance has been described as a “looming global health crisis” that – without urgent action – could render critical drugs ineffective and result in declines in lifespan and life quality by 2050.
In lab tests, the haemolymph protein alone was effective at killing the bacteria Streptococcus pneumoniae, which mainly causes pneumonia, and Streptococcus pyogenes, the culprit for strep throat and scarlet fever. It has not yet been tested in animals or humans.
When used in combination with antibiotics, including ampicillin and gentamicin, it improved their effectiveness from two- to 32-fold against bacteria such as Staphylococcus aureus (golden staph) and Pseudomonas aeruginosa, which often infects immunocompromised people.
The study’s co-author Prof Kirsten Benkendorff, of Southern Cross University, estimated that about two dozen oysters would contain enough haemolymph to provide an active dose of the protein for an average person, but she emphasised that more research was needed to purify the protein and understand how it works.
“We found that heating [the protein] does actually reduce the antimicrobial activity, so cooking would reduce the effect,” Benkendorff said.
It is uncertain, however, whether eating the protein would be effective, as unlike many conventional antibiotics, antimicrobial proteins can be broken down by the digestive system before they reach their target site.
“I definitely would not suggest that people ate oysters instead of taking antibiotics if they have got a serious infection,” Benkendorff said.
She said “oysters as filter feeding organisms are sucking bacteria in through their bodies all the time”, making them good candidates in which to look for new antimicrobial drugs – but also means that in places such as near stormwater drains, they can accumulate substances that can be harmful to humans if consumed.
Benkendorff said the protein could help treat respiratory infections that are resistant to regular antibiotics because of biofilms.
To protect themselves, infectious bacteria often aggregate into biofilms – sticky communities that enable them to better evade antibiotics and the human immune system.
The oyster haemolymph protein was effective against Streptococcus biofilms, the scientists found.
“We often think about bacteria just floating around in the blood. But in reality, a lot of them actually adhere to surfaces,” Benkendorff said. “The advantage of having something that disrupts the biofilm is … it’s stopping all of those bacteria from attaching to the surfaces. It’s releasing them back out into the blood, where then they can be attacked by antibiotics.”
Prof Jonathan Iredell, an infectious diseases physician and clinical microbiologist at the University of Sydney, who was not involved in the research, said the oyster protein belonged to a class of compounds called antimicrobial peptides. “There is a lot of excitement about their discovery because they often contain interesting kinds of mechanisms that we haven’t seen before.”
The study, he said, added “to an exciting field where we’re looking to naturally occurring antimicrobials of a different type to try and provide new prospects in the face of advancing adaptation by bacteria”.
Prof Branwen Morgan, who leads the CSIRO’s minimising antimicrobial resistance mission, described the protein’s properties as a “really interesting discovery, given biofilms are so problematic”.
Morgan, who was not involved in the research, said any potential treatment that reduced the reliance on traditional antibiotics was worth pursuing, in light of the increase in drug-resistant infections around thee world.
“Given the significant costs in developing new medicines, the idea of using excess and/or imperfect oysters to generate a sustainable supply of antimicrobial proteins … should be investigated further,” she said.
The study was published in the journal Plos One.
