Many would argue that we have won the war against bacteria since the development of antibiotics in the early 1900s. However, concerns about antimicrobial resistance (AMR) had already started arising as early as the 1940s, when researchers noticed that Staphylococcus aureus stopped responding to penicillin treatment. Bacteria can evade antibiotic effects through different mechanisms, including removing or degrading the drug’s active chemical, or modifying themselves so the drug won’t find its target.
While AMR is a naturally occurring phenomenon, inappropriate or excessive use of antibiotics by humans has exacerbated its effects. By consuming low concentrations of antibiotics that are not enough to kill bacteria, for example by eating a streptomycin-sprayed tomato, your commensal bacteria are exposed to the drug and get the chance to develop resistance against it. If the time comes when these bacteria become pathogenic, they will already be resistant to the drug, and they would be considerably more difficult to kill.
AMR has implications in many medical procedures as well, like surgery, caesarean sections, and cancer chemotherapy, where infections are common. In fact, in 2019, AMR was directly responsible for 1.27 million global deaths, while it contributed to 4.95 million deaths. As the inappropriate use of antibiotics continues, it has now become an extremely pressing issue with predictions that global deaths associated with AMR will reach 8.22 million in 2050.
Multidrug resistant S. pneumoniae kills millions each year
One of the bacteria that raises the most concern is Streptococcus pneumoniae, which causes pneumonia, one of the leading causes of death worldwide. S. pneumoniae results in around 2.5 million deaths each year, most of which are children and the elderly. One of the reasons why it’s so deadly is because up to 50% of pneumococcal infections are now multidrug resistant, meaning they have developed resistance to three or more drugs and are therefore very difficult to treat.
Researchers think that what contributes to this resistance is its capacity to form biofilm, which is when multiple bacterial cells cluster together and protect themselves by producing a polymeric matrix film. This evades drug action and makes them more persistent and virulent because they are more adhesive to host surfaces. Considering our extremely limited drug options, the development for new therapeutics against S. pneumoniae is dire.
Oysters to the rescue
It was known for centuries that certain molluscs like oysters have therapeutic abilities. Oysters are used in traditional Chinese medicine, Ayurveda, as well as by the indigenous people of Australia as a functional food but also to treat respiratory infections. Unsurprisingly, there is scientific basis to these practices. Oysters are filter feeders, meaning that they sequester nutrients by passing seawater through a filtering organ that traps solids. The catch is that seawater is full of microbes, so oysters have developed a strong immune system to combat infection.
The oyster immune system is very different to ours — it is reliant on antimicrobial proteins and peptides (AMPs) with strong chemical properties in their blood (or hemolymph). So far, the immune system of oysters was studied to prevent marine disease outbreaks that may destroy oyster farms. Recently, however, scientists started researching AMPs as potential treatment for human disease.
Doctor Kate Summer and colleagues recently published interesting findings from their research in Springer Nature. The group sourced Australian oysters, extracted their hemolymph and separated AMP clusters (fractions). Each fraction was tested for its ability to inhibit S. pneumoniae growth and biofilm formation. Interestingly, one of these fractions was able to inhibit 100% of biofilm formation, being on par with ampicillin, the most effective against S. pneumoniae. The group then analysed the fraction for individual AMPs with this antimicrobial action, isolating 4 potential active proteins. It is currently being investigated if these can function separately as antibiotics, and at what dosages they would be safe for human use.
For the moment, scientists are considering the possibility of combining them with other antibiotics currently in the market to boost their function.
