An untapped source of potential new antibiotics

While current antibiotics are becoming less effective against multidrug-resistant pathogens, researchers are looking for alternatives in some unlikely places. A team has now identified bacteria with promising antibiotic activity against known pathogens – even dangerous organisms, such as the microbe responsible for MRSA infections – in the protective mucus that covers young fish.

The researchers will present their findings today at the 2019 Spring National Meeting and Exposition of the American Chemical Society (ACS).

"For us, any microbe present in the marine environment that could provide a new compound deserves to be explored," says Sandra Loesgen, Ph.D., the group's lead researcher.

According to Loesgen, who works at Oregon State University, while new chemical reagents have been found in the human microbiome, the marine equivalent remains relatively unstudied. One of the potential gold mines of microbes is the mucus that covers the surface of fish. This viscous substance protects the fish from bacteria, fungi and viruses in its environment by trapping microbes before they cause infections. The sludge is also rich in polysaccharides and peptides known to have antibacterial activity.

"The fish mucus is really interesting because the environment in which the fish live is complex," says Molly Austin, a chemistry undergraduate student in chemistry at Loesgen's lab, who has conducted some of the studies. "They are in constant contact with their environment with many pathogenic viruses." According to Austin, it would be interesting to know if anything in the mucus, which protects the fish, could actually help protect humans.

Collaborator Erin (Misty) Paig-Tran, Ph.D., from California State University in Fullerton, provided mucus from juvenile fish caught off the coast off the coast Southern California. The team examined young fish because their immune system was less developed and more mucus on the outside of their scales that might contain a higher concentration of active bacteria than adult fish.

Loesgen, Austin and graduate student Paige Mandelare isolated and screened 47 different strains of slime bacteria. Five strongly inhibited bacterial extracts resistant to methicillin S. aureus (MRSA) and three inhibited Candida albicans, a pathogenic fungus for humans. A mucus bacterium from a Pacific pink perch showed strong activity against MRSA and against a cell line of colon carcinoma. Austin is now focusing his work on the Pseudomonas aeruginosa, a Gram-negative bacterium derived from this fish, to study the many natural products and antibiotics potentially interesting phenazine that this bacterium makes.

Team members are interested in new sources of antibiotics to help humans, but they are also looking for other ways to apply this knowledge. For example, the study of fish mucus could also help reduce the use of antibiotics in aquaculture by enabling the development of better antibiotics specifically targeting microbes. attaching to certain types of fish.

But first, researchers want to understand more fundamental issues. For example, "we do not even know what a healthy microbiome is," says Loesgen. She explains that it is unclear whether the bacteria they studied in the fish drool were typical of their microbiomes and were protecting their hosts, or if these bacteria had just taken the train from these fish . Learn more about the microbiomes of healthy fish and the impact that environmental factors may have on the Pacific could help inform conservation efforts, said the researchers.

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More information:
Diving into the Pacific Fish Microbiome: Exploring Antibiotics in a Unique Ecosystem, Spring National Exposition and Meeting of the American Chemical Society (ACS).