The growing threat of antibiotic-resistant bacteria is seeing scientists get more and more creative in their search for new drugs that might help us maintain the upper hand. Tobacco flowers, rattlesnake venom and Brazilian berries are just a few of the places to turn up exciting new antibiotic candidates of late, and now researchers have uncovered what they say is a potential goldmine of antibiotics in the form of fish slime.

The mucus that coats the surfaces of fish mightn’t seem like a great place to search for life-saving medicines, but this sticky slime plays a vital role in helping fish fend off a host of fungi, bacteria and dangerous pathogens by snaffling microbes before they can do their dirty work.

“Fish mucus is really interesting because the environment the fish live in is complex,” says Molly Austin, an undergraduate chemistry student at Oregon State University and member of the research team. “They are in contact with their environment all the time with many pathogenic viruses.”

That the slime is also known to hold vast amounts of polysaccharides and peptides with antibacterial properties was further impetus for the researchers to explore its antibiotic potential. To do this, they worked with mucus swabbed from juvenile deep-sea and surface dwelling fish caught off the coast of Southern California.

Younger fish were chosen for their underdeveloped immune systems and thicker layers of mucus, in the hope that they would offer a higher abundance of active bacteria. The team isolated and then screened 47 different strains of bacteria, and uncovered a number of new antibiotic candidates.

Five of the extracts strongly repelled the advances of methicillin-resistant S. aureus (MRSA), as did bacteria taken from the mucus of a particular Pacific pink perch. That same bacteria inhibited activity of a colon carcinoma cell line, and three others inhibited the pathogenic fungus Candida albicans.

While all of this is exciting, the researchers aren’t getting too carried away. Before they call jackpot on the antibiotic potential of fish slime, they will seek to determine whether these particular bacteria are a typical and essential part of the animal’s microbiomes, or had simply happened to hop on for a ride at the time of the swabbing.

And this kind of work could have ripple effects beyond simply leading to new drugs that keep humans healthy. Better understanding of fish microbiomes could be of huge assistance to the conservation of marine life, which is under increasing strain from overfishing, plastic pollution, and warming oceans.

The team is presenting the research at the American Chemical Society Spring 2019 National Meeting & Exposition this week.

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