As antibiotic resistance continues to make headlines, researchers are ramping up their search for ways to turn the tide. A recent study focuses on fish slime.

According to the Centers for Disease Control and Prevention (CDC), antibiotic resistance is "one of the biggest public health challenges of our time." Each year in the United States, an estimated 2 million people contract an antibiotic-resistant infection. Of these people, at least 23,000 die. Medical researchers urgently need to address this significant and growing issue.

Scientists are digging into the hidden corners of the planet in the hope of finding new and unusual organisms that might help defeat this foe. For instance, researchers recently found a new species of bacteria in a soil sample from Northern Ireland in the United Kingdom. According to Paul Dyson, one of the co-authors of the resulting paper, this bacterium "is effective against four of the top six pathogens that are resistant to antibiotics."

Other scientists have delved into the dark underworld of Canada's cave systems to examine biofilms for their potential use against antibiotic-resistant pathogens. Researchers from Oregon State University in Corvallis and California State University in Fullerton led the most recent foray into unexplored reservoirs of bacteria, concentrating their attention on the protective slime, or mucus, that coats fish. The researchers recently presented their findings at the American Chemical Society Spring 2019 National Meeting & Exposition.

Why fish slime?

This gloopy coating is of great use to fish because it traps and destroys pathogens in the environment, such as bacteria, fungi, and viruses. The slime contains novel polysaccharides and peptides, some of which have antibacterial activity.

One of the researchers, Molly Austin, explains that fish mucus is particularly interesting because fish are in constant contact with a complex environment that is dense with potential microbial enemies. As the authors write, "fish cohabitate with a multitude of bacteria and viruses but often resist deadly infections." It is worth finding out whether fish's protective mechanisms might also protect humans.

The marine environment remains relatively unstudied, according to the principal investigator Sandra Loesgen, PhD, "For us, any microbe in the marine environment that could provide a new compound is worth exploring."

Erin (Misty) Paig-Tran, PhD, who is from California State University, supplied the scientists with fish mucus from both bottom-dwelling and surface-dwelling fish off the coast of California. The team chose to focus on younger fish because they tend to have thicker mucus layers. The extra mucus is necessary because their immune systems are relatively undeveloped, which means that they need additional protection.

Mucus vs MRSA

In all, the researchers isolated 47 different strains of bacteria from the mucus. Of these, five were highly effective against methicillin-resistant Staphylococcus aureus (MRSA), and three were effective against Candida albicans, a fungus that is pathogenic to humans.

The slime that was from the skin of Pacific pink perch worked particularly well against MRSA, and interestingly, it also showed strong activity against colon carcinoma cells. For future studies, Austin has chosen to hone in on one specific species of bacteria that the team found on the Pacific pink perch—Pseudomonas aeruginosa. According to Austin, P. aeruginosa produces antibiotics that could be useful in the future.

For example, these bacteria produce interesting phenazines, which are a well-studied group of compounds that have "broad-spectrum antibiotic properties." Several bacterial species produce phenazines.

Aside from the pressing issue of antibiotic resistance, the scientists have other ideas about potential uses for fish slime. For instance, they think that fish mucus could help reduce the number of antibiotics that fish farms use. They believe that it would be possible to achieve this by designing antibiotics to target the microbes that are present in the mucus of specific fish.

Challenges ahead

Any discoveries that have the potential to help humanity in the war against antibiotic resistance are exciting, but we still need to overcome an array of challenges and answer many questions before scientists can create usable interventions.

For instance, the researchers conducted this study on cells in a laboratory rather than in a living animal. Chemical activity in an isolated environment can differ significantly from that in a living, breathing human.

As an example, in an earlier study that Loesgen worked on, the scientists extracted a compound called merochlorin A from marine bacteria. When they tested it in the lab, the metabolite was effective against multidrug-resistant MRSA. However, when they tested it again in the presence of human serum, it lost its activity. In other words, it could not be effective following its injection into blood vessels. This finding does not necessarily mean that merochlorin A will be useless though. For instance, it might be useful for topical application or to coat biomedical devices. Another option is to find a way to modify the compound chemically so that it works more effectively, which would, of course, be a long and technical path to tread.

In conclusion, these results are interesting and offer a new avenue to explore. Anything that provides insight into the antibiotic resistance conundrum is welcome, but it might be some time before fish slime saves humanity.