Slimy fish could aid the search for new drugs | Science News for Students

Slimy fish could aid the search for new drugs

Their protective coating is chock-full of bacteria — and maybe antibiotics
May 29, 2019 — 6:45 am EST
An underwater photo of a school of fish swimming past a reef. 

Researchers are studying the bacteria that live on fish in the Pacific Ocean in search of molecules that could be turned into drugs.

strmko/iStock/Getty Images Plus

ORLANDO, Fla. — If you’ve ever tried to hold a fish, you know how slippery they are. Their slick, slimy coating doesn’t just help them wriggle away from you. It also helps protect them against tiny threats like germs. Now scientists are searching that fish slime for molecules that might one day help protect people against infections, too.

Sandra Loesgen is a chemist at Oregon State University in Corvallis. Her research aims to find new antibiotic drugs for people. That’s important because many disease-causing microbes no longer respond to current drugs.

One of Loesgen’s colleagues, Erin (Misty) Paig-Tran, got her interested in fish. Paig-Tran is a marine biologist at California State University in Fullerton. Paig-Tran wondered if something in fish slime — especially on young, growing fish — might help protect them in the harsh environment of the sea. Many researchers have looked in the ocean for new drugs, but not many have looked at the bacteria that live on fish. Together, Paig-Tran and Loesgen decided to scout for bacteria living in the slime.

Paig-Tran sent Loesgen swabs of slime from 17 species of juvenile fish. Two students on Loesgen’s team searched the goo for bacteria that might help the fish.

Molly Austin is an undergraduate researcher and Paige Mandelare is a graduate student. They smeared the slimy swabs on petri dishes. These held a gel-like substance, called agar, and nutrients that bacteria can eat. Then the students waited to see if the bacteria from the slime would grow.

They did. And as they grew, each type looked slightly different. Some grew as blue-green streaks across a dish of agar. Others looked like orange splotches. The researchers also used a microscope to look at each microbe’s size and shape. Austin and Mandelare then used these features to classify each type of bacteria. In total, they found 47 different types in the sampled slime.

Researchers Paige Mandelare and Molly Austin holding petri dishes with bacteria grown from fish slime
Researchers Paige Mandelare (left) and Molly Austin hold petri dishes of bacteria grown from fish slime.
Loesgen Lab

Germs fighting germs

Next, Austin tested the bacteria to see if they might be useful for killing human pathogens (PATH-oh-jenz) — germs that cause disease. A surprising number of those bacteria she tested — about half — helped fight a pathogen called MRSA. (That’s short for methicillin-resistant Staphylococcus aureus.) MRSA can cause a serious infection because it is tough to treat. Many common antibiotic drugs do not kill it.

Five strains (or types) of bacteria from a pink surfperch seemed especially good at killing MRSA.

Austin studied one such strain more closely. She wanted to figure out how it might tackle the dangerous germ. It makes molecules called phenazines (FEN-uh-zeenz), she found. And these can kill other bacteria. Some scientists think phenazines might be useful as human drugs.

Loesgen’s team presented this work here at the spring national meeting of the American Chemical Society on March 31.

Next, her team wants to know if those phenazine-making bacteria normally live on pink surfperch. (The one Austin found could have just hitched a ride — what Loesgen calls a “one-hit wonder.”) The lab just got 10 more pink surfperch. If those fish also harbor the same strain, that may mean that it plays an important role in their slime ecosystem. And if the strain is there, the researchers will check if it makes phenazines on those fish, too.

Roger Linington is a chemist at Simon Fraser University in Vancouver, Canada. He studies bacterial communities inside fish, such as in their guts. The microbes in many fish species have not yet been explored, he notes. Loesgen’s approach of looking at slime from young fish is very thoughtful, he says.

Linington was not surprised that Loesgen’s group found so many microbes in the fish slime. “We know that niche environments often harbor a surprising array of different microorganisms,” he says. And finding even one MRSA-killing strain is “a very good result.”

There's a lot we still don't know about how microbes affect the health of their hosts, whether human or fish. But fish-dwelling bacteria may prove a promising source of new antibiotics, Loesgen says. So far, they’ve been overlooked, she adds. “We need to have much more effort in that area to isolate the bacteria and understand their function."

So far, the team has only found well-known bacteria and molecules. But as they explore more types of bacteria in the slime, Loesgen hopes to turn up something new and useful.

Power Words

(more about Power Words)

agar     A gelatinous material made from certain marine algae used as a material (and food source) in which to grow bacteria.

antibiotic     A germ-killing substance, usually prescribed as a medicine (or sometimes as a feed additive to promote the growth of livestock). It does not work against viruses.

array     A broad and organized group of objects. Sometimes they are instruments placed in a systematic fashion to collect information in a coordinated way. Other times, an array can refer to things that are laid out or displayed in a way that can make a broad range of related things, such as colors, visible at once. The term can even apply to a range of options or choices.

bacteria     (singular: bacterium) Single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals). Bacteria are one of the three domains of life on Earth.

bacterial     Having to do with bacteria.

biology     The study of living things. The scientists who study them are known as biologists.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

colleague     Someone who works with another; a co-worker or team member.

current     A fluid — such as of water or air — that moves in a recognizable direction. (in electricity) The flow of electricity or the amount of charge moving through some material over a particular period of time.

ecosystem     A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra. The term can also be applied to elements that make up some an artificial environment, such as a company, classroom or the internet.

environment     The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).

function     A relationship between two or more variables in which one variable (the dependent one) is exactly determined by the value of the other variables.

gel     A gooey or viscous material that can flow like a thick liquid.

germ     Any one-celled microorganism, such as a bacterium or fungal species, or a virus particle. Some germs cause disease. Others can promote the health of more complex organisms, including birds and mammals. The health effects of most germs, however, remain unknown.

graduate student     Someone working toward an advanced degree by taking classes and performing research. This work is done after the student has already graduated from college (usually with a four-year degree).

gut     An informal term for the gastrointestinal tract, especially the intestines.

host      (in biology and medicine) The organism (or environment) in which some other thing resides. Humans may be a temporary host for food-poisoning germs or other infective agents.

infection     A disease that can spread from one organism to another. It’s usually caused by some type of germ.

juvenile     Young, sub-adult animals. These are older than “babies” or larvae, but not yet mature enough to be considered an adult.

marine biologist     A scientist who studies creatures that live in ocean water, from bacteria and shellfish to kelp and whales.

methicillin-resistant Staphylococcus aureus (or MRSA)     Methicillin is a widely used antibiotic. And Staph aureus is a bacterium that can cause boils, food poisoning, toxic-shock syndrome and more. These bacteria sicken (and sometimes kill) by releasing into the body potent natural poisons, called toxins.

microbe     Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

microscope     An instrument used to view objects, like bacteria, or the single cells of plants or animals, that are too small to be visible to the unaided eye.

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

niche     A small or narrow pocket that sets something apart, or perhaps offers a region of protection. (In ecology) The term for the role that an organism plays in its community.

nutrient     A vitamin, mineral, fat, carbohydrate or protein that a plant, animal or other organism requires as part of its food in order to survive.

pathogen     An organism that causes disease.

sea     An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.

society     An integrated group of people or animals that generally cooperate and support one another for the greater good of them all.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

strain     (in biology) Organisms that belong to the same species that share some small but definable characteristics. For example, biologists breed certain strains of mice that may have a particular susceptibility to disease. Certain bacteria or viruses may develop one or more mutations that turn them into a strain that is immune to the ordinarily lethal effect of one or more drugs.

undergraduate     A term for a student who is attending college, and has not yet graduated.


Meeting: M. Austin, P.E. Mandelare, and S. Loesgen. Diving into the Pacific fish microbiome: Exploration of antibiotics in a unique ecosystem. American Chemical Society Spring National Meeting. March 31, 2019. Orlando, Fla.