A compound made by an ocean bacterium killed Naegleria fowleri, the so-called brain-eating amoeba, more quickly than the drug doctors currently rely on, according to laboratory experiments by scientists at UC San Diego. The molecule, rutamycin B, reached full strength against the amoeba within four hours in lab tests, compared with 16 hours for the standard drug amphotericin B, the university said in a release on Newswise.

These are early results from cells grown in dishes — the compound has not been tested in animals or people, and it is not a treatment anyone can receive today. The findings were published Oct. 26 as an early-access paper in the journal Marine Drugs.

The stakes are high for families who swim in lakes, rivers, and hot springs during hot weather. The infection the amoeba causes, primary amoebic meningoencephalitis or PAM, kills more than 97% of people who get it, and current treatment options are limited and harsh.

A Rare Infection That Starts in the Nose

Naegleria fowleri lives in warm fresh water and soil. Infection happens when contaminated water goes up the nose, usually during swimming, diving or other water play in summer, and the amoeba travels to the brain. According to the Centers for Disease Control and Prevention, "You cannot get a Naegleria fowleri infection from swallowing water containing the ameba." It does not spread from person to person.

The disease is rare. CDC reports 167 U.S. cases from 1962 through 2024, with only four survivors, and typically fewer than 10 cases a year. Most infections have been linked to lakes, rivers and hot springs in southern states, though cases have also occurred farther north after unusually hot stretches.

This summer brought fresh reminders. The Louisiana Department of Health confirmed an infection in August in an 8-year-old girl who had most likely been swimming in Lake Claiborne, and she later died, KNOE reported. North Carolina health officials also reported a teenager's death in late August.

Four Hours Versus Sixteen in the Lab

The research team, led by Anjan Debnath of UC San Diego's Skaggs School of Pharmacy and Pharmaceutical Sciences with chemists at the Scripps Institution of Oceanography, tested rutamycin B against five strains of Naegleria fowleri. It was potent at very low, nanomolar concentrations against all five, and it was 200 to 300 times more toxic to the amoeba than to mammalian cells, a measure called the selectivity index.

When combined with amphotericin B, the compound reached the same amoeba-killing effect at as little as 3% to 10% of its original dose, according to the university, without harming mammalian cells in the tests. Lower doses matter because amphotericin B can cause serious side effects, including kidney damage.

The researchers found that rutamycin B shuts down an enzyme the amoeba uses to make energy, called ATP synthase, and lowers its production of reactive oxygen molecules. The paper says the compound may target this enzyme, which means the mechanism is suggested by the data rather than fully proven.

Debnath said in the release that current PAM treatments often act too slowly or carry heavy toxicity, and that a faster, more selective compound could help stop the infection before it causes irreversible damage.

Limits of a Petri-Dish Result

The study has clear limits. All of the work was done in vitro, meaning on amoebae and cells in the lab, and only the abstract of the paper is public so far. The four-hour versus 16-hour comparison and the dose-reduction figure come from the university's release and could not yet be checked against the full text. Individual potency values, the mammalian cell types used and the identity of the bacterium that produces the compound have not yet been made public.

The biggest open question is whether rutamycin B can reach the brain — the team plans to test whether it crosses the blood-brain barrier and how it performs in living disease models. Many compounds that work in a dish fail at that stage because of toxicity, poor absorption or rapid breakdown in the body. The research was funded in part by the National Institutes of Health.

The Ocean as a Medicine Cabinet

Rutamycin B comes from marine bacteria studied by the Scripps Center for Marine Biotechnology and Biomedicine, a group that has spent decades collecting microbes from ocean environments. Marine microbes compete in crowded, chemically complex habitats and produce unusual molecules to defend themselves, which makes them a rich hunting ground for new antibiotics, cancer drugs and antiparasitic compounds.

William Fenical, a Distinguished Professor emeritus at Scripps and a pioneer of marine drug discovery, said in the release that the ocean holds a diverse library of chemicals and that scientists have "only just scratched its surface."Several approved medicines, including the cancer drug trabectedin, trace their origins to marine organisms.

For now, prevention remains the main protection. CDC advises holding your nose or wearing a nose clip when jumping or diving into fresh water, keeping your head above water in hot springs and avoiding digging in shallow, warm water where the amoeba is more likely to live. Anyone rinsing their sinuses should use distilled, sterile, or boiled and cooled tap water. Sudden severe headache, fever, nausea, and stiff neck within days of freshwater swimming warrant immediate medical care.

The bottom line: a marine compound showed fast, selective killing of Naegleria fowleri in lab tests and boosted the standard drug at low doses. It is years from any patient, and the next step is testing whether it works in living animals.

What Readers Want to Know

What is rutamycin B? A compound produced by a marine bacterium. In lab tests it killed Naegleria fowleri at very low doses and was far less toxic to mammalian cells.

Is it a cure for brain-eating amoeba infection? No. It has only been tested on cells in the lab, not in animals or people.

How do people get Naegleria fowleri? When warm fresh water containing the amoeba goes up the nose. Swallowing contaminated water does not cause infection.

How rare is the infection? CDC reports 167 U.S. cases from 1962 through 2024, usually fewer than 10 a year, with only four known survivors.

How can swimmers lower their risk? Hold your nose or use a nose clip in warm fresh water, keep your head above water in hot springs, and avoid stirring up sediment.

What symptoms should prompt a doctor visit? Severe headache, fever, nausea, vomiting, or stiff neck within days of freshwater swimming need urgent medical attention.