Arctic Actinobacteria Yield Novel Antivirulence Compounds Against E. coli

Researchers in Finland and Norway have developed innovative techniques to screen unknown bacterial substances for antivirulence activity. These substances, sourced from actinobacteria found in Arctic Sea crustaceans, hold promise for combating bacterial infections without promoting resistance.

Researchers have discovered two promising compounds with potent antivirulence and antibacterial properties against enteropathogenic E. coli. These findings suggest that exploring novel ecosystems for new antibacterial candidates could help address the global antibiotic crisis.

Antibiotics are crucial for modern medicine, protecting patients from serious infections during surgeries or when dealing with open wounds. However, the rise of antibiotic-resistant bacterial strains, coupled with the slow discovery of new antibiotics, has created a global crisis.

There's hope, though: Actinobacteria found in soil are the source of 70% of currently approved antibiotics, yet many environments remain unexplored. Focusing on actinobacteria in different habitats could be a fruitful strategy.

This approach is particularly promising if it leads to compounds that reduce bacteria's ability to cause disease (virulence) rather than killing them outright. These antivirulence drugs are less likely to drive resistance in targeted bacteria and tend to have fewer side effects.

Here we show how advanced screening assays can identify antivirulence and antibacterial metabolites from actinobacteria extracts, We discovered a compound that inhibits enteropathogenic E. coli (EPEC) virulence without affecting its growth, and a growth-inhibiting compound, both in actinobacteria from the Arctic Ocean.”

Dr. Päivi Tammela, Professor and Study Corresponding Author, University of Helsinki

Automated Screening of Candidate Compounds

A novel set of techniques created by Tammela and colleagues allows for the simultaneous testing of hundreds of unidentified chemicals for antivirulence and antibacterial activity. They selected an EPEC strain that, particularly in underdeveloped nations, causes severe and occasionally fatal diarrhea in children under five.

EPEC produces illness by attaching itself to human intestinal cells. After adhering to these cells, EPEC kills the host cell by injecting so-called “virulence factors” into it, which control its molecular machinery.

The four actinobacteria species that the tested chemicals were obtained from were isolated from invertebrates that were sampled in the Arctic Sea off the coast of Svalbard in August 2020 during a trip led by the Norwegian research vessel “Kronprins Haakon.”

Following their culture, the bacteria's cells were removed, and their contents were divided into fractions. The next test that each fraction underwent in vitro was the adhesion of EPEC to cultivated colorectal cancer cells.

The researchers discovered two unidentified substances with potent antivirulence or antibacterial action. One came from an unidentified strain of Rhodococcus (T091-5), and the other from an unidentified strain of Kocuria (T160-2).

Powerful Antivirulence Effects

The substances demonstrated two complementary forms of biological action. First, they prevented EPEC bacteria from creating what are known as “actin pedestals,” which is a crucial stage in the pathogen's attachment to the host's intestinal lining. Second, they prevented EPEC from attaching to the host cell's surface Tir receptor, which is a prerequisite for altering the internal processes of the cell and causing illness.

In contrast to the compounds from T160-2, the molecule from T091-5 did not inhibit the development of EPEC bacteria. Therefore, of the two strains, T091-5 is the most promising since EPEC is less likely to eventually develop resistance to its antivirulence actions.

The investigators concluded, using sophisticated analytical techniques, that the active component from T091-5 was most likely a phospholipid, a family of fatty phosphorus-containing molecules vital for cell metabolism.

The next steps are the optimization of the culture conditions for compound production and the isolation of sufficient amounts of each compound to elucidate their respective structures and further investigate their respective bioactivities.”

Dr. Päivi Tammela, Professor and Study Corresponding Author, University of Helsinki