New Antibiotic Could Combat Multidrug-Resistant Superbugs

Antibiotic resistance is a major public health problem. Few new molecules are in development, but a new antibiotic called clovibactin brings hope.

This drug, isolated from bacteria that haven't previously been studied, seems to be capable of combating multidrug-resistant "superbugs" thanks to unusual mechanisms of action.

The drug was discovered and has been studied by scientists from Utrecht University in the Netherlands, the University of Bonn in Germany, the German Center for Infection Research, Northeastern University in Boston, and NovoBiotic Pharmaceuticals in Cambridge, Massachusetts.

Their research was published in Cell.

"Since clovibactin was isolated from bacteria that could not be grown before, pathogenic bacteria have not seen such an antibiotic before and had no time to develop resistance," said Markus Weingarth, MD, PhD, researcher in Utrecht University's chemistry department, in a press release.

Microbial "Dark Matter"

Researchers isolated clovibactin from sandy soil from North Carolina and studied it using the iCHip device, which was developed in 2015. This technique allowed them to grow "bacterial dark matter," so-called unculturable bacteria, which compose a group to which 99% of bacteria belong.

This device also paved the way for the discovery of the antibiotic teixobactin in 2020. Teixobactin is effective against gram-positive bacteria and is one of the first truly new antibiotics in decades. Its mechanism of action is like that of clovibactin.

Combats Resistant Bacteria

In the Cell article, the researchers showed that clovibactin acts via several mechanisms and that it successfully treated mice infected with the superbug Staphylococcus aureus.

Clovibactin exhibited antibacterial activity against a broad range of gram-positive pathogens, including methicillin-resistant S aureus, daptomycin-resistant and vancomycin-resistant S aureus strains, and difficult-to-treat vancomycin-resistant Enterococcus faecalis and E faecium (vancomycin-resistant enterococci). Escherichia coli was only marginally affected "compared with an outer membrane deficient E coli WO153 strain, probably reflecting insufficient penetration of the compound," the authors write.

Original Mechanism of Action

Clovibactin acts not on one but three molecules, all of which are essential to the construction of bacterial walls: C55PP, lipid II, and lipid IIIWTA, which are from different cell wall biosynthetic pathways. Clovibactin binds to the pyrophosphate portion of these precursors.

"Clovibactin wraps around the pyrophosphate like [a] tight glove, like a cage that encloses its target," said Weingarth. This is what gives clovibactin its name, which is derived from Greek word klouvi, meaning cage.

The remarkable aspect of clovibactin's mechanism is that it only binds to the immutable pyrophosphate that is common to cell wall precursors, but it also ignores the variable sugar-peptide part of the targets. The bacteria therefore has a much harder time developing resistance against it. "In fact, we did not observe any resistance to clovibactin in our studies," Weingarth confirmed.

Upon binding the target molecules, it self-assembles into large fibrils on the surface of bacterial membranes. These fibrils are stable for a long time and thereby ensure that the target molecules remain sequestered for as long as necessary to kill bacteria.

Few Side Effects

Because of the mechanism of action of the antibiotic, few side effects are predicted. Indeed, clovibactin targets bacteria cells but not human cells.

"Since these fibrils only form on bacterial membranes and not on human membranes, they are presumably also the reason why clovibactin selectively damages bacterial cells but is not toxic to human cells," said Weingarth.

Other studies ― in particular, studies in humans ― are needed before the antibiotic can be considered a potential treatment. In the meantime, regulations regarding the proper use of antibiotics must continue to be applied to limit antibiotic resistance.

In 2019, 4.95 million deaths worldwide were associated with bacterial antimicrobial resistance, including 1.27 million deaths directly attributable to bacterial antimicrobial resistance. If this trend continues without new medicines becoming available to treat bacterial infections, it is estimated that by 2050, 10 million people will die every year from antimicrobial drug resistance.

This article was translated from the Medscape French Edition.