Scientists identify key antimicrobial peptides with activity against SRS bug

In the race to reduce the use of antibiotics in salmon farming, a new study by Chilean scientists identified antimicrobial peptides with potent inhibitory activity against the growth of Piscirickettsia salmonis, the bacterium that causes salmonid rickettsial septicaemia (SRS), reports Fish Farming Expert's Chilean sister site, Salmonexpert.cl.

Unlike traditional antibiotics, which usually interfere with specific metabolic processes, certain peptides act much more directly: they attack the bacterial membrane, compromising its integrity and causing it to collapse.

For this reason, the research evaluated the effect of 13 compounds, 11 cationic antimicrobial peptides (AMPs), along with two non-peptide reference compounds, florfenicol and chlorhexidine, against P. salmonis LF-89 during an incubation period of seven days.

Experts discovered that the most effective peptides share a key structural feature, a shape known as a beta-hairpin. Within this group, two names stood out strongly: tachyplecin I and protegrin-1, both capable of significantly inhibiting the growth of P. salmonis under controlled conditions.

Interestingly, not all peptides function the same way, even if they are similar. While tachyplecin I showed a more compact structure, allowing it to insert more efficiently into the bacterial membrane, protegrin-1 stood out for generating multiple interactions with lipids, weakening the structure from different points.

Promising candidates

To better understand this process, the researchers used molecular dynamics simulations, a tool that allows them to observe how these molecules interact with the bacterial surface. This confirmed that the primary target is the membrane, a critical point for the pathogen's survival.

“Both peptides adsorbed to the membrane and showed distinct interfacial behaviour: tachyplecin I remained more conformationally compact, while protegrin-1 formed more peptide-lipid contacts and hydrogen bonds, underscoring that monomeric adsorption metrics and growth inhibition potency are not interchangeable,” the authors explained.

From a production standpoint, this mechanism offers a significant advantage by targeting essential and less variable structures, where these peptides could potentially generate less resistance selection pressure compared to conventional antibiotics.

With these results, the researchers determined that the molecular dynamics results support and prioritise tachyplecin I and protegrin-1 as candidates with membrane activity for further studies against this pathogen.

“Specific studies of safety, serum stability, host cell selectivity and in vivo efficacy are justified as the next stage of translational evaluation,” the experts concluded.

Read the study titled “Comparative in vitro screening identifies beta-hairpin antimicrobial peptide leads against Piscirickettsia salmonis, supported by membrane-level molecular dynamics,” here.