Antimicrobial peptides: an alternative to conventional antibiotics?

Growing concern that the over-use of antibiotics in livestock could be leading to antibiotic resistance is driving interest in alternatives to conventional therapeutic antibiotics.

Antibiotic resistance is becoming particularly problematic for pig breeders using artificial insemination – the method most commonly used in assisted reproductive technology worldwide. Freshly retrieved boar ejaculates always contain bacteria, which are detrimental to the quality and longevity of the liquid preserved sperm. The addition of antibiotics to liquid semen is required by law and inhibits the growth of these bacteria. However, many types of bacteria quickly develop resistance to the antibiotics, which is why there is a need for new antimicrobial alternatives.

Antimicrobial peptides​

In recent studies, antimicrobial peptides have received considerable attention as candidates to overcome bacterial resistance.

“Antimicrobial peptides are naturally occurring molecules with a broad spectrum of antimicrobial activity that rapidly kills their target cells,”​ explained the researchers, writing in the online journal PLOS ONE.

These molecules are naturally occurring amino acid compounds, are toxic to bacteria and can be found in nearly all organisms as a first defence against germs. Roughly 5,000 antimicrobial peptides have been discovered, predicted or synthesised so far, most of which do not induce resistant mutant bacteria strains.

Study details​

Scientists from the IZW investigated the effect of two antimicrobial peptides (c-WWW and c-WFW) in cooperation with the Leibniz Institute of Molecular Pharmacology (FMP) and the Institute for Reproduction of Farm Animals Schoenow e.V.  The aim of the study was to evaluate whether selected synthetic antimicrobial peptides could be useful as substitutes for conventional antibiotics used in liquid sperm preservation.

Firstly they were able to show that antimicrobial peptides fight bacteria effectively in test tubes. Then they showed that two of the investigated compounds suppressed bacterial growth in liquid preserved semen preparations if combined with a small amount of the antibiotic ‘gentamicin’.

“Our results demonstrate activity of synthetic cationic antimicrobial peptides against different Gram-negative and Gram-positive bacteria in vitro. Furthermore, c-WWW and c-WFW suppressed bacterial growth in semen preparations in situ, especially when combined with a small concentration of gentacimin,”​ wrote the researchers.

Decreased antibiotic concentrations​

These findings suggest that antimicrobial peptides could offer a means of reducing the use of conventional antibiotics in pig breeding.

“Antimicrobial peptides do not offer a complete alternative for traditional antibiotics in liquid sperm preservation, but allow a substantial reduction in their concentration,”​ said Dr Karin Müller from the IZW. “This is a benefit for people as well, as the occurrence of resistance will be reduced if fewer antibiotics are used.”​

Co-researcher Dr Margitta Dathe from the FMP added that other applications for antimicrobial peptides were conceivable.

“Antimicrobial peptides could be used for the preservation of other cells as well. Furthermore, special antimicrobial peptides for the treatment of superficial infections could be developed,” ​she said.

Source: PLOS ONE 9(6): e100490. Doi: 10.1371/journal.pone.0100490

“Cationic synthetic peptides: assessment of their antimicrobial potency in liquid preserved boar semen”​

Authors: S. Speck, A. Courtiol, C. Junkes, M. Dathe, K. Mueller, M. Schulze