Leipzig, Germany. Research scientists have found that antimicrobial peptides are an attractive alternative for eliminating pathogenic bacteria that are increasingly immune to established antibiotic treatments.

Data from the World Health Organization (WHO) show that nearly half-a-million people were infected in 2010 with a virulent strain of tuberculosis which is resistant to many conventional antibiotics — killing one third of those who had been infected.


Increasing rates of bacterial resistance are expected to grow as a consequnce of non-compliant dosage. Even a single antibiotics dose exposes a patient to a greater risk of resistant organisms, with effects that can last up to a year. Increased hand washing by hospital staff can decreased the rates of infection, but compliance is inconsistent and not yet widespread. Dosage precision and effective hygiene are important to treating the critically ill and reducing infections rates from surgery.



Antimicrobial peptides have prevented the growth of Streptococcus mutans bacteria, which causes tooth decay. Image © Fraunhofer IZI.

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The World Health Organization (WHO) states that the growing spread of resistant pathogens is attributable to the indiscriminate use of penicillin and other antibiotics.

Director-general Margaret Chan points out that if measures are not taken quickly, it may soon not be possible to treat many frequently occurring infections.Dr. Andreas Schubert, group manager at the Fraunhofer Institute for Cell Therapy and Immunology IZI, says "We have already identified 20 of these short chains of amino acids which kill numerous microbes, including enterococci, yeasts and molds, as well as human pathogenic bacteria such as Streptococcus mutans, which is found in the human oral cavity and causes tooth decay. Even the multi-resistant hospital bug Staphylococcus aureus is not immune, and in our tests its growth was considerably inhibited."

From familiar fungicidal and bactericidal peptides the research scientists produced sequence variations and tested them in vitro on various microbes. Putrefactive bacteria, for example, were incubated for an hour with the artificially produced antimicrobial peptides. As the new peptides contain cationic amino acid residues, they can bond with the negatively charged bacterial membrane and penetrate it.

In their tests the research scientists compared the survivability of the pathogens with an untreated control. The experts focused on peptides with a length of less than 20 amino acids. "Antibiotic peptides unlock their microbicidal effect within a few minutes. They also work at a concentration of less than 1 µM, compared with conventional antibiotics which require a concentration of 10 µM," states Schubert, summarizing the test results.

"The spectrum of efficacy of the tested peptides includes not only bacteria and molds but also lipid-enveloped viruses. Another key factor is that the peptides identified in our tests do not harm healthy body cells," the scientist explains.

The food sector could benefit from the antimicrobial peptides given that the bacterial contamination of food products costs the industry billions every year. Fresh lettuce and other salad greens, for example, are badly contaminated by yeasts and molds.

The shelf-life of foodstuffs could be improved by adding antimicrobial peptides during the production process. "This is a definite possibility because the short-chain peptides tested during the project do not exhibit any allergological risk on being added to foodstuffs," says Schubert.

The research scientist is convinced that many possible applications exist, including in machinery manufacture — for instance to keep hydraulic fluids free of microbes. As a next step the expert and his team are going to test the antimicrobial peptides in vivo on infection models.

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