Discovery of Antimicrobial Peptides That Can Accelerate the Diagnostics of Slow-Growing Mycobacteria Including Mycobacterium Tuberculosis by Culture

Antimicrobial peptides (AMPs) can directly kill Gram-positive bacteria, Gram-negative bacteria, mycobacteria, fungi, enveloped viruses and parasites. At sublethal concentrations some AMPs and also conventional antibiotics can stimulate bacteria response to increase their resilience, also called the hormetic response. That can include stimulation of growth, mobility, and biofilm production. Here, we have discovered AMPs that stimulate the growth of certain mycobacteria. Peptide 14 for example showed growth stimulating effect on M. tuberculosis, M. bovis, M. avium subsp. paratuberculosis (MAP), M. marinum, M. avium-intracellulare, M. celatum and M. abscessus. The effect was more pronounced at low bacterial inocula. The peptides induce a faster transition from the lag phase to the log phase and keep the bacteria longer in the log phase before entering the stationary phase compared to non treated control. In some cases, an increase in the division rate was observed. An initial screen using MAP and a collection of 75 peptides revealed 13 peptides with a hormetic effect. For M. tuberculosis a collection of 25 artificial peptides were screened and 9 were found to reduce the time to positivity (TTP), improving growth. A screen of 43 naturally occurring peptides, 11 fragments of naturally occurring peptides and 5 designed peptides, all taken from the APD3, identified a further 44 peptides that also lowered TTP by at least 5%. Lasioglossin LL-III (Bee) and Ranacyclin E (Frog) were the most active natural peptides, the human cathelicidin LL37 fragment GF-17 and a porcine cathelicidin protegrin-1 fragment was the most active fragment of naturally occurring peptides. Peptide 14 showed growth-stimulating activity between 50 ng/ml and 10 µg/ml whereas the stability-optimised peptide 14D had a narrow activity range of 0.1 - 1 µg/ml. Peptides identified in this study are now part of novel products improving the diagnosis of mycobacteria in humans and animals.