Leishmania parasites are a major public health problem worldwide. Effective treatment of leishmaniasis is hampered by the high incidence of adverse effects to traditional drug therapy and the emergence of resistance to current therapeutics. A vaccine is currently not available. Host defense peptides have been investigated as novel therapeutic agents against a wide range of pathogens. Here we demonstrate that the antimicrobial peptide LL-37 and the three synthetic peptides E6, L-1018, and RI-1018 exhibit leishmanicidal activity against promastigotes and intramacrophage amastigotes of Leishmania donovani and Leishmania major. We also report that the Leishmania protease/virulence factor GP63 confers protection to Leishmania from the cytolytic properties of all L-form peptides (E6, L-1018, and LL-37) but not the D-form peptide RI-1018. The results suggest that RI-1018, E6, and LL-37 are promising peptides to develop further into components for antileishmanial therapy. Protozoan parasites belonging to the genus Leishmania are a global health problem, especially in resource-poor areas of Africa, Asia, the Americas, and Europe. Leishmania parasites cause leishmaniasis, which is classified as a neglected tropical disease. An estimated 20 million people are affected worldwide, with 1.3 million new cases each year and 20,000 to 30,000 deaths occurring annually (1). Transmission of Leishmania to the mammalian host occurs during a blood meal of infected sand flies of the genera Phlebotomus or Lutzomyia (2). Clinical manifestations of leishmaniasis vary depending on the infecting Leishmania strain. Leishmania major primarily causes a cutaneous form, with infected individuals developing characteristic but self-healing open sores. In contrast, Leishmania donovani infection can lead to a more invasive visceral leishmaniasis, also called kala-azar, which is potentially fatal if untreated.Leishmania parasites have a complex, digenetic life cycle, alternating between an extracellular, flagellated promastigote form that develops in the gut of a sand fly, and an intracellular nonmotile amastigote form that replicates in the macrophages of mammalian hosts.To date, no Leishmania vaccine is available, and current therapy is based on traditional pentavalent antimonials with considerable adverse side effects (3). Recently, oral miltefosine was approved by the U.S. Food and Drug Administration, while liposomal amphotericin B is in clinical trials for treatment against cutaneous and visceral leishmaniasis (4, 5). In addition, the increasing incidence of drug resistance in Leishmania renders currently available treatment options ineffective and further drives the need for new therapeutic agents.Cationic host defense (antimicrobial) peptides have been identified as an important part of the host innate immune response in all living species and have broad-spectrum antimicrobial, including antileishmanial, activity (6, 7). The actions of host defense peptides range from direct killing of invading pathogens to immune response modulation (8). A v...

Summary Co‐occurring microorganisms have been proved to influence the performance of each other by metabolic means in nature. Here we generated a synthetic fungal‐bacterial community comprising Penicillium citrinum and Pseudomonas aeruginosa employing the previously described membrane‐separated co‐culture device. By applying a newly designed molecular networking routine, new citrinin‐related metabolites induced by the fungal‐bacterial cross‐talk were unveiled in trace amounts. A mechanically cycled co‐culture setup with external pumping forces accelerating the chemically interspecies communication was then developed to boost the production of cross‐talk‐induced metabolites. Multivariate data analysis combined with molecular networking revealed the accumulation of a pair of co‐culture‐induced molecules whose productions were positively correlated to the exchange rate in the new co‐cultures, facilitating the discovery of the previously undescribed antibiotic citrinolide with a novel skeleton. This highly oxidized citrinin adduct showed significantly enhanced antibiotic property against the partner strain P. aeruginosa than its precursor citrinin, suggesting a role in the microbial competition. Thus, we propose competitive‐advantage‐oriented structural modification driven by microbial defence response mechanism in the interspecies cross‐talk might be a promising approach in the search for novel antibiotics. Besides, this study highlights the utility of MS‐based metabolomics as an effective tool in the direct biochemical analysis of the community metabolism.