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Summary Lyme disease is on the rise. Caused by a spirochete Borreliella burgdorferi, it affects an estimated 500,000 people in the United States alone. The antibiotics currently used to treat Lyme disease are broad spectrum, damage the microbiome, and select for resistance in non-target bacteria. We therefore sought to identify a compound acting selectively against B. burgdorferi. A screen of soil micro-organisms revealed a compound highly selective against spirochetes, including B. burgdorferi. Unexpectedly, this compound was determined to be hygromycin A, a known antimicrobial produced by Streptomyces hygroscopicus. Hygromycin A targets the ribosomes and is taken up by B. burgdorferi, explaining its selectivity. Hygromycin A cleared the B. burgdorferi infection in mice, including animals that ingested the compound in a bait, and was less disruptive to the fecal microbiome than clinically relevant antibiotics. This selective antibiotic holds the promise of providing a better therapeutic for Lyme disease and eradicating it in the environment.

The dichloromethane extract of the root bark of the Panamanian plant Cordia anisophylla J.S. Mill. (Boraginaceae) presented antifungal activity against a susceptible strain of Candida albicans in a bioautography primary screening. The susceptible strain was used to detect minor active compounds that would not have been detected using a classical approach. In order to identify the antimicrobial compounds, the active extract was fractionated by semi-preparative high-performance liquid chromatography and the fractions were submitted to the antifungal bioassay. This procedure enabled a precise localization of the antifungal compounds directly in the chromatogram of the crude extract and allowed for an efficient, targeted isolation. Four compounds were isolated, one of which is a new natural product. The structures were elucidated using spectroscopic methods. Their antifungal properties were evaluated by determination of the minimum inhibitory quantity and concentration by bioautography and dilution assay against a wild type strain of C. albicans.

As a part of a broad screening of antifungal agents from plant origin, crude extracts from Panamanian plants having related types of constituents displayed significant activities in an agar overlay thin layer chromatography assay against a susceptible strain of Candida albicans. These were the methanolic extract of the leaves of Schefflera systyla and Odontadenia puncticulosa and of the stems of Conostegia speciosa, that are species not previously investigated from a phytochemical viewpoint. For all plants, high-performance liquid chromatography (HPLC) antifungal activity based profiling allowed the rapid localization of antifungal agents that were further obtained by targeted isolation procedure by semi-preparative HPLC or medium pressure liquid chromatography (MPLC) after LC gradient transfer. Different hederagenin saponins and one aglycone were found to be responsible for the antifungal activities of the extracts. Alpha-hederin was the antifungal of S. systyla, pulsatilla saponin D and 3β-O-[β-D-xylopyranosyl-(1→3)-α-L-rhamnopyranosyl-(1→2)-[β-D-glucopyranosyl-(1→4)]-α-L-arabinopyranosylhederagenin of O. puncticulosa and arjunolic acid of C. speciosa. Their minimal inhibitory concentration (MIC) against planktonic and biofilm cells of C. albicans were determined. Alpha-hederin was the most potent compound with a MIC of 4 µg mL-1. Structurally related compounds (hederagenin, medicagenic acid 3-O-β-D-glucopyranoside and medicagenic acid) were used as standards and tested for comparison purposes. In order to better estimate the potential of these triterpenoids as antifungal agents, their cytological effects on C. albicans were determined by transmission electron microscopy (TEM) and the in vivo activity of alpha-hederin, medicagenic acid 3-O-β-D-glucopyranoside and medicagenic acid was evaluated for the first time in the Galleria mellonella larvae model.

In natural products research, the efficient purification of molecules from large amount of complex extracts is a key element. In this regard, an integrative strategy for efficient mass spectrometry (MS)-guided isolation of antifungal compounds has been developed. First, at-line HPLC antifungal activity based profiling and HPLC-PDA-MS profiling were used to localise the compounds of interest on the analytical scale. Then, the analytical gradient was geometrically transferred to the flash chromatographic level. Finally, an MS-triggered isolation of the localized bioactive molecules was realized using high resolution flash chromatographic columns (15 µm spherical particles) coupled to a single quadrupole mass spectrometer via a splitter system. This isolation strategy was applied for the MS-targeted purification of the antifungal principles from the Chinese liverwort Chiloscyphus polyanthos (L.) Cord. This rational methodology has a high potential for the targeted large-scale purification of bioactive compounds avoiding the need to repeat a given bioassay at each isolation step. Seven sesquiterpene lactones were isolated, of which five were found bioactive and one was reported as a new compound. The absolute configuration of some compounds was established for the first time by electronic circular dichroism (ECD) spectroscopy.