Farnesane-Type Sesquiterpenoids with Antibiotic Activity from Chiliadenus lopadusanus

Antiparasitic nitazoxanide potentiates colistin against colistin-resistant Acinetobacter baumannii and Escherichia coli in vitro and in vivo

IMPORTANCE

Colistin is used as a last resort in many infections caused by multidrug-resistant Gram-negative bacteria; however, colistin-resistant (COL-R) is on the rise. Hence, it is critical to develop new antimicrobial strategies to overcome COL-R. We found that nitazoxanide (NTZ) combined with colistin showed notable synergetic antibacterial activity. These findings suggest that the NTZ/colistin combination may provide an effective alternative route to combat COL-R A. baumannii and COL-R Escherichia coli infections.

Bioactive Lipodepsipeptides Produced by Bacteria and Fungi

Natural products are a vital source for agriculture, medicine, cosmetics and other fields. Lipodepsipeptides (LPDs) are a wide group of natural products distributed among living organisms such as bacteria, fungi, yeasts, virus, insects, plants and marine organisms. They are a group of compounds consisting of a lipid connected to a peptide, which are able to self-assemble into several different structures. They have shown different biological activities such as phytotoxic, antibiotic, antiviral, antiparasitic, antifungal, antibacterial, immunosuppressive, herbicidal, cytotoxic and hemolytic activities. Their biological activities seem to be due to their interactions with the plasma membrane (MP) because they are able to mimic the architecture of the native membranes interacting with their hydrophobic segment. LPDs also have surfactant properties. The review has been focused on the lipodepsipeptides isolated from fungal and bacterial sources, on their biological activity, on the structure–activity relationships of some selected LPD subgroups and on their potential application in agriculture and medicine. The chemical and biological characterization of lipodepsipeptides isolated in the last three decades and findings that resulted from SCI-FINDER research are reported. A critical evaluation of the most recent reviews dealing with the same argument has also been described.

Antibacterial and Antifungal Sesquiterpenoids: Chemistry, Resource, and Activity

Infectious diseases caused by bacteria and fungi are threatening human health all over the world. It is an increasingly serious problem that the efficacies of some antibacterial and antifungal agents have been weakened by the drug resistance of some bacteria and fungi, which makes a great need for new antibiotics. Sesquiterpenoids, with abundant structural skeleton types and a wide range of bioactivities, are considered as good candidates to be antibacterial and antifungal agents. In the past decades, many sesquiterpenoids were isolated from plants and fungi that exhibited good antibacterial and antifungal activities. In this review, the names, source, structures, antibacterial and antifungal degrees, and mechanisms of sesquiterpenoids with antibacterial and antifungal activity from 2012 to 2022 are summarized, and the structure-activity relationship of these sesquiterpenoids against bacteria and fungi is also discussed.

Antibiotic and Nematocidal Metabolites from Two Lichen Species Collected on the Island of Lampedusa (Sicily)

The antibiotic and nematocidal activities of extracts from two coastal lichen species collected on Lampedusa Island (Sicily), Ramalina implexa Nyl. and Roccella phycopsis Ach., were tested. Methyl orsellinate, orcinol, (+)-montagnetol, and for the first time 4-chlororcinol were isolated from Roccella phycopsis. (+)-Usnic acid was obtained from Ramalina implexa. The crude organic extract of both lichen species showed strong antibiotic activity against some bacterial species and nematocidal activity. Among all the pure metabolites tested against the infective juveniles (J2) of the root-knot nematode (RKN) Meloydogine incognita, (+)-usnic acid, orcinol, and (+)-montagnetol had significant nematocidal activity, comparable with that of the commercial nematocide Velum^® Prime, and thus they showed potential application in agriculture as a biopesticide. On the contrary, methyl orsellinate and 4-chlororcinol had no nematocidal effect. These results suggest that the substituent pattern at ortho-para-position in respect to both hydroxyl groups of resorcine moiety, which is present in all metabolites, seems very important for nematocidal activity. The organic extracts of both lichens were also tested against some Gram-positive and Gram-negative bacteria. Both extracts were active against Gram-positive species. The extract of Ramalina implexa showed, among Gram-negative species, activity against Escherichia coli and Acinetobacter baumannii, while that from Roccella phycopsis was effective towards all test strains, with the exception of Pseudomonas aeruginosa. The antimicrobial activity of (+)-usnic acid, methyl orsellinate, and (+)-montagnetol is already known, so tests were focused on orcinol and 4-chlororcinol. The former showed antibacterial activity against all Gram positive and Gram-negative test strains, with the exception of A. baumannii and K. pneumoniae, while the latter exhibited a potent antibacterial activity against Gram-positive test strains and among Gram-negative strains, was effective against A. baumannii and K. pneumonia. These results suggest, for orcinol and 4-chlororcinol, an interesting antibiotic potential against both Gram-positive and Gram-negative bacterial strains.

Plants with Antimicrobial Activity Growing in Italy: A Pathogen-Driven Systematic Review for Green Veterinary Pharmacology Applications

Drug resistance threatening humans may be linked with antimicrobial and anthelmintic resistance in other species, especially among farm animals and, more in general, in the entire environment. From this perspective, Green Veterinary Pharmacology was proven successful for the control of parasites in small ruminants and for the control of other pests such as varroa in bee farming. As in anthelmintic resistance, antimicrobial resistance (AMR) represents one of the major challenges against the successful treatment of infectious diseases, and antimicrobials use in agriculture contributes to the spread of more AMR bacterial phenotypes, genes, and proteins. With this systematic review, we list Italian plants with documented antimicrobial activity against possible pathogenic microbes. Methods: The literature search included all the manuscripts published since 1990 in PubMed, Web of Science, and Scopus using the keywords (i) “antimicrobial, plants, Italy”; (ii) “antibacterial, plant, Italy”; (iii) “essential oil, antibacterial, Italy”; (iv) “essential oil, antimicrobial, Italy”; (v) “methanol extract, antibacterial, Italy”; (vi) “methanol extract, antimicrobial, Italy”. Results: In total, 105 manuscripts that documented the inhibitory effect of plants growing in Italy against bacteria were included. One hundred thirty-five plants were recorded as effective against Gram+ bacteria, and 88 against Gram−. This will provide a ready-to-use comprehensive tool to be further tested against the indicated list of pathogens and will suggest new alternative strategies against bacterial pathogens to be employed in Green Veterinary Pharmacology applications.

Specialized Metabolites from the Allelopathic Plant Retama raetam as Potential Biopesticides

To cope with the rising food demand, modern agriculture practices are based on the indiscriminate use of agrochemicals. Although this strategy leads to a temporary solution, it also severely damages the environment, representing a risk to human health. A sustainable alternative to agrochemicals is the use of plant metabolites and plant-based pesticides, known to have minimal environmental impact compared to synthetic pesticides. Retama raetam is a shrub growing in Algeria’s desert areas, where it is commonly used in traditional medicine because of its antiseptic and antipyretic properties. Furthermore, its allelopathic features can be exploited to effectively control phytopathogens in the agricultural field. In this study, six compounds belonging to isoflavones and flavones subgroups have been isolated from the R. raetam dichloromethane extract and identified using spectroscopic and optical methods as alpinumisoflavone, hydroxyalpinumisoflavone, laburnetin, licoflavone C, retamasin B, and ephedroidin. Their antifungal activity was evaluated against the fungal phytopathogen Stemphylium vesicarium using a growth inhibition bioassay on PDA plates. Interestingly, the flavonoid laburnetin, the most active metabolite, displayed an inhibitory activity comparable to that exerted by the synthetic fungicide pentachloronitrobenzene, in a ten-fold lower concentration. The allelopathic activity of R. raetam metabolites against parasitic weeds was also investigated using two independent parasitic weed bioassays to discover potential activities on either suicidal stimulation or radicle growth inhibition of broomrapes. In this latter bioassay, ephedroidin strongly inhibited the growth of Orobanche cumana radicles and, therefore, can be proposed as a natural herbicide.

The Assignment of the Absolute Configuration of Non-Cyclic Sesquiterpenes by Vibrational and Electronic Circular Dichroism: The Example of Chiliadenus lopadusanus Metabolites

9-Hydroxynerolidol, 9-oxonerolidol, and chiliadenol B are three farnesane-type sesquiterpenoids isolated from Chiliadenus lopadusanus that have shown an interesting activity against human pathogens as Gram+ and Gram- bacteria resistant to antibiotics. However, the absolute configuration (AC) of these interesting sesquiterpenes has not been assigned so far. Vibrational and electronic circular dichroism spectra have been recorded and correlations are pointed out for the three compounds. Density functional theory (DFT) calculations are used in conjunction with Mosher's method of investigation to assign AC. Statistical analysis is considered to quantitatively define the choice of AC from VCD spectra.

Sesquiterpene Lactones from Cotula cinerea with Antibiotic Activity against Clinical Isolates of Enterococcus faecalis

Cotula cinerea, belonging to the tribe Anthemideae, is a plant widespread in the Southern hemisphere. It is frequently used in folk medicine in North African countries for several of its medical properties, shown by its extracts and essential oils. The dichloromethane extract obtained from its aerial parts demonstrated antibiotic activity against Enterococcus faecalis and was fractionated by bioguided purification procedures affording five main sesquiterpene lactones. They were identified by spectroscopic methods (NMR and ESIMS data) as guaiantrienolides, i.e., 6-acetoxy-1β-,6-acetoxy-1α-, and 6-acetoxy-10-β-hydroxyguaiantrienolide (1-3), and germacrenolides, i.e., haagenolide and 1,10-epoxyhaagenolide (4 and 5). The absolute configuration was assigned by applying the advanced Mosher's method to haagenolide and by X-ray diffraction analysis to 1,10-epoxyhaagenolide. The specific antibiotic and antibiofilm activities were tested toward the clinical isolates of Enterococcus faecalis. The results showed that compounds 3-5 have antibacterial activity against all the strains of E. faecalis, while compound 2 exhibited activity only toward some strains. Compound 1 did not show this activity but had only antibiofilm properties. Thus, these metabolites have potential as new antibiotics and antibiofilm against drug resistant opportunistic pathogens.