The increasing emergence of new forms of multidrug resistance among human pathogenic bacteria, coupled with the consequent increase of infectious diseases, urgently requires the discovery and development of novel antimicrobial drugs with new modes of action. Most of the antibiotics currently available on the market were obtained from terrestrial organisms or derived semisynthetically from fermentation products. The isolation of microorganisms from previously unexplored habitats may lead to the discovery of lead structures with antibiotic activity. The deep-sea environment is a unique habitat, and deep-sea microorganisms, because of their adaptation to this extreme environment, have the potential to produce novel secondary metabolites with potent biological activities. This review covers novel antibiotics isolated from deep-sea microorganisms. The chemical classes of the compounds, their bioactivities, and the sources of organisms are outlined. Furthermore, the authors report recent advances in techniques and strategies for the exploitation of deep-sea microorganisms.

Microorganisms living in extreme environments represent a huge reservoir of novel antimicrobial compounds and possibly of novel chemical families. Antarctica is one of the most extraordinary places on Earth and exhibits many distinctive features. Antarctic microorganisms are well known producers of valuable secondary metabolites. Specifically, several Antarctic strains have been reported to inhibit opportunistic human pathogens strains belonging to Burkholderia cepacia complex (Bcc). Herein, we applied a biodiscovery pipeline for the identification of anti-Bcc compounds. Antarctic sub-sea sediments were collected from the Ross Sea, and used to isolate 25 microorganisms, which were phylogenetically affiliated to three bacterial genera (Psychrobacter, Arthrobacter, and Pseudomonas) via sequencing and analysis of 16S rRNA genes. They were then subjected to a primary cell-based screening to determine their bioactivity against Bcc strains. Positive isolates were used to produce crude extracts from microbial spent culture media, to perform the secondary screening. Strain Pseudomonas BNT1 was then selected for bioassay-guided purification employing SPE and HPLC. Finally, LC-MS and NMR structurally resolved the purified bioactive compounds. With this strategy, we achieved the isolation of three rhamnolipids, two of which were new, endowed with high (MIC < 1 μg/mL) and unreported antimicrobial activity against Bcc strains.

Background Interleukin (IL)-26 is a signature T helper 17 cytokine described as a proinflammatory and antimicrobial mediator. So far, IL-26 has been reported in several immune-mediated inflammatory diseases, but its involvement in inflammatory skin disorders is poorly known. Objectives To investigate the role of IL-26 in hidradenitis suppurativa (HS), through its involvement in antimicrobial activity. Methods IL-26 was assessed in patients with HS through gene expression and protein analysis at skin and circulating levels. Ex vivo HS organ skin cultures, together with IL-26 antibody treatment, were performed to determine the IL-26 activity. Peripheral blood mononuclear cells (PBMCs) from patients with HS and healthy controls were either silenced or not with IL-26 small interfering (si)RNA in order to measure its antimicrobial, cytotoxic and phagocytic activities against Staphylococcus aureus. Results Firstly, we observed that IL-26 is able to modulate the proinflammatory response at the immune cell level. IL-26 was increased in the plasma of patients with HS compared with healthy controls. Subsequently, we explored the bactericidal, cytotoxic and phagocytic activities of PBMCs against S. aureus in patients with HS and healthy controls. These activities were lower in patients with HS than in controls. Remarkably, the killing activities were reduced when healthy control PBMCs were transfected with IL-26 siRNA. However, the transfection did not affect the killing activity of HS PBMCs, supporting the idea that IL-26 lacks efficacy in HS. Conclusions Our findings suggest that infection susceptibility in HS might be related to IL-26. Although the role of bacteria remains controversial in HS, this paper supports that there is a defect of antimicrobial response in these patients. What's already known about this topic?• Interleukin (IL)-26 is a T helper 17 cytokine described as an antimicrobial and proinflammatory mediator.• IL-26 has been reported in immune-mediated inflammatory diseases, but its involvement in inflammatory skin disorders remains unclear.• Hidradenitis suppurativa (HS) is a chronic inflammatory skin disorder characterized by deficiency of IL-20 and IL-22 (a close homologue of IL-26), which causes antimicrobial peptide pauperization leading to severe and recurrent skin infections.What does this study add?• IL-26 plasma levels are higher in patients with HS than in healthy control individuals.• The antimicrobial activity of IL-26 might be ineffective in patients with HS.