Biogenesis of antibiotics-viewing its history and glimpses of the future

Redefining development in Streptomyces venezuelae: integrating exploration into the classical sporulating life cycle

Two growth modes have been described for the filamentous Streptomyces bacteria. Their classic developmental life cycle culminates in the formation of dormant spores, where movement to new environments is mediated through spore dispersal. In contrast, exploratory growth proceeds as a rapidly expanding vegetative mycelium that leads to extensive surface colonization and is associated with the release of volatile compounds that promote alkalinization (and reduced iron bioavailability) of its surrounding environment. Here, we report that exploratory growth in Streptomyces venezuelae can proceed in tandem with classic sporulating development in response to specific nutritional cues. Sporulating exploration is not accompanied by a rise in environmental pH but has the same iron acquisition requirements as conventional exploration. We found that mutants that were defective in their ability to sporulate were unaffected in exploration, but mutants undergoing precocious sporulation were compromised in their exploratory growth and this appeared to be mediated through premature activation of the developmental regulator WhiI. Cell envelope integrity was also found to be critical for exploration, as mutations in the cell envelope stress-responsive extracytoplasmic function sigma factor SigE led to a failure to explore robustly under all exploration-promoting conditions. Finally, in expanding the known exploration-promoting conditions, we discovered that the model species Streptomyces lividans exhibited exploration capabilities, supporting the proposal that exploration is conserved across diverse streptomycetes.

IMPORTANCE

Streptomyces bacteria have evolved diverse developmental and metabolic strategies to thrive in dynamic environmental niches. Here, we report the amalgamation of previously disparate developmental pathways, showing that colony expansion via exploration can proceed in tandem with colony sporulation. This developmental integration extends beyond phenotype to include shared genetic elements, with sporulation-specific repressors being required for successful exploration. Comparing this new exploration mode with previously identified strategies has revealed key differences (e.g., no need for environmental alkalinization), and simultaneously allowed us to define unifying requirements for Streptomyces exploration. The "reproductive exploration" phenomenon reported here represents a unique bet-hedging strategy, with the Streptomyces colony engaging in an aggressive colonization strategy while transporting a protected genetic repository.

Fish Skin Mucus Extracts: An Underexplored Source of Antimicrobial Agents

The slow discovery of new antibiotics combined with the alarming emergence of antibiotic-resistant bacteria underscores the need for alternative treatments. In this regard, fish skin mucus has been demonstrated to contain a diverse array of bioactive molecules with antimicrobial properties, including peptides, proteins, and other metabolites. This review aims to provide an overview of the antimicrobial molecules found in fish skin mucus and its reported in vitro antimicrobial capacity against bacteria, fungi, and viruses. Additionally, the different methods of mucus extraction, which can be grouped as aqueous, organic, and acidic extractions, are presented. Finally, omic techniques (genomics, transcriptomics, proteomics, metabolomics, and multiomics) are described as key tools for the identification and isolation of new antimicrobial compounds. Overall, this study provides valuable insight into the potential of fish skin mucus as a promising source for the discovery of new antimicrobial agents.

Status and Future Scope of Soft Nanoparticles-Based Hydrogel in Wound Healing

Wounds are alterations in skin integrity resulting from any type of trauma. The healing process is complex, involving inflammation and reactive oxygen species formation. Therapeutic approaches for the wound healing process are diverse, associating dressings and topical pharmacological agents with antiseptics, anti-inflammatory, and antibacterial actions. Effective treatment must maintain occlusion and moisture in the wound site, suitable capacity for the absorption of exudates, gas exchange, and the release of bioactives, thus stimulating healing. However, conventional treatments have some limitations regarding the technological properties of formulations, such as sensory characteristics, ease of application, residence time, and low active penetration in the skin. Particularly, the available treatments may have low efficacy, unsatisfactory hemostatic performance, prolonged duration, and adverse effects. In this sense, there is significant growth in research focusing on improving the treatment of wounds. Thus, soft nanoparticles-based hydrogels emerge as promising alternatives to accelerate the healing process due to their improved rheological characteristics, increased occlusion and bioadhesiveness, greater skin permeation, controlled drug release, and a more pleasant sensory aspect in comparison to conventional forms. Soft nanoparticles are based on organic material from a natural or synthetic source and include liposomes, micelles, nanoemulsions, and polymeric nanoparticles. This scoping review describes and discusses the main advantages of soft nanoparticle-based hydrogels in the wound healing process. Herein, a state-of-the-art is presented by addressing general aspects of the healing process, current status and limitations of non-encapsulated drug-based hydrogels, and hydrogels formed by different polymers containing soft nanostructures for wound healing. Collectively, the presence of soft nanoparticles improved the performance of natural and synthetic bioactive compounds in hydrogels employed for wound healing, demonstrating the scientific advances obtained so far.

Composites Based on Gellan Gum, Alginate and Nisin-Enriched Lipid Nanoparticles for the Treatment of Infected Wounds

Due to growing antimicrobial resistance to antibiotics, novel methods of treatment of infected wounds are being searched for. The aim of this research was to develop a composite wound dressing based on natural polysaccharides, i.e., gellan gum (GG) and a mixture of GG and alginate (GG/Alg), containing lipid nanoparticles loaded with antibacterial peptide-nisin (NSN). NSN-loaded stearic acid-based nanoparticles (NP_NSN) were spherical with an average particle size of around 300 nm and were cytocompatible with L929 fibroblasts for up to 500 µg/mL. GG and GG/Alg sponges containing either free NSN (GG + NSN and GG/Alg + NSN) or NP_NSN (GG + NP_NSN and GG/Alg + NP_NSN) were highly porous with a high swelling capacity (swelling ratio above 2000%). Encapsulation of NSN within lipid nanoparticles significantly slowed down NSN release from GG-based samples for up to 24 h (as compared to GG + NSN). The most effective antimicrobial activity against Gram-positive Streptococcus pyogenes was observed for GG + NP_NSN, while in GG/Alg it was decreased by interactions between NSN and Alg, leading to NSN retention within the hydrogel matrix. All materials, except GG/Alg + NP_NSN, were cytocompatible with L929 fibroblasts and did not cause an observable delay in wound healing. We believe that the developed materials are promising for wound healing application and the treatment of bacterial infections in wounds.

Antibiotics: Conventional Therapy and Natural Compounds with Antibacterial Activity-A Pharmaco-Toxicological Screening

Antibiotics are considered as a cornerstone of modern medicine and their discovery offers the resolution to the infectious diseases problem. However, the excessive use of antibiotics worldwide has generated a critical public health issue and the bacterial resistance correlated with antibiotics inefficiency is still unsolved. Finding novel therapeutic approaches to overcome bacterial resistance is imperative, and natural compounds with antibacterial effects could be considered a promising option. The role played by antibiotics in tumorigenesis and their interrelation with the microbiota are still debatable and are far from being elucidated. Thus, the present manuscript offers a global perspective on antibiotics in terms of evolution from a historical perspective with an emphasis on the main classes of antibiotics and their adverse effects. It also highlights the connection between antibiotics and microbiota, focusing on the dual role played by antibiotics in tumorigenesis. In addition, using the natural compounds with antibacterial properties as potential alternatives for the classical antibiotic therapy is discussed.

Strain-level analysis of gut-resident pro-inflammatory viridans group Streptococci suppressed by long-term cotrimoxazole prophylaxis among HIV-positive children in Zimbabwe

Antimicrobials have become a mainstay of healthcare in the past century due to their activity against pathogens. More recently, it has become clear that they can also affect health via their impact on the microbiota and inflammation. This may explain some of their clinical benefits despite global increases in antimicrobial resistance (AMR) and reduced antimicrobial effectiveness. We showed in a randomized controlled trial of stopping versus continuing cotrimoxazole prophylaxis among HIV-positive Zimbabwean children taking antiretroviral therapy (ART), that continuation of cotrimoxazole persistently suppressed gut-resident viridans group streptococcal species (VGS) that were associated with intestinal inflammation. In this addendum, we provide a broader overview of how antibiotics can shape the microbiota and use high read-depth whole metagenome sequencing data from our published study to investigate whether (i) the impact of cotrimoxazole on gut VGS and (ii) VGS associated inflammation, is attributable to strain-level variability. We focus on S. salivarius, the VGS species that was most prevalent in the cohort and for which there was sufficient genome coverage to differentiate strains. We demonstrate that suppression of S. salivarius by cotrimoxazole is not strain specific, nor did stool concentration of the pro-inflammatory mediator myeloperoxidase vary by S. salivarius strain. We also show that gut-resident S. salivarius strains present in this study population are distinct from common oral strains. This is the first analysis of how cotrimoxazole prophylaxis used according to international treatment guidelines for children living with HIV influences the gut microbiome at the strain-level. We also provide a detailed review of the literature on the mechanisms by which suppression of VGS may act synergistically with cotrimoxazole's anti-inflammatory effects to reduce gut inflammation. A greater understanding of the sub-clinical effects of antibiotics offers new insights into their responsible clinical use.

Determination and Identification of Antibiotic Drugs and Bacterial Strains in Biological Samples

Antibiotics were initially natural substances. However, nowadays, they also include synthetic drugs, which show their activity against bacteria, killing or inhibiting their growth and division. Thanks to these properties, many antibiotics have quickly found practical application in the fight against infectious diseases such as tuberculosis, syphilis, gastrointestinal infections, pneumonia, bronchitis, meningitis and septicemia. Antibiotic resistance is currently a detrimental problem; therefore, in addition to the improvement of antibiotic therapy, attention should also be paid to active metabolites in the body, which may play an important role in exacerbating the existing problem. Taking into account the clinical, cognitive and diagnostic purposes of drug monitoring, it is important to select an appropriate analytical method that meets all the requirements. The detection and identification of the microorganism responsible for the infection is also an essential factor in the implementation of appropriate antibiotic therapy. In recent years, clinical microbiology laboratories have experienced revolutionary changes in the way microorganisms are identified. The MALDI-TOF MS technique may be interesting, especially in some areas where a quick analysis is required, as is the case with clinical microbiology. This method is not targeted, which means that no prior knowledge of the infectious agent is required, since identification is based on a database match.

The phosphoenolpyruvate-pyruvate-oxaloacetate node genes and enzymes in Streptomyces coelicolor M-145

The phosphoenolpyruvate-pyruvate-oxaloacetate node is a major branch within the central carbon metabolism and acts as a connection point between glycolysis, gluconeogenesis, and the TCA cycle. Phosphoenolpyruvate carboxylase, pyruvate carboxylase, phosphoenolpyruvate carboxykinase, malic enzymes, and pyruvate kinase, among others, are enzymes included in this node. We determined the mRNA levels and specific activity profiles of some of these genes and enzymes in Streptomyces coelicolor M-145. The results obtained in the presence of glucose demonstrated that all genes studied of the phosphoenolpyruvate-pyruvate-oxaloacetate node were expressed, although at different levels, with 10- to 100-fold differences. SCO3127 (phosphoenolpyruvate carboxylase gene) and SCO5261 (NADP⁺-dependent malic enzyme gene) showed the highest expression in the rapid growth phase, and the mRNA levels corresponding to SCO5896 (phosphoenolpyruvate-utilizing enzyme gene), and SCO0546 (pyruvate carboxylase gene) increased 5- to 10-fold towards the stationary phase. In casamino acids, in general mRNA levels of S. coelicolor were lower than in glucose, however, results showed greater mRNA expression of SCO4979 (PEP carboxykinase), SCO0208 (pyruvate phosphate dikinase gene), and SCO5261 (NADP⁺-dependent malic enzyme). These results suggest that PEP carboxylase (SCO3127) is an important enzyme during glucose catabolism and oxaloacetate replenishment. On the other hand, phosphoenolpyruvate carboxykinase, pyruvate phosphate dikinase, and NADP⁺-malic enzyme could have an important role in gluconeogenesis in S. coelicolor.

Antibiotic drug discovery

Due to the threat posed by the increase of highly resistant pathogenic bacteria, there is an urgent need for new antibiotics; all the more so since in the last 20 years, the approval for new antibacterial agents had decreased. The field of natural product discovery has undergone a tremendous development over the past few years. This has been the consequence of several new and revolutionizing drug discovery and development techniques, which is initiating a ‘New Age of Antibiotic Discovery’. In this review, we concentrate on the most significant discovery approaches during the last and present years and comment on the challenges facing the community in the coming years.