Search Results (124)

Anaerobes, the oldest evolutionary life forms, have been unexplored for their potential to produce secondary metabolites due to the difficulties observed in their cultivation. Antimicrobials derived from anaerobic bacteria are an emerging and valuable source of novel therapeutic agents. The urgent need for new antimicrobial agents due to rising antibiotic resistance has prompted an investigation into anaerobic bacteria. The conventional method of antimicrobial discovery is based on cultivation and extraction methods. Antibacterial and antifungal substances are produced by anaerobic bacteria, but reports are limited due to oxygen-deficient growth requirements. The genome mining approach revealed the presence of biosynthetic gene clusters involved in various antimicrobial compound synthesis. Thus, the current review is focused on antimicrobials derived from anaerobes to unravel the potential of anaerobic bacteria as an emerging valuable source of therapeutic agents. These substances frequently consist of peptides, lipopeptides, and other secondary metabolites. Many of these antimicrobials have distinct modes of action that may be able to go around established resistance pathways. To this effect, we discuss diverse antimicrobial compounds produced by anaerobic bacteria, their biosynthesis, heterologous production, and activity. The findings suggest that anaerobic bacteria harbor significant biosynthetic potential, warranting further exploration through recombinant production for developing new antibiotics. Full article

The increasing resistance of pathogenic microorganisms to antimicrobials has driven the search for safe and sustainable alternatives. In this context, microbial biosurfactants have gained prominence due to their antimicrobial activity, low toxicity, and high stability under extreme conditions. This study presents the production and characterization of a biosurfactant with antimicrobial potential, obtained from Bacillus subtilis isolated from soil, for application in the control of resistant strains. Bacterial identification was performed using mass spectrometry (MALDI-TOF), confirming it as Bacillus subtilis. The strain B. subtilis UCP 1533 was cultivated using different carbon sources (glucose, soybean oil, residual frying oil, and molasses) and nitrogen sources (ammonium chloride, sodium nitrate, urea, and peptone), with evaluations at 72, 96, and 120 h. The best condition involved a mineral medium supplemented with 2% soybean oil and 0.12% corn steep liquor, resulting in the production of 16 g·L⁻¹ of biosurfactant, with a critical micelle concentration (CMC) of 0.3 g·L⁻¹ and a reduction in water surface tension to 25 mN·m⁻¹. The biosurfactant showed an emulsification index of 100% for used motor oil and ranged from 50% to 100% for different vegetable oils, maintaining stability across a wide range of pH, salinity, and temperature. FT-IR and NMR analyses confirmed its lipopeptide nature and anionic charge. Toxicity tests with Tenebrio molitor larvae showed 100% survival at all the tested concentrations. In phytotoxicity assays, seed germination rates above 90% were recorded for Solanum lycopersicum and Lactuca sativa. Antimicrobial tests revealed inhibitory activity against resistant strains of Escherichia coli and Pseudomonas aeruginosa, as well as against species of the genus Candida (C. glabrata, C. lipolytica, C. bombicola, and C. guilliermondii), highlighting the biosurfactant as a promising alternative in combating antimicrobial resistance (AMR). These results indicate the potential application of this biosurfactant in the development of antimicrobial agents for pharmaceutical formulations and sustainable strategies for phytopathogen control in agriculture. Full article

Spore-forming Bacilli have been explored due to their potential biotechnological features and applications in human health and functional food research. This study focuses on the genetic and phenotypical characterization of the functional probiotic properties of Bacillus velezensis P45, a strain isolated from fish intestines. B. velezensis P45 exhibited antimicrobial activity against Gram-positive and Gram-negative pathogens and demonstrated strong autoaggregation and biofilm formation properties in vitro. The strain also showed tolerance to gastrointestinal conditions and ability to metabolize and adhere to mucin. In silico analysis confirmed the absence of virulence factors and antibiotic resistance genes, reinforcing its safety as a probiotic candidate. Genome mining revealed the presence of genes related to adhesion, such as fibronectin-binding protein and enolases, and for the synthesis of secondary metabolites, including the antimicrobial lipopeptides fengycin, surfactin, and bacillibactin. In addition, phylogenetic comparison using the yloA (rqcH) gene associated with gut adhesion clustered strain P45 with other probiotic Bacillus and B. velezensis strains, while separating it from pathogenic bacteria. Thus, the strain B. velezensis P45 could be a valuable candidate as a probiotic due to its functional properties and safety. Full article

Methicillin-resistant Staphylococcus aureus (MRSA) represents a major therapeutic challenge due to its multidrug-resistance and the associated clinical burden. Daptomycin (DAP), a cyclic lipopeptide antibiotic, has become a key agent for the treatment of severe MRSA infections owing to its rapid bactericidal activity and favourable safety profile. In this narrative review, we examine studies published between 2010 and April 2025. The data suggest that treatment with high-dose (8–10 mg kg⁻¹) DAP shortened the time to blood-culture sterilisation by a median of 2 days compared with standard-dose vancomycin without increasing toxicity when model-informed area-under-the-curve monitoring was employed. Particular attention is given to the synergistic effects of DAP combined with fosfomycin or β-lactams, especially ceftaroline and ceftobiprole, in overcoming persistent and refractory MRSA infections; this approach results in a reduction in microbiological failure relative to monotherapy. Resistance remains uncommon (<2% of isolates), but recurrent mutations in mprF, liaFSR, and walK underscore the need for proactive genomic surveillance. Despite promising preclinical and clinical evidence supporting combination strategies, further randomized controlled trials are necessary to establish their definitive role in clinical practice, as are head-to-head cost-effectiveness evaluations. DAP remains a critical option in the evolving landscape of MRSA management, provided its use is integrated with precision dosing, resistance surveillance, and antimicrobial-stewardship frameworks. Full article

Background: Antimicrobial resistance (AMR) is a global threat in the public healthcare sector. The emergence of carbapenem-resistant Enterobacterales (CRE) has become a serious public health threat in South Africa. The spread of CRE has led to the use of colistin for treating severe infections. Colistin is a cationic, lipopeptide antibacterial agent that is effective against most Gram-negative bacteria through its disruption of the bacterial cell membrane. This study aims to determine the colistin resistance (MIC) and mobile colistin resistance (mcr-1) gene in clinical isolates from healthcare facilities in Mthatha and its surrounding areas. Methods: Fifty-three CRE isolates were collected from health facilities between January 2019 and June 2021 and stored in skim milk 10% and 5% inositol broth. The carbapenemase confirmatory test involved a RESIST-4 O.K.N.V assay (Coris BioConcept, Gembloux, Belgium), which was conducted following manufacturer protocol. Broth microdilution was performed according to the ISO standard method (20776-1) using A ComAspTM colistin 0.25–16 μg/mL MIC Broth. Conventional polymerase reaction (PCR) was performed for the detection of mcr-1. Results: N = 53 (100%) isolates were used. A total of 53% were defined as Klebsiella pneumoniae, Escherichia coli constituted 8%, Enterobacter cloacae 8%, Serratia marcescens 8%, Serratia fonticola 2%, Enterobacter aerogenes 2%, Klebsiella oxytoca 2%, Citrobacter koseri 2%, and Citrobacter freundii 2%. The specimens were from the following wards: Pediatric and Neonatal 38%, Medical 30%, Gynecology, Labour, and Maternity 11%, OPD and A&E 11%, ENT 4%, and Others—Male TB ward, Trauma, and adult ICU 6%. In total, 13% of the isolates were resistant and 86% were sensitive to colistin. The common CRE genes detected were OXA-48 at 47%, NDM at 13%, VIM at 1%, and a combination of OXA-48 and NDM at 5%. Of the isolates, 66% were positive for the production of carbapenamase. In this study, we found that all N = 53 (100%) isolates did not have the mobile colistin resistance gene (mcr-1). Conclusions: Antimicrobial resistance is associated with the emergence of carbapenemases genes. Increasing resistance to colistin in clinical settings can lead to difficulties in treating CRE infections, which may lead to clinical failure. In our study, 13% of isolates were phenotypically resistant to colistin. Full article

Campylobacter spp. is one of the most prevalent causes of zoonotic foodborne infections associated with diarrhea in humans. The growing threat of antibiotic resistance calls for innovative approaches. The antimicrobial lipopeptide brevibacillin produced by Brevibacillus laterosporus and its synthetic analog brevibacillin Thr1 showed promising activity against Salmonella and E. coli. The latter is a 1602.13 Da positively charged (+3) synthetic peptide of 13 residues that showed reduced cytotoxicity (IC₅₀ of 32.2 µg/mL against Caco-2 cells) and hemolytic activity (1.2% hemolysis at 128 µg/mL) compared to the native peptide. It contains an N-terminal L-isoleucic fatty acid chain and four non-proteinogenic amino acids and ends with valinol at its C-terminus. One key structural modification is the substitution of α,β-dehydrobutyric acid with threonine. We investigated the antimicrobial potential of the synthetic brevibacillin Thr1 analog against a collection of 44 clinical Campylobacter spp. that were obtained from two reference laboratories. Susceptibility testing revealed marked resistance to ciprofloxacin, tetracycline, and ampicillin among the strains, with more than half expressing a multidrug-resistant phenotype. The genomes of the 44 strains were sequenced to study the genes responsible for their antimicrobial resistance. Tetracycline resistance was associated with tet(O), ciprofloxacin resistance with mutations in gyrA and regulatory sequences modulating the expression of an efflux system, and aminoglycoside resistance with genes of the aph family. The brevibacillin Thr1 analog was produced by chemical synthesis, and evaluation of its activity against a subset of clinical strains by microdilution revealed minimum inhibitory concentration and minimum bactericidal concentration ranging from 8 µg/mL to 64 µg/mL. The peptide was active against multidrug-resistant isolates with a bactericidal effect. Of note, despite numerous attempts, it proved impossible to select Campylobacter spp. for resistance to the brevibacillin Thr1 analog. These results underline the potential of lipopeptides, notably brevibacillin, as antimicrobial alternatives against antibiotic-resistant Campylobacter bacterial infections. Full article

Background: The emergence of multidrug-resistant (MDR) Staphylococcus aureus presents a critical global health challenge due to treatment failures and high mortality rates. Faced with this growing threat, new antimicrobials with original modes of action are urgently needed, and antimicrobial peptides proved to be promising alternatives. Objectives: The aim of this study is to explore the structure–function relationship of the lipopeptide humimycin A, compare the spectrum of activity of the synthetic analogs against a panel of S. aureus isolates, and investigate their binding to the humimycin target, the lipid II flippase MurJ. Methods: Humimycin A and 15 analogs were produced by solid-phase peptide synthesis, and their antimicrobial activity was evaluated by agar diffusion and microtitration assays against 19 S. aureus isolates from bovine mastitis and other pathogens. Results: Among the synthesized peptides, four humimycin analogs exhibited activity against methicillin-sensitive and methicillin-resistant S. aureus, as well as several isolates in the panel, including MDR S. aureus, with minimal inhibitory concentration values ranging from 0.5 to 256 µg/mL. Results from the structure–activity relationship study showed that the β-hydroxymyristoyl lipid chain and C-terminal carboxylic acid are essential for antimicrobial efficacy. In presence of human erythrocytes, the active humimycin analogs exhibited moderate hemolytic activity, suggesting selectivity indexes ranging from 3 to 27 against the more sensitive S. aureus strains. Critical micelle concentration measurements elucidated micelle formation and proved to not be essential for the antibacterial activity. Molecular docking and 100 ns simulations with the lipid II flippase MurJ (PDB: 5T77) provided favorable binding energy. Conclusions: The findings underscore the potential of humimycin analogs as antimicrobials for preventing and treating MDR S. aureus infections in veterinary, animal husbandry, and human medicine. Full article

Candidiasis belongs to common fungal infections and is usually mild and self-limiting. However, in patients with immunodeficiencies, it can transform into invasive infections with high mortality. Long-term antifungal treatment can lead to the emergence of resistance. The problem is further complicated by the development of fungal biofilm resistant to conventional antimicrobials. Due to a limited choice of available antifungals, the development of novel active agents, such as antimicrobial peptides (AMPs), is highly desirable. Human cathelicidin LL-37 is an intensively studied AMP with a confirmed broad spectrum of antimicrobial activities. Due to the relatively high costs of production, the design of shorter analogs of LL-37 has been recommended. In this study, we synthesized a KR12 amide, KRIVQRIKDFLR-NH₂, and its 24 derivatives obtained by substitution with fatty acids. The compounds were tested for their antifungal potential. They exhibited activity against the Candida albicans, C. glabrata, C. tropicalis and C. lipolytica. Five compounds: C₁₀-KR12-NH₂, C₁₂-KR12-NH₂, C₁₄-KR12-NH₂, 2-butyloctanoic acid-KR12-NH₂, and 4-phenylbenzoic acid-KR12-NH₂ were highly active against planktonic cells. C₁₄-KR12-NH₂ demonstrated also activity against C. albicans biofilm cultured on polystyrene for 24, 48 and 72 h. Lipidation has proven to be an effective strategy for improving microbiological activity of the KR12-NH₂ peptide. Full article

Isothermal titration calorimetry (ITC), circular dichroism (CD) spectroscopy, and molecular dynamics simulations were applied to describe interactions between lipopeptides and decavanadate ions ([V₁₀O₂₈]⁶⁻). The selected lipopeptides are conjugates of the amide of the KR12 peptide, the smallest antimicrobial peptide derived from human cathelicidin LL-37, with lauric acid (C12-KR12) and myristic acid (C14-KR12). The smaller sizes of C12-KR12 and C14-KR12 compared to proteins allow for the rigorous characterization of their non-covalent interactions with highly negatively charged [V₁₀O₂₈]⁶⁻ ions. The stoichiometry of the resulting decavanadate–peptide complexes and the thermodynamic parameters (ΔG, ΔH, and TΔS) of the interactions were determined. The ITC results, supported by the MD simulation, showed that the binding of cationic lipopeptides for decavanadate is rather non-specific and is driven by enthalpic contributions resulting from electrostatic interactions between the positively charged residues of the peptides and the anionic decavanadate. Furthermore, the influence of temperature and the interactions with decavanadate ions on the stability of the α-helical structure of the lipopeptides were assessed based on CD spectra. Under the experimental conditions (50 mM sodium cacodylate buffer, pH 5), the peptides adopt an α-helical conformation, with C14-KR12 showing greater thermal stability. The interactions with vanadium species disrupt the α-helical structure and reduce its thermal stability. Full article

Biosurfactants, amphiphilic metabolites produced by bacteria and yeasts, fulfill a variety of functions in microbial life. They exhibit a well-recognized multifunctionality, spanning from the reduction in surface tension to specific biological activities, including antimicrobial, antiviral, anti-inflammatory, and anticancer effects. These compounds have the potential to serve as environmentally friendly alternatives to synthetic surfactants in industrial formulations, where they could act as emulsifiers and wetting agents. The exploitation of their full potentiality could be a significant added value. Biosurfactants are often cited as effective antioxidants. However, experimental evidence for their antioxidant activity/capacity is sparse. To shed light on the subject, in this review we collect and critically examine all the available literature data for each of the major classes of microbial biosurfactants: rhamnolipids, mannosylerythritol lipids, sophorolipids, and lipopeptides. Despite the variability arising from the diverse composition and polydispersity of the samples analyzed, along with the variety of testing methodologies, the findings consistently indicate a moderate-to-strong antioxidant capacity. Several hypotheses are advanced about the molecular mechanisms behind this action; however, further studies are needed to gain a molecular understanding. This knowledge would fully define the biological roles of biosurfactants and is a prerequisite for the development of innovative formulations based on the valorization of their antioxidant properties. Full article

Hydrocarbon fuel biofouling and biocorrosion require expensive cleanup of aviation infrastructures unless appropriate sustainment measures are applied. The identification of novel biological control agents offers promising alternatives to the current chemical biocides used in fuel sustainment. In this study, 496 microbial fuel isolates from our in-house repository were screened to identify new endogenously produced antimicrobial compounds. Using agar plug screening, liquid culture growth testing, and Jet A fuel culture assays, the two fuel-isolate strains Pseudomonas protegens #133, and Bacillus subtilis #232 demonstrated promising biocontrol activity against bacteria, yeast, and filamentous fungi. Liquid chromatography-quadrupole time of flight tandem mass spectrometry (LC-QTOF-MS/MS) of #232 culture filtrate identified several common lipopeptide antimicrobials including gageostatin C, gageopeptin B, and miscellaneous macrolactins. In contrast, LC-QTOF-MS/MS identified the siderophore pyochelin as one of the predominant compounds in #133 culture filtrate with previously demonstrated antimicrobial effect. Jet fuel microbial consortium culture testing of #133 culture filtrate including flow-cytometry live/dead cell mechanism determination demonstrated antimicrobial action against Gram-positive bacteria. The study concludes that antimicrobial compounds secreted by #133 have bactericidal effects against Gordonia sp. and cause cell death through bacterial lysis and membrane damage with potential applications in the biocidal treatment of hydrocarbon-based aviation fuels. Full article

Background: Colistin, a lipopeptide antibiotic usually used as a last resort against multidrug-resistant bacterial strains, has also begun to address the challenge of antimicrobial resistance. Objective: this study evaluates whether hybrid nanoparticles (HNPs) composed of Phospholipon^® 90G, cholesterol, and colistin can enhance its effectiveness against resistant clinical isolates of Klebsiella pneumoniae, a clinically significant Gram-negative bacterium. Methods: HNPs were developed using the ethanol injection method and coated with chitosan through a layer-by-layer technique. HNP characterization included measurements of particle size, polydispersity index (PDI), and zeta potential, along with thermal (DSC) and spectrophotometric (FT-IR) analyses. Ultrafiltration and ATR-FTIR were employed to assess colistin’s association and release efficiencies. The biological evaluation followed CLSI guidelines. Results: uncoated hybrid nanoparticles (U-HNP) and chitosan-coated hybrid nanoparticles (Ch-HNP) described monodisperse populations, with respective PDI values of ~0.124 and ~0.150, Z-averages of ~249 nm and ~250 nm, and zeta potential values of +17 mV and +20 mV. Colistin’s association and release efficiencies were approximately 79% and 10%, respectively. Regarding antimicrobial activity, results showed that colistin as part of HNPs is poorly effective against this microorganism. However, in the most resistant strain, colistin activity increased slightly when the HNP was coated with chitosan. Conclusions: HNPs described high stability against disaggregation, limiting the colistin release and, therefore, affecting antimicrobial performance. Full article

Lipopeptides (LPs) are widely sourced surface-active natural products with a wide range of functions and low toxicity, high potency, and good biodegradability. In this paper, we summarize, for the first time, the plant, animal, microbial, and synthetic sources of LPs. We also introduce the applications of LPs in food and human health, including (1) LPs can inhibit the growth of food microorganisms during production and preservation. They can also be added to food packaging materials for preservation and freshness during transportation, and can be used as additives to improve the taste of food. (2) LPs can provide amino acids and promote protein synthesis and cellular repair. Due to their broad-spectrum antimicrobial properties, they exhibit good anticancer effects and biological activities. This review summarizes, for the first time, the sources of LPs and their applications in food and human health, laying the foundation for the development and application of LPs. Full article

Bacillus cyclic lipopeptides (CLP), part of the three main families—surfactins, iturins, and fengycins—are secondary metabolites with a unique chemical structure that includes both peptide and lipid components. Being amphiphilic compounds, CLPs exhibit antimicrobial activity in vitro, damaging the membranes of microorganisms. However, the concentrations of CLPs used in vitro are difficult to achieve in natural conditions. Therefore, in a natural environment, alternative mechanisms of antimicrobial action by CLPs are more likely, such as inducing apoptosis in fungal cells, preventing microbial adhesion to the substrate, and promoting the death of phytopathogens by stimulating plant immune responses. In addition, CLPs in low concentrations act as signaling molecules of Bacillus’s own metabolism, and when environmental conditions change, they form an adaptive response of the host bacterium. Namely, they trigger the differentiation of the bacterial population into various specialized cell types: competent cells, flagellated cells, matrix producers, and spores. In this review, we have summarized the current understanding of the antimicrobial action of Bacillus CLPs under both experimental and natural conditions. We have also shown the relationship between some regulatory pathways involved in CLP biosynthesis and bacterial cell differentiation, as well as the role of CLPs as signaling molecules that determine changes in the physiological state of Bacillus subpopulations in response to shifts in environmental conditions. Full article

This study examined the efficacy and mechanisms of action of the antimicrobial peptide BP15 and its lipopeptides, HBP15 and LBP15, against Penicillium digitatum, the primary causative agent of green mold in citrus fruits. The findings revealed that all three antimicrobial peptides markedly inhibited the spore germination and mycelial growth of P. digitatum, with minimum inhibitory concentrations (MICs) of 3.12 μM for BP15, HBP15, and LBP15. The peptides induced morphological alterations in hyphae and elevated intracellular Sytox Green (SG) fluorescence signals, which is indicative of increased cell membrane permeability and disruption. This membrane damage was further supported by the heightened extracellular conductivity and the release of intracellular nucleic acid and protein. A gel retardation assay demonstrated that the peptides showed significant DNA binding and retardation effects. Furthermore, the peptides exhibited significantly lower hemolytic activity (p < 0.05) compared to commercial prochloraz in normal mammalian erythrocytes (sheep erythrocytes) at the tested concentrations. Therefore, BP15 and its lipopeptides, HBP15 and LBP15, show potential as effective agents for preventing green mold in citrus fruits. Full article