How a natural antibiotic uses oxidative stress to kill oxidant-resistant bacteria.

Natural products that possess antibiotic and antitumor qualities are often suspected of working through oxidative mechanisms. In this study, two quinone-based small molecules were compared. Menadione, a classic redox-cycling compound, was confirmed to generate high levels of reactive oxygen species inside Escherichia coli. It inactivated iron-cofactored enzymes and blocked growth. However, despite the substantial levels of oxidants that it produced, it was unable to generate significant DNA damage and was not lethal. Streptonigrin, in contrast, was poorer at redox cycling and did not inactivate enzymes or block growth; however, even in low doses, it damaged DNA and killed cells. Its activity required iron and oxygen, and in vitro experiments indicated that its quinone moiety transferred electrons through the adjacent iron atom to oxygen. Additionally, in vitro experiments revealed that streptonigrin was able to damage DNA without inhibition by catalase, indicating that hydrogen peroxide was not involved. We infer that streptonigrin can reduce bound oxygen directly to a ferryl species, which then oxidizes the adjacent DNA, without release of superoxide or hydrogen peroxide intermediates. This scheme allows streptonigrin to kill a bacterial cell without interference by scavenging enzymes. Moreover, its minimal redox-cycling behavior avoids alerting either the OxyR or the SoxRS systems, which otherwise would block killing. This example highlights qualities that may be important in the design of oxidative drugs. These results also cast doubt on proposals that bacteria can be killed by stressors that merely stimulate intracellular O2- and H2O2 formation.

A systematic comparison of natural product potential, with an emphasis on RiPPs, by mining of bacteria of three large ecosystems.

The implementation of several global microbiome studies has yielded extensive insights into the biosynthetic potential of natural microbial communities. However, studies on the distribution of several classes of ribosomally synthesized and post-translationally modified peptides (RiPPs), non-ribosomal peptides (NRPs) and polyketides (PKs) in different large microbial ecosystems have been very limited. Here, we collected a large set of metagenome-assembled bacterial genomes from marine, freshwater and terrestrial ecosystems to investigate the biosynthetic potential of these bacteria. We demonstrate the utility of public dataset collections for revealing the different secondary metabolite biosynthetic potentials among these different living environments. We show that there is a higher occurrence of RiPPs in terrestrial systems, while in marine systems, we found relatively more terpene-, NRP-, and PK encoding gene clusters. Among the many new biosynthetic gene clusters (BGCs) identified, we analyzed various Nif-11-like and nitrile hydratase leader peptide (NHLP) containing gene clusters that would merit further study, including promising products, such as mersacidin-, LAP- and proteusin analogs. This research highlights the significance of public datasets in elucidating the biosynthetic potential of microbes in different living environments and underscores the wide bioengineering opportunities within the RiPP family.

Steroid Drugs Inhibit Bacterial Respiratory Oxidases and Are Lethal Toward Methicillin-Resistant Staphylococcus aureus.

BACKGROUND: Cytochrome bd complexes are respiratory oxidases found exclusively in prokaryotes that are important during infection for numerous bacterial pathogens. METHODS: In silico docking was employed to screen approved drugs for their ability to bind to the quinol site of Escherichia coli cytochrome bd-I. Respiratory inhibition was assessed with oxygen electrodes using membranes isolated from E. coli and methicillin-resistant Staphylococcus aureus strains expressing single respiratory oxidases (ie, cytochromes bd, bo', or aa3). Growth/viability assays were used to measure bacteriostatic and bactericidal effects. RESULTS: The steroid drugs ethinylestradiol and quinestrol inhibited E. coli bd-I activity with median inhibitory concentration (IC50) values of 47 ± 28.9 µg/mL (158 ± 97.2 µM) and 0.2 ± 0.04 µg/mL (0.5 ± 0.1 µM), respectively. Quinestrol inhibited growth of an E. coli "bd-I only" strain with an IC50 of 0.06 ± 0.02 µg/mL (0.2 ± 0.07 µM). Growth of an S. aureus "bd only" strain was inhibited by quinestrol with an IC50 of 2.2 ± 0.43 µg/mL (6.0 ± 1.2 µM). Quinestrol exhibited potent bactericidal effects against S. aureus but not E. coli. CONCLUSIONS: Quinestrol inhibits cytochrome bd in E. coli and S. aureus membranes and inhibits the growth of both species, yet is only bactericidal toward S. aureus.

Streptomyces extracellular vesicles are a broad and permissive antimicrobial packaging and delivery system.

Streptomyces are the primary source of bioactive specialized metabolites used in research and medicine, including many antimicrobials. These are presumed to be secreted and function as freely soluble compounds. However, increasing evidence suggests that extracellular vesicles are an alternative secretion system. We assessed environmental and lab-adapted Streptomyces (sporulating filamentous actinomycetes) and found frequent production of antimicrobial vesicles. The molecular cargo included actinomycins, anthracyclines, candicidin, and actinorhodin, reflecting both diverse chemical properties and diverse antibacterial and antifungal activity. The levels of packaged antimicrobials correlated with the level of inhibitory activity of the vesicles, and a strain knocked out for the production of anthracyclines produced vesicles that lacked antimicrobial activity. We demonstrated that antimicrobial containing vesicles achieve direct delivery of the cargo to other microbes. Notably, this delivery via membrane fusion occurred to a broad range of microbes, including pathogenic bacteria and yeast. Vesicle encapsulation offers a broad and permissive packaging and delivery system for antimicrobial specialized metabolites, with important implications for ecology and translation.IMPORTANCEExtracellular vesicle encapsulation changes our picture of how antimicrobial metabolites function in the environment and provides an alternative translational approach for the delivery of antimicrobials. We find many Streptomyces strains are capable of releasing antimicrobial vesicles, and at least four distinct classes of compounds can be packaged, suggesting this is widespread in nature. This is a striking departure from the primary paradigm of the secretion and action of specialized metabolites as soluble compounds. Importantly, the vesicles deliver antimicrobial metabolites directly to other microbes via membrane fusion, including pathogenic bacteria and yeast. This suggests future applications in which lipid-encapsulated natural product antibiotics and antifungals could be used to solve some of the most pressing problems in drug resistance.

Diabetes and infection: review of the epidemiology, mechanisms and principles of treatment.

An association between diabetes and infection has been recognised for many years, with infection being an important cause of death and morbidity in people with diabetes. The COVID-19 pandemic has re-kindled an interest in the complex relationship between diabetes and infection. Some infections occur almost exclusively in people with diabetes, often with high mortality rates without early diagnosis and treatment. However, more commonly, diabetes is a complicating factor in many infections. A reciprocal relationship occurs whereby certain infections and their treatments may also increase the risk of diabetes. People with diabetes have a 1.5- to 4-fold increased risk of infection. The risks are the most pronounced for kidney infection, osteomyelitis and foot infection, but are also increased for pneumonia, influenza, tuberculosis, skin infection and general sepsis. Outcomes from infection are worse in people with diabetes, with the most notable example being a twofold higher rate of death from COVID-19. Hyperglycaemia has deleterious effects on the immune response. Vascular insufficiency and neuropathy, together with altered skin, mucosal and gut microbial colonisation, contribute to the increased risk of infection. Vaccination is important in people with diabetes although the efficacy of certain immunisations may be compromised, particularly in the presence of hyperglycaemia. The principles of treatment largely follow those of the general population with certain notable exceptions.

Removal of common antimicrobial agents by sustained low-efficiency dialysis.

Adequate dosing of antimicrobials is paramount for treating infections in critically ill patients undergoing kidney replacement therapy; however, little is known about antimicrobial removal by sustained low-efficiency dialysis (SLED). The objective was to quantify the removal of cefepime, daptomycin, meropenem, piperacillin-tazobactam, and vancomycin in patients undergoing SLED. Adult patients ≥18 years with acute kidney injury (AKI) or end-stage kidney disease receiving one of the select antimicrobials and requiring SLED were included. Blood and dialysate flow rates were maintained at 250 and 100 mL/min, respectively. Simultaneous arterial and venous blood samples for the analysis of antibiotic concentrations were collected hourly for 8 hours during SLED (on-SLED). Arterial samples were collected every 2 hours for up to 6 hours while not receiving SLED (off-SLED) for the calculation of SLED clearance, half-life (t1/2) on-SLED and off-SLED, and the fraction of removal by SLED (fD). Twenty-one patients completed the study: 52% male, mean age (±SD) 53 ± 13 years, and mean weight of 98 ± 30 kg. Eighty-six percent had AKI, and 4 patients were receiving cefepime, 3 daptomycin, 10 meropenem, 6 piperacillin-tazobactam, and 13 vancomycin. The average SLED time was 7.3 ± 1.1 hours, and the mean ultrafiltration rate was 95 ± 52 mL/hour (range 10-211). The t1/2 on-SLED was substantially lower than the off-SLED t1/2 for all antimicrobials, and the SLED fD varied between 44% and 77%. An 8-hour SLED session led to significant elimination of most antimicrobials evaluated. If SLED is performed, modification of the dosing regimen is warranted to avoid subtherapeutic concentrations.

Duration of Simultaneous Exposure to High-Risk and Lower-Risk Nephrotoxic Antimicrobials in the Neonatal Intensive Care Unit (NICU) and Future Adolescent Kidney Health.

OBJECTIVE: To determine whether greater duration of simultaneous exposure to antimicrobials with high nephrotoxicity risk combined with lower-risk antimicrobials (simultaneous exposure) in the neonatal intensive care unit (NICU) is associated with worse later kidney health in adolescents born preterm with very low birth weight (VLBW). STUDY DESIGN: Prospective cohort study of participants born preterm with VLBW (<1500 g) as singletons between January 1, 1992, and June 30, 1996. We defined simultaneous exposure as a high-risk antimicrobial, such as vancomycin, administered with a lower-risk antimicrobial on the same date in the NICU. Outcomes were serum creatinine, estimated glomerular filtration rate (eGFR), and first-morning urine albumin-creatinine ratio (ACR) at age 14 years. We fit multivariable linear regression models with days of simultaneous exposure and days of nonsimultaneous exposure as main effects, adjusting for gestational age, birth weight, and birth weight z-score. RESULTS: Of the 147 out of 177 participants who had exposure data, 97% received simultaneous antimicrobials for mean duration 7.2 days (SD 5.6). No participant had eGFR <90 ml/min/1.73 m2. The mean ACR was 15.2 mg/g (SD 38.7) and 7% had albuminuria (ACR >30 mg/g). Each day of simultaneous exposure was associated only with a 1.04-mg/g higher ACR (95% CI 1.01 to 1.06). CONCLUSIONS: Despite frequent simultaneous exposure to high-risk combined with lower-risk nephrotoxic antimicrobials in the NICU, there were no clinically relevant associations with worse kidney health identified in adolescence. Although future studies are needed, these findings may provide reassurance in a population thought to be at increased risk of chronic kidney disease.

Sex-dependent effects of antimicrobials and lipopolysaccharide on blood-brain-barrier permeability in pubertal male and female CD1 mice.

Exposure to stressors during puberty can disrupt normal development and possibly increase susceptibility to neurodegenerative disorders later in life. However, the mechanisms underlying the relationship between pubertal stress exposure and neurodegeneration remain unclear. As such, the current study was designed to examine the effects of pubertal antimicrobial (AMNS) and lipopolysaccharide (LPS) treatments on intestinal and blood-brain-barrier (BBB) permeability in male and female mice. Moreover, we also examined the sex-specific effects of pubertal AMNS and LPS treatments on gross motor activity, heart rate, and core body temperature. At four weeks of age, male and female CD1 mice were implanted with the G2 HR E-Mitter telemetry system. At five weeks of age, mice received 200 µL of broad-spectrum antimicrobial or water, through oral gavage, twice daily for seven days. Mice received an intraperitoneal injection of either saline or LPS at six weeks of age. BBB and intestinal permeability were examined 24 h, 72 h, and one week post-LPS/saline treatment. Telemetric data was collected for 48 h post-LPS/saline treatment. The results showed that pubertal AMNS and LPS treatments increased sickness behaviours and decreased body temperature and heart rate, in a sex-dependent manner. Furthermore, pubertal AMNS and LPS treatments resulted in sex-dependent regional increases in BBB permeability 24 h and 72 h post-LPS/saline treatment, while global increases in BBB permeability were only observed one week post-LPS/saline treatment. These results further our understanding of the combined effects of AMNS and LPS treatments on physiology and on the enduring negative changes observed following pubertal exposure to stressors.

Unveiling the mechanism of essential oil action against skin pathogens: from ancient wisdom to modern science.

Essential oils are among the most well-known phyto-compounds, and since ancient times, they have been utilized in medicine. Over 100 essential oils have been identified and utilized as therapies for various skin infections and related ailments. While numerous commercial medicines are available in different dosage forms to treat skin diseases, the persisting issues include their side effects, toxicity, and low efficacy. As a result, researchers are seeking novel classes of compounds as substitutes for synthetic drugs, aiming for minimal side effects, no toxicity, and high efficacy. Essential oils have shown promising antimicrobial activity against skin-associated pathogens. This review presents essential knowledge and scientific information regarding essential oil's antimicrobial capabilities against microorganisms that cause skin infections. Essential oils mechanisms against different pathogens have also been explored. Many essential oils exhibit promising activity against various microbes, which has been qualitatively assessed using the agar disc diffusion experiment, followed by determining the minimum inhibitory concentration for quantitative evaluation. It has been observed that Staphylococcus aureus and Candida albicans have been extensively researched in the context of skin-related infections and their antimicrobial activity, including established modes of action. In contrast, other skin pathogens such as Staphylococcus epidermidis, Streptococcus pyogens, Propionibacterium acnes, and Malassezia furfur have received less attention or neglected. This review report provides an updated understanding of the mechanisms of action of various essential oils with antimicrobial properties. This review explores the anti-infectious activity and mode of action of essential against distinct skin pathogens. Such knowledge can be valuable in treating skin infections and related ailments.

Economic evaluations of therapeutic drug monitoring interventions in acute hospital-based settings: A systematic review.

AIMS: Therapeutic drug monitoring (TDM) aims to optimize drug therapy. As demand on health resources increases, and the technology underpinning TDM becomes more sophisticated, the economic benefits of TDM in hospitals is unclear. The aim of this systematic review was to summarize the economic evidence that could be used to support investment in TDM in hospital settings. In so doing, we sought to provide guidance for future economic evaluations. METHODS: Medline, Embase, CENTRAL, Econlit and NHS Economic Evaluation databases were searched (inception to December 2022) for economic evaluations of hospital-based TDM. Two authors reviewed the studies and extracted data. Overall quality of economic analysis reporting was assessed using the Consolidated Health Economic Evaluation Reporting Standards (CHEERS) checklist. RESULTS: Ten prospective studies (including six randomized studies) and nine retrospective studies were eligible. Overall study reporting was poor, publications meeting a median (range) of 61% (46-82%) of CHEERS checklist criteria. An antimicrobial TDM intervention for adult patients was the focus of most studies (n = 18). Variable clinical outcomes were reported, and length of stay was the primary economic outcome for most studies (n = 13). The majority of studies determined that TDM was economically and clinically favourable (n = 14), four studies reporting a cost-reduction in patient sub-populations. CONCLUSIONS: Significant improvements in both economic and clinical outcomes may be realized with TDM interventions, particularly when targeted to complex patient populations. Attainment of therapeutic target could serve as a feasible surrogate measure of benefit for hospital-based TDM interventions. However, systematic reporting of economic outcomes is needed to inform investment decisions.

Moderate and serious adverse reactions to antimicrobials among hospitalized children: A systematic review.

AIMS: This systematic review aimed to investigate the occurrence of moderate and severe adverse drug reactions (ADRs) to antimicrobials among hospitalized children. METHODS: The PubMed/Medline, Cochrane Library, Embase, Web of Science, Scopus, Lilacs and CINAHL databases were searched in April 2023 to systematically review the published data describing the characteristics of moderate and severe ADRs to antimicrobials among hospitalized children. The search was carried out without date restrictions, up to the search date (April, 2023). RESULTS: At the end of the selection process, 30 articles met the inclusion criteria. Cutaneous reactions were the primary serious clinical manifestations in most articles (19/30), followed by erythema multiforme (71 cases), Stevens-Johnson syndrome (72 cases), and toxic epidermal necrolysis (22 cases). The main antimicrobials involved in moderate and severe ADRs were penicillins, cephalosporins and sulfonamides. Regarding the primary outcomes, 30% (9/30) of the articles reported deaths, and 46.7% (14/30) of studies reported increased lengths of hospital stay, need for intensive care, and transfer to another hospital. Regarding the main interventions, 10% (3/30) of the articles mentioned greater monitoring, suspension, medication substitution or prescription of specific medications for the symptomatology. CONCLUSIONS: The findings of this review could be used to identify areas for improvement and help health professionals and policymakers develop strategies. In addition, we emphasize the importance of knowing about ADRs so that there is adequate management to avoid undesirable consequences.

Metagenomic Analysis of Rhizospheric Bacterial Community of Citrus Trees Expressing Phloem-Directed Antimicrobials.

Huanglongbing, also known as citrus greening, is currently the most devastating citrus disease with limited success in prevention and mitigation. A promising strategy for Huanglongbing control is the use of antimicrobials fused to a carrier protein (phloem protein of 16 kDa or PP16) that targets vascular tissues. This study investigated the effects of genetically modified citrus trees expressing Citrus sinensis PP16 (CsPP16) fused to human lysozyme and ß-defensin-2 on the soil microbiome diversity using 16S amplicon analysis. The results indicated that there were no significant alterations in alpha diversity, beta diversity, phylogenetic diversity, differential abundance, or functional prediction between the antimicrobial phloem-overexpressing plants and the control group, suggesting minimal impact on microbial community structure. However, microbiota diversity analysis revealed distinct bacterial assemblages between the rhizosphere soil and root environments. This study helps to understand the ecological implications of crops expressing phloem-targeted antimicrobials for vascular disease management, with minimal impact on soil microbiota.

Outpatient parenteral antimicrobial therapy (OPAT) in Germany: insights and clinical outcomes from the K-APAT cohort study.

PURPOSE: Outpatient parenteral antimicrobial therapy (OPAT) offers several key advantages, including enhanced patient quality of life, reduced healthcare costs, and a potential reduction of nosocomial infections. It is acknowledged for its safety and effectiveness. This study provides the first systematic clinical data for Germany, where OPAT has not yet been widely adopted. The aim is to establish a foundational reference point for further research and integration of OPAT into the German healthcare system. METHODS: This prospective observational study descriptively analyses data obtained from a cohort of patients receiving OPAT. Both in- and outpatients from all medical specialties could be recruited. Patients administered the anti-infective medications themselves at home using elastomeric pumps. RESULTS: 77 patients received OPAT, with a median duration of 15 days and saving 1782 inpatient days. The most frequently treated entities were orthopaedic infections (n = 20, 26%), S. aureus bloodstream infection (n = 16, 21%) and infectious endocarditis (n = 11, 14%). The most frequently applied drugs were flucloxacillin (n = 18, 23%), penicillin G (n = 13, 17%) and ceftriaxone (n = 10; 13%). Only 5% of patients (n = 4) reported to have missed more than one outpatient dose (max. 3 per patient). Only one catheter-related adverse event required medical intervention, and there were no catheter-related infections. CONCLUSION: The study demonstrates that OPAT can be safely conducted in Germany. In preparation for its broader implementation, crucial next steps include creating medical guidelines, fostering interdisciplinary and inter-sectoral communication, as well as creating financial and structural regulations that facilitate and encourage the adoption of OPAT. TRIAL REGISTRATION NUMBER: NCT04002453.

Pentafluorosulfanyl-substituted biaryl derivatives as MATE-type transporter inhibitors targeting drug-resistant bacteria.

Multidrug and toxin extrusion (MATE) inhibitors improve the antimicrobial susceptibility of drug-resistant bacteria by preventing the efflux of administered antibiotics. In this study, we optimized the chemical structure of a previously identified bacterial-selective MATE inhibitor 1 (EC50 > 30 µM) to improve its activity further. Compound 1 was divided into three fragments (aromatic part, linker part, and guanidine part), and each part was individually optimized. Compound 31 (EC50 = 1.8 µM), a novel pentafluorosulfanyl-containing molecule synthesized following optimized parts, showed antimicrobial activity against MATE-expressing strains at concentrations lower than conventional inhibitor 1 when co-administrated with norfloxacin. Furthermore, 31 was not cytotoxic at effective concentrations. This suggests that compound 31 can be a promising candidate for combating bacterial infections, particularly those resistant to conventional antibiotics by MATE expression.

Tailoring metal oxide nanozymes for biomedical applications: trends, limitations, and perceptions.

Nanomaterials with enzyme-like properties are known as 'nanozymes'. Nanozymes are preferred over natural enzymes due to their nanoscale characteristics and ease of tailoring of their physicochemical properties such as size, structure, composition, surface chemistry, crystal planes, oxygen vacancy, and surface valence state. Interestingly, nanozymes can be precisely controlled to improve their catalytic ability, stability, and specificity which is unattainable by natural enzymes. Therefore, tailor-made nanozymes are being favored over natural enzymes for a range of potential applications and better prospects. In this context, metal oxide nanoparticles with nanozyme-mimicking characteristics are exclusively being used in biomedical sectors and opening new avenues for future nanomedicine. Realising the importance of this emerging area, here, we discuss the mechanistic actions of metal oxide nanozymes along with their key characteristics which affect their enzymatic actions. Further, in this critical review, the recent progress towards the development of point-of-care (POC) diagnostic devices, cancer therapy, drug delivery, advanced antimicrobials/antibiofilm, dental caries, neurodegenerative diseases, and wound healing potential of metal oxide nanozymes is deliberated. The advantages of employing metal oxide nanozymes, their potential limitations in terms of nanotoxicity, and possible prospects for biomedical applications are also discussed with future recommendations.

A novel bioinformatic method for the identification of antimicrobial peptides in metagenomes.

AIMS: This study aimed to develop a new bioinformatic approach for the identification of novel antimicrobial peptides (AMPs), which did not depend on sequence similarity to known AMPs held within databases, but on structural mimicry of another antimicrobial compound, in this case an ultrashort, synthetic, cationic lipopeptide (C12-OOWW-NH2). METHODS AND RESULTS: When applied to a collection of metagenomic datasets, our outlined bioinformatic method successfully identified several short (8-10aa) functional AMPs, the activity of which was verified via disk diffusion and minimum inhibitory concentration assays against a panel of 12 bacterial strains. Some peptides had activity comparable to, or in some cases, greater than, those from published studies that identified AMPs using more conventional methods. We also explored the effects of modifications, including extension of the peptides, observing an activity peak at 9-12aa. Additionally, the inclusion of a C-terminal amide enhanced activity in most cases. Our most promising candidate (named PB2-10aa-NH2) was thermally stable, lipid-soluble, and possessed synergistic activity with ethanol but not with a conventional antibiotic (streptomycin). CONCLUSIONS: While several bioinformatic methods exist to predict AMPs, the approach outlined here is much simpler and can be used to quickly scan huge datasets. Searching for peptide sequences bearing structural similarity to other antimicrobial compounds may present a further opportunity to identify novel AMPs with clinical relevance, and provide a meaningful contribution to the pressing global issue of AMR.

Development of novel indole-quinoline hybrid molecules targeting bacterial proton motive force.

AIMS: This study aimed to develop an editable structural scaffold for improving drug development, including pharmacokinetics and pharmacodynamics of antibiotics by using synthetic compounds derived from a (hetero)aryl-quinoline hybrid scaffold. METHODS AND RESULTS: In this study, 18 CF3-substituted (hetero)aryl-quinoline hybrid molecules were examined for their potential antibacterial activity against Staphylococcus aureus by determining minimal inhibitory concentrations. These 18 synthetic compounds represent modifications to key regions of the quinoline N-oxide scaffold, enabling us to conduct a structure-activity relationship analysis for antibacterial potency. Among the compounds, 3 m exhibited potency against with both methicillin resistant S. aureus strains, as well as other Gram-positive bacteria, including Enterococcus faecalis and Bacillus subtilis. We demonstrated that 3 m disrupted the bacterial proton motive force (PMF) through monitoring the PMF and conducting the molecular dynamics simulations. Furthermore, we show that this mechanism of action, disrupting PMF, is challenging for S. aureus to overcome. We also validated this PMF inhibition mechanism of 3 m in an Acinetobacter baumannii strain with weaken lipopolysaccharides. Additionally, in Gram-negative bacteria, we demonstrated that 3 m exhibited a synergistic effect with colistin that disrupts the outer membrane of Gram-negative bacteria. CONCLUSIONS: Our approach to developing editable synthetic novel antibacterials underscores the utility of CF3-substituted (hetero)aryl-quinoline scaffold for designing compounds targeting the bacterial proton motive force, and for further drug development, including pharmacokinetics and pharmacodynamics.

The interactive effects of medicinal dyes with conventional antimicrobials against skin pathogens.

AIMS: This study aimed to explore potential synergistic effects of medicinal dyes with antimicrobials against pathogens responsible for skin infections. METHODS AND RESULTS: Antimicrobial testing was conducted using minimum inhibitory concentrations and minimum bactericidal/fungicidal concentration assays. The fractional inhibitory index (ΣFIC) of combinations was calculated, and isobolograms were constructed on selected combinations. Toxicity studies were conducted using the brine-shrimp lethality assay. Combination (1:1 ratio) studies noted that 26% of dye-antibiotic combinations were synergistic against the Gram-positive strains, 15% against the Gram-negative strains, and 14% against the yeasts. The Mercurochrome: Betadine® combination noted synergy at ratios against all the Staphylococcus aureus strains with ΣFIC values ranging from 0.05 to 0.48. The combination of Gentian violet with Gentamycin noted a 15-fold decrease in toxicity, and a selectivity index of 977.50 against the Escherichia coli (DSM 22314) strain. Time-kill studies were conducted on the combinations with the highest safe selectivity index (SI) value and lowest safe SI value i.e. Gentian violet with Gentamycin and Malachite green with Neomycin. Both combinations demonstrated better antimicrobial activity in comparison to the independent values and the controls. CONCLUSION: This study highlights the potential for medicinal dye combinations as a treatment for skin infections.

The antimicrobial potential of adarotene derivatives against Staphylococcus aureus strains.

Multidrug-resistant (MDR) pathogens are severely impacting our ability to successfully treat common infections. Here we report the synthesis of a panel of adarotene-related retinoids showing potent antimicrobial activity on Staphylococcus aureus strains (including multidrug-resistant ones). Fluorescence and molecular dynamic studies confirmed that the adarotene analogues were able to induce conformational changes and disfunctions to the cell membrane, perturbing the permeability of the phospholipid bilayer. Since the major obstacle for developing retinoids is their potential cytotoxicity, a selected candidate was further investigated to evaluate its activity on a panel of human cell lines. The compound was found to be well tolerated, with IC50 5-15-fold higher than the MIC on S. aureus strains. Furthermore, the adarotene analogue had a good pharmacokinetic profile, reaching a plasma concentration of about 6 µM after 0.5 h after administration (150 mg/kg), at least twice the MIC observed against various bacterial strains. Moreover, it was demonstrated that the compound potentiated the growth-inhibitory effect of the poorly bioavailable rifaximin, when used in combination. Overall, the collected data pave the way for the development of synthetic retinoids as potential therapeutics for hard-to-treat infectious diseases caused by antibiotic-resistant Gram-positive pathogens.

Evolution of microbiome composition, antibiotic resistance gene loads, and nitrification during the on-farm composting of the solid fraction of pig slurry using two bulking agents.

Composting is a nature-based method used to stabilize organic matter and to transform nitrogen from animal farm manure or solid fraction of slurry (SFS). The use of composted material as source of nutrients for agriculture is limited by its potential to facilitate the propagation of biological hazards like pathogens and antibiotic-resistant bacteria and their associated antibiotic-resistance genes (ARG). We show here an experimental on-farm composting (one single batch) of pig SFS, performed under realistic conditions (under dry continental Mediterranean climate) for 280 days, and using two different bulking agents (maize straw and tree pruning residues) for the initial mixtures. The observed reduction in potentially pathogenic bacteria (80-90%) and of ARG loads (60-100%) appeared to be linked to variations in the microbiome composition occurring during the first 4 months of composting, and concurrent with the reduction of water-soluble ammonium and organic matter loads. Nitrification during the composting has also been observed for both composting piles. Similar patterns have been demonstrated at small scale and the present study stresses the fact that the removal can also occur at full scale. The results suggest that adequate composition of the starting material may accelerate the composting process and improve its global performance. While the results confirm the sanitization potential of composting, they also issue a warning to limit ARG loads in soils and in animal and human gut microbiomes, as the only way to limit their presence in foodstuffs and, therefore, to reduce consumers' exposure.