Defining fractional inhibitory concentration index cutoffs for additive interactions based on self-drug additive combinations, Monte Carlo simulation analysis, and in vitro-in vivo correlation data for antifungal drug combinations against Aspergillus fumigatus

Characterization of sulopenem antimicrobial activity using in vitro time-kill kinetics, synergy, post-antibiotic effect, and sub-inhibitory MIC effect methods against Escherichia coli and Klebsiella pneumoniae isolates

Sulopenem is an oral and intravenous penem antibiotic in clinical development for treatment of urinary tract and intra-abdominal infections caused by multidrug-resistant pathogens. This study evaluated in vitro antimicrobial activity of sulopenem by post-antibiotic effect (PAE), sub-inhibitory minimal inhibitory concentration PAE effect (PAE-SME), checkerboard testing, and time-kill testing. Testing sulopenem at 1×, 5×, or 10× the baseline MIC resulted in a PAE interval of 0.0-0.7 hours. When exposed to 0.5× the sulopenem MIC following 5× MIC, all isolate/agent combinations had PAE-SME values of >4.8 hours. Checkerboard testing revealed no instances of antagonism between sulopenem and comparator agents-indifference was observed in most sulopenem checkerboard combinations. Sulopenem demonstrated bactericidal activity (≥3 log10 [99.9%] reduction in viable organism counts) in all time-kill assays following 24 hours of incubation at 8× the baseline MIC (6/6), 5/6 displaying this activity within 8 hours. The present antimicrobial parameters seen at concentrations surrounding the MIC support optimization of sulopenem dosing and further development. The oral dosing regimen of sulopenem etzadroxil/probenecid 500 mg/500 mg administered every 12 hours was recently evaluated in two phase 3 clinical trials where sulopenem demonstrated efficacy against amoxicillin-clavulanate in uncomplicated urinary tract infection (uUTI) and against ciprofloxacin in fluoroquinolone-resistant uUTI.IMPORTANCESulopenem is an oral and intravenous penem antibiotic in clinical development for treatment of urinary tract and intra-abdominal infections caused by multidrug-resistant pathogens. This study evaluated sulopenem via broth microdilution susceptibility testing, PAE, sub-inhibitory MIC PAE effect, checkerboard testing, and time-kill testing. The results of this study-interpreted along with recent pharmacodynamic in vitro one-compartment and hollow-fiber infection model work-provide insight into the in vitro activity of sulopenem.

A screen to identify antifungal antagonists reveals a variety of pharmacotherapies induce echinocandin tolerance in Candida albicans

Through screening a comprehensive collection of drugs approved for human use, we identified over 20 that oppose the antifungal activity of the echinocandins upon the infectious yeast, Candida albicans . More detailed evaluation of five such drugs, including the atypical antipsychotic aripiprazole and the tyrosine kinase inhibitor ponatinib, indicated they promote C. albicans survival following exposure to the echinocandin antifungals. The activity of the five selected antagonists was dependent upon the Mkc1p MAPK pathway, however, ponatinib was paradoxically shown to suppress phosphorylation and therefore activation of Mkc1p itself. Components of several other signaling pathways are also required, including those of calcineurin and casein kinase-2, suggesting the observed antagonism required much of the cell wall stress responses previously described for C. albicans . Transcriptome analysis revealed that the antagonists stimulated the expression of genes involved in xenobiotic and antifungal resistance, and suppressed the expression of genes associated with hyphal growth. Thus, the echinocandin antagonistic drugs modulate C. albicans physiology in ways that could impact its pathogenicity and/or response to therapeutic intervention. Finally, a mutant lacking the Efg1p transcription factor, which has a central role in the activation of C. albicans hyphal growth was found to have intrinsically high levels of echinocandin tolerance, suggesting a link between modulation of morphogenesis related signaling and echinocandin tolerance.

Importance

We report a substantial number of previously unknown drug interactions that modulate the echinocandin sensitivity of one of the most prevalent human fungal pathogens, Candida albicans . The echinocandins are the first line therapy for treating disseminated and often lethal Candida infections, that account for >75% of invasive fungal infections in the U.S.. For largely unknown reasons, a substantial number of patients with invasive candidiasis fail to respond to treatment with these drugs. The finding of this study suggest that co-administered medications have the potential to influence the therapeutic outcomes of invasive fungal infections through modulating antifungal drug tolerance and/or fungal pathogenicity. The potential for echinocandin antagonistic medications to influence therapeutic outcomes is discussed.

Synergistic antimicrobial activity of essential oils mixture of Moringa oleifera, Cinnamomum verum and Nigella sativa against Staphylococcus aureus using L-optimal mixture design

The urgent need to address the growing problem of antimicrobial resistance in multidrug-resistant bacteria requires the development of pioneering approaches to treatment. The present study aims to evaluate the antimicrobial potential of the essential oils (EOs) of Moringa oleifera (moringa), Cinnamomum verum (cinnamon), and Nigella sativa (black seed) and the synergistic effect of the mixture of these oils against Staphylococcus aureus MCC 1351. Statistical modeling revealed cinnamon oil had the highest individual antimicrobial potency, followed by black seed oil. The combination of the three EOs exhibited significant synergistic effects compared to the individual oils, with a Fractional Inhibitory Concentration (∑FIC) index of 0.27. L-Optimal mixture design of response surface methodology (RSM) identified the optimal mixture as moringa: cinnamon: black seed oils by the ratio of (1:1:1) in run 15 (0.338:0.307:0.355 mL) (v/v). This mixture exhibited significant antibacterial efficacy, outperforming individual oils and conventional antibiotics like tetracycline. Specifically, the combination reduced the MIC values from 3.12, 0.78, and 6.25 to 0.25, 0.06, and 0.78 μg/mL for moringa, cinnamon, and black seed oil, respectively. Synergistic interactions between oils further boosted efficacy, with moringa-cinnamon and cinnamon-black seed pairings exhibiting the strongest synergies. The developed predictive models for IZD and MIC showed excellent fit, with R2 values of 0.9843 and 0.9958, respectively. Pareto chart analysis highlighted the predominant individual and synergistic effects, with the Moringa-Cinnamon interaction exhibiting the highest positive synergy. Notably, the oil mixture of run 15 demonstrated excellent biocompatibility, maintaining 97.6% viability of normal human skin fibroblasts (HSF) after 24 h exposure to 200 μL EOs of the mixture per mL. Gas chromatography mass spectrometry (GC/MS) identified abundant bioactive phytochemicals like cinnamaldehyde, linoleic acid, and palmitic acid methyl esters underlying the observed antimicrobial effects. This rationally designed, synergistic phytochemical combination presents a promising natural therapeutic against antibiotic-resistant S. aureus while exhibiting minimal cytotoxicity. The results underscore how combining essential oils could help address the issue of antibiotic resistance in S. aureus.

Synergistic effect between taurine-induced silver ion and itraconazole against azole-resistant Candida species and Candida auris

BACKGROUND

Azole antifungals are the first-line choice for treating candidiasis within a limited antifungal option. However, azole-resistant Candida species have increased rapidly, causing severe clinical threats, especially multidrug-resistant (MDR) isolates. The emergence of Candida auris has also caused global concerns recently.

METHODS

Herein, we evaluated the antifungal activity of taurine-induced silver ions (Tau-Ag), prepared by the induction from silver-incorporated mesoporous bioactive glass to address this issue.

RESULTS

Our data demonstrated that minimum inhibitory concentrations (MICs) of Tau-Ag ranged from 0.020 to 0.078 mg/mL in 24h and from 0.039 to 0.156 mg/mL in 48h. No hemolysis and cytotoxicity were observed at the MICs. Furthermore, no in vivo toxicity related to Tau-Ag was observed in a Caenorhabditis elegans model. In the investigation of antifungal mechanisms, we observed that the reactive oxygen species (ROS) level significantly increased when Candida spp. treated with Tau-Ag. Biofilm formation inhibition assays found that Tau-Ag may penetrate the biofilm and eliminate biofilm-forming cells. In the time-kill method, Tau-Ag showed a long-lasting fungistatic effect and superior antifungal effect compared to itraconazole alone. Furthermore, Tau-Ag showed synergistic antifungal effects in combination with itraconazole, effectively restoring its activity.

CONCLUSION

Our results confirmed the potential of Tau-Ag and its combination use with itraconazole to serve as a novel antifungal agent to combat the plight of administration on azole-resistant and MDR Candida spp. and C. auris.

Enhanced Nitric Oxide Delivery Through Self-Assembling Nanoparticles for Eradicating Gram-Negative Bacteria

In the current battle against antibiotic resistance, the resilience of Gram-negative bacteria against traditional antibiotics is due not only to their protective outer membranes but also to mechanisms like efflux pumps and enzymatic degradation of drugs, underscores the urgent need for innovative antimicrobial tactics. Herein, this study presents an innovative method involving the synthesis of three furoxan derivatives engineered to self-assemble into nitric oxide (NO) donor nanoparticles (FuNPs). These FuNPs, notably supplied together with polymyxin B (PMB), achieve markedly enhanced bactericidal efficacy against a wide spectrum of bacterial phenotypes at considerably lower NO concentrations (0.1-2.8 µg mL-1), which is at least ten times lower than the reported data for NO donors (≥200 µg mL-1). The bactericidal mechanism is elucidated using confocal, scanning, and transmission electron microscopy techniques. Neutron reflectometry confirms that FuNPs initiate membrane disruption by specifically engaging with the polysaccharides on bacterial surfaces, causing structural perturbations. Subsequently, PMB binds to lipid A on the outer membrane, enhancing permeability and resulting in a synergistic bactericidal action with FuNPs. This pioneering strategy underscores the utility of self-assembly in NO delivery as a groundbreaking paradigm to circumvent traditional antibiotic resistance barriers, marking a significant leap forward in the development of next-generation antimicrobial agents.

Novel Epigallocatechin Gallate (EGCG) Analogs with Improved Biochemical Properties for Targeting Extracellular and Intracellular Staphylococcus aureus

Staphylococcus aureus is a leading cause of bloodstream infection (SAB), with up to 30% mortality. Despite treatment with standard antibiotics, one in three patients develops a persistent infection, which portends a five-fold increase in the risk of death. Persistent SAB has been attributed in part to the inability of antistaphylococcal antibiotics to eradicate intracellular S. aureus surviving inside macrophages. (-)- Epigallocatechin gallate (EGCG) is a catechin found in green tea that has been widely studied for its broad biological activities, ranging from anticancer to antibacterial activity. However, EGCG is greatly limited by its poor drug-like properties in terms of stability, membrane permeability, and bioavailability. In this study, we established through a series of in vitro experiments that structural modifications of EGCG enhanced drug-like properties while maintaining or improving its antistaphylococcal activity. Our lead EGCG analogs (MCC-1 and MCC-2) showed improved biochemical properties along with increased potency against extracellular S. aureus and restored susceptibility of β-lactam agents to methicillin-resistant S. aureus (MRSA). Importantly, the lead analogs but not EGCG potentiated macrophage- and antibiotic-mediated clearance of intracellular bacteria. Overall, EGCG analogs showed promise for further development as adjunctive therapy candidates for the treatment of SAB.

A Comparative Review of Eugenol and Citral Anticandidal Mechanisms: Partners in Crimes Against Fungi

Candida albicans is an emerging multidrug-resistant opportunistic pathogen that causes candidiasis, superficial infections on the mucosa, nails or skin, and life-threatening candidemia in deep tissue when disseminated through the bloodstream. Recently, there has been a sharp rise in resistant strains, posing a considerable clinical challenge for the treatment of candidiasis. There has been a resurged interest in the pharmacological properties of essential oils and their active components, for example, monoterpenes with alcohol (-OH) and aldehyde (-CHO) groups. Eugenol and citral have shown promising in vitro and in vivo activity against Candida species. Although there is substantial research on the efficacy of these essential oil components against C. albicans, a detailed knowledge of their mycological mechanisms is lacking. To explore the broad-spectrum effects of EOs, it is more meaningful and rational to study the whole essential oil, along with some of its major components. This review provides a comprehensive overview of eugenol and citral anticandidal and antivirulence activity, alone and together, along with the associated mechanisms and limitations of our current knowledge.

Gladiolin produced by pathogenic Burkholderia synergizes with amphotericin B through membrane lipid rearrangements

Amphotericin B (AmpB) is an effective but toxic antifungal drug. Thus, improving its activity/toxicity relationship is of interest. AmpB disrupts fungal membranes by two proposed mechanisms: ergosterol sequestration from the membrane and pore formation. Whether these two mechanisms operate in conjunction and how they could be potentiated remains to be fully understood. Here, we report that gladiolin, a polyketide antibiotic produced by Burkholderia gladioli, is a strong potentiator of AmpB and acts synergistically against Cryptococcus and Candida species, including drug-resistant C. auris. Gladiolin also synergizes with AmpB against drug-resistant fungal biofilms, while exerting no mammalian cytotoxicity. To explain the mechanism of synergy, we show that gladiolin interacts with membranes via a previously unreported binding mode for polyketides. Moreover, gladiolin modulates lipid binding by AmpB and, in combination, causes faster and more pronounced lipid rearrangements relative to AmpB alone which include membrane thinning consistent with ergosterol extraction, areas of thickening, pore formation, and increased membrane destruction. These biophysical data provide evidence of a functional interaction between gladiolin and AmpB at the membrane interface. The data further indicate that the two proposed AmpB mechanisms (ergosterol sequestration and pore formation) act in conjunction to disrupt membranes, and that gladiolin synergizes by enhancing both mechanisms. Collectively, our findings shed light on AmpB's mechanism of action and characterize gladiolin as an AmpB potentiator, showing an antifungal mechanism distinct from its proposed antibiotic activity. We shed light on the synergistic mechanism at the membrane, and provide insights into potentiation strategies to improve AmpB's activity/toxicity relationship.

IMPORTANCE

Amphotericin B (AmpB) is one of the oldest antifungal drugs in clinical use. It is an effective therapeutic, but it comes with toxicity issues due to the similarities between its fungal target (the membrane lipid ergosterol) and its mammalian counterpart (cholesterol). One strategy to improve its activity/toxicity relationship is by combinatorial therapy with potentiators, which would enable a lower therapeutic dose of AmpB. Here, we report on the discovery of the antibiotic gladiolin as a potentiator of AmpB against several priority human fungal pathogens and fungal biofilms, with no increased toxicity against mammalian cells. We show that gladiolin potentiates AmpB by increasing and accelerating membrane damage. Our findings also provide insights into the on-going debate about the mechanism of action of AmpB by indicating that both proposed mechanisms, extraction of ergosterol from membranes and pore formation, are potentiated by gladiolin.

CAF to the Rescue! Potential and Challenges of Combination Antifungal Therapy for Reducing Morbidity and Mortality in Hospitalized Patients With Serious Fungal Infections

The global burden of invasive fungal disease is substantial and escalating. Combination antifungal therapy (CAF) may improve patient outcomes by reducing development of resistance, improving drug penetration and rate of fungal clearance, and allowing for lower and less toxic antifungal drug doses; yet, increased cost, antagonism, drug-drug interactions, and toxicity are concerns. Clinical practice guidelines recommend antifungal monotherapy, rather than CAF, for most invasive fungal diseases due to a lack of comparative randomized clinical trials. An examination of the existing body of CAF research should frame new hypotheses and determine priorities for future CAF clinical trials. We performed a systematic review of CAF clinical studies for invasive candidiasis, cryptococcosis, invasive aspergillosis, and mucormycosis. Additionally, we summarized findings from animal models of CAF and assessed laboratory methods available to evaluate CAF efficacy. Future CAF trials should be prioritized according to animal models showing improved survival and observational clinical data supporting efficacy and safety.

Imidazoles and Quaternary Ammonium Compounds as Effective Therapies against (Multidrug-Resistant) Bacterial Wound Infections

BACKGROUND/OBJECTIVES

The rise and spread of antimicrobial resistance complicates the treatment of bacterial wound pathogens, further increasing the need for newer, effective therapies. Azoles such as miconazole have shown promise as antibacterial compounds; however, they are currently only used as antifungals. Previous research has shown that combining azoles with quaternary ammonium compounds yields synergistic activity against fungal pathogens, but the effect on bacterial pathogens has not been studied yet.

METHODS

In this study, the focus was on finding active synergistic combinations of imidazoles and quaternary ammonium compounds against (multidrug-resistant) bacterial pathogens through checkerboard assays. Experimental evolution in liquid culture was used to evaluate the possible emergence of resistance against the most active synergistic combination.

RESULTS

Several promising synergistic combinations were identified against an array of Gram-positive pathogens: miconazole/domiphen bromide, ketoconazole/domiphen bromide, clotrimazole/domiphen bromide, fluconazole/domiphen bromide and miconazole/benzalkonium chloride. Especially, miconazole with domiphen bromide exhibits potential, as it has activity at a low concentration against a broad range of pathogens and shows an absence of strong resistance development over 11 cycles of evolution.

CONCLUSIONS

This study provides valuable insight into the possible combinations of imidazoles and quaternary ammonium compounds that could be repurposed for (topical) wound treatment. Miconazole with domiphen bromide shows the highest application potential as a possible future wound therapy. However, further research is needed into the mode of action of these compounds and their efficacy and toxicity in vivo.

N-Acyl phenothiazines as mycobacterial ATP synthase inhibitors: Rational design, synthesis and in vitro evaluation against drug sensitive, RR and MDR-TB

The mycobacterial F-ATP synthase is responsible for the optimal growth, metabolism and viability of Mycobacteria, establishing it as a validated target for the development of anti-TB therapeutics. Herein, we report the discovery of an N-acyl phenothiazine derivative, termed PT6, targeting the mycobacterial F-ATP synthase. PT6 is bactericidal and active against the drug sensitive, Rifampicin-resistant as well as Multidrug-resistant tuberculosis strains. Compound PT6 showed noteworthy inhibition of F-ATP synthesis, exhibiting an IC50 of 0.788 µM in M. smegmatis IMVs and was observed that it could deplete intracellular ATP levels, exhibiting an IC50 of 30 µM. PT6 displayed a high selectivity towards mycobacterial ATP synthase compared to mitochondrial ATP synthase. Compound PT6 showed a minor synergistic effect in combination with Rifampicin and Isoniazid. PT6 demonstrated null cytotoxicity as confirmed by assessing its toxicity against VERO cell lines. Further, the binding mechanism and the activity profile of PT6 were validated by employing in silico techniques such as molecular docking, Prime MM/GBSA, DFT and ADMET analysis. These results suggest that PT6 presents an attractive lead for the discovery of a novel class of mycobacterial F-ATP synthase inhibitors.

A kalihinol analog disrupts apicoplast function and vesicular trafficking in P. falciparum malaria

We report the discovery of MED6-189, an analog of the kalihinol family of isocyanoterpene natural products that is effective against drug-sensitive and drug-resistant Plasmodium falciparum strains, blocking both asexual replication and sexual differentiation. In vivo studies using a humanized mouse model of malaria confirm strong efficacy of the compound in animals with no apparent hemolytic activity or toxicity. Complementary chemical, molecular, and genomics analyses revealed that MED6-189 targets the parasite apicoplast and acts by inhibiting lipid biogenesis and cellular trafficking. Genetic analyses revealed that a mutation in PfSec13, which encodes a component of the parasite secretory machinery, reduced susceptibility to the drug. Its high potency, excellent therapeutic profile, and distinctive mode of action make MED6-189 an excellent addition to the antimalarial drug pipeline.

Arcopilins: A New Family of Staphylococcus aureus Biofilm Disruptors from the Soil Fungus Arcopilus navicularis

Biofilms represent a key challenge in the treatment of microbial infections; for instance, Staphylococcus aureus causes chronic or fatal infections by forming biofilms on medical devices. Herein, the fungus Arcopilus navicularis was found to produce a novel family of PKS-NRPS metabolites that are able to disrupt preformed biofilms of S. aureus. Arcopilins A-F (1-6), tetramic acids, and arcopilin G (7), a 2-pyridone, were elucidated using HR-ESI-MS and one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy. Their absolute configuration was established by the synthesis of MPTA-esters for 2, analysis of 1H-1H coupling constants, and ROESY correlations, along with comparison with the crystal structure of 7. Arcopilin A (1) not only effectively disrupts preformed biofilms of S. aureus but also potentiates the activity of gentamicin and vancomycin up to 115- and 31-fold times, respectively. Our findings demonstrate the potential application of arcopilins for the conjugated treatment of infections caused by S. aureus with antibiotics unable to disrupt preformed biofilms.

Investigation on the Synergy between Membrane Permeabilizing Amphiphilic α-Hydrazido Acids and Commonly Used Antibiotics against Drug-Resistant Bacteria

The growth of (multi)drug resistance in bacteria is among the most urgent global health issues. Monocationic amphiphilic α-hydrazido acid derivatives are structurally simple mimics of antimicrobial peptides (AMPs) with fewer drawbacks. Their mechanism of membrane permeabilization at subtoxic concentrations was found to begin with an initial electrostatic attraction of isolated amphiphile molecules to the phospholipid heads, followed by a rapid insertion of the apolar portions. As the accumulation into the bilayer proceeded, the membrane increased its fluidity and permeability without being subjected to major structural damage. After having ascertained that α-hydrazido acid amphiphiles do not interact with bacterial DNA, they were subjected to synergy evaluation for combinations with conventional antibiotics. Synergy was observed for combinations with tetracycline against sensitive S. aureus and E. coli, as well as with ciprofloxacin and colistin against resistant strains. Additivity with a remarkable recovery in activity of conventional antibiotics (from 2-fold to ≥32-fold) together with largely subtoxic concentrations of α-hydrazido acid derivatives was found for combinations with ciprofloxacin toward susceptible S. aureus and methicillin toward MRSa. However, no potentiation of conventional antibiotics was observed for combinations with linezolid and gentamicin against the corresponding resistant S. aureus and E. coli strains.

A metabolomics pipeline highlights microbial metabolism in bloodstream infections

The growth of antimicrobial resistance (AMR) highlights an urgent need to identify bacterial pathogenic functions that may be targets for clinical intervention. Although severe infections profoundly alter host metabolism, prior studies have largely ignored microbial metabolism in this context. Here, we describe an iterative, comparative metabolomics pipeline to uncover microbial metabolic features in the complex setting of a host and apply it to investigate gram-negative bloodstream infection (BSI) in patients. We find elevated levels of bacterially derived acetylated polyamines during BSI and discover the enzyme responsible for their production (SpeG). Blocking SpeG activity reduces bacterial proliferation and slows pathogenesis. Reduction of SpeG activity also enhances bacterial membrane permeability and increases intracellular antibiotic accumulation, allowing us to overcome AMR in culture and in vivo. This study highlights how tools to study pathogen metabolism in the natural context of infection can reveal and prioritize therapeutic strategies for addressing challenging infections.

Enhancing outer membrane permeability of tetracycline antibiotics in P. aeruginosa using TOB-CIP conjugates

Pseudomonas aeruginosa is an opportunistic critical 'priority 1' Gram-negative bacterium that poses a severe threat to public healthcare due to rising antibiotic resistance. Particularly, low membrane permeability and overexpression of efflux pumps in P. aeruginosa lead to intrinsic resistance that compromises the antibacterial activity of antibiotics. The broad-spectrum antibiotics class, tetracyclines, are rarely used to treat P. aeruginosa infections. In the present study, we describe a series of tobramycin-ciprofloxacin (TOB-CIP) conjugates in which the carboxylic acid of ciprofloxacin is linked to the aminoglycoside tobramycin using various tethers thereby generating a cationic amphiphile. The emerging amphiphilic conjugates potentiate tetracycline antibiotics including minocycline, doxycycline, tigecycline, and eravacycline against multidrug-resistant P. aeruginosa isolates. The structure-activity relationship investigation indicates that the flexible hydrophobic C12 carbon-chain linker in TOB-CIP conjugate 1a is an optimal potentiator of tetracyclines against tetracycline-resistant and -susceptible strains of P. aeruginosa. Furthermore, conjugate 1a consistently synergized with the 3rd generation tetracycline, eravacycline, in P. aeruginosa PAO1 in the presence of up to 25% fetal bovine serum (FBS).

Selective in vitro Synergistic Evaluation of Probiotic Tolerant morpholinyl- and 4-ethylpiperazinyl-Imidazole-chalcone Derivatives on Gastrointestinal System Pathogens

Imidazole-chalcone compounds are recognised for their broad-spectrum antimicrobial properties. Probiotic-friendly, selective new-generation antimicrobials prove to be more efficient in combating gastrointestinal system pathogens. The aim of this study is to identify imidazole-chalcone derivatives that probiotics tolerate and evaluate their in vitro synergistic antimicrobial effects on pathogens. In this study, fifteen previously identified imidazole-chalcone derivatives were analyzed for their in vitro antimicrobial properties against gastrointestinal microorganisms. Initially, the antimicrobial activity of pathogens was measured using the agar well diffusion method, while the susceptibility of probiotics was determined by microdilution. The chosen imidazole-chalcone derivatives were assessed for synergistic effects using the checkerboard method. Four imidazole-chalcone derivatives to which probiotic bacteria were tolerant exhibited antibacterial and antifungal activity against the human pathogens tested. To our knowledge, this study is the first to reveal the fractional inhibitory concentration (FIC) of combinations of imidazole-chalcone derivatives. Indeed, the minimum inhibitory concentrations (MIC) for morpholinyl- (ZDO-3f) and 4-ethylpiperazinyl- (ZDO-3 m) imidazole-chalcones were notably low when tested against E. coli and B. subtilis, with values of 31.25 μg/mL and 125 μg/mL, respectively. The combination of morpholinyl- and 4-ethylpiperazinyl derivatives demonstrated an indifferent effect against E. coli, but an additive effect was observed for B. subtilis. Additionally, it was observed that imidazole-chalcone derivatives did not exhibit any inhibitory effects on probiotic organisms like Lactobacillus fermentum (CECT-5716), Lactobacillus rhamnosus (GG), and Lactobacillus casei (RSSK-591). This study demonstrates that imidazole-chalcone derivatives that are well tolerated by probiotics can potentially exert a synergistic effect against gastrointestinal system pathogens.

Novel antimony-based antimicrobial drug targets membranes of Gram-positive and Gram-negative bacterial pathogens

Antimicrobial resistance (AMR) poses a significant worldwide public health crisis that continues to threaten our ability to successfully treat bacterial infections. With the decline in effectiveness of conventional antimicrobial therapies and the lack of new antibiotic pipelines, there is a renewed interest in exploring the potential of metal-based antimicrobial compounds. Antimony-based compounds with a long history of use in medicine have re-emerged as potential antimicrobial agents. We previously synthesized a series of novel organoantimony(V) compounds complexed with cyanoximates with a strong potential of antimicrobial activity against several AMR bacterial and fungal pathogens. Here, five selected compounds were studied for their antibacterial efficacy against three important bacterial pathogens: Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus. Among five tested compounds, SbPh4ACO showed antimicrobial activity against all three bacterial strains with the MIC of 50-100 µg/mL. The minimum bactericidal concentration/MIC values were less than or equal to 4 indicating that the effects of SbPh4ACO are bactericidal. Moreover, ultra-thin electron microscopy revealed that SbPh4ACO treatment caused membrane disruption in all three strains, which was further validated by increased membrane permeability. We also showed that SbPh4ACO acted synergistically with the antibiotics, polymyxin B and cefoxitin used to treat AMR strains of P. aeruginosa and S. aureus, respectively, and that at synergistic MIC concentration 12.5 µg/mL, its cytotoxicity against the cell lines, Hela, McCoy, and A549 dropped below the threshold. Overall, the results highlight the antimicrobial potential of novel antimony-based compound, SbPh4ACO, and its use as a potentiator of other antibiotics against both Gram-positive and Gram-negative bacterial pathogens.

IMPORTANCE

Antibiotic resistance presents a critical global public health crisis that threatens our ability to combat bacterial infections. In light of the declining efficacy of traditional antibiotics, the use of alternative solutions, such as metal-based antimicrobial compounds, has gained renewed interest. Based on the previously synthesized innovative organoantimony(V) compounds, we selected and further characterized the antibacterial efficacy of five of them against three important Gram-positive and Gram-negative bacterial pathogens. Among these compounds, SbPh4ACO showed broad-spectrum bactericidal activity, with membrane-disrupting effects against all three pathogens. Furthermore, we revealed the synergistic potential of SbPh4ACO when combined with antibiotics, such as cefoxitin, at concentrations that exert no cytotoxic effects tested on three mammalian cell lines. This study offers the first report on the mechanisms of action of novel antimony-based antimicrobial and presents the therapeutic potential of SbPh4ACO in combating both Gram-positive and Gram-negative bacterial pathogens while enhancing the efficacy of existing antibiotics.

Uncovering the potentiality of quinazoline derivatives against Pseudomonas aeruginosa with antimicrobial synergy and SAR analysis

Antimicrobial resistance has emerged as a covert global health crisis, posing a significant threat to humanity. If left unaddressed, it is poised to become the foremost cause of mortality worldwide. Among the multitude of resistant bacterial pathogens, Pseudomonas aeruginosa, a Gram-negative, facultative bacterium, has been responsible for mild to deadly infections. It is now enlisted as a global critical priority pathogen by WHO. Urgent measures are required to combat this formidable pathogen, necessitating the development of novel anti-pseudomonal drugs. To confront this pressing issue, we conducted an extensive screening of 3561 compounds from the ChemDiv library, resulting in the discovery of potent anti-pseudomonal quinazoline derivatives. Among the identified compounds, IDD-8E has emerged as a lead molecule, exhibiting exceptional efficacy against P. aeruginosa while displaying no cytotoxicity. Moreover, IDD-8E demonstrated significant pseudomonal killing, disruption of pseudomonal biofilm and other anti-bacterial properties comparable to a well-known antibiotic rifampicin. Additionally, IDD-8E's synergy with different antibiotics further strengthens its potential as a powerful anti-pseudomonal agent. IDD-8E also exhibited significant antimicrobial efficacy against other ESKAPE pathogens. Moreover, we elucidated the Structure-Activity-Relationship (SAR) of IDD-8E targeting the essential WaaP protein in P. aeruginosa. Altogether, our findings emphasize the promise of IDD-8E as a clinical candidate for novel anti-pseudomonal drugs, offering hope in the battle against antibiotic resistance and its devastating impact on global health.

Discovery of novel secondary metabolites from the basidiomycete Lentinus cf. sajor-caju and their inhibitory effects on Staphylococcus aureus biofilms

Three novel derivatives of microporenic acid, microporenic acids H-J, were identified from submerged cultures of a Lentinus species obtained from a basidiome collected during a field trip in the tropical rainforest in Western Kenya. Their structures were elucidated via HR-ESIMS spectra and 1D/2D NMR spectroscopic analyses, as well as by comparison with known derivatives. Applying biofilm assays based on crystal violet staining and confocal microscopy, two of these compounds, microporenic acids H and I, demonstrated the ability to inhibit biofilm formation of the opportunistic pathogen Staphylococcus aureus. Thereby, they were effective in a concentration range that did not affect planktonic growth. Additionally, microporenic acid I enhanced the anti-biofilm activity of the antibiotics vancomycin and gentamicin when used in combination. This opens up possibilities for the use of these compounds in combination therapy to prevent the formation of S. aureus biofilms.

Combined effect of SAR-endolysin LysKpV475 with polymyxin B and Salmonella bacteriophage phSE-5

Endolysins are bacteriophage (or phage)-encoded enzymes that catalyse the peptidoglycan breakdown in the bacterial cell wall. The exogenous action of recombinant phage endolysins against Gram-positive organisms has been extensively studied. However, the outer membrane acts as a physical barrier when considering the use of recombinant endolysins to combat Gram-negative bacteria. This study aimed to evaluate the antimicrobial activity of the SAR-endolysin LysKpV475 against Gram-negative bacteria as single or combined therapies, using an outer membrane permeabilizer (polymyxin B) and a phage, free or immobilized in a pullulan matrix. In the first step, the endolysin LysKpV475 in solution, alone and combined with polymyxin B, was tested in vitro and in vivo against ten Gram-negative bacteria, including highly virulent strains and multidrug-resistant isolates. In the second step, the lyophilized LysKpV475 endolysin was combined with the phage phSE-5 and investigated, free or immobilized in a pullulan matrix, against Salmonella enterica subsp. enterica serovar Typhimurium ATCC 13311. The bacteriostatic action of purified LysKpV475 varied between 8.125 μg ml-1 against Pseudomonas aeruginosa ATCC 27853, 16.25 μg ml-1 against S. enterica Typhimurium ATCC 13311, and 32.50 μg ml-1 against Klebsiella pneumoniae ATCC BAA-2146 and Enterobacter cloacae P2224. LysKpV475 showed bactericidal activity only for P. aeruginosa ATCC 27853 (32.50 μg ml-1) and P. aeruginosa P2307 (65.00 μg ml-1) at the tested concentrations. The effect of the LysKpV475 combined with polymyxin B increased against K. pneumoniae ATCC BAA-2146 [fractional inhibitory concentration index (FICI) 0.34; a value lower than 1.0 indicates an additive/combined effect] and S. enterica Typhimurium ATCC 13311 (FICI 0.93). A synergistic effect against S. enterica Typhimurium was also observed when the lyophilized LysKpV475 at ⅔ MIC was combined with the phage phSE-5 (m.o.i. of 100). The lyophilized LysKpV475 immobilized in a pullulan matrix maintained a significant Salmonella reduction of 2 logs after 6 h of treatment. These results demonstrate the potential of SAR-endolysins, alone or in combination with other treatments, in the free form or immobilized in solid matrices, which paves the way for their application in different areas, such as in biocontrol at the food processing stage, biosanitation of food contact surfaces and biopreservation of processed food in active food packing.

Comparison of in vitro synergy between polymyxin B or colistin in combination with 16 antimicrobial agents against multidrug-resistant Acinetobacter baumannii isolates

PURPOSES

This study determined the synergy of polymyxin B (POLB) and colistin (COL) with 16 other tested antimicrobial agents in the inhibition of multidrug-resistant Acinetobacter baumannii (MDR-AB).

METHODS

We used chequerboard assays to determine synergy between the drugs against 50 clinical MDR-AB from a tertiary hospital in the Zhejiang province in 2019, classifying combinations as either antagonistic, independent, additive, or synergistic. The efficacy of hit combinations which showed highest synergistic rate were confirmed using time-kill assays.

RESULTS

Both POLB and COL displayed similar bactericidal effects when used in combination with these 16 tested drugs. Antagonism was only observed for a few strains (2%) exposed to a combination of POLB and cefoperazone/sulbactam (CSL). A higher percentage of synergistic combinations with POLB and COL were observed with rifabutin (RFB; 90%/96%), rifampicin (RIF; 60%/78%) and rifapentine (RFP; 56%/76%). Time-kill assays also confirmed the synergistic effect of POLB and rifamycin class combinations. 1/2 MIC rifamycin exposure can achieve bacterial clearance when combined with 1/2 MIC POLB or COL.

CONCLUSION

Nearly no antagonism was observed when combining polymyxins with other drugs by both chequerboard and time-kill assays, suggesting that polymyxins may be effective in combination therapy. The combinations of POLB/COL with RFB, RIF, and RFP displayed neat synergy, with RFB showing the greatest effect.

Application of tobramycin benzyl ether as an antibiotic adjuvant capable of sensitizing multidrug-resistant Gram-negative bacteria to rifampicin

The emergence of aminoglycoside resistance has prompted the development of amphiphilic aminoglycoside derivatives which target bacterial membranes. Tobramycin and nebramine ether derivatives initially designed for this purpose were optimized and screened for their potential application as outer membrane (OM) permeabilizing adjuvants. Structure-activity relationship (SAR) studies revealed that the tobramycin benzyl ether was the most optimal OM permeabilizer, capable of potentiating rifampicin, novobiocin, vancomycin, minocycline, and doxycycline against Gram-negative bacteria. The innovative use of this compound as an adjuvant is highlighted by its ability to sensitize multidrug-resistant (MDR) Gram-negative bacteria to rifampicin and restore the susceptibility of MDR Escherichia coli to minocycline.

Mimicking Charged Host-Defense Peptides to Tune the Antifungal Activity and Biocompatibility of Amphiphilic Polymers

Invasive fungal infections impose a substantial global health burden. They cause more than 1.5 million deaths annually and are insufficiently met by the currently approved antifungal drugs. Antifungal peptides are a promising alternative to existing antifungal drugs; however, they can be challenging to synthesize, and are often susceptible to proteases in vivo. Synthetic polymers which mimic the properties of natural antifungal peptides can circumvent these limitations. In this study, we developed a library of 29 amphiphilic polyacrylamides with different charged units, namely, amines, guanidinium, imidazole, and carboxylic acid groups, representative of the natural amino acids lysine, arginine, histidine, and glutamic acid. Ternary polymers incorporating primary ammonium (lysine-like) or imidazole (histidine-like) groups demonstrated superior activity against Candida albicans and biocompatibility with mammalian cells compared to the polymers containing the other charged groups. Furthermore, a combination of primary ammonium, imidazole, and guanidinium (arginine-like) within the same polymer outperformed the antifungal drug amphotericin B in terms of therapeutic index and exhibited fast C. albicans-killing activity. The most promising polymer compositions showed synergistic effects in combination with caspofungin and fluconazole against C. albicans and additionally demonstrated activity against other clinically relevant fungi. Collectively, these results indicate the strong potential of these easily producible polymers to be used as antifungals.

Activity of extracts and terpenoids from Tontelea micrantha (Mart. ex Schult.) A.C.Sm. (Celastraceae) against pathogenic bacteria

The pharmacological properties of plant extracts and phytochemicals, such as flavonoids and terpenoids, remain of great interest. In this work, the effect of extracts, friedelan-3,21-dione, and 3β-O-D-glucosyl-sitosterol isolated from Tontelea micrantha roots was evaluated against Staphylococcus aureus, Bacillus subtilis, Klebsiella pneumoniae, Klebsiella oxytoca and Escherichia coli. The antibacterial activity was evaluated by the minimum inhibitory and bactericidal concentrations (MIC and MBC, respectively), and the synergistic effect was assessed by the Checkerboard assay. Furthermore, the cytotoxicity of the plant-derived compounds against Vero cells was measured by the 3-(4 5-dimethylthiazol-2-yl)-2 5-diphenyltetrazolium bromide (MTT) method. The biological effects of the isolated compounds were predicted using the PASS online software. The chloroform and hexane extracts of T. micrantha roots showed promising antibacterial effect, with MIC in the range of 4.8-78.0 µg/mL. Further analyses showed that these compounds do not affect the integrity of the membrane. The combination with streptomycin strongly reduced the MIC of this antibiotic and extracts. The extracts were highly toxic to Vero cells, and no cytotoxicity was detected for the two terpenoids isolated from them (i.e. friedelan-3,21-dione and 3β-O-D-glucosyl-sitosterol; CC50 > 1000 μg/mL). Therefore, extracts obtained from T. micrantha roots significantly inhibited bacterial growth and are considered promising agents against pathogenic bacteria. The cytotoxicity results were very relevant and can be tested in bioassays.

Pre-formulation of an additive combination of two antimicrobial agents, clofazimine and nisin A, to boost antimicrobial activity

According to the World Health Organization, antimicrobial resistance is one of the top ten issues that pose a major threat to humanity. The lack of investment by the pharmaceutical industry has meant fewer novel antimicrobial agents are in development, exacerbating the problem. Emerging drug design strategies are exploring the repurposing of existing drugs and the utilization of novel drug candidates, like antimicrobial peptides, to combat drug resistance. This proactive approach is crucial in fighting global health threats. In this study, an additive combination of a repurposed anti-leprosy drug, clofazimine, and an antimicrobial peptide, nisin A, are preformulated using liquid antisolvent precipitation to generate a stable amorphous, ionized nanoparticle system to boost antimicrobial activity. The nanotechnology aims to improve the physicochemical properties of the inherently poorly water-soluble clofazimine molecules while also harnessing the previously unreported additive effect of clofazimine and nisin A. The approach transformed clofazimine into a more water-soluble salt, yielding amorphous nanoparticles stabilized by the antimicrobial peptide; and combined the two drugs into a more soluble and more active formulation. Blending pre-formulation strategies like amorphization, salt formation, and nanosizing to improve the inherent low aqueous solubility of drugs can open many new possibilities for the design of new antimicrobial agents. This fusion of pre-formulation technologies in combination with the multi-hurdle approach of selecting drugs with different effects on microbes could be key in the design platform of new antibiotics in the fight against antimicrobial resistance.

Polysaccharide-Targeting Lipid Nanoparticles to Kill Gram-Negative Bacteria

The rapid increase and spread of Gram-negative bacteria resistant to many or all existing treatments threaten a return to the preantibiotic era. The presence of bacterial polysaccharides that impede the penetration of many antimicrobials and protect them from the innate immune system contributes to resistance and pathogenicity. No currently approved antibiotics target the polysaccharide regions of microbes. Here, describe monolaurin-based niosomes, the first lipid nanoparticles that can eliminate bacterial polysaccharides from hypervirulent Klebsiella pneumoniae, are described. Their combination with polymyxin B shows no cytotoxicity in vitro and is highly effective in combating K. pneumoniae infection in vivo. Comprehensive mechanistic studies have revealed that antimicrobial activity proceeds via a multimodal mechanism. Initially, lipid nanoparticles disrupt polysaccharides, then outer and inner membranes are destabilized and destroyed by polymyxin B, resulting in synergistic cell lysis. This novel lipidic nanoparticle system shows tremendous promise as a highly effective antimicrobial treatment targeting multidrug-resistant Gram-negative pathogens.

Synergistic use of anti-inflammatory ketorolac and gentamicin to target staphylococcal biofilms

BACKGROUND

While antibiotics remain our primary tools against microbial infection, increasing antibiotic resistance (inherent and acquired) is a major detriment to their efficacy. A practical approach to maintaining or reversing the efficacy of antibiotics is the use of other commonly used therapeutics, which show synergistic antibacterial action with antibiotics. Here, we investigated the extent of antibacterial synergy between the antibiotic gentamicin and the anti-inflammatory ketorolac regarding the dynamics of biofilm growth, the rate of acquired resistance, and the possible mechanism of synergy.

METHODS

Control (ATCC 12600, ATCC 35984) and clinical strains (L1101, L1116) of Staphylococcus aureus and Staphylococcus epidermidis with varying antibiotic susceptibility profiles were used in this study to simulate implant-material associated low-risk and high-risk biofilms in vitro. The synergistic action of gentamicin sulfate (GS) and ketorolac tromethamine (KT), against planktonic staphylococcal strains were determined using the fractional inhibitory concentration measurement assay. Nascent (6 h) and established (24 h) biofilms were grown on 316L stainless steel plates and the synergistic biofilm eradication activity was determined and characterized using adherent bacteria count, minimum biofilm eradication concentration (MBEC) measurement for GS, visualization by live/dead imaging, scanning electron microscopy, gene expression of biofilm-associated genes, and bacterial membrane fluidity assessment.

RESULTS

Gentamicin-ketorolac (GS-KT) combination demonstrated synergistic antibacterial action against planktonic Staphylococci. Control and clinical strains showed distinct biofilm growth dynamics and an increase in biofilm maturity was shown to confer further resistance to gentamicin for both 'low-risk' and 'high-risk' biofilms. The addition of ketorolac enhanced the antibiofilm activity of gentamicin against acquired resistance in staphylococcal biofilms. Mechanistic studies revealed that the synergistic action of gentamicin-ketorolac interferes with biofilm morphology and subverts bacterial stress response altering bacterial physiology, membrane dynamics, and biofilm properties.

CONCLUSION

The results of this study have a significant impact on the local administration of antibiotics and other therapeutic agents commonly used in the prevention and treatment of orthopaedic infections. Further, these results warrant the study of synergy for the concurrent or sequential administration of non-antibiotic drugs for antimicrobial effect.

Host Defense Peptide Piscidin and Yeast-Derived Glycolipid Exhibit Synergistic Antimicrobial Action through Concerted Interactions with Membranes

Developing new antimicrobials as alternatives to conventional antibiotics has become an urgent race to eradicate drug-resistant bacteria and to save human lives. Conventionally, antimicrobial molecules are studied independently even though they can be cosecreted in vivo. In this research, we investigate two classes of naturally derived antimicrobials: sophorolipid (SL) esters as modified yeast-derived glycolipid biosurfactants that feature high biocompatibility and low production cost; piscidins, which are host defense peptides (HDPs) from fish. While HDPs such as piscidins target the membrane of pathogens, and thus result in low incidence of resistance, SLs are not well understood on a mechanistic level. Here, we demonstrate that combining SL-hexyl ester (SL-HE) with subinhibitory concentration of piscidins 1 (P1) and 3 (P3) stimulates strong antimicrobial synergy, potentiating a promising therapeutic window. Permeabilization assays and biophysical studies employing circular dichroism, NMR, mass spectrometry, and X-ray diffraction are performed to investigate the mechanism underlying this powerful synergy. We reveal four key mechanistic features underlying the synergistic action: (1) P1/3 binds to SL-HE aggregates, becoming α-helical; (2) piscidin-glycolipid assemblies synergistically accumulate on membranes; (3) SL-HE used alone or bound to P1/3 associates with phospholipid bilayers where it induces defects; (4) piscidin-glycolipid complexes disrupt the bilayer structure more dramatically and differently than either compound alone, with phase separation occurring when both agents are present. Overall, dramatic enhancement in antimicrobial activity is associated with the use of two membrane-active agents, with the glycolipid playing the roles of prefolding the peptide, coordinating the delivery of both agents to bacterial surfaces, recruiting the peptide to the pathogenic membranes, and supporting membrane disruption by the peptide. Given that SLs are ubiquitously and safely used in consumer products, the SL/peptide formulation engineered and mechanistically characterized in this study could represent fertile ground to develop novel synergistic agents against drug-resistant bacteria.

BCp12/PLA combination: A novel antibacterial agent targeting Mur family, DNA gyrase and DHFR

The combination of natural antimicrobial peptide BCp12/phenyllatic acid (BCp12/PLA) presents a more efficient antibacterial effect, but its antibacterial mechanism remains unclear. This study studied the synergistic antibacterial mechanism of BCp12 and PLA against S. aureus. The results demonstrated that the BCp12/PLA combination presented a synergistic antibacterial effect against S. aureus, with a fractional inhibitory concentration of 0.05. Furthermore, flow cytometry and scanning electron microscope analysis revealed that BCp12 and PLA synergistically promoted cell membrane disruption compared with the group treated only with one compound, inducing structural cell damage and cytoplasmic leakage. In addition, fluorescence spectroscopy analysis suggested that BCp12 and PLA synergistically influenced genomic DNA. BCp12 and PLA targeted enzymes related to peptidoglycan and DNA synthesis and interacted by hydrogen bonding and hydrophobic interactions with mur enzymes (murC, murD, murE, murF, and murG), dihydrofolate reductase, and DNA gyrase. Additionally, the combined treatment successfully inhibited microbial reproduction in the storage of pasteurized milk, indicating that the combination of BCp12 and PLA can be used as a new preservative strategy in food systems. Overall, this study could provide potential strategies for preventing and controlling foodborne pathogens.

A Potent Kalihinol Analogue Disrupts Apicoplast Function and Vesicular Trafficking in P. falciparum Malaria

Here we report the discovery of MED6-189, a new analogue of the kalihinol family of isocyanoterpene (ICT) natural products. MED6-189 is effective against drug-sensitive and -resistant P. falciparum strains blocking both intraerythrocytic asexual replication and sexual differentiation. This compound was also effective against P. knowlesi and P. cynomolgi. In vivo efficacy studies using a humanized mouse model of malaria confirms strong efficacy of the compound in animals with no apparent hemolytic activity or apparent toxicity. Complementary chemical biology, molecular biology, genomics and cell biological analyses revealed that MED6-189 primarily targets the parasite apicoplast and acts by inhibiting lipid biogenesis and cellular trafficking. Genetic analyses in P. falciparum revealed that a mutation in PfSec13, which encodes a component of the parasite secretory machinery, reduced susceptibility to the drug. The high potency of MED6-189 in vitro and in vivo, its broad range of efficacy, excellent therapeutic profile, and unique mode of action make it an excellent addition to the antimalarial drug pipeline.

Antimicrobial Properties of New Polyamines Conjugated with Oxygen-Containing Aromatic Functional Groups

Antibiotic resistance is now a first-order health problem, which makes the development of new families of antimicrobials imperative. These compounds should ideally be inexpensive, readily available, highly active, and non-toxic. Here, we present the results of our investigation regarding the antimicrobial activity of a series of natural and synthetic polyamines with different architectures (linear, tripodal, and macrocyclic) and their derivatives with the oxygen-containing aromatic functional groups 1,3-benzodioxol, ortho/para phenol, or 2,3-dihydrobenzofuran. The new compounds were prepared through an inexpensive process, and their activity was tested against selected strains of yeast, as well as Gram-positive and Gram-negative bacteria. In all cases, the conjugated derivatives showed antimicrobial activity higher than the unsubstituted polyamines. Several factors, such as the overall charge at physiological pH, lipophilicity, and the topology of the polyamine scaffold were relevant to their activity. The nature of the lipophilic moiety was also a determinant of human cell toxicity. The lead compounds were found to be bactericidal and fungistatic, and they were synergic with the commercial antifungals fluconazole, cycloheximide, and amphotericin B against the yeast strains tested.

Antimicrobial effects of Medicines for Malaria Venture Pathogen Box compounds on strains of Neisseria gonorrhoeae

Therapeutic options for Neisseria gonorrhoeae are limited due to emerging global resistance. New agents and treatment options to treat patients with susceptible and multi-extensively drug-resistant N. gonorrhoeae is a high priority. This study used an in vitro approach to explore the antimicrobial potential, as well as synergistic effects of Medicine for Malaria Venture (MMV) Pathogen Box compounds against ATCC and clinical N. gonorrhoeae strains. Microbroth dilution assay was used to determine pathogen-specific minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the Pathogen Box compounds against susceptible and resistant N. gonorrhoeae strains, with modification, by adding PrestoBlue HS Cell Viability Reagent. A checkerboard assay was used to determine synergy between the active compounds and in conjunction with ceftriaxone. Time-kill kinetics was performed to determine if the compounds were either bactericidal or bacteriostatic. The Pathogen Box compounds: MMV676501, MMV002817, MMV688327, MMV688508, MMV024937, MMV687798 (levofloxacin), MMV021013, and MMV688978 (auranofin) showed potent activity against resistant strains of N. gonorrhoeae at an MIC and MBC of ≤10 µM. Besides the eight compounds, MMV676388 and MMV272144 were active against susceptible N. gonorrhoeae strains, also at MIC and MBC of ≤10 µM. All the compounds were bactericidal and were either synergistic or additive with fractional inhibitory concentration index ranging between 0.40 and 1.8. The study identified novel Pathogen Box compounds with potent activity against N. gonorrhoeae strains and has the potential to be further investigated as primary or adjunctive therapy to treat gonococcal infections.

Synergistic use of anti-inflammatory ketorolac and gentamicin to target staphylococcal biofilms

Background

While antibiotics remain our primary tools against microbial infection, increasing antibiotic resistance (inherent and acquired) is a major detriment to their efficacy. A practical approach to maintaining or reversing the efficacy of antibiotics is the use of other commonly used therapeutics, which show synergistic antibacterial action with antibiotics. Here, we investigated the extent of antibacterial synergy between the antibiotic gentamicin and the anti-inflammatory ketorolac regarding the dynamics of biofilm growth, the rate of acquired resistance, and the possible mechanism of synergy.

Methods

Control (ATCC 12600, ATCC 35984) and clinical strains (L1101, L1116) of S. aureus and S. epidermidis with varying antibiotic susceptibility profiles were used in this study to simulate implant-material associated low-risk and high-risk biofilms in vitro. The synergistic action of gentamicin sulfate (GS) and ketorolac tromethamine (KT), against planktonic staphylococcal strains were determined using the fractional inhibitory concentration measurement assay. Nascent (6hr) and established (24hr) biofilms were grown on 316 stainless steel plates and the synergistic biofilm eradication activity was determined and characterized using adherent bacteria count, MBEC measurement for GS, gene expression of biofilm-associated genes, visualization by live/dead imaging, scanning electron microscopy, and bacterial membrane fluidity assessment.

Results

Gentamicin-ketorolac combination demonstrated synergistic antibacterial action against planktonic Staphylococci. Control and clinical strains showed distinct biofilm growth dynamics and an increase in biofilm maturity was shown to confer further resistance to gentamicin for both 'low-risk' and 'high-risk' biofilms. The addition of ketorolac enhanced the antibiofilm activity of gentamicin against acquired resistance in staphylococcal biofilms. Mechanistic studies revealed that the synergistic action of gentamicin-ketorolac interferes with biofilm morphology and subverts bacterial stress response altering bacterial physiology, membrane dynamics, and biofilm properties.

Conclusion

The results of this study have a significant impact on the local administration of antibiotics and other therapeutic agents commonly used in the prevention and treatment of orthopaedic infections. Further, these results warrant the study of synergy for the concurrent or sequential administration of non-antibiotic drugs for antimicrobial effect.

Identification of a Potential Antimycobacterial Drug Sensitizer Targeting a Flavin-Independent Methylenetetrahydrofolate Reductase

The increasing antibiotic resistance of Mycobacterium tuberculosis and pathogenic nontuberculosis mycobacteria highlights the urgent need for new prevention and treatment strategies. Recently, the cocrystal structure of a Mycobacterium smegmatis flavin-independent 5,10-methylenetetrahydrofolate reductase (MsmMTHFR) that binds with a reduced nicotinamide adenine dinucleotide (NADH) has been well-determined, providing a structural basis for the screening of antimycobacterial leads targeting MsmMTHFR, a new enzyme involved in tetrahydrofolic acid (THF) biosynthesis. In this study, we identified compound AB131 as a promising candidate that fits well into the NADH binding pocket of MsmMTHFR through virtual screening. We discovered that AB131 and its derivatives (13 and 14) can sensitize the antimycobacterial activity of the antitubercular drug para-aminosalicyclic acid (PAS) by 2-5-fold against various species of mycobacteria. Although the compounds themselves do not exhibit any antimycobacterial activity, the high binding affinity of AB131 with MsmMTHFR or Rv2172c was evaluated by microscale thermophoresis analysis. Additionally, we predicted and validated the key residues (V115, V117, P118, and R163) of MsmMTHFR that are involved in the interaction with AB131 by using molecular docking and mutagenesis analysis. These findings offer a potential exploitable target for developing potent and specific antimycobacterial drug sensitizers.

Identification of Novel, Potent, and Selective Compounds against Malaria Using Glideosomal-Associated Protein 50 as a Drug Target

Phylum apicomplexan consists of parasites, such as Plasmodium and Toxoplasma. These obligate intracellular parasites enter host cells via an energy-dependent process using specialized machinery, called the glideosome. In the present study, we used Plasmodium falciparum GAP50, a glideosome-associated protein, as a target to screen 951 different compounds from diverse chemical libraries. Using different screening methods, eight compounds (Hayatinine, Curine, MMV689758 (Bedaquiline), MMV1634402 (Brilacidin), and MMV688271, MMV782353, MMV642550, and USINB4-124-8) were identified, which showed promising binding affinity (KD < 75 μM), along with submicromolar range antiparasitic efficacy and selectivity index > 100 fold for malaria parasite. These eight compounds were effective against Chloroquine-resistant PfINDO and Artemisinin-resistant PfCam3.1R359T strains. Studies on the effect of these compounds at asexual blood stages showed that these eight compounds act differently at different developmental stages, indicating the binding of these compounds to other Plasmodium proteins, in addition to PfGAP50. We further studied the effects of compounds (Bedaquiline and USINB4-124-8) in an in vivoPlasmodium berghei mouse model of malaria. Importantly, the oral delivery of Bedaquiline (50 mg/kg b. wt.) showed substantial suppression of parasitemia, and three out of seven mice were cured of the infection. Thus, our study provides new scaffolds for the development of antimalarials that can act at multiple Plasmodium lifecycle stages.

Di-berberine conjugates as chemical probes of Pseudomonas aeruginosa MexXY-OprM efflux function and inhibition

The Resistance-Nodulation-Division (RND) efflux pump superfamily is pervasive among Gram-negative pathogens and contributes extensively to clinical antibiotic resistance. The opportunistic pathogen Pseudomonas aeruginosa contains 12 RND-type efflux systems, with four contributing to resistance including MexXY-OprM which is uniquely able to export aminoglycosides. At the site of initial substrate recognition, small molecule probes of the inner membrane transporter (e.g., MexY) have potential as important functional tools to understand substrate selectivity and a foundation for developing adjuvant efflux pump inhibitors (EPIs). Here, we optimized the scaffold of berberine, a known but weak MexY EPI, using an in-silico high-throughput screen to identify di-berberine conjugates with enhanced synergistic action with aminoglycosides. Further, docking and molecular dynamics simulations of di-berberine conjugates reveal unique contact residues and thus sensitivities of MexY from distinct P. aeruginosa strains. This work thereby reveals di-berberine conjugates to be useful probes of MexY transporter function and potential leads for EPI development.

Identification and targeting of microbial putrescine acetylation in bloodstream infections

The growth of antimicrobial resistance (AMR) has highlighted an urgent need to identify bacterial pathogenic functions that may be targets for clinical intervention. Although severe bacterial infections profoundly alter host metabolism, prior studies have largely ignored alterations in microbial metabolism in this context. Performing metabolomics on patient and mouse plasma samples, we identify elevated levels of bacterially-derived N-acetylputrescine during gram-negative bloodstream infections (BSI), with higher levels associated with worse clinical outcomes. We discover that SpeG is the bacterial enzyme responsible for acetylating putrescine and show that blocking its activity reduces bacterial proliferation and slows pathogenesis. Reduction of SpeG activity enhances bacterial membrane permeability and results in increased intracellular accumulation of antibiotics, allowing us to overcome AMR of clinical isolates both in culture and in vivo. This study highlights how studying pathogen metabolism in the natural context of infection can reveal new therapeutic strategies for addressing challenging infections.

Di-berberine conjugates as chemical probes of Pseudomonas aeruginosa MexXY-OprM efflux function and inhibition

The Resistance-Nodulation-Division (RND) efflux pump superfamily is pervasive among Gram-negative pathogens and contributes extensively to clinical antibiotic resistance. The opportunistic pathogen Pseudomonas aeruginosa contains 12 RND-type efflux systems, with four contributing to resistance including MexXY-OprM which is uniquely able to export aminoglycosides. At the site of initial substrate recognition, small molecule probes of the inner membrane transporter (e.g., MexY) have potential as important functional tools to understand substrate selectivity and a foundation for developing adjuvant efflux pump inhibitors (EPIs). Here, we optimized the scaffold of berberine, a known but weak MexY EPI, using an in-silico high-throughput screen to identify di-berberine conjugates with enhanced synergistic action with aminoglycosides. Further, docking and molecular dynamics simulations of di-berberine conjugates reveal unique contact residues and thus sensitivities of MexY from distinct P. aeruginosa strains. This work thereby reveals di-berberine conjugates to be useful probes of MexY transporter function and potential leads for EPI development.

Model-informed dose optimisation of polymyxin-rifampicin combination therapy against multidrug-resistant Acinetobacter baumannii

OBJECTIVES

Antimicrobial resistance is a major global threat. Because of the stagnant antibiotic pipeline, synergistic antibiotic combination therapy has been proposed to treat rapidly emerging multidrug-resistant (MDR) pathogens. We investigated antimicrobial synergy of polymyxin/rifampicin combination against MDR Acinetobacter baumannii.

METHODS

In vitro static time-kill studies were performed over 48 h at an initial inoculum of ∼107 CFU/mL against three polymyxin-susceptible but MDR A. baumannii isolates. Membrane integrity was examined at 1 and 4 h post-treatment to elucidate the mechanism of synergy. Finally, a semi-mechanistic PK/PD model was developed to simultaneously describe the time course of bacterial killing and prevention of regrowth by mono- and combination therapies.

RESULTS

Polymyxin B and rifampicin alone produced initial killing against MDR A. baumannii but were associated with extensive regrowth. Notably, the combination showed synergistic killing across all three A. baumannii isolates with bacterial loads below the limit of quantification for up to 48 h. Membrane integrity assays confirmed the role of polymyxin-driven outer membrane remodelling in the observed synergy. Subsequently, the mechanism of synergy was incorporated into a PK/PD model to describe the enhanced uptake of rifampicin due to polymyxin-induced membrane permeabilisation. Simulations with clinically utilised dosing regimens confirmed the therapeutic potential of this combination, particularly in the prevention of bacterial regrowth. Finally, results from a neutropenic mouse thigh infection model confirmed the in vivo synergistic killing of the combination against A. baumannii AB5075.

CONCLUSION

Our results showed that polymyxin B combined with rifampicin is a promising option to treat bloodstream and tissue infection caused by MDR A. baumannii and warrants clinical evaluations.

Trimeric Tobramycin/Nebramine Synergizes β-Lactam Antibiotics against Pseudomonas aeruginosa

β-Lactam antibiotics remain one of the most effective therapeutics to treat infections caused by Gram-negative bacteria (GNB). However, since ancient times, bacteria have developed multiple resistance mechanisms toward this class of antibiotics including overexpression of β-lactamases, suppression of porins, outer membrane impermeability, overexpression of efflux pumps, and target modifications. To cope with these challenges and to extend the lifetime of existing β-lactam antibiotics, β-lactamase inhibitors are combined with β-lactam antibiotics to prevent antibiotic inactivation by β-lactamases. The combination therapy of an outer membrane permeabilizer with β-lactam antibiotics is an alternative approach to overcoming bacterial resistance of β-lactams in GNB. This approach is of particular interest for pathogens with highly impermeable outer membranes like Pseudomonas aeruginosa. Previous studies have shown that outer membrane permeabilizers can be designed by linking tobramycin and nebramine units together in the form of dimers or chimeras. In this study, we developed trimeric tobramycin and nebramine-based outer membrane permeabilizers presented on a central 1,3,5-triazine framework. The resultant trimers are capable of potentiating outer membrane-impermeable antibiotics but also β-lactams and β-lactam/β-lactamase inhibitor combinations against resistant P. aeruginosa isolates. Furthermore, the microbiological susceptibility breakpoints of ceftazidime, aztreonam, and imipenem were reached by a triple combination consisting of an outer-membrane permeabilizer/β-lactam/β-lactamase inhibitor in β-lactam-resistant P. aeruginosa isolates. Overall, our results indicate that trimeric tobramycins/nebramines can rescue clinically approved β-lactams and β-lactam/β-lactamase inhibitor combinations from resistance.

Synergy Assessment of Four Antimicrobial Bioactive Compounds for the Combinational Treatment of Bacterial Pathogens

Antimicrobial resistance (AMR) has become a topic of great concern in recent years, with much effort being committed to developing alternative treatments for resistant bacterial pathogens. Drug combinational therapies have been a major area of research for several years, with modern iterations using combining well-established antibiotics and other antimicrobials with the aim of discovering complementary mechanisms. Previously, we characterised four GRAS antimicrobials that can withstand thermal polymer extrusion processes for novel medical device-based and therapeutic applications. In the present study, four antimicrobial bioactive-silver nitrate, nisin, chitosan and zinc oxide-were assessed for their potential combined use as an alternative synergistic treatment for AMR bacteria via a broth microdilution assay based on a checkerboard format. The bioactives were tested in arrangements of two-, three- and four-drug combinations, and their interactions were determined and expressed in terms of a synergy score. Results have revealed interesting interactions based on treatments against recognised test bacterial strains that cause human and animal infections, namely E. coli, S. aureus and S. epidermidis. Silver nitrate was seen to greatly enhance the efficacy of its paired treatment. Combinations with nisin, which is a lantibiotic, exhibited the most interesting results, as nisin has no effect against Gram-negative bacteria when used alone; however, it demonstrated antimicrobial effects when combined with silver nitrate or chitosan. This study constitutes the first study to both report on practical three- and four-drug combinational assays and utilise these methods for the assessment of established and emerging antimicrobials. The novel methods and results presented in this study show the potential to explore previously unknown drug combination compatibility measures in an ease-of-use- and high-throughput-based format, which can greatly help future research that aims to identify appropriate alternative treatments for AMR, including the screening of potential new bioactives biorefined from various sources.

Copper-Based Antibiotic Strategies: Exploring Applications in the Hospital Setting and the Targeting of Cu Regulatory Pathways and Current Drug Design Trends

Classical antibacterial drugs were designed to target specific bacterial properties distinct from host human cells to maximize potency and selectivity. These designs were quite effective as they could be easily derivatized to bear next-generation drugs. However, the rapid mutation of bacteria and their associated acquired drug resistance have led to the rise of highly pathogenic superbug bacterial strains for which treatment with first line drugs is no match. More than ever, there is a dire need for antibacterial drug design that goes beyond conventional standards. Taking inspiration by the body's innate immune response to employ its own supply of labile copper ions in a toxic attack against pathogenic bacteria, which have a very low Cu tolerance, this review article examines the feasibility of Cu-centric strategies for antibacterial preventative and therapeutic applications. Promising results are shown for the use of Cu-containing materials in the hospital setting to minimize patient bacterial infections. Studies directed at disrupting bacterial Cu regulatory pathways elucidate new drug targets that can enable toxic increase of Cu levels and perturb bacterial dependence on iron. Likewise, Cu intracellular chelation/prochelation strategies effectively induce bacterial Cu toxicity. Cu-based small molecules and nanoparticles demonstrate the importance of the Cu ions in their mechanism and display potential synergism with classical drugs.

Atazanavir Resensitizes Candida auris to Azoles

Candida auris represents an urgent health threat. Here, we identified atazanavir as a potent drug capable of resensitizing C. auris clinical isolates to the activity of azole antifungals. Atazanavir was able to significantly inhibit the efflux pumps, glucose transport, and ATP synthesis of all tested isolates of C. auris. In addition, the combination of itraconazole with atazanavir-ritonavir significantly reduced the burden of azole-resistant C. auris in murine kidneys by 1.3 log10 (95%), compared to itraconazole alone.

Harnessing the Dual Antimicrobial Mechanism of Action with Fe(8-Hydroxyquinoline)3 to Develop a Topical Ointment for Mupirocin-Resistant MRSA Infections

8-Hydroxyquinoline (8-hq) exhibits potent antimicrobial activity against Staphylococcus aureus (SA) bacteria with MIC = 16.0-32.0 µM owing to its ability to chelate metal ions such as Mn²⁺, Zn^2+, and Cu²⁺ to disrupt metal homeostasis in bacterial cells. We demonstrate that Fe(8-hq)₃, the 1:3 complex formed between Fe(III) and 8-hq, can readily transport Fe(III) across the bacterial cell membrane and deliver iron into the bacterial cell, thus, harnessing a dual antimicrobial mechanism of action that combines the bactericidal activity of iron with the metal chelating effect of 8-hq to kill bacteria. As a result, the antimicrobial potency of Fe(8-hq)₃ is significantly enhanced in comparison with 8-hq. Resistance development by SA toward Fe(8-hq)₃ is considerably delayed as compared with ciprofloxacin and 8-hq. Fe(8-hq)₃ can also overcome the 8-hq and mupirocin resistance developed in the SA mutant and MRSA mutant bacteria, respectively. Fe(8-hq)₃ can stimulate M1-like macrophage polarization of RAW 264.7 cells to kill the SA internalized in such macrophages. Fe(8-hq)₃ exhibits a synergistic effect with both ciprofloxacin and imipenem, showing potential for combination therapies with topical and systemic antibiotics for more serious MRSA infections. The in vivo antimicrobial efficacy of a 2% Fe(8-hq)₃ topical ointment is confirmed by the use of a murine model with skin wound infection by bioluminescent SA with a reduction of the bacterial burden by 99 ± 0.5%, indicating that this non-antibiotic iron complex has therapeutic potential for skin and soft tissue infections (SSTIs).

Broad-Spectrum Antimicrobial Activity of Ultrafine (BiO)2CO3 NPs Functionalized with PVP That Can Overcome the Resistance to Ciprofloxacin, AgNPs and Meropenem in Pseudomonas aeruginosa

Although it has no known biochemical role in living organisms, bismuth has been used to treat syphilis, diarrhea, gastritis and colitis for almost a century due to its nontoxic nature to mammalian cells. When prepared via a top-down sonication route from a bulk sample, bismuth subcarbonate (BiO)₂CO₃ nanoparticles (NPs) with an average size of 5.35 ± 0.82 nm exhibit broad-spectrum potent antibacterial activity against both the gram-positive and gram-negative bacteria including methicillin-susceptible Staphylococcus aureus (DSSA), methicillin-resistant Staphylococcus aureus (MRSA), drug-susceptible Pseudomonas aeruginosa (DSPA) and multidrug-resistant Pseudomonas aeruginosa (DRPA). Specifically, the minimum inhibitory concentrations (MICs) are 2.0 µg/mL against DSSA and MRSA and 0.75 µg/mL against DSPA and DRPA. In sharp contrast to ciprofloxacin, AgNPs and meropenem, (BiO)₂CO₃ NPs show no sign of developing Bi-resistant phenotypes after 30 consecutive passages. On the other hand, such NPs can readily overcome the resistance to ciprofloxacin, AgNPs and meropenem in DSPA. Finally, the combination of (BiO)₂CO₃ NPs and meropenem shows a synergistic effect with the fractional inhibitory concentration (FIC) index of 0.45.

Characterization of a broad-spectrum endolysin rLysJNwz and its utility against Salmonella in foods

Salmonella is a common foodborne pathogen worldwide. The use of bacteriophage-encoded endolysins as antimicrobial agents is a promising approach for controlling pathogenic contamination. In this context, a recombinant endolysin named rLysJNwz, consisting of a single domain falling with the L-alanogyl-D-glutamate peptidase-like family, was cloned, expressed, and characterized. The yield of rLysJNwz was about 25 mg/L. Synergy between 7.5 μg/mL rLysJNwz and 0.5 mmol/L EDTA could decrease the viable counts of Salmonella NCTC 8271 by 93.28%. A synergistic effect between rLysJNwz and polymyxin B was demonstrated, exhibiting the MIC of polymyxin B decreased by twofold. Specifically, rlysJNwz had strong thermostability at temperatures (4-95 °C) and maintained high activity at pHs from 5.0 to 11.0. rlysJNwz was a metal ion-dependent peptidase, which activated by divalent metal ions such as Zn²⁺, Mn²⁺, or Ca²⁺. Moreover, it was also found that the synergism of rlysJNwz and EDTA had bactericidal activities against a broad range of Gram-negative bacteria, including several multidrug-resistant bacteria. The application of rLysJNwz combined with EDTA was evaluated on contaminated eggs and lettuce for 60 min, displaying more than 86.7% and 86.5% reduction of viable Salmonella, respectively. Hence, these results suggest that rLysJNwz is a potential antibacterial agent to control Salmonella, especially antibiotic-resistant pathogen contamination in the field of food safety. KEY POINTS: • rLysJNwz shows lytic activities against a broad range of Gram-negative bacteria. • Endolysin rLysJNwz is a stable metalloenzyme and has high thermostability. • rLysJNwz and 0.5 mmol/L EDTA synergistically inactivate Salmonella on eggs and lettuce.

Combination of Farnesol with Common Antifungal Drugs: Inhibitory Effect against Candida Species Isolated from Women with RVVC

Background and Objectives: Vulvovaginal candidiasis (VVC) is a mucous membrane infection, with an increased rate of antifungal resistance of Candida species. In this study, the in vitro efficacy of farnesol alone or in combination with traditional antifungals was assessed against resistant Candida strains recovered from women with VVC. Materials and Methods: Eighty Candida isolates were identified by multiplex polymerase chain reaction (PCR), and the antifungal susceptibility to amphotericin B (AMB), fluconazole (FLU), itraconazole (ITZ), voriconazole (VOR), clotrimazole (CTZ), and farnesol was tested by the standard microdilution method. The combinations of farnesol with each antifungal were calculated based on the fractional inhibitory concentration index (FICI). Result: Candida glabrata was the predominant species (48.75%) isolated from vaginal discharges, followed by C. albicans (43.75%), C. parapsilosis (3.75%), a mixed infection of C. albicans and C. glabrata (2.5%) and C. albicans and C. parapsilosis (1%). C. albicans and C. glabrata isolates had lower susceptibility to FLU (31.4% and 23.0%, respectively) and CTZ (37.1% and 33.3%, respectively). Importantly, there was "synergism" between farnesol-FLU and farnesol-ITZ against C. albicans and C. parapsilosis (FICI = 0.5 and 0.35, respectively), reverting the original azole-resistant profile. Conclusion: These findings indicate that farnesol can revert the resistance profile of azole by enhancing the activity of FLU and ITZ in resistant Candida isolates, which is a clinically promising result.

Evaluation of the antibacterial activity of selected Kenyan medicinal plant extract combinations against clinically important bacteria

BACKGROUND

Infectious diseases are a major global public health concern as antimicrobial resistance (AMR) currently accounts for more than 700,000 deaths per year worldwide. The emergence and spread of resistant bacterial pathogens remain a key challenge in antibacterial chemotherapy. This study aims to investigate the antibacterial activity of combined extracts of various Kenyan medicinal plants against selected microorganisms of medical significance.

METHODS

The antibacterial activity of various extract combinations of Aloe secundiflora, Toddalia asiatica, Senna didymobotrya and Camelia sinensis against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Methicillin Resistant Staphylococcus aureus was assessed using the agar well diffusion and the minimum inhibitory concentration in-vitro assays. The checkerboard method was used to evaluate the interactions between the various extract combinations. ANOVA test followed by Tukey's post hoc multiple comparison test was used to determine statistically significant differences in activity (P < 0.05).

RESULTS

At concentrations of 100 mg/ml (10,000 µg/well), the different combinations of the aqueous, methanol, dichloromethane and petroleum ether extracts of the selected Kenyan medicinal plants revealed diverse activity against all the test bacteria. The combination of methanolic C. sinensis and A. secundiflora was the most active against E. coli (14.17 ± 0.22 mm, diameter of zones of inhibition (DZI); MIC 2500 µg/well). The combination of methanolic C. sinensis and S. didymobotrya was the most active against S. aureus (16.43 ± 0.10 mm; MIC 1250 µg/well), K. pneumonia (14.93 ± 0.35 mm, DZI; MIC 1250 µg/well), P. aeruginosa (17.22 ± 0.41 mm, DZI; MIC 156.25 µg/well) and MRSA (19.91 ± 0.31 mm, DZI; MIC 1250 µg/well). The Minimum Inhibitory Concentration of the different plant extract combinations ranged from 10,000 µg/ well to 156.25 µg/well. The ANOVA test indicated statistically significant differences (P < 0.05) between single extracts and their combinations. The fractional inhibitory concentration indices (FICI) showed that the interactions were either synergistic (10.5%), additive (31.6%), indifferent (52.6%), or antagonistic (5.3%) for the selected combinations.

CONCLUSION

This study findings validate the ethnopractice of selectively combining medicinal plants in the management of some bacterial infections in traditional medicine.