Fractional Inhibitory Concentration Index Research Articles

Assessing the Potential of Gallic Acid and Methyl Gallate to Enhance the Efficacy of β-Lactam Antibiotics against Methicillin-Resistant Staphylococcus aureus by Targeting β-Lactamase: In Silico and In Vitro Studies.

Methicillin-resistant Staphylococcus aureus (MRSA), a global health concern, has prompted research into antibiotic adjuvants as a potential solution. Although our group previously reported the enhancing effects of gallic acid (GA) and methyl gallate (MG) on penicillin G activity against MRSA, the synergistic potential with other β-lactam antibiotics and the underlying mechanism have not been fully explored. Therefore, this study primarily aimed to investigate the antibacterial synergism with β-lactam antibiotics through disc diffusion, checkerboard, and time-kill assays. The β-lactamase inhibition was also examined through both molecular modeling and in vitro experiments. Additionally, bacterial morphology changes were studied using a scanning electron microscopy (SEM). The results revealed that both GA and MG exhibited anti-MRSA activity and showed indifferent effects when combined with β-lactam antibiotics against methicillin susceptible S. aureus (MSSA). Interestingly, MG demonstrated synergism with only the β-lactamase-unstable antibiotics against MRSA with the lowest fractional inhibitory concentration (FIC) indexes of ≤3.75. However, GA and MG exhibited weak β-lactamase inhibition. Furthermore, GA, MG, and the combination with ampicillin induced the morphological changes in MRSA, suggesting a possible mechanism affecting the cell membrane. These findings suggest that MG could potentially serve as an adjunct to β-lactam antibiotics to combat MRSA infections.

Microbial Transformation of Hesperidin and Biological Evaluation.

The main aim of the study was the biotransformation evaluation of hesperidin for functionalization by 25 different nonhuman pathogenic microorganisms. As a result, four metabolites were identified and characterized. The structure of pinocembrin and naringenin from the microbial transformation of hesperidin was determined initially with LC/MS-MS. The metabolites eriodictyol and hesperetin were isolated, and their molecular structure was determined by NMR and MS. Pinocembrin, eriodictyol, and naringenin were characterized as new hesperidin microbial transformation metabolites, to the best of our knowledge. In order to evaluate the bioactivity, in vitro 5-lipoxygenase (5-LOX) enzyme inhibition, antioxidant, antimicrobial, and acute toxicity evaluations using the brine shrimp assay of hesperidin and its metabolites were performed comparatively. According to antioxidant and anti-inflammatory activity results, hesperetin metabolite was more active than naringenin and hesperidin. The antimicrobial activity of hesperetin and naringenin against the human pathogenic Staphylococcus aureus strain was relatively higher when compared with the substrate hesperidin. In line with this result, biofilm activity of hesperetin and naringenin against S. aureus with combination studies using biofilm formation methods was carried out. The checkerboard combination method was utilized for biofilm layering, also for the first time in the present study. As an initial result, it was observed that hesperidin and naringenin exerted a synergistic activity with a fractional inhibitory concentration index (FICI) value of 1.063. Considering the bioactivity of hesperidin, hesperetin, and naringenin used as substrates are relatively nontoxic. The microbial and enzymatic biotransformation of natural products such as hesperetin and its new bioactive metabolites still have pharmacological potential, which needs further experimentation at the molecular level..

Antimicrobial peptides in combination with citronellal efficiently kills multidrug resistance bacteria.

Antimicrobial peptides (AMPs) are considered as the most potential alternatives to antibiotics, but they have several drawbacks, including high cost, medium antimicrobial efficacy, poor cell selectivity, which limit clinical application. To overcome the above problems, combination therapy of AMPs with adjuvants might maximize the effectiveness of AMPs. We found that citronellal can substantially potentiate the ZY4R peptide efficacy against Escherichia coli ATCC25922. However, it is unclear whether ZY4R/citronellal combination poses synergistic antimicrobial effects against most bacteria, and their synergy mechanism has not been elucidated. To investigate synergistic antimicrobial efficacies, biosafety, and synergy mechanism of ZY4R/citronellal combination. Checkerboard, time-kill curves, cytotoxicity assays, and in vivo animal models were conducted to assess synergistic antimicrobial effects and biosafety of the ZY4R/citronellal combination. To evaluate their synergy mechanism, a series of cell-based assays and transcriptome analysis were performed. ZY4R/citronellal combination exhibited synergistic antimicrobial effects against 20 clinically significant pathogens, with the fractional inhibitory concentration index (FICI) ranging from 0.313 to 0.047. Meanwhile, ZY4R/citronellal combination enhanced antimicrobial efficacies without compromising cell selectivity, contributing to decreasing drug dosage and improving biosafety. Compared with ZY4R (4 mg/kg) and citronellal (25 mg/kg) alone, ZY4R (4 mg/kg)/citronellal (25 mg/kg) combination significantly decreased the bacterial load in peritoneal fluid, liver, and kidney (P < 0.05) and alleviated pathological damage of the organs of mice. Mechanistic studies showed that ZY4R allowed citronellal to pass through the outer membrane rapidly and acted on the inner membrane together with citronellal, causing more potent membrane damage. The membrane damage prompted the continuous accumulation of citronellal in cells, and citronellal further induced energy breakdown and inhibited exopolysaccharide (EPS) production, which aggravated ZY4R-induced outer membrane damage, thereby resulting in bacterial death. ZY4R/citronellal combination exhibited broad-spectrum synergy with a low resistance development and high biosafety. Their synergy mechanism acted on two important cellular targets (energy metabolism and membrane integrity). Combination therapy of ZY4R with citronellal may be a promising mixture to combat bacterial infections facing an antibiotic-resistance crisis.

Synergistic antifungal properties of lauraldehyde and geraniol against Aspergillus flavus in pistachio

Natural plant-derived compounds have been recognized as promising fungicides for reducing Aspergillus flavus growth in agricultural commodities. In this study, the synergistic antifungal activity of plant-derived compounds against A. flavus growth in stored pistachios was investigated. The minimum inhibitory concentration (MIC) of lauraldehyde, geraniol, dihydrocoumarin, and p-anisaldehyde against A. flavus in potato dextrose broth (PDB) were 0.40, 0.20, 0.40, and 0.80 mg/mL, respectively. Whereas, after screening 6 groups of agents using the checkerboard method, only one combination, i.e., that of lauraldehyde and geraniol (SLG), showed synergistic effect (fractional inhibitory concentration index = 0.5) on A. flavus. In addition, at 2 MIC, SLG completely inhibited the spore germination of A. flavus, colony radial growth, and aflatoxin biosynthesis. At the same time, the mycelial growth was inhibited by more than 98%. Further research found that fumigation with SLG significantly inhibited the growth of A. flavus in stored pistachios and reduced aflatoxin biosynthesis. Moreover, the pistachios with SLG fumigation exhibited higher soluble protein content, lower malonaldehyde (MDA) content, and lower carbonyl values, indicating that fumigation with SLG could effectively delay the trend of quality deterioration in stored pistachios. These results supported SLG as a potential green antifungal agent for the shelf-life extension of stored pistachios.

Synergistic effects of polymyxin and vancomycin combinations on carbapenem- and polymyxin-resistant Klebsiella pneumoniae and their molecular characteristics.

The emergence and spread of polymyxin resistance, especially among Klebsiella pneumoniae isolates, threaten the effective management of infections. This study profiled for polymyxin resistance mechanisms and investigated the activity of polymyxins plus vancomycin against carbapenem- and polymyxin-resistant K. pneumoniae. The entire genome sequences of seven isolates were profiled for resistance and virulence determinants. The effects of combination therapy were evaluated using the checkerboard technique, time-kill assay, and population profile analysis. Protein profiles of the isolates treated with monotherapy were compared to that of combination therapy. The whole-genome sequencing data revealed that the isolates harbored β-lactams, carbapenems, aminoglycoside, fluoroquinolones, macrolides, and tetracycline resistance genes, with several virulence-associated genes. The plasmids including the bla OXA-232-bearing ColKP3 plasmid were also identified in our isolates. Profiling for polymyxin resistance mechanism revealed a missense mutation in the crrB gene that resulted in a Q180L variant that conferred a deleterious effect on protein function. The combination assay indicated fractional inhibitory concentration index ranging from 0.31 to 1.13, whereas the time-kill assay demonstrated synergistic log reduction in colony-forming units per milliliter. Furthermore, population analysis profiling using dual antibiotics indicated enhancement in bacterial log reduction at lower antibiotics concentrations, compared to higher concentrations of single polymyxins. For protein profiling, 796 proteins were identified, and 56 and 94 of them were increased and decreased in the combined drug treatment groups, respectively, while other differentially produced proteins were detected in all treatment groups, except for the control group. The results demonstrated that the vancomycin combination might benefit the antimicrobial activities of polymyxins. IMPORTANCE This study provides insights into the mechanisms of polymyxin resistance in K. pneumoniae clinical isolates and demonstrates potential strategies of polymyxin and vancomycin combinations for combating this resistance. We also identified possible mechanisms that might be associated with the treatment of these combinations against carbapenem- and polymyxin-resistant K. pneumoniae clinical isolates. The findings have significant implications for the development of alternative therapies and the effective management of infections caused by these pathogens.

Boron Compound-Based Treatments Against Multidrug-Resistant Bacterial Infections in Lung Cancer In Vitro Model.

Multidrug-resistant bacteria is one of the most important public health problems. Increasing rates of antibacterial resistance also affect the outcomes of medical approaches. Cancer treatment because of immune system deficiency (chemotherapy or steroids usage) commonly can cause infection. Lung cancer is the dominant cause of cancer-related deaths, and infection is the most common cause of death among those patients. In this study, it was aimed to determine the antimicrobial, antibiofilm, and anticancer activity of boron compounds. A549 lung cancer cell line was infected with Acinetobacter baumannii (ATCC 19606), Klebsiella pneumoniae (ATCC 700603), and Pseudomonas aeruginosa (ATCC 27853). In order to determine the fractional inhibitory concentration (FIC) index, antibiotics and boron compound concentrations prepared according to the minimum inhibitory concentration (MIC) values were determined by the checkerboard method. In our study results, the antibiofilm activity was an average of 46% in A. baumannii+boron compounds, 45% in P. aeruginosa+boron compounds, and 43% in K. pneumoniae. Cell culture analysis results show a decrease in viability and antioxidant capacity and an increase in total oxidant status after adding boron compounds to the culture. Immunofluorescence results show a correlation with MTT, and boron compounds increased 8-OHdG expression in comparison to antibiotic administration. In conclusion, boron compounds have promising effects on bacteria, especially in resistant bacteria spp.

In vitro effects of omeprazole in combination with antifungal compounds against Malassezia pachydermatis.

Fungal and yeast infections, including those caused by Malassezia spp., are becoming increasingly difficult to treat, likely due to the occurrence of drug resistance. This study aimed to evaluate the antifungal effects of omeprazole (OME), a proton pump inhibitor, against antifungal-resistant Malassezia pachydermatis and to investigate the potential synergistic effects between OME and other antifungal compounds. In total, 15 samples of M. pachydermatis isolated from the skin of dogs were tested. The susceptibility of M. pachydermatis to itraconazole, ketoconazole, miconazole, terbinafine and OME was assessed using a modified broth microdilution (BM) method. The in vitro efficacy of OME alone and in combination with other antifungal compounds was evaluated for all isolates using the BM chequerboard method. The data obtained were analysed using the fractional inhibitory concentration index (FICI). The minimum inhibitory concentration (MIC) values of antifungal compounds and OME against quality control strain (M. pachydermatis CBS1879) were lower than the MIC90 values of same drugs against clinically collected strains. There was no significant difference in MIC values between drugs alone and combination. According to the analysis by the FICI method, no interaction was observed with OME and antifungal compounds. Most M. pachydermatis strains were resistant to azole antifungal compounds. OME exerted antifungal effects against Malassezia spp. and even showed good effects on antifungal-resistant strains. No synergistic effects were observed between the antifungal compounds and OME.

Synergistic effect of commercial mangosteen extract (Garcinia mangostana L.) and amoxicillin against methicillin-resistant Staphylococcus aureus (MRSA)

Antibiotic resistance occurs worldwide, and has become a threat to humankind. Previous data have shown that antimicrobial resistance is a global issue demanding immediate resolution because it threatens the environment and society. The present work thus investigated the synergistic effects of commercial Garcinia mangostana L. (GML) extract and amoxicillin on the growth of methicillin-resistant Staphylococcus aureus (MRSA) bacterial cells. A commercial GML extract was screened for phytochemical properties, and the presence of α-mangostin was detected using high-performance liquid chromatography (HPLC). The antibacterial activity of the commercial GML extract with amoxicillin was analysed by minimum inhibitory concentration (MIC) and checkerboard assays. The morphology ultrastructure of bacteria was observed using transmission electron microscopy (TEM), after treatment with commercial GML extract, either single or in combination with amoxicillin. The MICs of amoxicillin and commercial GML extract against MRSA bacteria were 250.00 and 137.50 μg/mL, respectively. The checkerboard assay showed synergistic activity in the combination of commercial GML extract (34.38 µg/mL) and amoxicillin (62.50 µg/mL) at fractional inhibitory concentration (FIC) index of &lt; 0.5. Damage to the structure of bacteria occurred due to the commercial GML extract plus amoxicillin. It was observed that the loss of bacterial cell membranes led to an irregular bacterial structure. These findings provided evidence that the combination of commercial GML extract and amoxicillin could reverse bacterial resistance in order to determine the susceptibility of traditional drugs.

Synergistic effect of eravacycline combined with fluconazole against resistant Candida albicans in vitro and in vivo

ABSTRACT Background The limited availability of antifungal drugs for candidiasis and the persistent problem of drug resistance, necessitates the urgent development of new antifungal drugs and alternative treatment options. Research design and methods This study examined the synergistic antifungal activity of the combination of eravacycline (ERV) and fluconazole (FLC) both in vitro by microdilution checkerboard assay and in vivo by Galleria mellonella model. The underlying synergistic mechanisms of this drug combination was investigated using RNA-sequencing and qPCR. Results ERV (2 μg/mL) + FLC (0.25–0.5 μg/mL) had strong synergistic antifungal activity against resistant Candida albicans (C. albicans) in vitro, as evidenced by a fractional inhibitory concentration index of 0.0044–0.0088. In vivo experiments in Galleria mellonella larvae infected with resistant C. albicans revealed that ERV (2 μg/larva) + FLC (1 μg/larva) improved survival rates and reduced fungal burden. The results of RNA-sequencing and qPCR showed that the mechanism of synergistic inhibition on resistant C. albicans was related to the inhibition of DNA replication and cell meiosis. Conclusions These results indicate that the combination of ERV and FLC effectively inhibits resistant C. albicans both in vitro and in vivo and lay the foundation for a potential novel treatment option for candidiasis.

Exploring synergy between azole antifungal drugs and statins for Candida auris.

Global emergence of rapidly developing resistance to multiple antifungal drugs and high mortality pose challenges to the treatment of invasive Candida auris infections. New therapeutic approaches are needed, such as repurposing drugs including combination with antifungals. Statins have been reported to exert antifungal effects against various Candida species. Our study investigated potential synergy between the statins (rosuvastatin and fluvastatin) and azoles (voriconazole, posaconazole and isavuconazole) on clinical isolates of C. auris. Twenty-one clinical isolates of C. auris were obtained. Chequerboard assays based on the CLSI broth microdilution method were used to assess synergy based on FIC index (FICI) calculations of MICs of individual drugs and in combinations. Single drug geometric mean (GM) MICs of fluvastatin and rosuvastatin were ≥128 mg/L in all 21 isolates. GM (range) MICs of posaconazole, voriconazole and isavuconazole were 0.259 (0.016-1 mg/L), 0.469 (0.016-2 mg/L) and 0.085 (0.004-1 mg/L), respectively. Combination of azoles with fluvastatin showed synergy in 70%-90% of C. auris isolates. In particular, voriconazole/fluvastatin resulted in 16-fold reduction in voriconazole MIC and synergy in 14/21 (67%) isolates. Posaconazole/fluvastatin resulted in 8-fold reduction in posaconazole MIC and synergy in 19/21 (90%) isolates.Combining rosuvastatin with the azoles also showed synergy against C. auris in 40%-60% of the isolates and additive effect in 40%-50%. None of the combinations was antagonistic. Our results provide a rationale for pursuing in vivo synergy tests as well as clinical studies to explore tolerability, treatment outcomes, optimal dose and exposure targets.

Polymer-Stabilized Silver (Gold)–Zinc Oxide Nanoheterodimer Structures as Antimicrobials

A simple one-pot method is proposed for obtaining the colloidal nanohybrid structures of silver (gold) and zinc oxide as well as nanostructures doped with zinc ions. The copolymers of maleic acid were used for the stabilization of nanoheterostructures. To characterize the preparation, UV–Vis spectroscopy, TEM, FTIR, XPS, and XRD were used. The bactericidal properties of the nanoheterostructures were studied in relation to the fungus C. albicans and the bacteria E. coli and S. aureus, used in planktonic form. In general, the samples containing nanosilver were the most active, and the preparations containing gold nanoparticles were the least active. The minimum inhibitory concentrations (MICs) of the Ag/ZnO samples, based on all copolymers, were in the ranges of 1.4–1.7 μg/mL for C. albicans, 2.9–6.8 μg/mL for E. coli, and 23–27 μg/mL for S. aureus; the MIC values of Au/ZnO samples were 472 μg/mL for S. aureus and 945 μg/mL for C. albicans and E. coli. The additional introduction of zinc cations into heterodimers had practically no effect on the antimicrobial properties of the composites. For all prepared composites and all tested microorganisms, the fractional inhibitory concentration indexes were in the range of 0.5–2.2, which indicates a close-to-additive contribution of the bioactive components in the samples used in the bactericidal process.

Anticandidal Activity of Cajuput and Lemongrass Essential Oils Supplemented in Alcohol-Free Mouthwash Against Candida albicans Biofilm Formation on 96-Well Plate and Acrylic Surfaces

The present study aimed to evaluate the efficacy of alcohol-free mouthwash containing cajuput and lemongrass essential oils and their synergistic effect on eliminating Candida albicans biofilm formation, the most common causative agent of denture stomatitis. The inhibitory activity against C. albicans ATCC10231 biofilm formation on 96-well plate and acrylic surfaces of this formula was significantly different from 0.12% chlorhexidine solution at 20 minutes (P &lt; 0.0001). At one hour and eight hours of immersion, the activity of this formula was similar to the activity of 0.12% chlorhexidine mouthwash. After treatment with this formula, there were less densely active cells and biofilm compared to the negative control, and the action was close to that of 0.12% chlorhexidine mouthwash. The minimal inhibitory concentrations of cajuput and lemongrass essential oils were 2 and 4 µL/mL (for 0.2% and 0.4% v/v, respectively). For chequerboard assays, the fractional inhibitory concentrations of these oils were 0.5 and 0.25 µL/mL, respectively. The combination of cajuput and lemongrass oils in this formula exhibited partial synergism against C. albicans ATCC10231 biofilm formation with a fractional inhibitory concentration index of 0.75. This study demonstrated the inhibitory activity of this formula against C. albicans biofilm formation on 96-well plate and acrylic surfaces after quantitated by colony enumeration and the XTT reduction assay resembled 0.12% chlorhexidine mouthwash. In conclusion, that C. albicans could be inhibited by the partial synergism of these essential oils in this mouthwash formula. Keywords: Inhibitory activity, Natural essential oils, Candida albicans, Microbial biofilm, Solid surface

PK-PD integration of enrofloxacin and cefquinome alone and in combination against Klebsiella pneumoniae using an in vitro dynamic model.

Introduction: Klebsiella pneumoniae is classified as a critical pathogen in both animals and humans and infections can be fatal in chickens resulting in substantial economic losses. However, the misuse of antibiotics can also lead to drug resistance and a potential transmission chain between animals and humans. Three K. pneumoniae strains with different susceptibility phenotypes were chosen to study the pharmacokinetic/pharmacodynamic (PK/PD) integration of enrofloxacin (ENR) and cefquinome (CEQ) alone and in combination. Results: Checkerboard assay results indicated that the combination treatment for type strain ATCC 700603 was synergistic effect with a fractional inhibitory concentration index (FICI) of ≤0.5. The other two clinical strains demonstrated an additive effect (FICI >0.5 to ≤1). Furthermore, static time-kill curves indicated that enrofloxacin and cefquinome added singly were effective in killing K. pneumoniae at concentrations of >2 MIC and ≥1 MIC, respectively. Additionally, the combination of enrofloxacin and cefquinome led to an enhanced antibacterial activity of cefquinome. The dynamic time-kill curves indicated that enrofloxacin and cefquinome had bactericidal and bacteriostatic activities, respectively at ≥1.5mg/L (single-dose) and 4mg/L (8h split-dose) causing a decrease in bacterial counts of ≥4.45 and >2log10CFU/mL. Enrofloxacin possessed no bacteriostatic effects against K. pneumoniae at a constant concentration of 1× MIC. Cefquinome used in combination with 1× MIC enrofloxacin exhibited bactericidal activity at ≥4mg/L (12h split-dose) with reductions of ≥3.65log10CFU/mL. The PK/PD parameters were also analyzed to determine the concentration and duration of the drugs needed to reduce bacteria by 3log10CFU/mL. For enrofloxacin alone, the AUC24h/MIC was 23.29h and the Cmax/MIC was 3.18. For cefquinome alone, the %T > MIC was 48.66 and when used in combination with enrofloxacin was 18.04. The combined use of cefquinome and enrofloxacin can increase the antibacterial activity of cefquinome against K. pneumoniae under a 12-h split-dose regimen regardless of individual drug susceptibility. Discussion: The static and dynamic time-kill curves indicated that enrofloxacin exhibited concentration-dependent activity, while cefquinome exhibited time-dependent activity. In the in vitro dynamic model, enrofloxacin alone exhibited better antimicrobial effects against K. pneumoniae compared to cefquinome alone. However, the antibacterial effect of cefquinome can be enhanced by combining it with enrofloxacin. These findings suggest a potentially effective approach for combating K. pneumoniae infections.

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.

Fractional inhibitory concentration index of the allicin and flavonoids combinations against Ganoderma boninense

Allicin and several flavonoids were known to have antifungal activity against various fungi. The antifungal capability of allicin and flavonoids varies depending on the target fungi; the combination of both compounds was expected to increase its antifungal activity. As a major disease of oil palm, basal stem rot (BSR) caused by Ganoderma boninense always be a top concern of oil palm farmers. This study aimed to evaluate the effect of combining allicin with hesperidin and rutin on antifungal activity against G. boninense through the fractional inhibitory concentration (FIC) index. The FIC index was determined using a checkerboard assay with media poisoning methods. The allicin concentration tested was 0.1%, 0.2%, 0.4%, and 0.8%, while the hesperidin and rutin concentrations were 1.25%, 2.5%, 5%, and 10%. All combinations were done in triplicate and incubated for twelve days. The result showed that a combination of allicin with hesperidin or rutin was the additive interaction that lowers the concentration of each compound with similar inhibition rate of G. boninense in vitro. Combining allicin with rutin was considered better than hesperidin due to the higher inhibition rate of G. boninense. The allicin-rutin combination has a lower concentration with a 100% inhibition rate of G. boninense in vitro.

Investigation of in vitro efficacy of quercetin-meropenem combination in carbapenemase-producing Klebsiella pneumoniae isolates.

In recent years, the rapid spread of carbapenem-resistant K. pneumoniae, their higher mortality rates, and limited treatment alternatives cause difficulties in the treatment of these infections. New treatment alternatives are needed to cope with resistant strains. In recent years, natural products such as Quercetin have started to be preferred in combination studies due to their antimicrobial effects and low side-effect profiles. The aim of this study was to investigate the in vitro efficacy of the combination of Quercetin and Meropenem on carbapenemase-producing (blaKPC, blaNDM, blaVIM, blaOXA-48, and blaIMP), carbapenem-resistant K.pneumoniae isolates using the checkerboard method. Thirty Carbapenem-resistant K.pneumoniae strains in the culture collection of our laboratory were included in our study. Carbapenemase genes were determined using the Xpert® Carba-R (Cepheid, USA). Synergism with meropenem was assessed by checkerboard analysis, followed by FIC index, and combination index calculation. Twenty (66.6%) strains had OXA-48, 6 (20%) NDM, 1 (3.3%) KPC, 1 (3.3%) OXA-48+NDM genes, and 2 strains (6.6%) gene could not be detected. In the Quercetin and Meropenem combination study, synergy was found in 24 (80%) of the strains; an additive effect was found in 5 (16.6%) and an antagonist effect in 1 (3.3%). In 19 (63.3%) of the strains, meropenem MIC values were below the sensitive limit (MIC ≤ 2 μg/mL). Although the combination of quercetin and meropenem has a high synergistic effect in carbapenem-resistant K. pneumoniae isolates, it seems that the carbapenemase species affects this situation. however, more work is needed on this subject.

Menthol- and thymol-based ciprofloxacin derivatives against Mycobacterium tuberculosis: in vitro activity, lipophilicity, and computational studies

In this work, we investigated the antitubercular properties of Ciprofloxacin derivatives conjugated with menthol and thymol moieties. For the sixteen derivatives, we established minimal inhibitory concentrations (MIC) using isolates of Mycobacterium tuberculosis that were resistant or susceptible to other antibiotics. For the most potent compound 1‐cyclopropyl‐6‐fluoro‐7‐{4‐[6‐((1R,2S,5R)‐2‐isopropyl‐5‐methylcyclohexyloxy)‐6‐oxohexyl]piperazin‐1‐yl}‐4‐oxo‐1,4‐dihydroquinoline‐3‐carboxylic acid (6), we determined fractional inhibitory concentration index (FICI) values to confirm antibacterial susceptibility and synergistic effects with other reference drugs. In addition, chromatographic studies of all the derivatives demonstrated a significant three to four-fold increase in lipophilicity and affinity to phospholipids compared to Ciprofloxacin. Finally, we conducted structure-based studies of the investigated compounds using molecular docking and taking into account protein target mutations associated with fluoroquinolone resistance. In summary, our findings indicate that the investigated compounds possess tuberculostatic properties, with some showing similar or even better activity against resistant strains compared to reference drugs. Increased lipophilicity and affinity to phospholipids of the new derivatives can offer several advantages for new drug candidates, beyond just improved cell membrane penetration. However, further studies are needed to fully understand their safety, efficacy, and mechanism of action.

Designing peptide amphiphiles as novel antibacterials and antibiotic adjuvants against gram-negative bacteria

Gram-negative strains are intrinsically resistant to most antibiotics due to the robust and impermeable characteristic of their outer membrane. Self-assembling cationic peptide amphiphiles (PAs) have the ability to disrupt bacteria membranes, constituting an excellent antibacterial alternative to small molecule drugs that can be used alone or as antibiotic adjuvants to overcome bacteria resistance. PA1 (C16KHKHK), self-assembled into micelles, which exhibited low antibacterial activity against all strains tested, and showed strong synergistic antibacterial activity in combination with Vancomycin with a Fractional Inhibitory Concentration index (FICi) of 0.15 against E. coli. The molecules, PA2 (C16KRKR) and PA3 (C16AAAKRKR), also self-assembled into micelles, displayed a broad-spectrum antibacterial activity against all strains tested, and low susceptibility to resistance development over 21 days. Finally, PA1, PA 2 and PA3 displayed low cytotoxicity against mammalian cells, and PA2 showed a potent antibacterial activity and low toxicity in preliminary in vivo models using G. mellonella. The results show that PAs are a great platform for the future development of effective antibiotics to slow down the antibiotic resistance and can act as antibiotic adjuvants with synergistic mechanism of action, which can be repurposed for use with existing antibiotics commonly used to treat gram-positive bacteria to treat infections caused by gram-negative bacteria.

Partnering essential oils with antibiotics: proven therapies against bovine Staphylococcus aureus mastitis.

There is an urgent need to develop therapeutic options for biofilm-producing Staphylococcus aureus (S. aureus). Therefore, the renewed interest in essential oils (EOs), especially carvacrol, linalool and eugenol, has attracted the attention of our research group. Multidrug resistance and multivirulence profiles in addition to biofilm production of S. aureus strains isolated from cows with mastitis were evaluated using both phenotypic and genotypic methods. The antimicrobial and antibiofilm activities of EOs were tested using both in vitro and molecular docking studies. Moreover, the interactions between commonly used antibiotics and the tested EOs were detected using the checkerboard method. We found that all our isolates (n= 37) were biofilm methicillin resistant S. aureus (MRSA) producers and 40.5% were vancomycin resistant S. aureus (VRSA). Unfortunately, 73 and 43.2% of the recovered MRSA isolates showed multidrug resistant (MDR) and multivirulence patterns, respectively. The antimicrobial activities of the tested EOs matched with the phenotypic evaluation of the antibiofilm activities and molecular docking studies. Linalool showed the highest antimicrobial and antibiofilm activities, followed by carvacrol and eugenol EOs. Fortunately, synergistic interactions between the investigated EOs and methicillin or vancomycin were detected with fractionalinhibitory concentration index (FICI) values ≤ 0.5. Moreover, the antimicrobial resistance patterns of 13 isolates changed to sensitive phenotypes after treatment with any of the investigated EOs. Treatment failure of bovine mastitis with resistant S. aureus can be avoided by combining the investigated EOs with available antimicrobial drugs. We hope that our findings can be translated into a formulation of new pharmaceutical dosage forms against biofilm-producing S. aureus pathogens.

Tigecycline-Rifampicin Restrains Resistance Development in Carbapenem-Resistant Klebsiella pneumoniae.

The goal of this study was to clarify the synergistic antibacterial activity of the combination of tigecycline (TGC) and rifampicin (RIF). Additionally, the study sought to investigate the impact of this combination on the development of mutational resistance and to assess its efficacy in an in vivo model using Galleria mellonella. Through a checkerboard test, we found that the combination of TGC and RIF showed synergistic antibacterial activity against carbapenem-resistant Klebsiella pneumoniae (CRKP). The fractional inhibition concentration index (FICI) was found to be ≤0.5, confirming the potency of the combination. Additionally, this synergistic effect was further validated in vivo using the G. mellonella infection model. TGC-RIF treatment had a lower mutant prevention concentration (MPC) than that of monotherapy, indicating its potential to reduce the development of mutational resistance. We observed a substantial variation in the MPCs of TGC and RIF when they were measured at different proportions in the combinations. Furthermore, during the resistant mutant selection window (MSW) test, we noticed a correlation between strains with low FICI and low MSW. The expression of efflux-pump-related genes, namely rarA and acrB, is significantly decreased in the combination therapy group. This indicates that altered expression levels of certain efflux pump regulator genes are associated with a combined decrease in bacterial mutation resistance. In conclusion, the combination of TGC and RIF effectively suppresses antibiotic resistance selection in CRKP. This study establishes a paradigm for evaluating drug-resistant mutant suppression in antimicrobial combination therapy.