Antibiotic combinations: should they be tested?

Ceftazidime-avibactam in the treatment of bacteremia due to carbapenem-resistant gram-negative bacteria in hematological patients: Experience in a single center

INTRODUCTION

Limited experience exists with ceftazidime-avibactam (CAZ-AVI) in treating bacteremia caused by carbapenem-resistant Enterobacterales (CRE) and Pseudomonas aeruginosa (CRPA) in hematological patients.

METHODS

We performed a single-center, retrospective, observational study including patients who received CAZ-AVI for bacteremia due to CRE or CRPA between 2018 and 2022. The primary outcome was 30-day survival. We conducted a multivariable analysis to identify predictors of survival.

RESULTS

56 patients were included and 57 (41 CRE and 16 CRPA) strains were isolated. 35 strains produced carbapenemase, including 25 metallo-beta-lactamase (MBL) and 10 serine-beta-lactamase. 48 patients (85.7 %) received combination therapy. All patients with MBL-CRE bacteremia (n = 24) received combination therapy with aztreonam (AZT). The susceptibility rates to CAZ-AVI were only 26.8 % (11/41) in CRE and 80.0 % (8/10) in CRPA. The 30-day survival rates were 85.0 % (34/40) in the CRE group and 81.3 % (13/16) in the CRPA group. In patients with MBL-CRE bacteremia, the 30-day survival was as high as 91.7 % (22/24) due to combination with AZT. Ceftazidime did not influence the activity of aztreonam-avibactam against MBL-CRE in-vitro. Multivariable cox analysis revealed neutropenia >14 days (P = 0.002, HR: 34.483, 95%CI: 3.846-333.333) and a higher Pitt bacteremia score (P = 0.005, HR: 2.074, 95%CI: 1.253-3.436) were risk factors for 30-day survival.

CONCLUSIONS

CAZ-AVI is highly effective in treating bacteremia due to CRPA and serine-beta-lactamase CRE. The combination of avibactam with AZT is highly effective in treating bacteremia due to AZT-resistant MBL producers.

Within-species variability of antibiotic interactions in Gram-negative bacteria

Treatments with antibiotic combinations are becoming increasingly important even though the supposed clinical benefits of combinations are, in many cases, unclear. Here, we systematically examined how several clinically used antibiotics interact and affect the antimicrobial efficacy against five especially problematic Gram-negative pathogens. A total of 232 bacterial isolates were tested against different pairwise antibiotic combinations spanning five classes, and the ability of all combinations in inhibiting growth was quantified. Descriptive statistics, principal component analysis (PCA), and Spearman's rank correlation matrix were used to determine the correlations between the different combinations on interaction outcome. Several important conclusions can be drawn from the 696 examined interactions. Firstly, within a species, the interactions are in general conserved but can be isolate-specific for a given antibiotic combination and can range from antagonistic to synergistic. Secondly, additive and antagonistic interactions are the most common observed across species and antibiotics, with 87.1% of isolate-antibiotic combinations being additive, 11.6% antagonistic, and only 0.3% showing synergy. These findings suggest that to achieve the highest precision and efficacy of combination therapy, not only isolate-specific interaction profiling ought to be routinely performed, in particular to avoid using drug combinations that show antagonistic interaction and an expected associated reduction in efficacy, but also discovering rare and potentially valuable synergistic interactions.IMPORTANCEAntibiotic combinations are often used to treat bacterial infections, which aim to increase treatment efficacy and reduce resistance evolution. Typically, it is assumed that one specific antibiotic combination has the same effect on different isolates of the same species, i.e., the interaction is conserved. Here, we tested this idea by examining how several clinically used antibiotics interact and affect the antimicrobial efficacy against several bacterial pathogens. Our results show that, even though within a species the interactions are often conserved, there are also isolate-specific differences for a given antibiotic combination that can range from antagonistic to synergistic. These findings suggest that isolate-specific interaction profiling ought to be performed in clinical microbiology routine to avoid using antagonistic drug combinations that might reduce treatment efficacy.

Berberine-fluconazole microparticle-based combination therapy to treat candidiasis infections

AIM

This study aims to incorporate alginate microparticles containing berberine and fluconazole into two different types of pharmaceutical formulations, to subsequently evaluate the antifungal activity against Candida albicans.

METHODS AND RESULTS

Alginate microparticles containing BBR (berberine) and FLU (fluconazole) were produced by the spray-drying technique, characterized and incorporated in two pharmaceutical formulations, a vaginal cream and artificial saliva. Broth microdilution, checkerboard, time-kill curve, and scanning electron microscopy were carried out to determine the antifungal effects of BBR and FLU against C. albicans. The minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) values of free BBR were 125 μg ml-1. Synergism between BBR and FLU was demonstrated by a fractional inhibitory concentration index (FICI) = 0.0762. The time-kill curve for the combination BBR + FLU showed a more pronounced decrease in fungal growth in comparison to free drugs, and an antibiofilm effect of BBR occurred in the formation and preformed biofilm.

CONCLUSION

Alginate microparticles containing BBR and FLU were obtained and incorporated in a vaginal cream and artificial saliva. Both formulations showed good stability, antifungal effects, and organoleptic characteristics, which suggest that BBR-FLU microparticles in formulations have potential as antifungal therapy.

Fabrication and characterisation of poly(sulfonated) and poly(sulfonic acid) dissolving microneedles for delivery of antibiotic and antifungal agents

Skin and soft tissue infections (SSTIs) arise from microbial ingress into the skin. In this study, poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (polyAMPS), which has been reported to exhibit antimicrobial properties was synthesised for the manufacture of microarray patches (MAPs). The free acid and sodium salt of polyAMPS with controlled molar masses and narrow dispersity were synthesised via reversible addition - fragmentation chain-transfer (RAFT) polymerisation reaction with a monomer conversion of over 99%, as determined by 1H NMR. The polymers were shown to be biocompatible when evaluated using a fibroblast dermal cell line while agar plating assay using cultures of C. albican demonstrated that the acid form of polyAMPS exhibited antimicrobial inhibition, which is potentiated in the presence of antimicrobial agents. The synthesised polymers were then used to fabricate dissolving MAPs, which were loaded with either ITRA or levofloxacin (LEV). The MAPs displayed acceptable mechanical resistance and punctured ex vivo skin to a depth of 600 µm. Skin deposition studies revealed that the MAPs were able to administer up to ∼ 1.9 mg of LEV (delivery efficiency: 94.7%) and ∼ 0.2 mg of ITRA (delivery efficiency: 45.9%), respectively. Collectively, the synthesis and development of this novel pharmaceutical system may offer a strategy to manage SSTIs.

Aminoglycosides-Related Ototoxicity: Mechanisms, Risk Factors, and Prevention in Pediatric Patients

Aminoglycosides are broad-spectrum antibiotics largely used in children, but they have potential toxic side effects, including ototoxicity. Ototoxicity from aminoglycosides is permanent and is a consequence of its action on the inner ear cells via multiple mechanisms. Both uncontrollable risk factors and controllable risk factors are involved in the pathogenesis of aminoglycoside-related ototoxicity and, because of the irreversibility of ototoxicity, an important undertaking for preventing ototoxicity includes antibiotic stewardship to limit the use of aminoglycosides. Aminoglycosides are fundamental in the treatment of numerous infectious conditions at neonatal and pediatric age. In childhood, normal auditory function ensures adequate neurocognitive and social development. Hearing damage from aminoglycosides can therefore strongly affect the normal growth of the child. This review describes the molecular mechanisms of aminoglycoside-related ototoxicity and analyzes the risk factors and the potential otoprotective strategies in pediatric patients.

Nanoencapsulation of Grapefruit Seed Extract and Cinnamon Oil for Oral Health: Preparation, In Vitro, and Clinical Antimicrobial Activities

This study aimed to formulate mucoadhesive antimicrobial nanoparticles using natural antimicrobials and biopolymers for oral health and verify their antimicrobial activity in clinical studies. A combination of grapefruit seed extract and cinnamon oil (GCN) and chitosan/carrageenan (CS/CR) were selected as synergistic antimicrobial combinations and mucoadhesive wall materials for nanoparticles, respectively. GCN nanoparticles (NPs; size = 357 nm and polydispersity index = 0.188) prepared by ionic gelation between CS and CR exhibited synergistic antimicrobial activity between grapefruit seed extract and cinnamon oil and significantly higher antimicrobial activity against Streptococcus mutans and sobrinus than free GCN in a time-kill assay. The clinical antibacterial activity of GCN was significantly increased and sustained by nanoencapsulation in the mouth-rinse test and GCN NP-treated drinking yogurt. These results suggest that GCN-loaded CS/CR nanoencapsulation is a promising technique that can inhibit oral bacteria with or without the presence of other food ingredients.

Loss of erm(B)-Mediated rRNA Dimethylation and Restoration of Erythromycin Susceptibility in Erythromycin-Resistant Enterococci Following Induced Linezolid Resistance

Linezolid has been reported to restore erythromycin susceptibility in erythromycin-resistant Staphylococcus aureus. This phenomenon has not been reported in enterococci and the mechanisms involved therein are still unknown. The purpose of this study was to investigate the mechanisms involved and the effect of combining linezolid with erythromycin on erythromycin-resistant enterococci. Checkerboard techniques were used to determine drug interactions, and 12 of 14 isolates showed a synergistic effect between erythromycin and linezolid (fractional inhibitory concentration <0.5). We observed that the erm(B) gene, which encodes a dimethyltransferase responsible for erythromycin resistance, was expressed from transposon Tn1545 in the tested erythromycin-resistant enterococci. After exposure to linezolid, erm(B)-mediated rRNA dimethylation at A2071 could not be detected, and the erm(B) gene was lost following acquisition of erythromycin susceptibility. Thus, in conclusion, linezolid combined with erythromycin exerts a synergistic effect against erythromycin-resistant enterococci. Linezolid treatment suppressed erm(B)-mediated rRNA dimethylation at A2071, which could lead to loss of the erm(B) gene.

The Potential of Antibiotics and Nanomaterial Combinations as Therapeutic Strategies in the Management of Multidrug-Resistant Infections: A Review

Antibiotic resistance has become a major public health concern around the world. This is exacerbated by the non-discovery of novel drugs, the development of resistance mechanisms in most of the clinical isolates of bacteria, as well as recurring infections, hindering disease treatment efficacy. In vitro data has shown that antibiotic combinations can be effective when microorganisms are resistant to individual drugs. Recently, advances in the direction of combination therapy for the treatment of multidrug-resistant (MDR) bacterial infections have embraced antibiotic combinations and the use of nanoparticles conjugated with antibiotics. Nanoparticles (NPs) can penetrate the cellular membrane of disease-causing organisms and obstruct essential molecular pathways, showing unique antibacterial mechanisms. Combined with the optimal drugs, NPs have established synergy and may assist in regulating the general threat of emergent bacterial resistance. This review comprises a general overview of antibiotic combinations strategies for the treatment of microbial infections. The potential of antibiotic combinations with NPs as new entrants in the antimicrobial therapy domain is discussed.

Interaction of lytic phage T1245 with antibiotics for enhancement of antibacterial and anti-biofilm efficacy against multidrug-resistant Acinetobacter baumannii

Biofilms associated with multidrug-resistant (MDR) Acinetobacter baumannii on medical devices remain a big clinical problem. Antibiotic susceptibility tests were performed with eight commonly employed antibiotics against clinical isolates. The effects of antibiotics in combination with well-characterized lytic phage T1245 were studied to assess their antibacterial and anti-biofilm efficacy. Ceftazidime, colistin, imipenem, and meropenem significantly reduced bacterial density up to approximately 80% when combined with phage T1245, compared with control. Phage T1245 in combination with ceftazidime, colistin, and meropenem at subinhibitory concentrations demonstrated significant reduction in biomass and bacterial viability of 3-day established biofilms, compared with antibiotic alone. In addition, electron microscopy further confirmed the disruption of biofilm structure and cell morphology upon treatment with phage T1245 and antibiotics, including ceftazidime, colistin, and meropenem. Combined treatment of phage T1245 with these antibiotics could be employed for the management of A. baumannii infections and eradication of the bacterial biofilms.

Interactions between Medical Plant-Derived Bioactive Compounds: Focus on Antimicrobial Combination Effects

It is accepted that the medicinal use of complex mixtures of plant-derived bioactive compounds is more effective than purified bioactive compounds due to beneficial combination interactions. However, synergy and antagonism are very difficult to study in a meticulous fashion since most established methods were designed to reduce the complexity of mixtures and identify single bioactive compounds. This study represents a critical review of the current scientific literature on the combined effects of plant-derived extracts/bioactive compounds. A particular emphasis is provided on the identification of antimicrobial synergistic or antagonistic combinations using recent metabolomics methods and elucidation of approaches identifying potential mechanisms that underlie their interactions. Proven examples of synergistic/antagonistic antimicrobial activity of bioactive compounds are also discussed. The focus is also put on the current challenges, difficulties, and problems that need to be overcome and future perspectives surrounding combination effects. The utilization of bioactive compounds from medicinal plant extracts as appropriate antimicrobials is important and needs to be facilitated by means of new metabolomics technologies to discover the most effective combinations among them. Understanding the nature of the interactions between medicinal plant-derived bioactive compounds will result in the development of new combination antimicrobial therapies.

In vitro Investigation of Antibiotic Combinations against Multi- and Extensively Drug-Resistant Klebsiella pneumoniae

Objectives: Community and hospital acquired K. pneumoniae infections have become a ubiquitous medical issue due to the limited treatment options and high mortality rate therefore the aims of this study are in vitro investigation of double antimicrobial combinations against multidrug resistant (MDR) and extensively drug resistant (XDR) isolates. Materials and Methods: Antimicrobial susceptibility of twelve isolates from eight Bulgarian hospitals was determined to study the interaction effect of selected double combinations in accordance to fractional inhibitory concentration (FIC) method. Furthermore, the isolates were subjected to genotyping by Multilocus sequence typing (MLST) and detection of carbapenemase genes by multiplex PCR. The results were assessed by groups of strains with either NDM or KPC carbapenemase. Results: Nine antimicrobial combinations: meropenem-colistin, meropenem-fosfomycin, meropenem-gentamicin, meropenem-rifampicin, meropenem-tigecycline, colistin-fosfomycin, colistin-gentamicin, colistin-rifampicin and colistin-tigecycline were tested for synergism on twelve K. pneumoniae, producing either KPC-2 (KPC-KP, 41.7%, 5/12) or NDM-1 (NDM-KP, 58.3%, 7/12). The isolates were distributed in three sequence types: ST11 (58.3%, 7/12), ST15 (25%, 3/12) and ST258 (16.7%, 2/12). All KPC-KP (ST258 and ST15) originated from three hospitals. The rest were NDM-1 carriers isolated from six hospitals and belonged to ST11. The highest synergistic effect was determined for MER-GEN (83.3%, 10/12) and COL-RIF (83.3%, 10/12). The MER-FOS combination was most efficient against NDM-KP, opposite to the KPC strains. Antagonism was not observed for any combinations. Conclusions: The evaluated joint synergistic effect of the MER-GEN and COL-RIF may facilitate the treatment options for patients infected with NDM- and KPC-KP, whereas MER-FOS is highly synergetic against NDM-KP.

Enhanced antibacterial effect of a novel Friunavirus phage vWU2001 in combination with colistin against carbapenem-resistant Acinetobacter baumannii

The emergence of carbapenem-resistant Acinetobacter baumannii (CRAB) has been increasingly reported, leading to greater challenges in treating infections. With the development of phage therapy and phage-antibiotic combinations, it is promising to improve the treatment of bacterial infections. In the present study, a novel vB_AbaP_WU2001 (vWU2001) phage-specific CRAB with a genome of 40,792 bp was isolated. Genomic analysis disclosed that it belongs to the Autographiviridae family of the order Caudovirales. Phage vWU2001 had a broad host range with a high adsorption rate, short latent period, large burst size and good stability. The phage could reduce preformed biofilms and inhibit biofilm formation. The combination of phage vWU2001 and colistin had significantly higher bacterial growth inhibition activity than that of phage, or colistin alone. The efficacy of the combined treatment was also evaluated in Galleria mellonella. Evaluation of its therapeutic potential showed that the combination of phage and colistin resulted in a significantly greater increase in G. mellonella survival and in bacterial clearance, as compared with that of phage or colistin alone, indicating that the combination was synergistic against CRAB. The results demonstrated that phage vWU2001 has the potential to be developed as an antibacterial agent.

The Antimicrobial Peptide Esc(1-21) Synergizes with Colistin in Inhibiting the Growth and in Killing Multidrug Resistant Acinetobacter baumannii Strains

Multidrug-resistant microbial infections and the scarce availability of new antibiotics capable of eradicating them are posing a serious problem to global health security. Among the microorganisms that easily acquire resistance to antibiotics and that are the etiological cause of severe infections, there is Acinetobacter baumannii. Carbapenems are the principal agents used to treat A. baumannii infections. However, when strains develop resistance to this class of antibiotics, colistin is considered one of the last-resort drugs. However, the appearance of resistance to colistin also makes treatment of the Acinetobacter infections very difficult. Antimicrobial peptides (AMP) from the innate immunity hold promise as new alternative antibiotics due to their multiple biological properties. In this study, we characterized the activity and the membrane-perturbing mechanism of bactericidal action of a derivative of a frog-skin AMP, namely Esc(1-21), when used alone or in combination with colistin against multidrug-resistant A. baumannii clinical isolates. We found that the mixture of the two compounds had a synergistic effect in inhibiting the growth and killing of all of the tested strains. When combined at dosages below the minimal inhibitory concentration, the two drugs were also able to slow down the microbial growth and to potentiate the membrane-perturbing effect. To the best of our knowledge, this is the first report showing a synergistic effect between AMPs, i.e., Esc(1-21), and colistin against colistin-resistant A. baumannii clinical isolates, highlighting the potential clinical application of such combinational therapy.

Isolation and Characterization of a Novel Autographiviridae Phage and Its Combined Effect with Tigecycline in Controlling Multidrug-Resistant Acinetobacter baumannii-Associated Skin and Soft Tissue Infections

Multidrug-resistant Acinetobacter baumannii (MDR A. baumannii) is one of the ESKAPE pathogens that restricts available treatment options. MDR A. baumannii is responsible for a dramatic increase in case numbers of a wide variety of infections, including skin and soft tissue infections (SSTIs), resulting in pyoderma, surgical debridement, and necrotizing fasciitis. To investigate an alternative medical treatment for SSTIs, a broad range lytic Acinetobacter phage, vB _AbP_ABWU2101 (phage vABWU2101), for lysing MDR A. baumannii in associated SSTIs was isolated and the biological aspects of this phage were investigated. Morphological characterization and genomic analysis revealed that phage vABWU2101 was a new species in the Friunavirus, Beijerinckvirinae, family Autographiviridae, and order Caudovirales. Antibiofilm activity of phage vABWU2101 demonstrated good activity against both preformed biofilms and biofilm formation. The combination of phage vABWU2101 and tigecycline showed synergistic antimicrobial activities against planktonic and biofilm cells. Scanning electron microscopy confirmed that the antibacterial efficacy of the combination of phage vABWU2101 and tigecycline was more effective than the phage or antibiotic alone. Hence, our findings could potentially be used to develop a therapeutic option for the treatment of SSTIs caused by MDR A. baumannii.

Activity of the combination of colistin and fosfomycin against NDM-1-producing Escherichia coli with variable levels of susceptibility to colistin and fosfomycin in a murine model of peritonitis

BACKGROUND

Alternative treatments are needed against NDM-1-producing Escherichia coli. Colistin (COL) and fosfomycin (FOS) often remain active in vitro but selection of resistant mutants is frequent if used separately. We determined whether the combination of colistin and fosfomycin may be useful to treat infections with NDM-1-producing E. coli with varying levels of resistance.

METHODS

Isogenic derivatives of E. coli CFT073 with blaNDM-1 and variable levels of resistance to colistin and fosfomycin (CFT073-NDM1, CFT073-NDM1-COL and CFT073-NDM1-FOS, respectively) were used. The combination (colistin + fosfomycin) was tested in vitro and in a fatal peritonitis murine model. Mortality and bacterial loads were determined and resistant mutants detected.

RESULTS

Colistin MICs were 0.5, 16 and 0.5 mg/L and fosfomycin MICs were 1, 1 and 32 mg/L against CFT073-NDM1, CFT073-NDM1-COL and CFT073-NDM1-FOS, respectively. In time-kill curves, combining colistin with fosfomycin was synergistic and bactericidal against CFT073-NDM1 and CFT073-NDM1-FOS, with concentrations of 4× MIC (for both drugs), but not against CFT073-NDM1-COL (concentrations of colistin = 0.5× MIC), due to regrowth with fosfomycin-resistant mutants. Mice died less and bacterial counts were lower in spleen with the combination compared with monotherapy against all strains; the combination prevented selection of resistant mutants except for CFT073-NDM1-COL where fosfomycin-resistant mutants were found in all mice.

CONCLUSIONS

Combining colistin and fosfomycin was beneficial in vitro and in vivo against NDM-1-producing E. coli, even with strains less susceptible to colistin and fosfomycin. However, the combination failed to prevent the emergence of fosfomycin-resistant mutants against colistin-resistant strains. Combining colistin and fosfomycin constitutes an alternative for treatment of NDM-1 E. coli, except against colistin-resistant strains.

Lesion Penetration and Activity Limit the Utility of Second-Line Injectable Agents in Pulmonary Tuberculosis

Amikacin and kanamycin are second-line injectables used in the treatment of multidrug-resistant tuberculosis (MDR-TB) based on the clinical utility of streptomycin, another aminoglycoside and first-line anti-TB drug. While streptomycin was tested as a single agent in the first controlled TB clinical trial, introduction of amikacin and kanamycin into MDR-TB regimens was not preceded by randomized controlled trials. A recent large retrospective meta-analysis revealed that compared with regimens without any injectable drug, amikacin provided modest benefits, and kanamycin was associated with worse outcomes. Although their long-term use can cause irreversible ototoxicity, they remain part of MDR-TB regimens because they have a role in preventing emergence of resistance to other drugs. To quantify the contribution of amikacin and kanamycin to second-line regimens, we applied two-dimensional matrix-assisted laser desorption ionization (MALDI) mass spectrometry imaging in large lung lesions, quantified drug exposure in lung and in lesions of rabbits with active TB, and measured the concentrations required to kill or inhibit growth of the resident bacterial populations. Using these metrics, we applied site-of-action pharmacokinetic and pharmacodynamic (PK-PD) concepts and simulated drug coverage in patients' lung lesions. The results provide a pharmacological explanation for the limited clinical utility of both agents and reveal better PK-PD lesion coverage for amikacin than kanamycin, consistent with retrospective data of contribution to treatment success. Together with recent mechanistic studies dissecting antibacterial activity from aminoglycoside ototoxicity, the limited but rapid penetration of streptomycin, amikacin, and kanamycin to the sites of TB disease supports the development of analogs with improved efficacy and tolerability.

Drug resistance reversal potential of multifunctional thieno[3,2-c]pyran via potentiation of antibiotics in MDR P. aeruginosa

We explored the antibacterial potential (alone and combination) against multidrug resistant (MDR) Pseudomonas aeruginosa isolates KG-P2 using synthesized thieno[3,2-c]pyran-2-ones in combination with different antibiotics. Out of 14 compounds, two compounds (3g and 3l) abridged the MIC of tetracycline (TET) by 16 folds. Compounds was killing the KG-P2 cells, in time dependent manner, lengthened post-antibiotic effect (PAE) of TET and found decreased the mutant prevention concentration (MPC) of TET. In ethidium bromide efflux experiment, two compounds repressed the drug transporter (efflux pumps) which is further supported by molecular docking of these compounds with efflux complex MexAB-OprM. In another study, these compounds inhibited the synthesis of biofilm.

Mechanistic insights into synergy between nalidixic acid and tetracycline against clinical isolates of Acinetobacter baumannii and Escherichia coli

The increasing prevalence of antimicrobial resistance has become a global health problem. Acinetobacter baumannii is an important nosocomial pathogen due to its capacity to persist in the hospital environment. It has a high mortality rate and few treatment options. Antibiotic combinations can help to fight multi-drug resistant (MDR) bacterial infections, but they are rarely used in the clinics and mostly unexplored. The interaction between bacteriostatic and bactericidal antibiotics are mostly reported as antagonism based on the results obtained in the susceptible model laboratory strain Escherichia coli. However, in the present study, we report a synergistic interaction between nalidixic acid and tetracycline against clinical multi-drug resistant A. baumannii and E. coli. Here we provide mechanistic insight into this dichotomy. The synergistic combination was studied by checkerboard assay and time-kill curve analysis. We also elucidate the mechanism behind this synergy using several techniques such as fluorescence spectroscopy, flow cytometry, fluorescence microscopy, morphometric analysis, and real-time polymerase chain reaction. Nalidixic acid and tetracycline combination displayed synergy against most of the MDR clinical isolates of A. baumannii and E. coli but not against susceptible isolates. Finally, we demonstrate that this combination is also effective in vivo in an A. baumannii/Caenorhabditis elegans infection model (p < 0.001).

Pseudomonas aeruginosa Virulence Factors Support Voriconazole Effects on Aspergillus fumigatus

Pseudomonas aeruginosa and Aspergillus fumigatus are pathogens that are associated with deterioration of lung function, e.g., in persons with cystic fibrosis (CF). There is evidence that co-infections with these pathogens cause airway inflammation and aggravate pathology in CF lungs. Intermicrobial competition of P. aeruginosa and A. fumigatus has been described, but it is unknown how anti-fungal therapy is affected. The anti-fungal azole voriconazole (VCZ), supernatants of P. aeruginosa laboratory isolates PA14 or PAO1, or clinical isolate Pa10 independently inhibited biofilm metabolism of A. fumigatus isolates 10AF and AF13073. When VCZ and supernatants were combined at their IC₅₀s, synergistic effects on A. fumigatus were found. Synergistic effects were no longer observed when P. aeruginosa supernatants were prepared in the presence of iron, or when P. aeruginosa mutants were lacking the ability to produce pyoverdine and pyochelin. Combination of pure P. aeruginosa products pyoverdine, pyochelin, and pyocyanin with VCZ showed synergistic anti-fungal effects. Combining VCZ with P. aeruginosa supernatants also improved its MIC and MFC against planktonic A. fumigatus. In summary, in the case of P. aeruginosa–A. fumigatus co-infections, it appeared that the P. aeruginosa co-infection facilitated therapy of the Aspergillus; lower concentrations of VCZ might be sufficient to control fungal growth.

Design, synthesis and drug resistance reversal potential of novel curcumin mimics Van D: Synergy potential of curcumin mimics

Being crucial part of plant-based novel discovery of drug from natural resources, a study was done to explore the antibacterial potential of curcumin mimics in combination with antibiotics against multidrug resistant isolates of Pseudomonas aeruginosa. The best candidate Van D, a curcumin mimics reduced the MIC of tetracycline (TET) up to 16 folds against multidrug resistant clinical isolates. VanD further inhibited the efflux pumps as evident by ethidium bromide efflux and by in-silico docking studies. In another experiment, it was also found that Van D inhibits biofilm synthesis. This derivative kills the KG-P2, an isolate of P. aeruginosa in a time dependent manner, the post-antibiotic effect (PAE) of tetracycline was extended as well as mutant prevention concentration (MPC) of TET was also decreased. In Swiss albino mice, Van D reduced the proinflammatory cytokines concentration. In acute oral toxicity study, this derivative was well tolerated and found to be safe up to 1000 mg/kg dose. To the best of our knowledge, this is the first report on curcumin mimics as synergistic agent via inhibition of efflux pump.

Synergistic antimicrobial properties of nanoencapsulated clove oil and thymol against oral bacteria

This study aimed to improve the antimicrobial activity of natural extracts against oral bacteria by synergistic combination and nanoencapsulation. Among five natural antimicrobials: clove oil, thymol, naringin, naringenin, and licorice, clove oil and thymol were selected by comparing the antimicrobial activities against Streptococcus mutans and Streptococcus sobrinus before and after nanoencapsulation. The combination of clove oil and thymol (CLTY) was nanoencapsulated using chitosan and poly-γ-glutamic acid. While free CLTY showed additive and synergistic antimicrobial activity against S. mutans and S. sobrinus, respectively, CLTY nanoparticles (NPs) exhibited synergistic activity against both strains in a time-kill kinetic assay. CLTY NPs significantly decreased the growth of salivary S. mutans during testing, compared with free CLTY in the mouth rinse test. These results indicate that nanoencapsulation can significantly increase the synergistic antimicrobial activity of CLTY and maintain its antimicrobial activity in oral cavities for a longer time.

Weakest-Link Dynamics Predict Apparent Antibiotic Interactions in a Model Cross-Feeding Community

With the growing global threat of antimicrobial resistance, novel strategies are required for combatting resistant pathogens. Combination therapy, in which multiple drugs are used to treat an infection, has proven highly successful in the treatment of cancer and HIV. However, this practice has proven challenging for the treatment of bacterial infections due to difficulties in selecting the correct combinations and dosages. An additional challenge in infection treatment is the polymicrobial nature of many infections, which may respond to antibiotics differently than a monoculture pathogen.

With the growing global threat of antimicrobial resistance, novel strategies are required for combatting resistant pathogens. Combination therapy, in which multiple drugs are used to treat an infection, has proven highly successful in the treatment of cancer and HIV. However, this practice has proven challenging for the treatment of bacterial infections due to difficulties in selecting the correct combinations and dosages. An additional challenge in infection treatment is the polymicrobial nature of many infections, which may respond to antibiotics differently than a monoculture pathogen. This study tests whether patterns of antibiotic interactions (synergy, antagonism, or independence/additivity) in monoculture can be used to predict antibiotic interactions in an obligate cross-feeding coculture. Using our previously described weakest-link hypothesis, we hypothesized antibiotic interactions in coculture based on the interactions we observed in monoculture. We then compared our predictions to observed antibiotic interactions in coculture. We tested the interactions between 10 previously identified antibiotic combinations using checkerboard assays. Although our antibiotic combinations interacted differently than predicted in our monocultures, our monoculture results were generally sufficient to predict coculture patterns based solely on the weakest-link hypothesis. These results suggest that combination therapy for cross-feeding multispecies infections may be successfully designed based on antibiotic interaction patterns for their component species.

Proximate and ultimate causes of the bactericidal action of antibiotics

During the past 85 years of antibiotic use, we have learned a great deal about how these ‘miracle’ drugs work. We know the molecular structures and interactions of these drugs and their targets and the effects on the structure, physiology and replication of bacteria. Collectively, we know a great deal about these proximate mechanisms of action for virtually all antibiotics in current use. What we do not know is the ultimate mechanism of action; that is, how these drugs irreversibly terminate the ‘individuality’ of bacterial cells by removing barriers to the external world (cell envelopes) or by destroying their genetic identity (DNA). Antibiotics have many different ‘mechanisms of action’ that converge to irreversible lethal effects. In this Perspective, we consider what our knowledge of the proximate mechanisms of action of antibiotics and the pharmacodynamics of their interaction with bacteria tell us about the ultimate mechanisms by which these antibiotics kill bacteria.

We know a lot about antibiotics and their targets; however, how antibiotics actually kill bacteria is not entirely clear and is up for debate. In this Perspective, Baquero and Levin reflect on this ultimate action of antibiotics and consider different mechanisms and modulating factors.

The use of 4-Hexylresorcinol as antibiotic adjuvant

Ever decreasing efficiency of antibiotic treatment due to growing antibiotic resistance of pathogenic bacteria is a critical issue in clinical practice. The two generally accepted major approaches to this problem are the search for new antibiotics and the development of antibiotic adjuvants to enhance the antimicrobial activity of known compounds. It was therefore the aim of the present study to test whether alkylresorcinols, a class of phenolic lipids, can be used as adjuvants to potentiate the effect of various classes of antibiotics. Alkylresorcinols were combined with 12 clinically used antibiotics. Growth-inhibiting activity against a broad range of pro- and eukaryotic microorganisms was determined. Test organisms did comprise 10 bacterial and 2 fungal collection strains, including E. coli and S. aureus, and clinical isolates of K. pneumoniae. The highest adjuvant activity was observed in the case of 4-hexylresorcinol (4-HR), a natural compound found in plants with antimicrobial activity. 50% of the minimal inhibitory concentration (MIC) of 4-HR caused an up to 50-fold decrease in the MIC of antibiotics of various classes. Application of 4-HR as an adjuvant revealed its efficiency against germination of bacterial dormant forms (spores) and prevented formation of antibiotic-tolerant persister cells. Using an in vivo mouse model of K. pneumoniae-induced sepsis, we could demonstrate that the combination of 4-HR and polymyxin was highly effective. 75% of animals were free of infection after treatment as compared to none of the animals receiving the antibiotic alone. We conclude that alkylresorcinols such as 4-HR can be used as an adjuvant to increase the efficiency of several known antibiotics. We suggest that by this approach the risk for development of genetically determined antibiotic resistance can be minimized due to the multimodal mode of action of 4-HR.

Synergistic bactericidal profiling of prodigiosin extracted from Serratia marcescens in combination with antibiotics against pathogenic bacteria

The emergence of multidrug-resistant (MDR) bacteria is on the rise and the situation has been worsening with each passing day, which is evident from the outpouring number of reports about how more and more pathogens are becoming resistant to even the third and fourth generations of antibiotics. Lately, combination therapies or drug synergy have been giving promising results in curbing infections since it delineates its action on multiple aspects as compared to monotherapies. In this study, we used prodigiosin, a bacterial pigment endowed with magnificent biological properties, in combination with six antibiotics to study its effect on Pseudomonas aeruginosa, Staphylococcus aureus and Chromobacterium violaceum. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of prodigiosin against the test organisms was determined and a checkerboard assay of prodigiosin with various antibiotic combinations was performed with an aim to abate antimicrobial resistance. MIC and MBC of prodigiosin was obtained in the range of 4–16 μg/mL, which was lower than that of most test antibiotics. Coupling prodigiosin with other test antibiotics exhibited an excellent synergy profile against all test organisms and the effects were reported to be either synergistic or additive. In the case of S. aureus and C. violaceum, all combinations were found to be synergic, and remarkably for S. aureus, FBC index was reported to be as low as ≤0.25 with all of the test antibiotics. Therefore, it is deduced that prodigiosin augments and intensifies the action of antibiotics, and results in a double-whammy against the MDR strains.

•

Prodigiosin showed excellent bactericidal activity against P. aeruginosa, S. aureus and C. violaceum.

•

Prodigiosin in combination with antibiotics exhibited synergic effect in majority of the cases against all test pathogens.

•

For S. aureus, prodigiosin-antibiotic combinations showed excellent synergic effect with an FBC index as low as ≤0.25.

•

Prodigiosin augments the action of antibiotics against pathogenic bacteria.

Diphenyl diselenide and its interaction with antifungals against Aspergillus spp

Given the few antifungal classes available to treat aspergillosis, this study aimed to evaluate the in vitro antifungal activity of diphenyl diselenide (PhSe)2 alone and in combination with classical antifungals against Aspergillus spp., and its in vivo activity in a systemic experimental aspergillosis model. We performed in vitro broth microdilution assay of (PhSe)2 against 32 Aspergillus isolates; and a checkboard assay to test the interaction of this compound with itraconazole (ITC), voriconazole (VRC), amphotericin B (AMB), and caspofungin (CAS), against nine Aspergillus isolates. An experimental model of invasive aspergillosis in mice was studied, and survival curves were compared between an untreated group and groups treated with 100 mg/kg ITC, or (PhSe)2 in different dosages (10 mg/kg, 50 mg/kg and 100 mg/kg). All Aspergillus non-fumigatus and 50% of A. fumigatus were inhibited by (PhSe)2 in concentrations ≤ 64 µg/ml, with significant differences in MICs between the sections. Synergism or additive effect in the in vitro (PhSe)2 interaction with VRC and CAS was observed against the majority of isolates, and with ITC against the non-fumigatus strains. In addition to the inhibitory interaction, (PhSe)2 was able to add a fungicidal effect to CAS. Survival curves from the systemic experimental aspergillosis model demonstrated that the inoculum caused an acute and lethal infection in mice, and no treatment applied significantly prolonged survival over that of the control group. The results highlight the promising activity of (PhSe)2 against Aspergillus species, but more in vivo studies are needed to determine its potential applicability in aspergillosis treatment.

LAY SUMMARY

The activity of diphenyl diselenide (PhSe)2 alone and in combination with itraconazole, voriconazole, and caspofungin, is described against three of the most pathogenic Aspergillus sections. (PhSe)2 may prove useful in therapy of infection in future; further study is required.

Synergy of Linezolid with Several Antimicrobial Agents against Linezolid-Methicillin-Resistant Staphylococcal Strains

Linezolid is a synthetic oxazolydinone active against multi-resistant Gram-positive cocci that inhibits proteins synthesis by interacting with the 50S ribosomal subunit. Although linezolid-resistant strains are infrequent, several outbreaks have been recently described, associated with prolonged treatment with the antibiotic. As an alternative to monotherapy, the combination of different antibiotics is a commonly used option to prevent the selection of resistant strains. In this work, we evaluated combinations of linezolid with classic and new aminoglycosides (amikacin, gentamicin and plazomicin), carbapenems (doripenem, imipenem and meropenem) and fosfomycin on several linezolid- and methicillin-resistant strains of Staphylococcus aureus and S. epidermidis, isolated in a hospital intensive care unit in Madrid, Spain. Using checkerboard and time-kill assays, interesting synergistic effects were encountered for the combination of linezolid with imipenem in all the staphylococcal strains, and for linezolid-doripenem in S.epidermidis isolates. The combination of plazomicin seemed to also have a good synergistic or partially synergistic activity against most of the isolates. None of the combinations assayed showed an antagonistic effect.

Profiling of gene expression in methicillin-resistant Staphylococcus aureus in response to cyclo-(L-Val-L-Pro) and chloramphenicol isolated from Streptomyces sp., SUK 25 reveals gene downregulation in multiple biological targets

Chloramphenicol (CAP) and cyclo-(L-Val-L-Pro) were previously isolated from Streptomyces sp., SUK 25 which exhibited a high potency against methicillin-resistant Staphylococcus aureus (MRSA). This study aimed to profile gene expression of MRSA treated with CAP and cyclo-(L-Val-L-Pro) compounds using DNA microarray. Treatment of MRSA with CAP resulted in upregulation of genes involved in protein synthesis, suggesting the coping mechanism of MRSA due to the inhibition of protein synthesis effect from CAP. Most upregulated genes in cyclo-(L-Val-L-Pro) were putative genes with unknown functions. Interestingly, genes encoding ribosomal proteins, cell membrane synthesis, DNA metabolism, citric acid cycle and virulence were downregulated in MRSA treated with cyclo-(L-Val-L-Pro) compound, suggesting the efficacy of this compound in targeting multiple biological pathways. Contrary to CAP, with only a single target, cyclo-(L-Val-L-Pro) isolated from this study had multiple antimicrobial targets that can delay antibiotic resistance and hence is a potential antimicrobial agent of MRSA.

Venturicidin A, A Membrane-active Natural Product Inhibitor of ATP synthase Potentiates Aminoglycoside Antibiotics

Despite the remarkable advances due to the discovery and development of antimicrobials agents, infectious diseases remain the second leading cause of death worldwide. This fact underlines the importance of developing new therapeutic strategies to address the widespread antibiotic resistance, which is the major contributing factor for clinical failures of the current therapeutics. In a screen for antibiotic adjuvants, we identified a natural product from actinomycetes, venturicidin A (VentA), that potentiates the aminoglycoside antibiotic gentamicin against multidrug-resistant clinical isolates of Staphylococcus, Enterococcus, and Pseudomonas aeruginosa. Furthermore, the combination of gentamicin and VentA was bactericidal and rapidly eradicated methicillin-resistant S. aureus (MRSA). The molecular mechanism of gentamicin potentiation activity is attributed to uncoupling of ATP synthesis by VentA from electron transport presumably by blocking the proton flow through ATP synthase, which results in an elevated concentration of extracellular protons and subsequent anticipated raise in gentamicin uptake. The disruption of the proton flux was characterized by perturbed membrane potential in MRSA. These results demonstrate that inhibition of ATP synthase along with the subsequent membrane dysregulation, as shown here with VentA, complements aminoglycoside antibiotics against MDR bacteria, and that this approach may be employed to combat bacterial resistance.

The in vitro activity of polymyxin B and tigecycline alone and combination with other antibiotics against carbapenem-resistant Enterobacter cloacae complex isolates, including high-risk clones

Background

The emergence of carbapenem-resistant Enterobacteriaceae (CRE) has become a significant problem for global public health. Currently, treatments program is minimal. This study aimed to evaluate the molecular mechanisms of carbapenem-resistant Enterobacter cloacae complex isolates (CREC) infections. Methods: Resistance genes were detected using PCR with specific primers. Multilocus sequence typing (MLST) was also performed. Furthermore, we evaluated the effects of polymyxin B (PMB) and tigecycline (TGC) antibiotics (Abs) alone and in combination with meropenem (MEM), amikacin (AMK), and levofloxacin (LEV) against CREC isolates. The results were then compared with in vitro synergy testing results obtained from time-kill assays (TKAs), and the microdilution checkerboard method.

Results

The synergistic efficiency of PMB + TGC was also evaluated. Abs use clinically achievable concentrations to determine the antibacterial effects of the Ab. Similar sequence type (ST) classifications had a comparably resistant phenotype; PMB-based combination therapy is better than TGC-based combination therapy.

Conclusions

we found that the combination of PMB + AMK is promising for the treatment of AMK-sensitive CREC. The high-risk ST93 carrying the bla _KPC-2 gene should be monitored.

In vitro and in vivo Synergistic Effects of Florfenicol and Thiamphenicol in Combination Against Swine Actinobacillus pleuropneumoniae and Pasteurella multocida

Potential synergism between florfenicol (FF) and thiamphenicol (TAP) was investigated for in vitro efficacy against Actinobacillus pleuropneumoniae and/or Pasteurella multocida as well as in vivo efficacy in swine. Among isolates of A. pleuropneumoniae (n = 58) and P. multocida (n = 79) from pigs in Taiwan that were tested, high percentages showed resistance to FF (52 and 53%, respectively) and TAP (57 and 53%, respectively). Checkerboard microdilution assay indicated that synergism [fractional inhibitory concentration index (FICI) ≤ 0.5] was detected in 17% of A. pleuropneumoniae (all serovar 1) and 24% of P. multocida isolates. After reconfirming the strains showing FICI ≤ 0.625 with time kill assay, the synergism increased to around 32% against both bacteria and the number could further increase to 40% against resistant A. pleuropneumoniae and 65% against susceptible P. multocida isolates. A challenge-treatment trial in pigs with P. multocida showed that the FF + TAP dosage at ratios correspondent to their MIC deduction was equally effective to the recommended dosages. Further on the combination, the resistant mutation frequency is very low when A. pleuropneumoniae is grown with FF + TAP and similar to the exposure to sub-inhibitory concentration of FF or TAP alone. The degree of minimum inhibitory concentration (MIC) reduction in FF could reach 75% (1/4 MIC) or more (up to 1/8 MIC for P. multocida, 1/16 for A. pleuropneumoniae) when combined with 1/4 MIC of TAP (or 1/8 for A. pleuropneumoniae). The synergism or FICI ≤ 0.625 of FF with oxytetracycline (47%), doxycycline (69%), and erythromycin (56%) was also evident, and worth further investigation for FF as a central modulator facilitating synergistic effects with these antimicrobials. Taken together, synergistic FF + TAP combination was effective against swine pulmonary isolates of A. pleuropneumoniae and P. multocida both in vitro and in vivo. Thus, this study may offer a potential alternative for the treatment of A. pleuropneumoniae and P. multocida infections and has the potential to greatly reduce drug residues and withdrawal time.

Methyl gallate and tylosin synergistically reduce the membrane integrity and intracellular survival of Salmonella Typhimurium

Nymphaea tetragona Georgi (Nymphaceae) is traditionally used in Asia for the treatment of diarrhea, dysentery and fever. The plant contains various active compounds, including methyl gallate (MG) which are reported to inhibit bacterial virulence mechanisms. This study aimed to evaluate the alterations on viability, membrane potential and integrity of Salmonella enterica Serovar Typhimurium exposed to MG in combination with Tylosin (Ty), which is relatively inactive against Gram-negative bacteria, but it is commonly used as a feed additive in livestock. Besides, the effects of sub-inhibitory concentrations of the combination (MT) on the interaction between S. Typhimurium and the host cell, as well as on the indirect host responses, were characterized. Flow cytometry, confocal and electron microscopic examinations were undertaken to determine the effects of MT on S. Typhimurium. The impacts of sub-inhibitory concentrations of MT on biofilm formation, as well as on the adhesion, invasion and intracellular survival of S. Typhimurium were assessed. The result demonstrated significant damage to the bacterial membrane, leakage of cell contents and a reduction in the membrane potential when treated with MT. Sub-inhibitory concentrations of MT significantly reduced (P < 0.05) the biofilm-forming, adhesive and invasive abilities of S. Typhimurium. Exposure to MT drastically reduced the bacterial count in macrophages. Up-regulation of interleukin (IL)-6, IL-8 and IL-10 cytokine genes were detected in intestinal epithelial cells pre-treated with MT. This report is the first to describe the effects of MT against S. Typhimurium. The result indicates a synergistic interaction between MG and Ty against S. Typhimurium. Therefore, the combination may be a promising option to combat S. Typhimurium in swine and, indirectly, safeguard the health of the public.

In Vitro Activity of Imipenem-Relebactam Alone or in Combination with Amikacin or Colistin against Pseudomonas aeruginosa

Relebactam is a novel class A/C β-lactamase inhibitor that restores imipenem in vitro activity against multidrug-resistant and carbapenem-nonsusceptible Pseudomonas aeruginosa Time-kill analyses were performed to evaluate the potential role of imipenem-relebactam in combination with amikacin or colistin against P. aeruginosa Ten clinical P. aeruginosa isolates (9 imipenem nonsusceptible) with imipenem-relebactam MICs ranging from 1/4 to 8/4 μg/ml were included. The isolates had varied susceptibilities to imipenem (1 to 32 μg/ml), amikacin (4 to 128 μg/ml), and colistin (0.5 to 1 μg/ml). Duplicate 24-h time-kill studies were conducted using the average steady-state concentrations (Css_avg) observed after the administration of imipenem-relebactam at 500 mg/250 mg every 6 hours (q6h) alone and in combination with the Css_avg of 25 mg/kg of body weight/day amikacin and 360 mg/day colistin in humans. Imipenem-relebactam alone resulted in 24-h bacterial densities of -2.93 ± 0.38, -1.67 ± 0.29, +0.38 ± 0.96, and +0.15 ± 0.65 log₁₀ CFU/ml at imipenem-relebactam MICs of 1/4, 2/4, 4/4, and 8/4 μg/ml, respectively. No synergy was demonstrated against the single imipenem-susceptible isolate. Against the imipenem-nonsusceptible isolates (n = 9), imipenem-relebactam combined with amikacin resulted in synergy (-2.61 ± 1.50 log₁₀ CFU/ml) against all amikacin-susceptible isolates and in two of three amikacin-intermediate (i.e., MIC, 32 μg/ml) isolates (-2.06 ± 0.19 log₁₀ CFU/ml). Synergy with amikacin was not observed when the amikacin MIC was >32 μg/ml. Imipenem-relebactam combined with colistin demonstrated synergy in eight out of the nine imipenem-resistant isolates (-3.17 ± 1.00 log₁₀ CFU/ml). Against these 10 P. aeruginosa isolates, imipenem-relebactam combined with either amikacin or colistin resulted in synergistic activity against the majority of strains. Further studies evaluating combination therapy with imipenem-relebactam are warranted.

Comparative Drug Resistance Reversal Potential of Natural Glycosides: Potential of Synergy Niaziridin & Niazirin

Background:

Due to the limited availability of antibiotics, Gram-negative bacteria (GNB) acquire different levels of drug resistance. It raised an urgent need to identify such agents, which can reverse the phenomenon of drug resistance.

Objective:

To understand the mechanism of drug resistance reversal of glycosides; niaziridin and niazirin isolated from the pods of Moringa oleifera and ouabain (control) against the clinical isolates of multidrug-resistant Escherichia coli.

Methods:

The MICs were determined following the CLSI guidelines for broth micro-dilution. In-vitro combination studies were performed by broth checkerboard method followed by Time-Kill studies, the efflux pump inhibition assay, ATPase inhibitory activity, mutation prevention concentration and in-silico studies.

Results:

The results showed that both glycosides did not possess antibacterial activity of their own, but in combination, they reduced the MIC of tetracycline up to 16 folds. Both were found to inhibit efflux pumps, but niaziridin was the best. In real time expression pattern analysis, niaziridin was also found responsible for the down expression of the two important efflux pump acrB & yojI genes alone as well as in combination. Niaziridin was also able to over express the porin forming genes (ompA & ompX). These glycosides decreased the mutation prevention concentration of tetracycline.

Conclusion:

This is the first ever report on glycosides, niazirin and niaziridin acting as drug resistance reversal agent through efflux pump inhibition and modulation of expression pattern drug resistant genes. This study may be helpful in preparing an effective antibacterial combination against the drug-resistant GNB from a widely growing Moringa oleifera.

The new buzz: Investigating the antimicrobial interactions between bioactive compounds found in South African propolis

ETHNOPHARMACOLOGICAL RELEVANCE

Propolis, a resinous substance produced by the Apis mellifera bee, contains a number of flavonoids sourced from plants found in the surrounding region. Whilst bees use this substance to seal off and protect the beehive, humans have used propolis therapeutically for centuries, making use of its antibacterial, antiseptic, antipyretic and wound healing properties, among others. South African propolis is rich in the flavonoids pinocembrin, galangin, and chrysin and very little previous research has been conducted on the antimicrobial effects of these compounds.

AIM OF THE STUDY

To obtain an understanding of the antimicrobial activity of the compounds pinocembrin, galangin, and chrysin, both independently and in combination.

MATERIALS AND METHODS

The compounds pinocembrin, galangin and chrysin were investigated for interactive antimicrobial activity by determining the minimum inhibitory concentrations (MIC), minimum bactericidal concentrations (MBC), anti-quorum sensing activity, biofilm studies, and toxicity studies (brine shrimp lethality assay).

RESULTS

Minimum inhibitory concentration results demonstrated that combinations of compounds showed better inhibitory activity than single compounds. When the flavonoids were tested in combination using the MIC assay, synergy was noted for 22% of the 1:1 ratio combinations and for 66% of the triple 1:1:1 ratio combinations. Similarly, MBC results showed bactericidal activity from selected combinations, while the compounds on their own demonstrated no cidal activity. Quorum sensing studies showed that compound combinations are more effective at inhibiting bacterial communication than the individual compounds. Biofilm assays showed that the highest percentage inhibition was observed for the triple combination against E. coli at 24 h. Finally, brine shrimp lethality studies revealed that combinations of the three compounds had reduced cytotoxicity when compared to the individual compounds.

CONCLUSION

The results obtained in this study demonstrate that the compounds found in South African propolis work synergistically to achieve an optimal antimicrobial effect, whilst simultaneously minimizing cytotoxicity.

When One Drug Is Not Enough: Context, Methodology, and Future Prospects in Antibacterial Synergy Testing

Antibacterial combinations have long been used to accomplish a variety of therapeutic goals, including prevention of resistance and enhanced antimicrobial activity. In vitro synergy testing methods, including the checkerboard array, the time-kill study, diffusion assays, and pharmacokinetic/pharmacodynamic models, are used commonly in the research setting, but are not routinely performed in the clinical microbiology laboratory because of test complexity and uncertainty about their predictive value for patient outcomes. Optimized synergy testing techniques and better data on the relationship between in vitro results and clinical outcomes are needed to guide the rational use of antimicrobial combinations in the multidrug resistance era.

A review on anti-bacterials to combat resistance: From ancient era of plants and metals to present and future perspectives of green nano technological combinations

In the primitive era, humans benefited partially from plants and metals to treat microbial infections. Later these infections were cured with antibiotics but further suffered from resistance issues. In searching of an alternative, researchers developed an adjuvant therapy but were hampered by spreading resistance. Subsequently, nanoparticles (NPs) were proposed to cease the multi-drug resistant bacteria but were hindered due to toxicity issues. Recently, a novel adjuvant therapy employed metals and botanicals into innovative nanotechnology as nano-antibiotics. The combination of green synthesized metallic NPs with antibiotics seems to be a viable platform to combat against MDR bacteria by alleviating resistance and toxicity. This review focuses on the primitive to present era dealings with bacterial resistance mechanisms, newer innovations of nanotechnology and their multiple mechanisms to combat resistance. In addition, special focus is paid on greener NPs as antibiotic carriers, and their future prospects of controlled release and toxicity study.

Antibiotic Adjuvants: Make Antibiotics Great Again!

Multiple approaches have been developed to combat bacterial resistance. However, the combination of antibiotic resistance mechanisms by bacteria and the limited number of effective antibiotics available decreases the effective interventions for the treatment of current bacterial infections. This review covers the many ways that bacteria resist antibiotics including antibiotic target modification, the use of efflux pumps, and antibiotic inactivation. As a pertinent example, the use of beta lactamase inhibitors in combination with β-lactam containing antibiotics is discussed in detail. The solution to emerging antibiotic resistance may involve combination therapies of existing antibiotics and potentiating adjuvants, which re-empower the antibiotic agent to become efficacious against the resistant strain of interest. We report herein that a reasoned adjuvant design permits one to perform polypharmacy on bacteria by not only providing greater internal access to the codosed antibiotics but also by de-energizing the efflux pumps used by the bacteria to escape antibiotic action.

Comparison of in vitro static and dynamic assays to evaluate the efficacy of an antimicrobial drug combination against Staphylococcus aureus

An easily implementable strategy to reduce treatment failures in severe bacterial infections is to combine already available antibiotics. However, most in vitro combination assays are performed by exposing standard bacterial inocula to constant concentrations of antibiotics over less than 24h, which can be poorly representative of clinical situations. The aim of this study was to assess the ability of static and dynamic in vitro Time-Kill Studies (TKS) to identify the potential benefits of an antibiotic combination (here, amikacin and vancomycin) on two different inoculum sizes of two S. aureus strains. In the static TKS (sTKS), performed by exposing both strains over 24h to constant antibiotic concentrations, the activity of the two drugs combined was not significantly different the better drug used alone. However, the dynamic TKS (dTKS) performed over 5 days by exposing one strain to fluctuating concentrations representative of those observed in patients showed that, with the large inoculum, the activities of the drugs, used alone or in combination, significantly differed over time. Vancomycin did not kill bacteria, amikacin led to bacterial regrowth whereas the combination progressively decreased the bacterial load. Thus, dTKS revealed an enhanced effect of the combination on a large inoculum not observed in sTKS. The discrepancy between the sTKS and dTKS results highlights that the assessment of the efficacy of a combination for severe infections associated with a high bacterial load could be demanding. These situations probably require the implementation of dynamic assays over the entire expected treatment duration rather than the sole static assays performed with steady drug concentrations over 24h.

Effects of Phage Endolysin SAL200 Combined with Antibiotics on Staphylococcus aureus Infection

Phages and their derivatives are increasingly being reconsidered for use in the treatment of bacterial infections due to the rising rates of antibiotic resistance. We assessed the antistaphylococcal effect of the endolysin SAL200 in combination with standard-of-care (SOC) antibiotics. The activity of SAL200 when it was combined with SOC antibiotics was assessed in vitro by checkerboard and time-kill assays and in vivo with murine bacteremia and Galleria mellonella infection models. SAL200 reduced the SOC antibiotic MICs and showed a ≥3-log₁₀-CFU/ml reduction of Staphylococcus aureus counts within 30 min in time-kill assays. Combinations of SAL200 and SOC antibiotics achieved a sustained decrease of >2 log₁₀ CFU/ml. SAL200 significantly lowered the blood bacterial density within 1 h by >1 log₁₀ CFU/ml in bacteremic mice (P < 0.05 versus untreated mice), and SAL200 and SOC antibiotic combinations achieved the lowest levels of bacteremia. The bacterial density in splenic tissue at 72 h postinfection was the lowest in mice treated with SAL200 and SOC antibiotic combinations. SAL200 combined with SOC antibiotics also improved Galleria mellonella larva survival at 96 h postinfection. The combination of the phage endolysin SAL200 with SOC antistaphylococcal antibiotics showed synergistic effects in vitro and in vivo The combination of SAL200 with SOC antibiotics could help in the treatment of difficult-to-treat S. aureus infections.

An update on technical, interpretative and clinical relevance of antimicrobial synergy testing methodologies

Testing for antimicrobial interactions has gained popularity in the last decade due to the increasing prevalence of drug-resistant organisms and limited options for the treatment of these infections. In vitro combination testing provides information, on which two or more antimicrobials can be combined for a good clinical outcome. Amongst the various in vitro methods of drug interactions, time-kill assay (TKA), checkerboard (CB) assay and E-test-based methods are most commonly used. Comparative performance of these methods reveals the TKA as the most promising method to detect synergistic combinations followed by CB assay and E-test. Various combinations of antimicrobials have been tested to demonstrate synergistic activity. Promising results were obtained for the combinations of meropenem plus colistin and rifampicin plus colistin against Acinetobacter baumannii, colistin plus carbapenem and carbapenem plus fluoroquinolones against Pseudomonas aeruginosa and colistin/polymyxin B plus rifampicin/meropenem against Klebsiella pneumoniae. Antagonism was detected in only few instances. The presence of synergy or antagonism with a combination seems to correlate with minimum inhibitory concentration of the agent and molecular mechanism involved in the resistance. Further studies need to be conducted to assess the utility of in vitro testing to predict clinical outcome and direct therapy for drug-resistant organisms.

Evaluation of Telavancin Alone and Combined with Ceftaroline or Rifampin against Methicillin-Resistant Staphylococcus aureus in an In Vitro Biofilm Model

Infections caused by biofilm-producing methicillin-resistant Staphylococcus aureus (MRSA) bacteria are challenging due to increasing antibiotic resistance. Synergistic activities of lipopeptides and lipoglycopeptides with β-lactams have been demonstrated for MRSA, but little is known about biofilm-embedded organisms. Our objective was to evaluate two telavancin (TLV) dosage regimens (7.5 mg/kg of body weight and 10 mg/kg every 24 h [q24h]) alone and in combination with ceftaroline (CPT) (600 mg every 8 h [q8h]) or rifampin (RIF) (450 mg every 12 h [q12h]) against two biofilm-producing MRSA strains (494 and N315). Pharmacokinetic/pharmacodynamic CDC biofilm reactor models with polyurethane coupons were used to evaluate the efficacies of the antibiotic combinations over 72 h. Overall, there were no significant differences observed between the two TLV dosing regimens either alone or in combination with RIF or CPT against these strains. Both TLV dosing regimens and CPT alone demonstrated killing but did not reach bactericidal reduction at 72 h. However, both TLV regimens in combination with RIF demonstrated enhanced activity against both strains, with a rapid decrease in CFU/ml at 4 h that was bactericidal and maintained over the 72-h experiment (-Δ3.75 log10 CFU/ml from baseline; P < 0.0001). Of interest, no enhanced activity was observed for TLV combined with CPT. No development of resistance was observed in any of the combination models. However, resistance to RIF developed as early as 24 h, with MIC values exceeding 32 mg/liter. Our results show that TLV plus RIF displayed therapeutic improvement against biofilm-producing MRSA. These results suggest that TLV at 7.5 and 10 mg/kg q24h are equally effective in eradicating biofilm-associated MRSA strains in vitro.

Combination of Epicatechin 3-Gallate from Euphorbia hirta and Cefepime Promotes Potential Synergistic Eradication Action against Resistant Clinical Isolate of Pseudomonas aeruginosa

Pseudomonas aeruginosa is naturally resistant to many classes of antipseudomonal antibiotics due to the species ability to easily acquire resistance. Plant-based antibacterial agent in combination with the existing antibiotic proposes an alternative treatment regimen for the eradication of resistant bacterial infections. The antibacterial effects of the isolated epicatechin 3-gallate compound from Euphorbia hirta in combination with cefepime were investigated in vitro against resistant P. aeruginosa. The fractional inhibitory concentration index of the combination was determined using checkerboard broth microdilution method. Epicatechin 3-gallate combined with cefepime had produced synergistic effect against P. aeruginosa (with average FIC index of 0.24). The MIC of epicatechin 3-gallate was effectively reduced to MIC/4, MIC/8, MIC/16, and MIC/32 in the presence of cefepime. Time-kill study of epicatechin 3-gallate combined with cefepime exhibited remarkable bactericidal activity where the eradication of P. aeruginosa occurred within 4 h of treatment. Scanning electron micrographs revealed apparent cell membrane damage and leakage of cytoplasmic contents from P. aeruginosa cells which eventually led to the cell lysis after the combination treatment of epicatechin 3-gallate and cefepime. The potential of epicatechin 3-gallate to act synergistically with cefepime against clinically resistant P. aeruginosa strain possibly will maximize the successful outcomes when choosing empirical antibiotic treatment in hospitals or health care institutions.

Synergy of clavine alkaloid 'chanoclavine' with tetracycline against multi-drug-resistant E. coli

The emergence of multi drug resistance (MDR) in Gram-negative bacteria (GNB) and lack of novel classes of antibacterial agents have raised an immediate need to identify antibacterial agents, which can reverse the phenomenon of MDR. The purpose of present study was to evaluate synergy potential and understanding the drug resistance reversal mechanism of chanoclavine isolated from Ipomoea muricata against the multi-drug-resistant clinical isolate of Escherichia coli (MDREC). Although chanoclavine did not show antibacterial activity of its own, but in combination, it could reduce the minimum inhibitory concentration (MIC) of tetracycline (TET) up to 16-folds. Chanoclavine was found to inhibit the efflux pumps which seem to be ATPase-dependent. In real-time expression analysis, chanoclavine showed down-regulation of different efflux pump genes and decreased the mutation prevention concentration of tetracycline. Further, in silico docking studies revealed significant binding affinity of chanoclavine with different proteins known to be involved in drug resistance. In in silico ADME/toxicity studies, chanoclavine was found safe with good intestinal absorption, aqueous solubility, medium blood-brain barrier (BBB), no CYP 2D6 inhibition, no hepatotoxicity, no skin irritancy, and non-mutagenic indicating towards drug likeliness of this molecule. Based on these observations, it is hypothesized that chanoclavine might be inhibiting the efflux of tetracycline from MDREC and thus enabling the more availability of tetracycline inside the cell for its action.

Antibiotic Driven Changes in Gut Motility Suggest Direct Modulation of Enteric Nervous System

Antibiotic-mediated changes to the intestinal microbiome have largely been assumed to be the basis of antibiotic-induced neurophysiological and behavioral changes. However, relatively little research has addressed whether antibiotics act directly on the host nervous system to produce these changes. We aimed to identify whether acute exposure of the gastrointestinal tract to antibiotics directly modulates neuronally dependent motility reflexes, ex vivo. Motility of colon and jejunum segments in a perfusion organ bath was recorded by video and alterations to neuronally dependent propagating contractile clusters (PCC), measured using spatiotemporal maps of diameter changes. Short latency (<10 min) changes to PCC serve as an index of putative effects on the host nervous system. Bacitracin, penicillin V, and neomycin, all produced dose-dependent alterations to the velocity, frequency, and amplitude of PCC. Most significantly, colonic PCC velocity increased by 53% [probability of superiority (PS) = 87%] with 1.42 mg/ml bacitracin, 19% (PS = 81%) with 0.91 mg/ml neomycin, and 19% (PS = 86%) with 3.88 mg/ml penicillin V. Colonic frequency increased by 16% (PS = 73%) with 1.42 mg/ml bacitracin, 21% (PS = 79%) with 0.91 mg/ml neomycin, and 34% (PS = 85%) at 3.88 mg/ml penicillin V. Conversely, colonic amplitude decreased by 41% (PS = 79%) with 1.42 mg/ml bacitracin, 30% (PS = 80%) with 0.27 mg/ml neomycin and 25% (PS = 79%) at 3.88 mg/ml penicillin V. In the jejunum, antibiotic-specific changes were identified. Taken together, our findings provide evidence that acute exposure of the gastrointestinal lumen to antibiotics modulates neuronal reflexes. Future work should acknowledge the importance of this mechanism in mediating antibiotic-driven changes on gut-brain signaling.

Phytochemical study of Helichrysum italicum (Roth) G. Don: Spectroscopic elucidation of unusual amino-phlorogucinols and antimicrobial assessment of secondary metabolites from medium-polar extract

Three unusual amino-phloroglucinols, named helichrytalicines A-C, along with seventeen known compounds including acetophenones, tremetrone derivatives, low-molecular weight phenols, flavonol glucosides, have been isolated from the medium-polar extract of Helichrysum italicum (Roth) G. Don, a medicinal plant typical of the Mediterranean vegetation. The structures of the compounds have been elucidated based on extensive 2D-NMR spectroscopic analyses, including COSY, TOCSY, HSQC, CIGAR-HMBC, H2BC and HSQC-TOCSY, along with Q-TOF HRMS² analysis. Stereostructure of the new compounds has been elucidated by Mosher's method and NOESY experiment. Antimicrobial properties against Staphylococcus epidermidis of selected compounds have been evaluated.