Enhancement of the antibiotic activity by quercetin against Staphylococcus aureus efflux pumps.

The objective of this work was to evaluate the inhibitory effect of quercetin on S. aureus Efflux Pumps. The MIC of Quercetin was evaluated through the broth microdilution method, as well as the Efflux Pump inhibition assay through the method of reducing the antibiotic minimum inhibitory concentration as well as that of ethidium bromide. The in silico approach through bioinformatics was performed to demonstrate the molecular mechanism of interaction of the substrate and the binding cavity. The Quercetin inhibition concentration was not clinically relevant. With respect to the reversal of bacterial resistance effect by efflux pump inhibition, this effect was observed with the strains carrying the TetK and NorA pumps. Regarding the interaction between the Quercetin complex and the NorA pump, the extra stability was provided by hydrogen bonds produced by the hydroxyl group.

Enhancement of Antibiotic Activity by 1,8-Naphthyridine Derivatives against Multi-Resistant Bacterial Strains.

The search for new antibacterial agents has become urgent due to the exponential growth of bacterial resistance to antibiotics. Nitrogen-containing heterocycles such as 1,8-naphthyridine derivatives have been shown to have excellent antimicrobial properties. Therefore, the purpose of this study was to evaluate the antibacterial and antibiotic-modulating activities of 1,8-naphthyridine derivatives against multi-resistant bacterial strains. The broth microdilution method was used to determine the minimum inhibitory concentration (MIC) of the following compounds: 7-acetamido-1,8-naphthyridin-4(1H)-one and 3-trifluoromethyl-N-(5-chloro-1,8-naphthyridin-2-yl)-benzenesulfonamide. The antibiotic-modulating activity was analyzed using subinhibitory concentrations (MIC/8) of these compounds in combination with norfloxacin, ofloxacin, and lomefloxacin. Multi-resistant strains of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus were used in both tests. Although the compounds had no direct antibacterial activity (MIC ≥ 1.024 µg/mL), they could decrease the MIC of these fluoroquinolones, indicating synergism was obtained from the association of the compounds. These results suggest the existence of a structure-activity relationship in this group of compounds with regard to the modulation of antibiotic activity. Therefore, we conclude that 1,8-naphthyridine derivatives potentiate the activity of fluoroquinolone antibiotics against multi-resistant bacterial strains, and thereby interesting candidates for the development of drugs against bacterial infections caused by multidrug resistant strains.

Cytotoxicity of Essential Oil Cordia verbenaceae against Leishmania brasiliensis and Trypanosoma cruzi.

The species Cordia verbenacea DC (Boraginaceae), known as the whaling herb and camaradinha, is a perennial shrub species native to the Atlantic Forest. Its leaves are used in folk medicine as an anti-inflammatory, analgesic, antiulcerogenic and curative agent, in the form of teas or infusions for internal or topical use. The present study aimed to verify the cytotoxicity of the essential oil and the leishmanicidal and trypanocidal potential of C. verbenacea. The essential oil was characterized by GC-MS. The in vitro biological activity was determined by anti-Leishmania and anti-Trypanosoma assays. The cytotoxixity was determined using mammalian fibroblasts. The C. verbenacea species presented α-pinene (45.71%), ß-caryophyllene (18.77%), tricyclo[2,2,1-(2.6)]heptane (12.56%) as their main compounds. The essential oil exhibited strong cytotoxicity at concentrations below 250 µg/mL (LC50 138.1 µg/mL) in mammalian fibroblasts. The potent anti-trypanosome and anti-promastigote activities occurred from the concentration of 62.5 µg/mL and was considered clinically relevant. The results also demonstrate that at low concentrations (<62.5 µg/mL), the essential oil of C. verbenacea managed to be lethal for these activities. This can be considered an indication of the power used in daily human consumption. Therefore, it can be concluded that the essential oil of C. verbenacea contains a compound with remarkable antiparasitic activities and requires further research.

Potentiation of Antibiotic Activity by a Meldrum's Acid Arylamino Methylene Derivative against Multidrug-Resistant Bacterial Strains.

This study aimed to evaluate the intrinsic antibacterial activity and antibiotic-enhancing effect of an arylamino methylene derivative (MAD) in association with fluoroquinolones. The antibacterial activity against multiresistant Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli was analyzed by determining the minimum inhibitory concentration (MIC) using the broth micro dilution method. A reduction in the MIC of the fluoroquinolones against strains treated simultaneously with the MAD was interpreted as an enhanced antibiotic activity. While the MAD exhibited no clinically effective action (MIC ≥ 1.024 µg/mL), it was found to significantly potentiate the activity of norfloxacin, ofloxacin and lomefloxacin against all the strains, which may be related to structural similarities between the MAD and quinolones. Our findings suggest that Meldrum's acid arylamino derivatives may represent promising molecules in the elaboration of new drugs to reverse resistance to fluoroquinolones.

Evaluation of antibacterial and enhancement of antibiotic action by the flavonoid kaempferol 7-O-ß-D-(6″-O-cumaroyl)-glucopyranoside isolated from Croton piauhiensis müll.

There has been a rapid increase in the incidence and prevalence of opportunistic bacterial infections. Inappropriate use of current antibiotics has continuously contributed to the emergence of resistance to conventional antibiotic therapy. Therefore, the search for natural molecules that are able to combat infections is of great public interest, and many of these compounds with antimicrobial properties can be obtained from phytochemical studies of medicinal plants. In this context, this study reports the isolation and characterization of the flavonoid, kaempferol 7-O-ß-D-(6″-O-cumaroyl)-glucopyranoside, from Croton piauhiensis leaves. Additionally, the intrinsic antimicrobial action of the compound and its enhancement against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus strains were assessed. The minimum inhibitory concentration (MIC) of the compound was determined using broth microdilution assays. To evaluate the modulatory effect of the flavonoid, the MIC of antibiotics amikacin and gentamicin, belonging to the class aminoglycosides was assessed, with and without the compound in sterile microplates. The results of intrinsic antibacterial activity tests revealed that the compound had no antibacterial activity against strains tested at concentrations <1024 µg/mL. The combination of the flavonoid at a concentration of 128 µg/mL with gentamicin presented synergistic effects against S. aureus 10 and E. coli 06, and also reduced the MIC from 16 µg/mL to 4 µg/mL and 8 µg/mL, respectively. Amikacin also showed synergistic effects against S. aureus 10 and E. coli 06. We also observed reduced MIC for both, from 128 µg/mL to 32 µg/mL; however, antagonism for P. aeruginosa increased the MIC from 16 µg/mL to 64 µg/mL. The combination of the flavonoid with the aminoglycosides may be an alternative to potentiate the expected results in treatment against S. aureus and E. coli, since their association leads to a synergistic effect, reducing the MIC of these drugs and decreasing the dose necessary for therapeutic success.

Potentiation of antibiotic activity by chalcone (E)-1-(4'-aminophenyl)-3-(furan-2-yl)-prop-2-en-1-one against gram-positive and gram-negative MDR strains.

Chalcones are α,ß-unsaturated ketones containing the 1,3-diarylprop-2-en-1-one framework. This study aims to evaluate the potentiation of antibacterial activity by the chalcone (E)-1-(4-aminophenyl)-3-(furan-2-yl)-prop-2-en-1-one (C13H11NO2), hereafter named AFPO, against multi-resistant strains of Staphylococcus aureus and Escherichia coli. AFPO was synthesized using the Claisen-Schmidt condensation reaction, and the molecular structure was confirmed by nuclear magnetic resonance (NMR). The antibacterial and potentiating properties of AFPO were evaluated by measuring the minimum inhibitory concentration (MIC) using microdilution plates. The AFPO MIC was 1024 µg/mL for the S. aureus 10 strain, revealing synergy in combination with the following antibiotics: penicillin, norfloxacin, ampicillin/sulbactam, and gentamicin. The AFPO MIC was 256 µg/mL for the E. coli 06 strain, and synergy was observed with norfloxacin, gentamicin, and penicillin. The potentiation of antibacterial activity by AFPO was observed against the strains of S. aureus 10 and E. coli 06.

Cholecalciferol, Ergosterol, and Cholesterol Enhance the Antibiotic Activity of Drugs.

Background: This is the first report demonstrating the antibiotic-modifying activity of cholecalciferol. AIM: In this study, cholecalciferol was evaluated against multiresistant strains of Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli. METHODS: The antibacterial and modulatory effects of cholecalciferol, ergosterol, and cholesterol (8-512 µg/mL) were evaluated by microdilution assay against multiresistant bacterial strains. RESULTS: Cholecalciferol, when combined with aminoglycosides, was more effective against P. aeruginosa, reducing the concentration of amikacin and gentamicin necessary to inhibit bacterial growth from 156.25 to 39.06 µg/mL and from 39.06 to 9.76 µg/mL, respectively. It is possible that cholecalciferol, due to its lipid-soluble nature, had a lipophilic interaction with the cell membrane, enhancing antibiotic uptake. Cholesterol and ergosterol were used to see if the mechanism of action of cholecalciferol was similar to that of these lipid compounds. Ergosterol and cholesterol increased aminoglycoside activity, where the effect was greater with higher subinhibitory concentration of sterol. CONCLUSIONS: There is no reported study on the use of cholesterol and ergosterol as modulators of antibiotics or any other drug, making this the first study in this area highlighting the interaction between cholesterol, ergosterol, and cholecalciferol with regard to modifying aminoglycoside activity.

Tannic acid affects the phenotype of Staphylococcus aureus resistant to tetracycline and erythromycin by inhibition of efflux pumps.

The widespread use of antibiotics created selective pressure for the emergence of strains that would persist despite antibiotic toxicity. The bacterial resistance mechanisms are several, with efflux pumps being one of the main ones. These pumps are membrane proteins with the function of removing antibiotics from the cell cytoplasm. Due to this importance, the aim of this work was to evaluate the inhibitory effect of tannic acid against efflux pumps expressed by the Staphylococcus aureus RN4220 and IS-58 strains. The efflux pump inhibition was assayed using a sub-inhibitory concentration of efflux pump standard inhibitors and tannic acid (MIC/8), observing their capacity to decrease the MIC of Ethidium bromide (EtBr) and antibiotics due the possible inhibitory effect of these substances. The MICs of EtBr and antibiotics were significantly different in the presence of tannic acid, indicating the inhibitory effect of this product against efflux pumps of both strains. These results indicate the possible usage of tannic acid asan inhibitor and an adjuvant in the antibiotic therapy against multidrug resistant bacteria (MDR).

Antimicrobial and enhancement of the antibiotic activity by phenolic compounds: Gallic acid, caffeic acid and pyrogallol.

The indiscriminate use of antimicrobial drugs has increased the spectrum of exposure of these organisms. In our studies, these phenolic compounds were evaluated: gallic acid, caffeic acid and pyrogallol. The antibacterial, antifungal and modulatory of antibiotic activities of these compounds were assayed using microdilution method of Minimum Inhibitory Concentration (MIC) to bacteria and Minimum Fungicide Concentration (MFC) to fungi. The modulation was made by comparisons of the MIC and MFC of the compounds alone and combined with drugs against bacteria and fungi respectively, using a sub-inhibitory concentration of 128 µg/mL of substances (MIC/8). All substances not demonstrated clinically relevant antibacterial activity with a MIC above ≥1024 µg/mL. As a result, we observed that the caffeic acid presented a potentiating antibacterial effect over the 3 groups of bacteria studied. Pyrogallol showed a synergistic effect with two of the antibiotics tested, but only against Staphylococcus aureus. In general, caffeic acid was the substance that presented with the greatest number of antibiotics and with the greatest number of bacteria. In relation to the antifungal activity of all the compounds, the verified results were ≥1024 µg/mL, not demonstrating significant activity. Regarding potentiation of the effect of fluconazole, was observed synergistic effect only when assayed against Candida tropicalis, with all substances. Therefore, as can be seen, the compounds presented as substances that can be promising potentiating agents of antimicrobial drugs, even though they do not have direct antibacterial and antifungal action.

Evaluation of the tannic acid inhibitory effect against the NorA efflux pump of Staphylococcus aureus.

During the early periods of antibiotic usage, bacterial infections were considered tamed. However, widespread antibiotic use has promoted the emergence of antibiotic-resistant pathogens, including multidrug resistant strains. Active efflux is a mechanism for bacterial resistance to inhibitory substances, known simply as drug efflux pumps. The bacterium Staphylococcus aureus is an important pathogenic bacterium responsible for an array of infections. The NorA efflux pump has been shown to be responsible for moderate fluoroquinolone resistance of S. aureus. The inhibition of the efflux pump was assayed using a sub-inhibitory concentration of standard efflux pump inhibitors and tannic acid (MIC/8), where its capacity to decrease the MIC of Ethidium bromide (EtBr) and antibiotics due to the possible inhibitory effect of these substances was observed. The MICs of EtBr and antibiotics were significantly reduced in the presence of tannic acid, indicating the inhibitory effect of this agent against the efflux pumps of both strains causing a three-fold reduction of the MIC when compared with the control. These results indicate the possible usage of tannic acid as an adjuvant in antibiotic therapy against multidrug resistant bacteria (MDR).

Psidium guajava L. and Psidium brownianum Mart ex DC.: Chemical composition and anti - Candida effect in association with fluconazole.

The therapeutic combinations have been increasingly used against fungal resistance. Natural products have been evaluated in combination with pharmaceutical drugs in the search for new components able to work together in order to neutralize the multiple resistance mechanisms found in yeasts from the genus Candida. The aqueous and hydroethanolic extracts from Psidium brownianum Mart ex DC. and Psidium guajava L. species were evaluated for their potential to change the effect of commercial pharmaceutical drugs against Candida albicans and Candida tropicalis strains. The tests were performed according to the broth microdilution method. Plate readings were carried out by spectrophotometry, and the data generated the cell viability curve and IC50 of the extracts against the yeasts. A chemical analysis of all the extracts was performed for detection and characterization of the secondary metabolites. The total phenols were quantified in gallic acid eq/g of extract (GAE/g) and the phenolic composition of the extracts was determined by HPLC. Fluconazole and all extracts presented high Minimum Inhibitories Concentrations (MICs). However, when associated with the extracts at sub-inhibitory concentrations (MIC/16), fluconazole had its effect potentiated. A synergistic effect was observed in the combination of fluconazole with Psidium brownianum extracts against all Candida strains. However, for Psidium guajava extracts the synergistic effect was produced mainly against the Candida albicans LM77 and Candida tropicalis INCQS 400042 strains. The IC50 values of fluconazole ranged from 19.22 to 68.1 µg/mL when it was used alone, but from 2.2 to 45.4 µg/mL in the presence of the extracts. The qualitative chemical characterization demonstrated the presence of phenols, flavonoids and tannins among the secondary metabolites. The concentration of total phenols ranged from 49.25 to 80.77 GAE/g in the P. brownianum extracts and from 68.06 to 82.18 GAE/g in the P. guajava extracts. Our results indicated that both P. brownianum and P. guajava extracts are effective on potentiating the effect of fluconazole, and therefore, these plants have the potential for development of new effective drugs for treating fungal infections.

HPLC-DAD phenolic profile, cytotoxic and anti-kinetoplastidae activity of Melissa officinalis.

Context Melissa officinalis subsp. inodora Bornm. (Lamiaceae) has been used since ancient times in folk medicine against various diseases, but it has not been investigated against protozoa. Objective To evaluate the activities of M. officinalis against Leishmania braziliensis, Leishmania infantum and Trypanosoma cruzi as well as its cytotoxicity in fibroblast cell line. Materials and methods The fresh leaves were chopped into 1 cm(2) pieces, washed and macerated with 99.9% of ethanol for 72 h at room temperature. Antiparasitic activity of M. officinalis was accessed by direct counting of cells after serial dilution, while the cytotoxicity of M. officinalis was evaluated in fibroblast cell line (NCTC929) by measuring the reduction of resazurin. The test duration was 24 h. High-performance liquid chromatography (HPLC) was used to characterise the extract. Results The extract at concentrations of 250 and 125 µg/mL inhibited 80.39 and 54.27% of promastigote (LC50 value = 105.78 µg/mL) form of L. infantum, 80.59 and 68.61% of L. brasiliensis (LC50 value = 110.69 µg/mL) and against epimastigote (LC50 value = 245.23 µg/mL) forms of T. cruzi with an inhibition of 54.45 and 22.26%, respectively, was observed. The maximum toxicity was noted at 500 µg/mL with 95.41% (LC50 value = 141.01 µg/mL). The HPLC analysis identified caffeic acid and rutin as the major compounds. Discussion The inhibition of the parasites is considered clinically relevant (< 500 µg/mL). Rutin and caffeic acids may be responsible for the antiprotozoal effect of the extract. Conclusion The ethanol extract of M. officinalis can be considered a potential alternative source of natural products with antileishmania and antitrypanosoma activities.

Chemical composition and evaluation of modulatory of the antibiotic activity from extract and essential oil of Myracrodruon urundeuva.

CONTEXT: The combination of antibiotics with natural products has demonstrated promising synergistic effects in several therapeutic studies. OBJECTIVE: The aim of this study was to determine the effect of a combination of an ethanol extract of Myracrodruon urundeuva Fr. All. (Anacardiaceae) (aroeira plant) and its essential oil with six antimicrobial drugs against multiresistant strains of Staphylococcus aureus and Escherichia coli from clinical isolates. MATERIALS AND METHODS: After identification of the chemical components by GC-MS, the antibacterial activity of the natural products and antibiotics was assessed by determining the minimal inhibitory concentration (MIC) using the microdilution method and concentrations ranging 8-512 µg/mL and 0.0012-2.5 mg/mL, respectively. Assays were performed to test for a possible synergistic action between the plant products and the antimicrobials, using the extract and the oil at a sub-inhibitory concentration (128 µg/mL) and antibiotic at concentrations varying between 8 and 512 µg/mL. RESULTS: The GC-MS analysis identified the main compound as δ-carene (80.41%). The MIC of the natural products was >1024 µg/mL, except against S. aureus ATCC25923. Only the combinations of the natural products with gentamicin, amikacin and clindamycin were effective against S. aureus 358, enhancing the antibiotic activity by reducing the MIC. CONCLUSIONS: The extract from aroeira showed a higher antibacterial activity and the oil was more effective in potentiating the activity of conventional antibiotics.

Thiazine-derived compounds in inhibiting efflux pump in Staphylococcus aureus K2068, mepA gene expression, and membrane permeability alteration.

Staphylococcus aureus is a bacterium responsible for resistance to multiple drugs and the efflux system is widely studied among the resistance mechanisms developed by this species. The present study evaluates the inhibition of the MepA efflux pump by thiadiazine-derived compounds. For this purpose, thiadiazine-derived compounds (IJ-14 to IJ-20) were tested against S. aureus K2068 strains. Microdilution tests were initially conducted to assess the Minimum Inhibitory Concentration (MIC) of the compounds and their efflux pump inhibition activity. In addition, fluorimetry tests were performed using BrEt emission and tests were conducted to inhibit the expression of the mepA gene. This involved comparing the bacterial gene expression with the antibiotic alone to the gene expression after combining compounds (IJ-17 and IJ-20) with the antibiotic. Furthermore, membrane permeability assessment tests and in silico molecular docking tests were performed. It was observed that the IJ17 and IJ20 compounds exhibited direct activity against the tested strain. The IJ17 compound produced significant results in the gene inhibition tests, which was also evidenced through the membrane permeability alteration test. These findings suggest that thiadiazine-derived compounds have promising effects against one of the main resistance mechanisms, with the IJ17 compound presenting observable mechanisms of action.

3-Substituted Coumarins Inhibit NorA and MepA Efflux Pumps of Staphylococcus aureus.

Coumarins are compounds with scientifically proven antibacterial properties, and modifications to the chemical structure are known to improve their effects. This information is even more relevant with the unbridled advances of antibiotic resistance, where Staphylococcus aureus and its efflux pumps play a prominent role. The study's objective was to evaluate the potential of synthetic coumarins with different substitutions in the C-3 position as possible inhibitors of the NorA and MepA efflux pumps of S. aureus. For this evaluation, the following steps took place: (i) the determination of the minimum inhibitory concentration (MIC); (ii) the association of coumarins with fluoroquinolones and ethidium bromide (EtBr); (iii) the assessment of the effect on EtBr fluorescence emission; (iv) molecular docking; and (v) an analysis of the effect on membrane permeability. Coumarins reduced the MICs of fluoroquinolones and EtBr between 50% and 87.5%. Coumarin C1 increased EtBr fluorescence emission between 20 and 40% by reinforcing the evidence of efflux inhibition. The molecular docking results demonstrated that coumarins have an affinity with efflux pumps and establish mainly hydrogen bonds and hydrophobic interactions. Furthermore, C1 did not change the permeability of the membrane. Therefore, we conclude that these 3-substituted coumarins act as inhibitors of the NorA and MepA efflux pumps of S. aureus.

Anti-Trypanosoma cruzi and cytotoxic activities of Eugenia uniflora L.

Chagas disease is caused by Trypanosoma cruzi, being considered a public health problem. An alternative to combat this pathogen is the use of natural products isolated from fruits such as Eugenia uniflora, a plant used by traditional communities as food and medicine due to its antimicrobial and biological activities. Ethanolic extract from E. uniflora was used to evaluate in vitro anti-epimastigote and cytotoxic activity. This is the first record of anti-Trypanosoma activity of E. uniflora, demonstrating that a concentration presenting 50% of activity (EC(50)) was 62.76 µg/mL. Minimum inhibitory concentration (MIC) was ≤ 1024 µg/mL. Our results indicate that E. uniflora could be a source of plant-derived natural products with anti-epimastigote activity with low toxicity.

Trypanocide, cytotoxic, and antifungal activities of Momordica charantia.

CONTEXT: Chagas disease, caused by Trypanosoma cruzi, is a public health problem. Currently, chemotherapy is the only available treatment for this disease, and the drugs used, nifurtimox and benzonidazol, present high toxicity levels. An alternative for replacing these drugs are natural extracts from Momordica charantia L. (Cucurbitaceae) used in traditional medicine because of their antimicrobial and biological activities. OBJECTIVE: In this study, we evaluated the extract of M. charantia for its antiepimastigote, antifungal, and cytotoxic activities. MATERIALS AND METHODS: An ethanol extract of leaves from M. charantia was prepared. To research in vitro antiepimastigote activity, T. cruzi CL-B5 clone was used. Epimastigotes were inoculated at a concentration of 1 × 10(5) cells/mL in 200 µl tryptose-liver infusion. For the cytotoxicity assay, J774 macrophages were used. The antifungal activity was evaluated by microdilution using strains of Candida albicans, Candida tropicalis, and Candida krusei. RESULTS: The effective concentration capable of killing 50% of parasites (IC(50)) was 46.06 µg/mL. The minimum inhibitory concentration (MIC) was ≤ 1024 µg/mL. Metronidazole showed a potentiation of its antifungal effect when combined with an extract of M. charantia. CONCLUSIONS: Our results indicate that M. charantia could be a source of plant-derived natural products with antiepimastigote and antifungal-modifying activity with moderate toxicity.

Modulation of Drug Resistance by Limonene: Inhibition of Efflux Pumps in Staphylococcus aureus Strains RN-4220 and IS-58.

AIMS: This study aimed to investigate the potential of limonene as an efflux pump (EP) inhibitor in Staphylococcus aureus strains, RN-4220 and IS-58, which carry EPs for erythromycin (MrsA) and tetracycline (TetK), respectively. BACKGROUND: The evolution of bacterial resistance mechanisms over time has impaired the action of most classes of antibiotics. Staphylococcus aureus is a notable bacterium, with high pathogenic potential and demonstrated resistance to conventional antibiotics. Considering the importance of discovering novel compounds to combat antibiotic resistance, our group previously demonstrated the antibacterial properties of limonene, a compound present in the essential oils of several plant species. OBJECTIVE: This study aimed to investigate the potential of limonene as an efflux pump (EP) inhibitor in Staphylococcus aureus strains RN-4220 and IS-58, which carry EPs for erythromycin (MrsA) and tetracycline (TetK), respectively. METHODS: The minimum inhibitory concentrations (MIC) of limonene and other efflux pump inhibitors were determined through the broth microdilution method. A reduction in the MIC of ethidium bromide was used as a parameter of EP inhibition. RESULT: While limonene was not shown to exhibit direct antibacterial effects against EP-carrying strains, in association with ethidium bromide and antibiotics, this compound demonstrated enhanced antibacterial activity, indicating the inhibition of the MrsA and TetK pumps. CONCLUSION: In conclusion, this pioneering study demonstrated the effectiveness of limonene as an EP inhibitor in S. aureus strains, RN-4220 and IS-58. Nevertheless, further studies are required to characterize the molecular mechanisms associated with limonene-mediated EP inhibition.

Inhibition of Efflux Pumps by Monoterpene (α-pinene) and Impact on Staphylococcus aureus Resistance to Tetracycline and Erythromycin.

INTRODUCTION: Infectious diseases have been responsible for an increasing number of deaths worldwide. Staphylococcus aureus has been recognized as one of the most notable causative agents of severe infections, while efflux pump (EP) expression is one of the main mechanisms associated with S. aureus resistance to antibiotics. OBJECTIVE: This study aimed to investigate the potential of &#945;-pinene as an efflux pump inhibitor in species of S. aureus carrying the TetK and MrsA proteins. METHODS: The minimum inhibitory concentrations (MIC) of &#945;-pinene and other efflux pump inhibitors were assessed using serial dilutions of each compound at an initial concentration above 1024 µg/mL. Solutions containing culture medium and bacterial inoculums were prepared in test tubes and subsequently transferred to 96-well microdilution plates. The modulation of ethidium bromide (EtBr) and antibiotics (tetracycline and erythromycin) was investigated through analysis of the modification in their MICs in the presence of a subinhibitory concentration of &#945;-pinene (MIC/8). Wells containing only culture medium and bacterial inoculums were used as negative control. Carbonyl cyanide m-chlorophenylhydrazone (CCCP) was used as a positive control. RESULTS: The MIC of ethidium bromide against S. aureus strains RN-4220 and IS-58 was reduced by association with α-pinene. This monoterpene potentiated the effect of tetracycline against the IS-58 strain but failed in modulating the antibacterial effect of erythromycin against RN-4220, suggesting a selective inhibitory effect on the TetK EP by &#945;- pinene. CONCLUSION: In conclusion, α-pinene has promising effects against S.aureus strains, which should be useful in the combat of antibacterial resistance associated with EP expression. Nevertheless, further research is required to fully characterize its molecular mechanism of action as an EP inhibitor.

Characterization, antibacterial activity and antibiotic modifying action of the Caryocar coriaceum Wittm. pulp and almond fixed oil.

In this study the physicochemical characterization of the pulp and almond fixed oil was carried out; their antibacterial activity and aminoglycoside antibiotic modifying action against standard and multiresistant Gram-positive and -negative bacteria were investigated using the broth microdilution assay. Physical properties such as moisture, pH, acidity, peroxide index, relative density and refractive index indicate stability and chemical quality of the oils. In the GC/MS chemical composition analysis, a high unsaturated fatty acid content and the presence of oleic and palmitic acids were observed in the oils. In the antibacterial assay, more significant results were obtained for Escherichia coli, while other standard and multi-resistant strains presented MIC values ≥ 1024 µg/mL. Furthermore, the fixed oils in association with antibiotics were able to significantly improve antibacterial activity against S. aureus with a reduction in MICs.