Insect immunity: Induction of cecropin and attacin-like antibacterial factors in the haemolymph of Glossina morsitans morsitans

Injections of live Escherichia coli into adult tsetse flies, Glossina morsitans morsitans induced an antibacterial activity in the haemolymph after a lag period of 6–18 hr. Peak activity occurred after 24–72 hr with a dose of 10⁴ bacteria/fly. Acidic electrophoresis of immune haemolymph from G. m. morsitans followed by an antibacterial assay on the gel revealed the presence of cecropin- and attacin-like factors. The induction of antibacterial activity in tsetse was completely blocked by injection of cycloheximide, a known inhibitor of protein synthesis in eukaryotic organisms. Purified InA from Bacillus thuringiensis, a proteolytic enzyme with specificity for cecropins and attacins in haemolymph, inactivated the antibacterial activity in tesetse immune haemolymph. When tested against 10 different bacterial species, the spectrum was the same for the antibacterial activity in immune haemolymph from tsetse and Cecropia.     

Streptococcus mutans SMU.623c codes for a functional, metal-dependent polysaccharide deacetylase that modulates interactions with salivary agglutinin

The genome sequence of the oral pathogen Streptococcus mutans predicts the presence of two putative polysaccharide deacetylases. The first, designated PgdA in this paper, shows homology to the catalytic domains of peptidoglycan deacetylases from Streptococcus pneumoniae and Listeria monocytogenes, which are both thought to be involved in the bacterial defense mechanism against human mucosal lysozyme and are part of the CAZY family 4 carbohydrate esterases. S. mutans cells in which the pgdA gene was deleted displayed a different colony texture and a slightly increased cell surface hydrophobicity and yet did not become hypersensitive to lysozyme as shown previously for S. pneumoniae. To understand this apparent lack of activity, the high-resolution X-ray structure of S. mutans PgdA was determined; it showed the typical carbohydrate esterase 4 fold, with metal bound in a His-His-Asp triad. Analysis of the protein surface showed that an extended groove lined with aromatic residues is orientated toward the active-site residues. The protein exhibited metal-dependent de-N-acetylase activity toward a hexamer of N-acetylglucosamine. No activity was observed toward shorter chitooligosaccharides or a synthetic peptidoglycan tetrasaccharide. In agreement with the lysozyme data this would suggest that S. mutans PgdA does not act on peptidoglycan but on an as-yet-unidentified polysaccharide within the bacterial cell surface. Strikingly, the pgdA-knockout strain showed a significant increase in aggregation/agglutination by salivary agglutinin, in agreement with this gene acting as a deacetylase of a cell surface glycan.     

Antibacterial activity and dual mechanisms of peptide analog derived from cell-penetrating peptide against Salmonella typhimurium and Streptococcus pyogenes

A number of research have proven that antimicrobial peptides are of greatest potential as a new class of antibiotics. Antimicrobial peptides and cell-penetrating peptides share some similar structure characteristics. In our study, a new peptide analog, APP (GLARALTRLLRQLTRQLTRA) from the cell-penetrating peptide ppTG20 (GLFRALLRLLRSLWRLLLRA), was identified simultaneously with the antibacterial mechanism of APP against Salmonella typhimurium and Streptococcus pyogenes. APP displayed potent antibacterial activity against Gram-negative and Gram-positive strains. The minimum inhibitory concentration was in the range of 2 to 4 μM. APP displayed higher cell selectivity (about 42-fold increase) as compared to the parent peptide for it decreased hemolytic activity and increased antimicrobial activity. The calcein leakage from egg yolk l-α-phosphatidylcholine (EYPC)/egg yolk l-α-phosphatidyl-dl-glycerol and EYPC/cholesterol vesicles demonstrated that APP exhibited high selectivity. The antibacterial mechanism analysis indicated that APP induced membrane permeabilization in a kinetic manner for membrane lesions allowing O-nitrophenyl-β-d-galactoside uptake into cells and potassium release from APP-treated cells. Flow cytometry analysis demonstrated that APP induced bacterial live cell membrane damage. Circular dichroism, fluorescence spectra, and gel retardation analysis confirmed that APP interacted with DNA and intercalated into the DNA base pairs after penetrating the cell membrane. Cell cycle assay showed that APP affected DNA synthesis in the cell. Our results suggested that peptides derived from the cell-penetrating peptide have the potential for antimicrobial agent development, and APP exerts its antibacterial activity by damaging bacterial cell membranes and binding to bacterial DNA to inhibit cellular functions, ultimately leading to cell death.     

Antibacterial activity of phellodendron bark against Streptococcus mutans

Streptococcus mutans is a major cause of tooth decay due to its promotion of biofilm formation and acid production. Several plant extracts have been reported to have multiple biological activities such as anti-inflammation and antibacterial effects. This study investigated the antibacterial activity of three plant extracts, phellodendron bark (PB), yucca, and black ginger, and found that PB had a stronger effect than the other extracts. Then, the minimum inhibitory concentration (MIC) of PB against 100 S. mutans strains was investigated. The MIC range of PB was 9.8–312.5 µg/mL. PB suppressed the growth kinetics of S. mutans in a dose-dependent manner, even at sub-MICs of PB. Then, we investigated the effect of PB on S. mutans virulence. The PB suppressed biofilm formation at high concentrations, although PB did not affect the expression of glucosyltransferase genes. Additionally, PB suppressed the decrease in pH from adding an excess of glucose. The expression of genes responsible for acid production was increased by the addition of excess glucose without PB, whereas their expression levels were not increased in the presence of 1× and 2× MIC of PB. Although PB showed a bacteriostatic effect on planktonic S. mutans cells, it was found that more than 2× MIC of PB showed a partial bactericidal effect on biofilm cells. In conclusion, PB not only showed antibacterial activity against S. mutans but also decreased the cariogenic activity in S. mutans.     

Antibacterial Activity and Inhibition of Adherence of Streptococcus mutans by Propolis Electrospun Fibers

Mouth-dissolving fibers with antibacterial activity for the oral cavity were prepared by an electrospinning technique. Propolis extract was used as an active ingredient and polyvinylpyrrolidone (PVP) K90 as the polymer matrix. The morphology and diameter of the fibers were characterized by scanning electron microscopy. Antibacterial activity against Streptococcus mutans and the inhibition of S. mutans adhesion on a smooth glass surface during the biofilm formation were tested. Propolis, 5% (w/v), was combined with a PVP K90 solution, 8% (w/v), with or without Tween 80 including flavor additives and electrospun with an applied voltage of 15 kV. Uniform and smooth fibers of propolis-PVP K90 were obtained. The results showed that electrospun fibers with propolis extract can dissolve and release the propolis in water. Propolis-PVP electrospun fibers showed better antibacterial activity by reduction of bacteria adhesion on a smooth glass surface when compared to some commercial mouthwash products. These results indicated the potential of electrospun fibers to be used as mouth-dissolving fibers for effective antibacterial activity in the oral cavity.KEY WORDS: antibacterial activity, electrospun fibers, inhibition of adherence, propolis, Streptococcus mutans     

Moxifloxacin modulates inflammation during murine pneumonia

Background

Moxifloxacin is a synthetic antibacterial agent belonging to the fluoroquinolone family. The antimicrobial activity of quinolones against Gram-positive and Gram-negative bacteria is based on their ability to inhibit topoisomerases. Quinolones are described to have immunomodulatory features in addition to their antimicrobial activities. It was the goal of this study to examine whether a short term treatment with moxifloxacin modulates the inflammation during a subsequently induced bacterial infection in an animal model.

Methods

Mice were treated with moxifloxacin or saline for two consecutive days and were subsequently intranasally infected with viable or heat-inactivated bacterial pathogens (Streptococcus pneumoniae, Pseudomonas aeruginosa) for 6 and 24 hours. Measurements of cytokines in the lungs and plasma were performed. Alveolar cells were determined in bronchoalveolar lavage fluits.

Results

The inflammation was increased after the inoculation of viable bacteria compared to inactivated bacteria. Numbers of total immune cells and neutrophils and concentrations of inflammatory mediators (e.g. KC, IL-1β, IL-17A) were significantly reduced in lungs of moxifloxacin-treated mice infected with inactivated and viable bacterial pathogens as compared to infected control mice. Plasma concentrations of inflammatory mediators were significantly reduced in moxifloxacin-treated mice. Immunohistochemistry showed a stronger infiltrate of TNF-α-expressing cells into lungs of saline-treated mice infected with viable P. aeruginosa as compared to moxifloxacin-treated mice.

Conclusions

These data show that in this pneumonia model moxifloxacin has anti-inflammatory properties beyond its antibacterial activity.     

Antibacterial activity of disodium succinoyl glycyrrhetinate,a derivative of glycyrrhetinic acid against Streptococcus mutans

Streptococcus mutans is a cariogenic bacterium that localizes in the oral cavity. Glycyrrhetinic acid (GRA) is a major component of licorice extract. GRA and several derivatives, including disodium succinoyl glycyrrhetinate (GR‐SU), are known to have anti‐inflammatory effects in humans. In this study, the antimicrobial effect of GRA and its derivatives against the S. mutans UA159 strain were investigated. Minimum inhibitory concentrations (MICs) of GRA and GR‐SU showed antibacterial activity against the S. mutans strain, whereas other tested derivatives did not. Because GR‐SU is more soluble than GRA, GR‐SU was used for further experiments. The antibacterial activity of GR‐SU against 100 S. mutans strains was evaluated and it was found that all strains are susceptible to GR‐SU, with MIC values below 256 µg/mL. A cell viability assay showed that GR‐SU has a bacteriostatic effect on S. mutans cells. As to growth kinetics, sub‐MICs of GR‐SU inhibited growth. The effect of GR‐SU on S. mutans virulence was then investigated. GR‐SU at sub‐MICs suppresses biofilm formation. Additionally, GR‐SU greatly suppresses the pH drop caused by the addition of glucose and glucose‐induced expression of the genes responsible for acid production (ldh and pykF) and tolerance (aguD and atpD). Additionally, expression of enolase, which is responsible for the carbohydrate phosphotransferase system, was not increased in the presence of GR‐SU, indicating that GR‐SU suppresses incorporation of sugars into S. mutans. In conclusion, GR‐SU has antibacterial activity against S. mutans and also decreases S. mutans virulence.     

In Vitro Evaluation of the Risk of Inducing Bacterial Resistance to Disinfection Treatment with Photolysis of Hydrogen Peroxide

The purpose of the present study was to evaluate the risk of inducing bacterial resistance to disinfection treatment with photolysis of H₂O₂ and comparing this with existing antibacterial agents. We tested seven antibacterial agents, including amoxicillin, cefepime hydrochloride, erythromycin, ofloxacin, clindamycin hydrochloride, ciprofloxacin hydrochloride, and minocycline hydrochloride, as positive controls for validation of the assay protocol. For all of the agents tested, at least one of the four bacterial species (Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, and Streptococcus salivarius) was resistant to these agents by repeated exposure to subinhibitory concentrations of the agents up to 10 times. In contrast, antibacterial activity against any of the bacterial species tested (S. aureus, E. faecalis, E. coli, S. salivarius, Pseudomonas aeruginosa, Streptococcus mutans, and Aggregatibacter actinomycetemcomitans) was not affected by repeated exposure to the disinfection treatment up to 40 times. This finding suggested that the risk of inducing bacterial resistance by disinfection treatment was low. The active ingredient of this disinfection treatment is hydroxyl radicals generated by photolysis of H₂O₂. Therefore, hydroxyl radicals interact with several cell structures and different metabolic pathways in microbial cells, probably resulting in a lack of development of bacterial resistance. In conclusion, disinfection treatment with photolysis of H₂O₂ appears to be a potential alternative for existing antimicrobial agents in terms of a low risk of inducing bacterial resistance.     

Production,purification, sequencing and activity spectra of mutacins D-123.1 and F-59.1

Background  

The increase in bacterial resistance to antibiotics impels the development of new anti-bacterial substances. Mutacins (bacteriocins) are small antibacterial peptides produced by Streptococcus mutans showing activity against bacterial pathogens. The objective of the study was to produce and characterise additional mutacins in order to find new useful antibacterial substances.     

Immune reactions of Chironomus larvae (Insecta: Diptera) against bacteria

Humoral encapsulation (“melanization”) represents the predominant defence reaction of Chironomus larvae against injected bacteria. Only low levels of phagocytic activity were observed; cellular encapsulation and nodule formation were completely missing due to low numbers of haemocytes. No other humoral antibacterial activity was detected in normal Chironomus haemolymph and even haemolymph of preinjected (“immunized”) Chironomus larvae showed little inhibition of bacterial growth on agar test plates.Low cellular and lytic activity of Chironomus haemolymph against bacteria is well compensated for by its fast and efficient capacity of humoral encapsulation. Within 5–10 min, even high numbers of injected bacteria (up to 10⁵ per larva) were surrounded by capsular material. Within this range of injection dose, the fates of pathogenic and non-pathogenic strains were identical, and bacteria which are highly pathogenic for many other insects, e.g. larvae of Galleria mellonella, proved to be harmless to Chironomus larvae. The rapidity of humoral encapsulation may prevent the release of toxins or enzymes by which pathogenic bacteria normally damage its host and weaken its immune system.     

A comparative study of the effect of probiotics on cariogenic biofilm model for preventing dental caries

Dental caries is induced by oral biofilm containing Streptococcus mutans. Probiotic bacteria were mainly studied for effect on the gastrointestinal tract and have been known to promote human health. However, the information of probiotics for oral health has been lack yet. In this study, we investigated influence of various probiotics on oral bacteria or cariogenic biofilm and evaluated candidate probiotics for dental caries among them. The antimicrobial activity of the spent culture medium of probiotics for oral streptococci was performed. Probiotics were added during the biofilm formation with salivary bacteria including S. mutans. The oral biofilms were stained with a fluorescent dye and observed using the confocal laser scanning microscope. To count bacteria in the biofilm, the bacteria were plated on MSB and BHI agar plates after disrupting the biofilm and cultivated. Glucosyltransferases (gtfs) expression of S. mutans and integration of lactobacilli into the biofilm were evaluated by real-time RT-PCR. Among probiotics, Lactobacillus species strongly inhibited growth of oral streptococci. Moreover, Lactobacillus species strongly inhibited formation of cariogenic biofilm model. The expression of gtfs was significantly reduced by Lactobacillus rhamnosus. The integration of L. rhamnosus into the biofilm model did not exhibit. However, L. acidophilus and L casei integrated into the biofilm model. These results suggest that L. rhamnosus may inhibit oral biofilm formation by decreasing glucan production of S. mutans and antibacterial activity and did not integrate into oral biofilm, which can be a candidate for caries prevention strategy.     

Isolation of a Novel Phage with Activity against Streptococcus mutans Biofilms

Streptococcus mutans is one of the principal agents of caries formation mainly, because of its ability to form biofilms at the tooth surface. Bacteriophages (phages) are promising antimicrobial agents that could be used to prevent or treat caries formation by S. mutans. The aim of this study was to isolate new S. mutans phages and to characterize their antimicrobial properties. A new phage, ɸAPCM01, was isolated from a human saliva sample. Its genome was closely related to the only two other available S. mutans phage genomes, M102 and M102AD. ɸAPCM01 inhibited the growth of S. mutans strain DPC6143 within hours in broth and in artificial saliva at multiplicity of infections as low as 2.5x10^-5. In the presence of phage ɸAPCM01 the metabolic activity of a S. mutans biofilm was reduced after 24 h of contact and did not increased again after 48 h, and the live cells in the biofilm decreased by at least 5 log cfu/ml. Despite its narrow host range, this newly isolated S. mutans phage exhibits promising antimicrobial properties.     

Bactericidal activity and oral pathogen inactivation by electromagnetic wave irradiation

Aims: The aim of this work was to clarify the effects of electromagnetic wave irradiation (EMWI) on oral bacterial pathogens. Methods and Results: A Gram‐negative (Porphyromonas gingivalis) or Gram‐positive (Streptococcus mutans, S. intermedius, Enterococcus faecalis) bacterial suspension was irradiated by EMW apparatus (500–1000 kHz, 5–15 times, 1 s time^?1). Quantification of survival bacteria by CFU counting revealed that EMWI exhibited marked bactericidal activity against all tested bacteria and bactericidal activity at 500 kHz increased in an irradiation number‐dependent manner. After EMWI at 500 kHz, scanning electron microscopic observations showed that the chain of S. mutans cells was shortened after 5 irradiations and the outlines of bacterial cells (S. mutans and P. gingivalis) were unclear after 5–10 irradiations. EMWI inhibited the inductive effect of S. mutans on pro‐inflammatory cytokine production in human monocytes and this inhibitory effect was comparable with that of heat‐killed bacteria. Furthermore, using an enzyme activity assay, EMWI partially inactivated the activities of gingipains from P. gingivalis. Conclusions: These findings demonstrated that EMWI has inactivation and bactericidal activities against single microbial species among four kinds of oral pathogens. Significance and Impact of the Study: Electromagnetic wave irradiation may be applicable for medical disinfection and sterilization, such as refractory periapical periodontitis.     

Antimicrobial effects of herbal extracts on Streptococcus mutans and normal oral streptococci

Streptococcus mutans is associated with dental caries. A cariogenic biofilm, in particular, has been studied extensively for its role in the formation of dental caries. Herbal extracts such as Cudrania tricuspidata, Sophora flavescens, Ginkgo biloba, and Betula Schmidtii have been used as a folk remedy for treating diseases. The purpose of this study was to evaluate and compare the antibacterial activity of herbal extracts against normal oral streptococci, planktonic and biofilm of S. mutans. Streptococcus gordonii, Streptococcus oralis, Streptococcus salivarius, Streptococcus sanguinis, and S. mutans were cultivated with brain heart infusion broth and susceptibility assay for the herbal extracts was performed according to the protocol of Clinical and Laboratory Standard Institute. Also, S. mutans biofilm was formed on a polystyrene 12-well plate and 8-well chamber glass slip using BHI broth containing 2% sucrose and 1% mannose after conditioning the plate and the glass slip with unstimulated saliva. The biofilm was treated with the herbal extracts in various concentrations and inoculated on Mitis-Salivarius bacitracin agar plate for enumeration of viable S. mutans by counting colony forming units. Planktonic S. mutans showed susceptibility to all of the extracts and S. mutans biofilm exhibited the highest level of sensitivity for the extracts of S. flavescens. The normal oral streptococci exhibited a weak susceptibility in comparison to S. mutans. S. oralis, however, was resistant to all of the extracts. In conclusion, the extract of S. flavescens may be a potential candidate for prevention and management of dental caries.     

Effects of quorum sensing on cell viability in Streptococcus mutans biofilm formation

Streptococcus mutans (S. mutans) uses a quorum sensing (QS) signaling system, which is dependent on competence stimulating peptide (CSP), to regulate diverse physiological activities including bacteriocin production, genetic transformation, and biofilm formation. However, the mechanism of the QS system-induced biofilm formation remains unclear. Here, we demonstrated that the late-stage biofilm formation was increased by the addition of exogenous CSP in S. mutans. The numbers of dead cells in biofilms formed in presence of CSP was 64.5% higher than that without CSP after 12 h (p < 0.05) and 76.3% higher after 24 h (p < 0.05), the numbers of live cells in biofilms formed in presence of CSP were 89.3% higher than that without CSP after 24 h (p < 0.01). The expression of QS-associated genes was increased 3.4-5.3-fold by CSP in biofilms. Our results revealed that cell viability of S. mutans grown in biofilms is affected by the CSP-dependent QS system.     

Antimicrobial and anti-biofilm effect of Bac8c on major bacteria associated with dental caries and Streptococcus mutans biofilms

Dental caries is a common oral bacterial infectious disease. Its prevention and treatment requires control of the causative pathogens within dental plaque, especially Streptococcus mutans (S. mutans). Antimicrobial peptides (AMPs), one of the promising substitutes for conventional antibiotics, have been widely tested and used for controlling bacterial infections. The present study focuses on evaluating the potential of the novel AMPs cyclic bactenecin and its derivatives against bacteria associated with dental caries. The results indicate that Bac8c displayed highest activity against the bacteria tested, whereas both cyclic and linear bactenecin had weak antimicrobial activity. The cytotoxicity assay showed that Bac8c did not cause detectable toxicity at concentrations of 32–128 μg/ml for 5 min or 32–64 μg/ml for 60 min. S. mutans and Lactobacillus fermenti treated with Bac8c showed variable effects on bacterial structure via scanning electron microscopy and transmission electron microscopy. There appeared to be a large amount of extracellular debris and obvious holes on the cell surface, as well as loss of cell wall and nucleoid condensation. The BioFlux system was employed to generate S. mutans biofilms under a controlled flow, which more closely resemble the formation process of natural biofilms. Bac8c remarkably reduced the viability of cells in biofilms formed in the BioFlux system. This phenomenon was further analyzed and verified by real-time PCR results of a significant suppression of the genes involved in S. mutans biofilm formation. Taken together, this study suggests that Bac8c has a potential clinical application in preventing and treating dental caries.     

Streptococcus mutans Can Modulate Biofilm Formation and Attenuate the Virulence of Candida albicans

Streptococcus mutans and Candida albicans are found together in the oral biofilms on dental surfaces, but little is known about the ecological interactions between these species. Here, we studied the effects of S. mutans UA159 on the growth and pathogencity of C. albicans. Initially, the effects of S. mutans on the biofilm formation and morphogenesis of C. albicans were tested in vitro. Next, we investigate the influence of S. mutans on pathogenicity of C. albicans using in vivo host models, in which the experimental candidiasis was induced in G. mellonella larvae and analyzed by survival curves, C. albicans count in hemolymph, and quantification of hyphae in the host tissues. In all the tests, we evaluated the direct effects of S. mutans cells, as well as the indirect effects of the subproducts secreted by this microorganism using a bacterial culture filtrate. The in vitro analysis showed that S. mutans cells favored biofilm formation by C. albicans. However, a reduction in biofilm viable cells and inhibition of hyphal growth was observed when C. albicans was in contact with the S. mutans culture filtrate. In the in vivo study, injection of S. mutans cells or S. mutans culture filtrate into G. mellonella larvae infected with C. albicans increased the survival of these animals. Furthermore, a reduction in hyphal formation was observed in larval tissues when C. albicans was associated with S. mutans culture filtrate. These findings suggest that S. mutans can secrete subproducts capable to inhibit the biofilm formation, morphogenesis and pathogenicity of C. albicans, attenuating the experimental candidiasis in G. mellonella model.     

Phagocytic activity and encapsulation rate of Galleria mellonella larval haemocytes during bacterial infection by Bacillus thuringiensis

The bacterium Bacillus thuringiensis (Bt) is a pathogen of many insect species and is actively used in biocontrol. After the peroral inoculation of Galleria mellonella by the Bt in 5% sublethal concentration (LC₅), a 1.5-fold increase in the phagocytic activity of infected larvae has been registered on the second and third days after the inoculation. With the increase of Bt-inoculum amount to 15% of sublethal concentration (LC₁₅), a further increase of the phagocytic activity and enhanced encapsulation rates in the haemolymph of infected larvae has been observed. The enhanced cellular immunity during the bacteriosis seems to have resulted from the destruction of midgut epithelium cells followed by the subsequent exposure of gut content to lymph factors activating the immune system of haemocoel.     

Anti-biofilm and anti-inflammatory effects of Lycosin-II isolated from spiders against multi-drug resistant bacteria

Currently, multidrug-resistant bacteria are rapidly increasing worldwide because of the misuse or overuse of antibiotics. In particular, few options exist for treating infections caused by long-persisting oxacillin-resistant strains and recently proliferating carbapenem-resistant strains. Therefore, alternative treatments are urgently needed. The antimicrobial peptide (AMP) Lycosin-II is a peptide consisting of 21 amino acids isolated from the venom of the spider Lycosa singoriensis. Lycosin-II showed strong antibacterial activity and biofilm inhibition effects against gram-positive and gram-negative bacteria including oxacillin-resistant Staphylococcus aureus (S. aureus) and meropenem-resistant Pseudomonas aeruginosa (P. aeruginosa) isolated from patients. In addition, Lycosin-II was not cytotoxic against human foreskin fibroblast Hs27 or hemolytic against sheep red blood cells at the concentration of which exerted antibacterial activity. The mechanism of action of Lycosin-II involves binding to lipoteichoic acid and lipopolysaccharide of gram-positive and gram-negative bacterial membranes, respectively, to destroy the bacterial membrane. Moreover, Lycosin-II showed anti-inflammatory effects by inhibiting the expression of pro-inflammatory cytokines that are increased during bacterial infection in Hs27 cells. These results suggest that Lycosin-II can serve as a therapeutic agent against infections with multidrug-resistant strains.     

Menadione (vitamin K) enhances the antibiotic activity of drugs by cell membrane permeabilization mechanism

Menadione, vitamin K3, belongs to the class of lipid-soluble vitamins and lipophilic substances as menadione cause disturbances in the bacterial membrane, resulting in damage to the fundamental elements for the integrity of the membrane, thus allowing increased permeability. Accordingly, the aim of this study was to evaluate in vitro the antibiotic-modifying activity of menadione in multiresistant strains of Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli, with a gradual increase in its subinhibitory concentration. In addition, menadione was compared with cholesterol and ergosterol for similarity in mechanism of drug modulatory action. Antibiotic-modifying activity and antibacterial effect were determined by the broth microdilution assay. Menadione, cholesterol and ergosterol showed modulatory activity at clinically relevant concentrations, characterizing them as modifiers of bacterial drug resistance, since they lowered the MIC of the antibiotics tested. This is the first report of the antibacterial activity of menadione and its potentiation of aminoglycosides against multiresistant bacteria.