The aim of this study was to evaluate the antimicrobial activity of aqueous extract of Psidium guineense Swartz (Araçá-do-campo) and five antimicrobials (ampicillin, amoxicillin/clavulanic acid, cefoxitin, ciprofloxacin, and meropenem) against twelve strains of Staphylococcus aureus with a resistant phenotype previously determined by the disk diffusion method. Four S. aureus strains showed resistance to all antimicrobial agents tested and were selected for the study of the interaction between aqueous extract of P. guineense and antimicrobial agents, by the checkerboard method. The criteria used to evaluate the synergistic activity were defined by the fractional inhibitory concentration index (FICI). All S. aureus strains were susceptible to P. guineense as determined by the microdilution method. The combination of the P. guineense extract with the antimicrobial agents resulted in an eight-fold reduction in the MIC of these agents, which showed a FICI ranging from 0.125 to 0.5, suggesting a synergistic interaction against methicillin-resistant Staphylococcus aureus (MRSA) strains. The combination of the aqueous extract of P. guineense with cefoxitin showed the lowest FICI values. This study demonstrated that the aqueous extract of P. guineense combined with beta lactamics antimicrobials, fluoroquinolones, and carbapenems, acts synergistically by inhibiting MRSA strains.
Through bioassay-guided fractionation of the extracts from the aerial parts of the Chinese herb Hypericum japonicum Thunb. Murray, Isojacareubin (ISJ) was characterized as a potent antibacterial compound against the clinical methicillin-resistant Staphylococcus aureus (MRSA). The broth microdilution assay was used to determine the minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) of ISJ alone. The results showed that its MICs/MBCs ranged from 4/16 to 16/64 μg/mL, with the concentrations required to inhibit or kill 50% of the strains (MIC50/MBC50) at 8/16 μg/mL. Synergistic evaluations of this compound with four conventional antibacterial agents representing different types were performed by the chequerboard and time-kill tests. The chequerboard method showed significant synergy effects when ISJ was combined with Ceftazidime (CAZ), Levofloxacin (LEV) and Ampicillin (AMP), with the values of 50% of the fractional inhibitory concentration indices (FICI50) at 0.25, 0.37 and 0.37, respectively. Combined bactericidal activities were also observed in the time-kill dynamic assay. The results showed the ability of ISJ to reduce MRSA viable counts by log10CFU/mL at 24 h of incubation at a concentration of 1 × MIC were 1.5 (LEV, additivity), 0.92 (CAZ, indifference) and 0.82 (AMP, indifference), respectively. These in vitro anti-MRSA activities of ISJ alone and its synergy with conventional antibacterial agents demonstrated that ISJ enhanced their efficacy, which is of potential use for single and combinatory therapy of patients infected with MRSA.
anti-MRSA activity; Hypericum japonicum; Isojacareubin; MIC; synergy
The aim of this study was to determine the effects of combinations of fosfomycin, minocycline and polymyxin B in the treatment of pan-drug-resistant Acinetobacter baumannii (PDR-Ab). The in vitro antibacterial activities of the drugs were evaluated by determination of the minimum inhibitory concentration (MIC) and the fractional inhibitory concentration index (FICI). A total of 25 strains of PDR-Ab were selected using the VITEK32 microbial analysis instrument and the Kirby-Bauer (K-B) method. A broth microdilution method was used to determine the MIC for each of the three drugs, and the checkerboard method was simultaneously used to determine the MICs for combinations of the drugs. FICI values were also calculated. While fosfomycin alone was ineffective for the treatment of PDR-Ab, its MIC value was significantly reduced when used in combination with minocycline or polymyxin B. The combined use of minocycline and polymyxin B also significantly reduced the MIC value of each drug. The FICI values revealed that the drugs had synergistic or additive effects when used in combination. The determination of the MIC and FICI values for the combinations of drugs demonstrated that there is synergistic or additive effect upon the combined use of fosfomycin with minocycline or polymyxin B. The combined use of minocycline and polymyxin B also results in a significant reduction in the MIC values of the two drugs. These experimental results may provide a basis for the future clinical treatment of Acinetobacter baumannii.
pan-drug resistant Acinetobacter baumannii; minocycline; fosfomycin; polymyxin B; minimum inhibitory concentration; fractional inhibitory concentration index
The emergence of multidrug-resistant bacteria is a world health problem. Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA) strains, is one of the most important human pathogens associated with hospital and community-acquired infections. The aim of this work was to evaluate the antibacterial activity of a Pseudomonas aeruginosa-derived compound against MRSA strains.
Thirty clinical MRSA strains were isolated, and three standard MRSA strains were evaluated. The extracellular compounds were purified by vacuum liquid chromatography. Evaluation of antibacterial activity was performed by agar diffusion technique, determination of the minimal inhibitory concentration, curve of growth and viability and scanning electron microscopy. Interaction of an extracellular compound with silver nanoparticle was studied to evaluate antibacterial effect.
The F3 (ethyl acetate) and F3d (dichloromethane- ethyl acetate) fractions demonstrated antibacterial activity against the MRSA strains. Phenazine-1-carboxamide was identified and purified from the F3d fraction and demonstrated slight antibacterial activity against MRSA, and synergic effect when combined with silver nanoparticles produced by Fusarium oxysporum. Organohalogen compound was purified from this fraction showing high antibacterial effect. Using scanning electron microscopy, we show that the F3d fraction caused morphological changes to the cell wall of the MRSA strains.
These results suggest that P. aeruginosa-produced compounds such as phenazines have inhibitory effects against MRSA and may be a good alternative treatment to control infections caused by MRSA.
Antibacterial activity; Methicillin-resistant; Pseudomonas aeruginosa; Staphylococcus aureus
There has been considerable effort to discover plant-derived antibacterials against methicillin-resistant strains of Staphylococcus aureus (MRSA) which have developed resistance to most existing antibiotics, including the last line of defence, vancomycin. Pentacyclic triterpenoid, a biologically diverse plant-derived natural product, has been reported to show anti-staphylococcal activities. The objective of this study is to evaluate the interaction between three pentacyclic triterpenoid and standard antibiotics (methicillin and vancomycin) against reference strains of Staphylococcus aureus.
Methods and Results
The activity of the standard antibiotics and compounds on reference methicillin-sensitive and resistant strains of S. aureus were determined using the macrodilution broth method. The minimum inhibitory concentration (MIC) of the compounds was compared with that of the standard antibiotics. The interaction between any two antimicrobial agents was estimated by calculating the fractional inhibitory concentration (FIC index) of the combination. The various combinations of antibiotics and compounds reduced the MIC to a range of 0.05 to 50%.
Pentacyclic triterpenoids have shown anti-staphylococcal activities and although individually weaker than common antibiotics produced from bacteria and fungi, synergistically these compounds may use different mechanism of action or pathways to exert their antimicrobial effects, as implicated in the lowered MICs. Therefore, the use of current antibiotics could be maintained in their combination with plant-derived antibacterial agents as a therapeutic option in the treatment of S. aureus infections.
Sida urens L. (Malvaceae) is in flora of Asian medicinal herbs and used traditionally in West of Burkina Faso for the treatment of infectious diseases and particularly used against, dental caries bacteria, fever, pain and possesses analgesic properties. This study was conducted to reveal the antibacterial effect against dental caries bacteria on the one hand, and evaluate their analgesic capacity in experimental model with Swiss mice and on the other hand, with an aim to provide a scientific basis for the traditional use of this plant for the management of dental caries bacteria.
The antibacterial assays in this study were performed by using inhibition zone diameters, MIC (Minimum inhibitory concentration) and MBC (Minimal bactericidal concentration) methods. On the whole the dental caries bacteria (Gram-positive and Gram-negative bacterial strains) were used. Negative control was prepared using discs impregnated with 10% DMSO in water and commercially available Gentamicin from Alkom Laboratories LTD was used as positive reference standards for all bacterial strains. In acute toxicity test, mice received doses of extract (acetone/water extract) from Sida urens L. by intraperitoneal route and LD50 was determined in Swiss mice. As for analgesic effects, acetic acid writhing method was used in mice. The acetic acid-induced writhing method was used in mice with aim to study analgesic effects.
The results showed that the highest antibacterial activities were founded with the polyphenol-rich fractions against all bacterial strains compared to the standard antibiotic. About preliminary study in acute toxicity test, LD50 value obtained was more than 5000 mg/kg b.w. Polyphenol-rich fractions produced significant analgesic effects in acetic acid-induced writhing method and in a dose-dependent inhibition was observed.
These results validate the ethno-botanical use of Sida urens L. (Malvaceae) and demonstrate the potential of this herbaceous as a potential antibacterial agent of dental caries that could be effectively used for future health care purposes.
The therapeutic value of antibiotics depends on the susceptibility of the infecting microorganism and the pharmacological profile of the drugs. To assess the value of an antibiotic combination of polymyxin B and miconazole this study examined the in vitro synergistic potential of the two drugs on Gram-negative and Gram-positive bacteria and yeast. Antifungal and antibacterial activity was tested by minimum inhibitory concentration (MIC) of broth macrodilution and urea broth microdilution, by fluorescence microscopy and flow cytometry. Synergism was calculated using the fractional inhibitory concentration index (FICi). With Staphylococcus intermedius as target we found up to an eightfold reduction of the individual MICs when both drugs were combined. However, the FICi was 0.63 suggesting no real interaction between the two drugs. With Escherichia coli, Pseudomonas aeruginosa, and Malassezia pachydermatis as targets the antimicrobial drug combination reduced the MICs of polymyxin B and miconazole from fourfold to hundredfold resulting in FICi between 0.06 and 0.5 which defines a synergistic action. Thus, if polymyxin B and miconazole are combined their effect is greater than the sum of the effects observed with polymyxin B and miconazole independently, revealing bactericidal and fungicidal synergism. Our results indicate a strong therapeutic value for the combination of these antimicrobial agents against Gram-negative bacteria and yeast and a weaker value against Gram positive bacteria for clinical situations where these pathogens are involved.
Miconazole; Polymyxin; Antibiotic synergism; Otitis externa
Antibacterial activity of organic and aqueous extracts of Acacia aroma was evaluated against methicillin-resistant Staphylococcus aureus (MRSA), methicillin sensitive Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus epidermidis. Inhibition of bacterial growth was determined using agar diffusion and bioautographic methods. Among all assayed organic extracts only ethanolic and ethyl acetate extracts presented highest activities against all tested Staphylococcus strains with minimal inhibitory concentration (MIC) values ranging from 2.5 to 10 mg/ml and from 2.5 to 5 mg/ml respectively. The aqueous extracts show little antibacterial activity against Staphylococcus strains. The bioautography assay demonstrated well-defined growth inhibition zones against S. aureus in correspondence with flavonoids and saponins. A. aroma would be an interesting topic for further study and possibly for an alternative treatment for skin infections.
Acacia aroma; Antibacterial activity; Staphylococcus; Tusca
The treatment of Gram-negative infections is increasingly compromised by the spread of resistance. With few agents currently in development, clinicians are now considering the use of unorthodox combination therapies for multidrug-resistant strains. Here we assessed the in vitro activity of the novel lipoglycopeptide telavancin (TLV) when combined with colistin (COL) versus 13 Gram-negative type strains and 66 clinical isolates. Marked synergy was observed in either checkerboard (fractional inhibitory concentration index [FICI], <0.5; susceptibility breakpoint index [SBPI], >2) or time-kill assays (>2-log reduction in viable counts compared with starting inocula at 24 h) versus the majority of COL-susceptible enterobacteria, Stenotrophomonas maltophilia, and Acinetobacter baumannii isolates, but only limited effects were seen against Pseudomonas aeruginosa or strains with COL resistance. Using an Etest/agar dilution method, the activity of TLV was potentiated by relatively low concentrations of COL (0.25 to 0.75 μg/ml), reducing the MIC of TLV from >32 μg/ml to ≤1 μg/ml for 35% of the clinical isolates. This provides further evidence that glycopeptide-polymyxin combinations may be a useful therapeutic option in the treatment of Gram-negative infections.
The in vitro antibacterial effects of cefoxitin, a semisynthetic cephamycin, cefuroxime, a new cephalosporin antibiotic, and cephaloridine were compared. With gram-positive bacteria, marked differences were found only in the effects against Streptococcus faecalis, where cephaloridine and cefuroxime were superior to cefoxitin. With gram-negative aerobic bacteria, cefoxitin, which is known to be more resistant to beta-lactamases from gram-negative bacteria than any cephalosporin, was found to be more effective than cefuroxime and cephaloridine against ampicillin-resistant strains of Escherichia coli and indole-positive strains of Proteus. Haemophilus influenzae was found to be more susceptible to cefuroxime than to cefoxitin and cephaloridine. When ampicillin-resistant strains of H. influenzae were tested, markedly higher minimal inhibitory concentration values were obtained with cephaloridine in comparison to those obtained with ampicillin-susceptible strains. These increases in the minimal inhibitory concentration values were not observed with cefoxitin and cefuroxime, probably due to the resistance of these two compounds to beta-lactamases. Strains of Bacteroides fragilis were found to be much more susceptible to cefoxitin than to cefuroxime, which in turn was superior to cephaloridine. The results obtained indicate that cefoxitin and cefuroxime both are superior in their antibacterial spectra to the cephalosporins that are now in clinical use.
In vitro and in vivo antibacterial activities of cefmetazole alone and in combination with fosfomycin against methicillin- and cephem-resistant (MR) strains of Staphylococcus aureus were investigated, and the mechanism of synergistic effect between cefmetazole and fosfomycin was also studied. Cefmetazole inhibited the growth of 71 strains of MR S. aureus at concentrations ranging from 1.56 to 50 micrograms/ml; the antibacterial activity of cefmetazole against these strains was enhanced approximately 4 times with the addition of fosfomycin at a concentration of 1.56 micrograms/ml. The binding affinity of cefmetazole for the penicillin-binding protein 2' fraction specific for MR S. aureus was higher than that of methicillin, cloxacillin, cefazolin, and cefotaxime. A synergy experiment in vitro was performed by checkerboard titration with Mueller-Hinton agar plates containing various concentrations and ratios of cefmetazole and fosfomycin. The fractional inhibitory concentration index ranged from 0.09 to 0.75. Exposure of cefmetazole plus fosfomycin to exponentially growing cultures at a concentration at which both antibiotics had no bactericidal effect when given alone exerted bactericidal action. Combined administration of cefmetazole with fosfomycin at a ratio of 1:1 against systemic MR S. aureus infections with mice showed an excellent therapeutic efficacy as compared with administration of either antibiotic alone. Penicillin-binding protein 2', 2, and 4 fractions were scarcely detectable in MR S. aureus strains grown in the presence of fosfomycin at concentrations of 0.25 MIC and 0.5 MIC, respectively.
Strains of bacteria resistant to beta-lactam antibiotics have been increasing in number and are becoming troublesome in clinical medicine. The in vitro antibacterial activity of amoxicillin combined with clavulanic acid was determined on selected ampicillin-resistant clinical isolates. Synergistic effects were produced by amoxicillin with clavulanic acid against ampicillin-resistant strains of Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Proteus vulgaris, and Bacteroides fragilis. Inhibition of the beta-lactamases produced by the ampicillin-resistant strains was confirmed, especially against the penicillinases mediated by the R factor and the cephalosporinases produced by P.vulgaris and B. fragilis. The inhibitory effect of clavulanic acid against beta-lactamases was irreversible because of the high affinity of clavulanic acid to the enzymes.
Cefuroxime is a new broad-spectrum cephalosporin antibiotic with increased stability to β-lactamases. This stability, although no absolute in all cases, has the effect of widening the antibacterial spectrum of the compound so that many organisms resistant to the established cephalosporins are susceptible to cefuroxime. It is active against gram-positive organisms, including penicillinase-producing staphylococci, but it is less active against methicillin-resistant strains. In addition to its high activity against non-β-lactamase-producing gram-negative bacteria, cefuroxime effectively inhibits the growth of many β-lactamase-producing strains, including Enterobacter, Klebsiella, and indole-positive Proteus spp. It is highly active against Neisseria gonorrhoeae, Neisseria meningitidis, and also Haemophilus influenzae, including ampicillin-resistant strains. Cefuroxime is rapidly bactericidal and induces the formation and subsequent lysis of filamentous forms over a small concentration range.
Subminimal inhibitory concentrations of antibiotics have been shown to induce bacterial biofilm formation. Few studies have investigated antibiotic-induced biofilm formation in Staphylococcus aureus, an important human pathogen. Our goal was to measure S. aureus biofilm formation in the presence of low levels of β-lactam antibiotics. Fifteen phylogenetically diverse methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) strains were employed. Methicillin, ampicillin, amoxicillin, and cloxacillin were added to cultures at concentrations ranging from 0× to 1× MIC. Biofilm formation was measured in 96-well microtiter plates using a crystal violet binding assay. Autoaggregation was measured using a visual test tube settling assay. Extracellular DNA was quantitated using agarose gel electrophoresis. All four antibiotics induced biofilm formation in some strains. The amount of biofilm induction was as high as 10-fold and was inversely proportional to the amount of biofilm produced by the strain in the absence of antibiotics. MRSA strains of lineages USA300, USA400, and USA500 exhibited the highest levels of methicillin-induced biofilm induction. Biofilm formation induced by low-level methicillin was inhibited by DNase. Low-level methicillin also induced DNase-sensitive autoaggregation and extracellular DNA release. The biofilm induction phenotype was absent in a strain deficient in autolysin (atl). Our findings demonstrate that subminimal inhibitory concentrations of β-lactam antibiotics significantly induce autolysin-dependent extracellular DNA release and biofilm formation in some strains of S. aureus.
The widespread use of antibiotics as growth promoters in agriculture may expose bacteria to low levels of the drugs. The aim of this study was to investigate the effects of low levels of antibiotics on bacterial autoaggregation and biofilm formation, two processes that have been shown to foster genetic exchange and antibiotic resistance. We found that low levels of β-lactam antibiotics, a class commonly used in both clinical and agricultural settings, caused significant autoaggregation and biofilm formation by the important human pathogen Staphylococcus aureus. Both processes were dependent on cell lysis and release of DNA into the environment. The effect was most pronounced among multidrug-resistant strains known as methicillin-resistant S. aureus (MRSA). These results may shed light on the recalcitrance of some bacterial infections to antibiotic treatment in clinical settings and the evolution of antibiotic-resistant bacteria in agricultural settings.
The ethanolic extract from Rhodomyrtus tomentosa leaf exhibited good antibacterial activities against both methicillin-resistant Staphylococcus aureus (MRSA) and S. aureus ATCC 29213. Its minimal inhibitory concentration (MIC) values ranged from 31.25–62.5 µg/ml, and the minimal bactericidal concentration (MBC) was 250 µg/ml. Rhodomyrtone, an acylphloroglucinol derivative, was 62.5–125 times more potent at inhibiting the bacteria than the ethanolic extract, the MIC and MBC values were 0.5 µg/ml and 2 µg/ml, respectively. To provide insights into antibacterial mechanisms involved, the effects of rhodomyrtone on cellular protein expression of MRSA have been investigated using proteomic approaches. Proteome analyses revealed that rhodomyrtone at subinhibitory concentration (0.174 µg/ml) affected the expression of several major functional classes of whole cell proteins in MRSA. The identified proteins involve in cell wall biosynthesis and cell division, protein degradation, stress response and oxidative stress, cell surface antigen and virulence factor, and various metabolic pathways such as amino acid, carbohydrate, energy, lipid, and nucleotide metabolism. Transmission electron micrographs confirmed the effects of rhodomyrtone on morphological and ultrastructural alterations in the treated bacterial cells. Biological processes in cell wall biosynthesis and cell division were interrupted. Prominent changes including alterations in cell wall, abnormal septum formation, cellular disintegration, and cell lysis were observed. Unusual size and shape of staphylococcal cells were obviously noted in the treated MRSA. These pioneer findings on proteomic profiling and phenotypic features of rhodomyrtone-treated MRSA may resolve its antimicrobial mechanisms which could lead to the development of a new effective regimen for the treatment of MRSA infections.
2-(2′,4′-Dibromophenoxy)-4,6-dibromophenol isolated from the marine sponge Dysidea granulosa (Bergquist) collected off the coast of Lakshadweep islands, Indian Ocean, exhibited potent and broad spectrum in-vitro antibacterial activity, especially against methicillin resistant Staphylococcus aureus (MRSA), methicillin sensitive Staphylococcus aureus (MSSA), vancomycin resistant Enterococci (VRE), vancomycin sensitive Enterococci (VSE) and Bacillus spp. Minimal inhibitory concentration (MIC) was evaluated against 57 clinical and standard strains of Gram positive and Gram negative bacteria. The observed MIC range was 0.117–2.5 μg/mL against all the Gram positive bacteria and 0.5–2 μg/mL against Gram negative bacteria. The in-vitro antibacterial activity observed was better than that of the standard antibiotic linezolid, a marketed anti-MRSA drug. The results establish 2-(2′,4′-dibromophenoxy)-4,6-dibromophenol, as a potential lead molecule for anti-MRSA and anti-VRE drug development.
Dysidea granulosa; 2-(2′,4′-dibromophenoxy)-4,6-dibromophenol; antibacterial activity; methicillin resistant Staphylococcus aureus; vancomycin resistant enterococci
Ro 63-9141 is a new member of the pyrrolidinone-3-ylidenemethyl cephem series of cephalosporins. Its antibacterial spectrum was evaluated against significant gram-positive and gram-negative pathogens in comparison with those of reference drugs, including cefotaxime, cefepime, meropenem, and ciprofloxacin. Ro 63-9141 showed high antibacterial in vitro activity against gram-positive bacteria except ampicillin-resistant enterococci, particularly vancomycin-resistant strains of Enterococcus faecium. Its MIC at which 90% of the isolates tested were inhibited (MIC90) for methicillin-resistant Staphylococcus aureus (MRSA) was 4 μg/ml. Ro 63-9141 was bactericidal against MRSA. Development of resistance to the new compound in MRSA was not observed. Ro 63-9141 was more potent than cefotaxime against penicillin-resistant Streptococcus pneumoniae (MIC90 = 2 μg/ml). It was active against ceftazidime-susceptible strains of Pseudomonas aeruginosa and against Enterobacteriaceae except Proteus vulgaris and some isolates producing extended-spectrum β-lactamases. The basis for the antibacterial spectrum of Ro 63-9141 lies in its affinity to essential penicillin-binding proteins, including PBP 2′ of MRSA, and its stability towards β-lactamases. The in vivo findings were in accordance with the in vitro susceptibilities of the pathogens. These data suggest the potential utility of Ro 63-9141 for the therapy of infections caused by susceptible pathogens, including MRSA. Since insufficient solubility of Ro 63-9141 itself precludes parenteral administration in humans, a water-soluble prodrug, Ro 65-5788, is considered for development.
CP-45,899 is a new, semisynthetic beta-lactamase inhibitor. When tested alone, CP-45,899 displayed only weak antibacterial activity, with the notable exception of its potent action against penicillin-susceptible and -resistant Neisseria gonorrhoeae. A combination of 3.12 microgram of CP-45,899 per ml with 3.12 microgram of ampicillin per ml, tested in broth cultures, inhibited ca. 90% of resistant Staphylococcus and Haemophilus influenzae strains; similar data were obtained in a variety of media. The same combination of CP-45,899 with ampicillin or penicillin G inhibited 90% of Bacteroides fragilis as interpreted from agar dilution minimal inhibitory concentrations. Inhibitory concentrations of CP-45,899-ampicillin were bactericidal against H. influenzae strains and were as bactericidal as nafcillin or cephalothin against S. aureus. Ampicillin-resistant S. aureus, H. influenzae, and B. fragilis strains did not develop resistance to CP-45,899-ampicillin when transferred as many as six passages in the presence of a sublethal concentration of the combination.
The emergence of multidrug-resistant bacteria highlights the need for new antibacterial agents. Arminin 1a is a novel antimicrobial peptide discovered during investigations of the epithelial defense of the ancient metazoan Hydra. Following proteolytic processing, the 31-amino-acid-long positively charged C-terminal part of arminin 1a exhibits potent and broad-spectrum activity against bacteria, including multiresistant human pathogenic strains, such as methicillin-resistant Staphylococcus aureus (MRSA) strains (minimal bactericidal concentration, 0.4 μM to 0.8 μM). Ultrastructural observations indicate that bacteria are killed by disruption of the bacterial cell wall. Remarkably, the antibacterial activity of arminin 1a is not affected under the physiological salt conditions of human blood. In addition, arminin 1a is a selective antibacterial agent that does not affect human erythrocyte membranes. Arminin 1a shows no sequence homology to any known antimicrobial peptide. Because of its high level of activity against multiresistant bacterial strains pathogenic for humans, the peptide arminin 1a is a promising template for a new class of antibiotics. Our data suggest that ancient metazoan organisms such as Hydra hold promise for the detection of novel antimicrobial molecules and the treatment of infections caused by multiresistant bacteria.
The continuous escalation of resistant bacteria against a wide range of antibiotics necessitates discovering novel unconventional sources of antibiotics. B. oleracea L (red cabbage) is health-promoting food with proven anticancer and anti-inflammatory activities. However, it has not been researched adequately for its antimicrobial activity on potential resistant pathogens. The methanol crude extract of B. oleracea L. was investigated for a possible anti-microbial activity. The screening method was conducted using disc diffusion assay against 22 pathogenic bacteria and fungi. It was followed by evaluation of the minimum inhibitory concentration (MIC). Moreover, the antibacterial and the antifungal activities were confirmed using the minimum bactericidal concentration (MBC) and the minimum fungicidal concentration (MFC), respectively. Remarkable, antibacterial activity was evident particularly against highly infectious microorganisms such as Methicillin-resistant Staphylococcus aureus, Escherichia coli O157:H7, Pseudomonas aeruginosa, Klebsiella pneumoniae, Staphylococcus aureus, and Salmonella enterica serovar Typhimurium as well as against human fungal pathogens, Trichophyton rubrum and Aspergillus terreus. Red cabbage is a rich source of phenolic compounds, anthocyanins being the most abundant class, which might explain its potent antimicrobial action. This extract is potentially novel for future antimicrobials, inexpensive, and readily available at a large scale for pharmaceutical companies for further investigation and processing.
Antibacterial; antifungal; red cabbage; anthocyanins.
With polidocanol, it was possible to reduce the MIC as well as the MBC of methicillin, oxacillin, penicillin G, and ampicillin against resistant staphylococci. The strongest effects were obtained with methicillin and oxacillin. All strains tested could be resensitized to these penicillins independent of the original resistance levels. Polidocanol was not inhibitory by itself for Staphylococcus aureus. Furthermore, it did not inhibit the activity of staphylococcal beta-lactamase. This permits the conclusion that an intrinsic resistance mechanism is affected by this substance. Its action cannot be simply explained by an improved accessibility of the penicillin targets as uptake, and binding of methicillin and penicillin G in resistant cells was not changed by polidocanol. On the other hand, the lysis induced by combinations of this substance with small amounts of a penicillin was antagonized by chloramphenicol. This suggests that autolytic enzymes are involved in the polidocanol effect and possibly in the intrinsic resistance mechanism itself. Before polidocanol can trigger lysis, the penicillin must act first in some way. As could be seen with a susceptible strain, the resulting lysis did not exceed that obtained with penicillins alone. Thus, polidocanol does not exhibit an independent lytic mechanism but obviously is able to substitute penicillins in their lytic action.
Compared to MICs (more than 800 μg/ml) of (−)-epigallocatechin gallate (EGCg) against Escherchia coli, MICs of EGCg against methicillin-susceptible and methicillin-resistant Staphylococcus aureus (MSSA and MRSA) were 100 μg/ml or less. Furthermore, less than 25 μg EGCg per ml obviously reversed the high level resistance of MRSA to all types of tested β-lactams, including benzylpenicillin, oxacillin, methicillin, ampicillin, and cephalexin. EGCg also induced a supersusceptibility to β-lactams in MSSA which does not express mecA, encoding penicillin-binding protein 2′ (PBP2′). The fractional inhibitory concentration (FIC) indices of the tested β-lactams against 25 isolates of MRSA were from 0.126 to 0.625 in combination with 6.25, 12.5 or 25 μg of EGCg per ml. However, no synergism was observed between EGCg and ampicillin against E. coli. EGCg largely reduced the tolerance of MRSA and MSSA to high ionic strength and low osmotic pressure in their external atmosphere, indicating damage of the cell wall. Unlike dextran and lipopolysaccharide, peptidoglycan from S. aureus blocked both the antibacterial activity of EGCg and the synergism between EGCg and oxacillin, suggesting a direct binding of EGCg with peptidoglycan on the cell wall. EGCg showed a synergistic effect with dl-cycloserine (an inhibitor of cell wall synthesis unrelated to PBP2′) but additive or indifferent effect with inhibitors of protein and nuclear acid synthesis. EGCg did not suppress either PBP2′ mRNA expression or PBP2′ production, as confirmed by reverse transcription-PCR and a semiquantitative PBP2′ latex agglutination assay, indicating an irrelevance between the synergy and PBP2′ production. In summary, both EGCg and β-lactams directly or indirectly attack the same site, peptidoglycan on the cell wall. EGCg synergizes the activity of β-lactams against MRSA owing to interference with the integrity of the cell wall through direct binding to peptidoglycan.
Ceragenin CSA-13 is a synthetic mimic of cationic antibacterial peptides, with facial amphiphilic morphology reproduced using a cholic acid scaffold. Previous data have shown that this molecule displays broad-spectrum antibacterial activity, which decreases in the presence of blood plasma. However, at higher concentrations, CSA-13 can cause lysis of erythrocytes. This study was designed to assess in vitro antibacterial and haemolytic activity of CSA-13 in the presence of pluronic F-127.
Methods and Results
CSA-13 bactericidal activity against clinical strains of bacteria associated with topical infections and in an experimental setting relevant to their pathophysiological environment, such as various epithelial tissue fluids and the airway sputum of patients suffering from cystic fibrosis (CF), was evaluated using minimum inhibitory and minimum bactericidal concentration (MIC /MBC) measurements and bacterial killing assays. We found that in the presence of pluronic F-127, CSA-13 antibacterial activity was only slightly decreased, but CSA-13 haemolytic activity was significantly inhibited. CSA-13 exhibits bacterial killing activity against clinical isolates of Staphylococcus aureus, including methicillin-resistant strains, Pseudomonas aeruginosa present in CF sputa, and biofilms formed by different Gram (+) and Gram (−) bacteria. CSA-13 bactericidal action is partially compromised in the presence of plasma, but is maintained in ascites, cerebrospinal fluid, saliva, and bronchoalveolar lavage fluid. The synergistic action of CSA-13, determined by the use of a standard checkerboard assay, reveals an increase in CSA-13 antibacterial activity in the presence of host defence molecules such as the cathelicidin LL-37 peptide, lysozyme, lactoferrin and secretory phospholipase A (sPLA).
These results suggest that CSA-13 may be useful to prevent and treat topical infection.
Significance and Impact of the Study
Combined application of CSA-13 with pluronic F-127 may be beneficial by reducing CSA-13 toxicity.
antibacterial agents; microbiological assay; pluronic F-127
RWJ-54428 (MC-02,479) is a new cephalosporin active against gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). The potency of this new cephalosporin against MRSA is related to a high affinity for penicillin-binding protein 2a (PBP 2a), as assessed in a competition assay using biotinylated ampicillin as the reporter molecule. RWJ-54428 had high activity against MRSA strains COL and 67-0 (MIC of 1 μg/ml) and also showed affinity for PBP 2a, with a 50% inhibitory concentration (IC50) of 0.7 μg/ml. RWJ-54428 also displayed excellent affinity for PBP 5 from Enterococcus hirae R40, with an IC50 of 0.8 μg/ml and a MIC of 0.5 μg/ml. The affinity of RWJ-54428 for PBPs of β-lactam-susceptible S. aureus (MSSA), enterococci (E. hirae), and Streptococcus pneumoniae showed that the good affinity of RWJ-54428 for MRSA PBP 2a and E. hirae PBP 5 does not compromise its binding to susceptible PBPs. RWJ-54428 showed stability to hydrolysis by purified type A β-lactamase isolated from S. aureus PC1. In addition, RWJ-54428 displayed low MICs against strains of S. aureus bearing the four classes of staphylococcal β-lactamases, including β-lactamase hyperproducers. The frequency of isolation of resistant mutants to RWJ-54428 from MRSA strains was very low. In summary, RWJ-54428 has high affinity to multiple PBPs and is stable to β-lactamase, properties that may explain our inability to find resistance by standard methods. These data are consistent with its excellent activity against β-lactam-resistant gram-positive bacteria.
Honey has previously been shown to have wound healing and antimicrobial properties, but this is dependent on the type of honey, geographical location and flower from which the final product is derived. We tested the antimicrobial activity of a Chilean honey made by Apis mellifera (honeybee) originating from the Ulmo tree (Eucryphia cordifolia), against selected strains of bacteria.
Ulmo 90 honey was compared with manuka UMF® 25+ (Comvita®) honey and a laboratory synthesised (artificial) honey. An agar well diffusion assay and a 96 well minimum inhibitory concentration (MIC) spectrophotometric-based assay were used to assess antimicrobial activity against five strains of methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli and Pseudomonas aeruginosa.
Initial screening with the agar diffusion assay demonstrated that Ulmo 90 honey had greater antibacterial activity against all MRSA isolates tested than manuka honey and similar activity against E. coli and P. aeruginosa. The MIC assay, showed that a lower MIC was observed with Ulmo 90 honey (3.1% - 6.3% v/v) than with manuka honey (12.5% v/v) for all five MRSA isolates. For the E. coli and Pseudomonas strains equivalent MICs were observed (12.5% v/v). The MIC for artificial honey was 50% v/v. The minimum bactericidal concentration for all isolates tested for Ulmo 90 honey was identical to the MIC. Unlike manuka honey, Ulmo 90 honey activity is largely due to hydrogen peroxide production.
Due to its high antimicrobial activity, Ulmo 90 may warrant further investigation as a possible alternative therapy for wound healing.