Postantibiotic Effect Research Articles

The anti-Staphylococcus aureus activity of the phenanthrene fraction from fibrous roots of Bletilla striata.

BackgroundBletillae Rhizoma, the tuber of Bletilla striata, has been used in Chinese traditional medicine to treat infectious diseases. Chemical studies indicated that phenanthrene was one of the most important components of the herb, with a broad spectrum of antibiotic activity against Gram-positive bacteria. The objective of this study was to further characterize the antibacterial activity of the phenanthrene fraction from the fibrous root of the pseudobulb of B. striata.MethodsThe phenanthrene fraction (EF60) from the ethanol extract of fibrous roots of Bletilla striata pseudobulbs was isolated using polyamide column chromatography. The antibacterial activity of the fraction was evaluated in vitro using a 96-well microtiter plate and microbroth dilution method. The cytotoxicity of EF60 against mammalian cells was tested by hemolysis and MTT assays.ResultsEF60 was obtained using alcohol extraction and polyamide column chromatography, with a yield of 14.9 g per 1 kg of the fibrous roots of B. striata. In vitro tests indicated that EF60 was active against all tested strains of Staphylococcus aureus, including clinical isolates and methicillin-resistant S. aureus (MRSA). The minimum inhibitory concentration (MIC) values of EF60 against these pathogens ranged from 8 to 64 μg/mL. Minimum bactericidal concentration tests demonstrated that EF60 was bactericidal against S. aureus 3304 and ATCC 29213 and was bacteriostatic against S. aureus 3211, ATCC 25923, and ATCC 43300. Consistently, the time-kill assay indicated that EF60 could completely kill S. aureus ATCC 29213 at 2× the MIC within 3 h but could kill less than two logarithmic units of ATCC 43300, even at 4× the MIC within 24 h. The postantibiotic effects (PAE) of EF60 (4× MIC) against strains 29213 and 43300 were 2.0 and 0.38 h, respectively. Further studies indicated that EF60 (160 μg/mL) showed no cytotoxicity against human erythrocytes, and was minimally toxic to Human Umbilical Vein Endothelial Cells with an IC50 of 75 μg/mL.ConclusionsOur studies indicated that EF60 is worthy of further investigation as a potential phytotherapeutic agent for treating infections caused by S. aureus and MRSA.Electronic supplementary materialThe online version of this article (doi:10.1186/s12906-016-1488-z) contains supplementary material, which is available to authorized users.

Structure-Activity Relationships of Spectinamide Antituberculosis Agents: A Dissection of Ribosomal Inhibition and Native Efflux Avoidance Contributions.

Spectinamides are a novel class of antitubercular agents with the potential to treat drug-resistant tuberculosis infections. Their antitubercular activity is derived from both ribosomal affinity and their ability to overcome intrinsic efflux mediated by the Mycobacterium tuberculosis Rv1258c efflux pump. This study explores the structure-activity relationships through analysis of 50 targeted spectinamides. Compounds are evaluated for ribosomal translational inhibition, MIC activity in Rv1258c efflux pump deficient and wild type tuberculosis strains, and efficacy in an acute model of tuberculosis infection. The results of this study show a narrow structure-activity relationship, consistent with a tight ribosome-binding pocket and strict structural requirements to overcome native efflux. Rationalization of ribosomal inhibition data using molecular dynamics simulations showed stable complex formation for halogenated spectinamides consistent with the long post antibiotic effects observed. The lead spectinamides identified in this study demonstrated potent MIC activity against MDR and XDR tuberculosis and had desirable antitubercular class specific features including low protein binding, low microsomal metabolism, no cytotoxicity, and significant reductions in bacterial burdens in the lungs of mice infected with M.tuberculosis. The structure-activity relationships detailed here emphasize the need to examine efflux-mediated resistance in the design of antituberculosis drugs and demonstrate that it is possible to overcome intrinsic efflux with synthetic modification. The ability to understand the structure requirements for this class has produced a variety of new substituted spectinamides, which may provide useful alternative candidates and promote the further development of this class.

In Vitro and In Vivo Activities of a Bi-Aryl Oxazolidinone, RBx 11760, against Gram-Positive Bacteria.

RBx 11760, a bi-aryl oxazolidinone, was investigated for antibacterial activity against Gram-positive bacteria. The MIC90s of RBx 11760 and linezolid against Staphylococcus aureus were 2 and 4 mg/liter, against Staphylococcus epidermidis were 0.5 and 2 mg/liter, and against Enterococcus were 1 and 4 mg/liter, respectively. Similarly, against Streptococcus pneumoniae the MIC90s of RBx 11760 and linezolid were 0.5 and 2 mg/liter, respectively. In time-kill studies, RBx 11760, tedizolid, and linezolid exhibited bacteriostatic effect against all tested strains except S. pneumoniae RBx 11760 showed 2-log10 kill at 4× MIC while tedizolid and linezolid showed 2-log10 and 1.4-log10 kill at 16× MIC, respectively, against methicillin-resistant S. aureus (MRSA) H-29. Against S. pneumoniae 5051, RBx 11760 showed bactericidal activity, with 4.6-log10 kill at 4× MIC compared to 2.42-log10 and 1.95-log10 kill for tedizolid and linezolid, respectively, at 16× MIC. RBx 11760 showed postantibiotic effects (PAE) at 3 h at 4 mg/liter against MRSA H-29, and linezolid showed the same effect at 16 mg/liter. RBx 11760 inhibited biofilm production against methicillin-resistant S. epidermidis (MRSE) ATCC 35984 in a concentration-dependent manner. In a foreign-body model, linezolid and rifampin resulted in no advantage over stasis, while the same dose of RBx 11760 demonstrated a significant killing compared to the initial control against S. aureus (P < 0.05) and MRSE (P < 0.01). The difference in killing was statistically significant for the lower dose of RBx 11760 (P < 0.05) versus the higher dose of linezolid (P > 0.05 [not significant]) in a groin abscess model. In neutropenic mouse thigh infection, RBx 11760 showed stasis at 20 mg/kg of body weight, whereas tedizolid showed the same effect at 40 mg/kg. These data support RBx 11760 as a promising investigational candidate.

Postantibiotic effect of colistin alone and combined with vancomycin or meropenem against Acinetobacter spp. with well defined resistance mechanisms

Previous studies found short postantibiotic effect of colistin on Acinetobacter baumannii. Many studies have evaluated the potential for synergy between colistin and other antibiotics against A. baumannii. The aim of this study was to determine in vitro synergy and postantibiotic effect (PAE) of colistin alone and combined with other antibiotics (vancomycin or meropenem) against eight carbapenem-non-susceptible Acinetobacter spp. strains with defined resistance mechanisms. It was hypothesised that vancomycin or meropenem would prologue the PAE of colistin since it was previously found that they exert synergism with colistin in time-kill kinetics and chequerboard analysis. After exposure of 1 hour colistin alone exhibited the negative ( − 0.07 hour) (OXA-143), short (0.2–1.82 hours) (OXA-24, OXA-58, OXA-72, VIM-1+OXA-23, OXA-58+NDM-1, ISAba1/OXA-69) or moderate PAE (3.2 hours) for OXA-23 positive strain. When combined with vancomycin, the PAE was moderate (1.7–4 hours) with OXA-23, OXA-23+VIM-1, OXA-72 and OXA-24 positive strains while with OXA-58, OXA-143, OXA-58/NDM-1 and ISAba1/OXA-69 positive strains, it was not possible to calculate mean duration of PAE because there was no regrowth after exposure to antibiotics or it was longer than 5 hours. The combination with meropenem resulted in short (0.2 hours) (OXA-143), moderate (2.4–3.73 hours) (OXA-24, OXA-58, OXA-23, OXA-23+VIM-1), long PAE of 5 hours (OXA-23) or longer than 5 hours (OXA-58+VIM-1, ISAba1/OXA-69). From the clinical point of view, the prolongation of colistin PAE when combined with other antibiotics could provide a rationale for the modification of the dosing interval and could be important for the optimization of the treatment regimen and the minimization of drug-induced side effects.

The postantibiotic effect and post-β-lactamase-inhibitor effect of ceftazidime, ceftaroline and aztreonam in combination with avibactam against target Gram-negative bacteria.

The magnitudes of the postantibiotic effect (PAE) and post-β-lactamase-inhibitory effect (PLIE) of ceftazidime-avibactam, ceftaroline-avibactam, and aztreonam-avibactam were determined against isolates of Enterobacteriaceae and Pseudomonas aeruginosa that either harboured genes encoding serine and/or metallo-β-lactamases, or did not harbour bla genes. The bla genes includedones that encoded extended spectrum β-lactamases, AmpC and KPC β-lactamases, and one metallo-β-lactamase, NDM-1. No substantial PAE was observed for any combination against any isolate. One substantial PLIE was found: a value of 1·9h for ceftazidime-avibactam against Klebsiella pneumoniae (blaKPC-2 ). From comparison with results in the literature, we propose that the existence of a substantial PLIE depends on the bacterial isolate and on the specific β-lactamase inhibitor and β-lactam combination. A wave of new β-lactamase inhibitors is entering either therapeutic use or clinical trials. The present work characterizes the postantibiotic effect (PAE) and post-β-lactamase-inhibitory effect (PLIE) of the clinically most advanced of these compounds, avibactam. We show that the existence of a measurable PLIE is strain- (and possibly compound-) dependent, and cannot be relied upon as a standard component of the primary pharmacology of a new β-lactamase inhibitor. This variability was not reported in earlier studies of clavulanic acid or sulbactam.

In Vitro and In Vivo Synergy of the Oxadiazole Class of Antibacterials with β-Lactams.

The oxadiazole antibacterials target the bacterial cell wall and are bactericidal. We investigated the synergism of ND-421 with the commonly used β-lactams and non-β-lactam antibiotics by the checkerboard method and by time-kill assays. ND-421 synergizes well with β-lactam antibiotics, and it also exhibits a long postantibiotic effect (4.7 h). We also evaluated the in vivo efficacy of ND-421 in a murine neutropenic thigh infection model alone and in combination with oxacillin. ND-421 has in vivo efficacy by itself in a clinically relevant infection model (1.49 log10 bacterial reduction for ND-321 versus 0.36 log10 for linezolid with NRS119) and acts synergistically with β-lactam antibiotics in vitro and in vivo, and the combination of ND-421 with oxacillin is efficacious in a mouse neutropenic thigh methicillin-resistant Staphylococcus aureus (MRSA) infection model (1.60 log10 bacterial reduction). The activity of oxacillin was potentiated in the presence of ND-421, as the strain would have been resistant to oxacillin otherwise.

Antimicrobial susceptibility and the in vitro postantibiotic effects of vancomycin and ciprofloxacin against Bacillus cereus isolates

Background: Vancomycin and ciprofloxacin were often used in the therapy of infections associated with Bacillus cereus.Methods: Four B. cereus food and clinical isolates were chosen for determination of time–kill curves and postantibiotic effects (PAE) of ciprofloxacin and vancomycin.Results: According to the minimum inhibition concentration (MIC), breakpoints defined by CLSI for Staphylococcus spp. were all four strains intermediate for vancomycin (MIC = 4 μg/ml) and sensitive to ciprofloxacin (MIC = 0.2 μg/ml) except the strain Bc63 resistant to the last antimicrobial (MIC = 1.6 μg/ml). The lowest CFU values of tested strains were reached after 3–5 hours of exposure to 4 × MIC of vancomycin, and after 6–7 hours exposure to 10 × MIC of ciprofloxacin. The maximum reduction of the CFU in the presence of vancomycin and ciprofloxacin was about 2.46 log10 and 2.48 log10, respectively. The average duration of the PAE of vancomycin and ciprofloxacin was 0.94 and 1.60 hours, respectively. The statistically significant differences between PAEs induced with 3 × MIC, 4 × MIC and 8 × MIC of vancomycin were observed (P < 0.05). Both antibiotics did not affect the sporulation of tested bacterial strains.Conclusions: The differences in PAE duration were strain and antimicrobial dependent.

Physiological Activities of Abscisic Acid Isolated from Honey of Black Locust (Robinia pseudoacacia) in Korea

Pathogenic effects associated with Helicobacter pylori infection include peptic ulcer. Eradication of H. pylori by triple therapy often results in emerging resistance of H. pylori. Thus there is a need to seek alternative treatments. The aim of this study was to estimate abscisic acid (ABA) isolated from honey of Black Locust (Robinia pseudoacacia) in Korea. The anti-H. pylori activity of ABA was the minimun inhibitory concentrations (MIC), minimum bactericidal concentration (MBC), and postantibiotic effect (PAE). The MIC and MBC of ABA were 2.7±1.3μg/ml and 6.9±1.3μg/ml, respectively. The PAE of ABA was highest at 32×MIC concentrations for 8.5 hr. We determined that ABA may be the potential lead phytochemical constituents with anti-H. pylori activity. The acacia honey in Korea could be useful chemopreventive agents for peptic ulcer in H. pylori-infected individuals

Ex vivo pharmacokinetic/pharmacodynamic relationship of valnemulin against Clostridium perfringens in plasma, the small intestinal and caecal contents of rabbits

The pharmacokinetic (PK) and ex vivo pharmacodynamic (PD) of valnemulin against Clostridium perfringens were investigated in plasma, the small intestinal and caecal contents of rabbits following intravenous (IV) or oral administration at 3 mg/kg bodyweight (BW). The postantibiotic effect (PAE) and postantibiotic sub-MIC effect (PA-SME) of valnemulin against C. perfringens ATCC13124 were also determined. The time-kill curves were established in vitro and ex vivo to evaluate the antibacterial activity of valnemulin against C. perfringens.The elimination half-lives (T1/2λz) of valnemulin in the jejunal fluids (7.82 h) or caecal contents (14.8 h) of rabbits was significantly longer than that in plasma (2.94 h). The MIC values of valnemulin against C. perfringens ATCC13124 were both 0.063 μg/mL in the artificial medium and jejunal fluids. The PAEs of valnemulin against C. perfringens were 2.9 h (1 × MIC) and 5.03 h (4 × MIC), and the PA-SMEs ranged from 7.9 h to 11.1 h. Valnemulin exhibited rapid, time-dependent killing feature, and the ex vivo dose-response profile was closely fitted to sigmoid Emax model (r2 = 0.9985). The surrogate index of AUC24 h/MIC ratios required to achieve the bactericidal and virtual bacterial elimination effects were 57.5 and 90.1 h, respectively. Accordingly, the calculated daily dosage regimens of valnemulin for the bactericidal activity (1.96 mg/kg) and bacterial elimination (3.08 mg/kg) would be therapeutically effective in rabbits against C. perfringens with MIC ≤0.5 μg/mL.

A clerodane diterpene from Polyalthia longifolia as a modifying agent of the resistance of methicillin resistant Staphylococcus aureus

BackgroundStaphylococcus aureus infections are raising serious concern across the world. The effectiveness of conventional drugs is continuously decreasing due to global emergence of multidrug resistance (MDR) and therefore, new resistance-modifying agents (RMAs) are highly needed. HypothesisClerodane diterpene 16α-hydroxycleroda-3,13(14)-Z-dien-15,16-olide (CD) from leaves of Polyalthia longifolia (Sonn.) Thwaites (Annonaceae) as RAM will be useful in improving the current treatment strategies for staphylococcal infections. Study designIn the present study, we determine the resistance-modifying activity of CD using clinical isolates of MRSA. Further, the influence of CD on innate immune response was also evaluated in vitro and in vivo. The nature of potential interactions was determined by fractional inhibitory concentration indices (FICIs) calculated from microdilution assays and time–kill curves. ResultsThe result of in vitro combination study showed that CD significantly reduced MIC of fluoroquinolones up to 16-folds (FICI 0.315-0.500), while in S. aureus infected Swiss albino mice model, combination of CD with norfloxacin, significantly (p<0.01, p<0.001) lowered the systemic microbial burden in blood, liver, kidney, lung and spleen tissues in comparison to CD, norfloxacin alone as well as untreated control. Flow cytometry analysis clearly showed that CD significantly inhibited EtBr efflux and extended post-antibiotic effect. In qRT-PCR analysis, CD alone as well as in combination, significantly modulated the expression of various efflux pump genes including norA up to 2-fold in clinical isolate MRSA-ST2071. Further, the in vitro combination study of the CD (10, 5, 2.5µg/ml) along with the norfloxacin (10µg/ml) depicted a significant decline in the pro-inflammatory cytokines, IL6 and TNF-α. In septic shock mice model, CD did not exhibit any significant changes in the level of pro-inflammatory cytokines. ConclusionThis is the first report on drug resistance-modifying potential of CD through inhibition of MDR efflux pump.

In vitro profiling of antimethicillin-resistant Staphylococcus aureus activity of thymoquinone against selected type and clinical strains

This study explores antimethicillin-resistant Staphylococcus aureus (MRSA) activity of a bioactive phytochemical constituent, thymoquinone obtained from the medicinal herb, Nigella sativa Linn. Based on initial assessment on crude extract of seeds of Nigella sativa Linn, the pure active constituent was employed in the study. A total of 99 MRSA strains which comprised of 40 types and 59 clinical strains were selected for the study. Minimum inhibitory concentration (MIC), bactericidal activity, postantibiotic effect (PAE) and propensity to select resistant mutants were determined using standard protocols. Results revealed that thymoquinone exhibited MIC in the range of 8-16μgml(-1) and MIC90 of 16μgml(-1) against MRSA strains. It was bactericidal to MRSA by demonstrating >3log kill. It showed a longer PAE of 3·2±0·2h. Upon exposure to high-density inoculum of MRSA, it did not select resistant mutants. Transmission electron microscopy of thymoquinone-treated MRSA showed no lysis but damage to cell wall and cell membrane which corroborated well with the salt tolerance and bacteriolysis assays. In conclusion, MIC90 , bactericidal property, longer PAE, absence of resistant mutant selection and damages in cell membrane and cell wall imply a promising anti-MRSA activity of thymoquinone. This is the first detailed report on anti-MRSA activity of thymoquinone. The assessment was made with both type and clinical strains. Thymoquinone may be a potential lead compound which can be further optimized to discover novel anti-MRSA agents.

Electron microscopy study of antibacterial effect of selimakcid against salmonella and escherichia

Aim. To assess Selimakcid effect on the submicroscopic organization of Salmonella and enteropathogenic Escherichia. Methods. Salmonella enteritidis and enteropathogenic Escherichia coli isolates were used in a study. Their morphological and functional characteristics after Selimakcid exposure were studied using methods of negative staining and ultrathin sections. Selimakcid was taken at 10, 15 and 25 mg/ml concentration in a physiological isotonic sodium chloride solution. Results. Incubation of Salmonella and Escherichia cultures with Selimakcid has no effect on the cells size compared to the control. Ultrastructural picture of Selimakcid post antibiotic effect on the Salmonella enteritidis cells demonstrated the outer membrane vesicles increase and cell wall changes, which can be attributed to the adaptation. In the Escherichia coli culture after incubation in medium containing Selimakcid at 25 mg/ml concentration, the presence of both damaged (with flake-like cytoplasm and plasma membrane ruptures) and lysed (release their content into the environment) cells was observed. Conclusion. The effect of Selimakcid on Salmonella enteritidis cells is characterized by the outer membrane vesicles increase and cell wall changes; in the Escherichia coli culture after Selimakcid exposure the presence of damaged and lysed cells was observed.

Do We Bury Antibacterials When Launching? Cefaclor Example

This study aimed to compare existing dosing regimens of cefaclor with recommended pharmacokinetic/pharmacodynamic (PK/PD) parameters and to see if the proposed dosing regimen could have been the reason for development of bacterial resistance. PKs of cefaclor were determined after administrating the highest therapeutic dose of 750 mg in standard release (SF) and modified release form (MRF) in 12 volunteers. The study was performed on clinical isolates of the most frequent causative agents in urinary and respiratory infections. Minimum inhibitory concentration (MIC), postantibiotic effect, and PK/PD efficacy indices were determined. Peak plasma concentrations of 23.142 ± 5.67 (SF) and 8.7 ± 2.09 μg/mL (MRF) were observed after 40-60 min and 3.04 ± 0.75 h, respectively. MIC for investigated bacterial strains ranged from 1 to 4 mg/L. Postantibiotic effect lasted from 2.10-2.18 ± 0.2 h for Gram-positive to 0.58-0.90 ± 0.05 h for Gram-negative bacteria. PK/PD indices (t > MIC) ranged from 27.08 ± 5.93% to 43.23 ± 6.54% of 8-h dosing interval (SF) and 22.57 ± 8.93% to 49.65 ± 1.95% of 12-h dosing interval (MRF). Plasma levels were below MIC for more than 50% of the dosing interval even for the most sensitive pathogens (MIC = 1 mg/L). During both dosing intervals the total “antibacterial activity” was not longer than 6 h for Gram-positive and 5 h for Gram-negative bacteria for SF and 9 h for Gram-positive and 5 h for Gram-negative bacteria for MRF.

Pharmacokinetic/Pharmacodynamic Correlation of Cefquinome Against Experimental Catheter-Associated Biofilm Infection Due to Staphylococcus aureus.

Biofilm formations play an important role in Staphylococcus aureus pathogenesis and contribute to antibiotic treatment failures in biofilm-associated infections. The aim of this study was to evaluate the pharmacokinetic/pharmacodynamic (PK/PD) profiles of cefquinome against an experimental catheter-related biofilm model due to S. aureus, including three clinical isolates and one non-clinical isolate. The minimal inhibitory concentration (MIC), minimal biofilm inhibitory concentration (MBIC), biofilm bactericidal concentration (BBC), minimal biofilm eradication concentration (MBEC) and biofilm prevention concentration (BPC) and in vitro time-kill curves of cefquinome were studied in both planktonic and biofilm cells of study S. aureus strains. The in vivo post-antibiotic effects (PAEs), PK profiles and efficacy of cefquinome were performed in the catheter-related biofilm infection model in murine. A sigmoid Emax model was utilized to determine the PK/PD index that best described the dose-response profiles in the model. The MICs and MBICs of cefquinome for the four S. aureus strains were 0.5 and 16 μg/mL, respectively. The BBCs (32–64 μg/mL) and MBECs (64–256 μg/mL) of these study strains were much higher than their corresponding BPC values (1–2 μg/mL). Cefquinome showed time-dependent killing both on planktonic and biofilm cells, but produced much shorter PAEs in biofilm infections. The best-correlated PK/PD parameters of cefquinome for planktonic and biofilm cells were the duration of time that the free drug level exceeded the MIC (fT > MIC, R2 = 96.2%) and the MBIC (fT > MBIC, R2 = 94.7%), respectively. In addition, the AUC24h/MBIC of cefquinome also significantly correlated with the anti-biofilm outcome in this model (R2 = 93.1%). The values of AUC24h/MBIC for biofilm-static and 1-log10-unit biofilm-cidal activity were 22.8 and 35.6 h; respectively. These results indicate that the PK/PD profiles of cefquinome could be used as valuable guidance for effective dosing regimens treating S. aureus biofilm-related infections.

Pterostilbene Reduced Post-Antibiotic Effect Time of Linezolid against Methicillin-Resistant Staphylococcus aureus

Pterostilbene is biologically classified as a phytoalexin, which is part of the plant's defense system in response to pathogen infection. The present study is to identify the type of interaction and post-antibiotic effect time of pterostilbene in combination with linezolid against methicillin-resistant Staphylococcus aureus American type culture collection 43300 and methicillin-resistant S. aureus American type culture collection 33591. The minimum inhibitory concentration values of individual antimicrobial agents were determined using microbroth dilution technique whereas the microdilution checker board assay was employed to verify the type of interaction of the combined agents from the fractional inhibitory concentration index values. The post-antibiotic effect time of pterostilbene and linezolid and in combination treatment was evaluated using viable plate count method. The minimum inhibitory concentration value of pterostilbene against both strains were the same (31.25 μg/ml) compared to linezolid at 0.78 μg/ml and 1.56 μg/ml, against 43300 and 33591 strain, respectively. microdilution checker analysis of pterostilbene in combination with linezolid against both methicillin-resistant S. aureus strains displayed fractional inhibitory concentration value of 1.25. Despite the indifference interaction between pterostilbene and linezolid as shown by microdilution checker study, post-antibiotic effect analysis demonstrated antagonism as depicted by a decrease of post-antibiotic effect time of linezolid by pterostilbene against both methicillin-resistant S. aureus strains. The duration of post-antibiotic effect time obtained for pterostilbene were twice (3.6±0.15 h) that of linezolid (1.8±0.31 h) against methicillin-resistant S. aureus American type culture collection 43300. However, pterostilbene exhibited shorter post-antibiotic effect time of 0.3±0.10 h compared to linezolid (0.9±0.06 h) against 33591 strain. In conclusion, pterostilbene was not able to prolong the post-antibiotic effect duration of linezolid in both strains and each of the antimicrobials demonstrated a more favorable timing of doses when these agents were used singly.

Short-Term Pretreatment of Sub-Inhibitory Concentrations of Gentamycin Inhibits the Swarming Motility of Escherichia Coli by Down-Regulating the Succinate Dehydrogenase Gene

Background/Aims: Motility is a feature of many pathogens that contributes to the migration and dispersion of the infectious agent. Whether gentamycin has a post-antibiotic effect (PAE) on the swarming and swimming motility of Escherichia coli (E. coli) remains unknown. In this study, we aimed to examine whether short-term pretreatment of sub-inhibitory concentrations of gentamycin alter motility of E. coli and the mechanisms involved therein. Methods: After exposure to sub-inhibitory concentrations (0.8 μg/ml) of gentamicin, the swarming and swimming motility of E. coli was tested in semi-solid media. Real-time PCR was used to detect the gene expression of succinate dehydrogenase (SDH). The production of SDH and fumarate by E. coli pretreated with or without gentamycin was measured. Fumarate was added to swarming agar to determine whether fumarate could restore the swarming motility of E. coli. Results: After pretreatment of E. coli with sub-inhibitory concentrations of gentamycin, swarming motility was repressed in the absence of growth inhibition. The expression of all four subunits of SDH was down-regulated, and the intracellular concentration of SDH and fumarate, produced by E. coli, were both decreased. Supplementary fumarate could restore the swarming motility inhibited by gentamycin. A selective inhibitor of SDH (propanedioic acid) could strongly repress the swarming motility. Conclusion: Sub-inhibitory concentrations of gentamycin inhibits the swarming motility of E. coli. This effect is mediated by a reduction in cellular fumarate caused by down-regulation of SDH. Gentamycin may be advantageous for treatment of E. coli infections.

Prolonged or Continuous Infusion of IV Antibiotics as Initial Treatment Strategy.

Prolonged or Continuous Infusion of IV Antibiotics as Initial Treatment Strategy.

In Vivo Pharmacodynamics of Cefquinome in a Neutropenic Mouse Thigh Model of Streptococcus suis Serotype 2 at Varied Initial Inoculum Sizes.

Streptococcus suis serotype 2 is an emerging zoonotic pathogen and causes severe disease in both pigs and human beings. Cefquinome (CEQ), a fourth-generation cephalosporin, exhibits broad-spectrum activity against Gram-positive bacteria such as S. suis. This study evaluated the in vitro and in vivo antimicrobial activities of CEQ against four strains of S. suis serotype 2 in a murine neutropenic thigh infection model. We investigated the effect of varied inoculum sizes (10(6) to 10(8) CFU/thigh) on the pharmacokinetic (PK)/pharmacodynamic (PD) indices and magnitudes of a particular PK/PD index or dose required for efficacy. Dose fractionation studies included total CEQ doses ranging from 0.625 to 640 mg/kg/24 h. Data were analyzed via a maximum effect (Emax) model using nonlinear regression. The PK/PD studies demonstrated that the percentage of time that serum drug levels were above the MIC of free drug (%ƒT>MIC) in a 24-h dosing interval was the primary index driving the efficacy of both inoculum sizes (R(2) = 91% and R(2) = 63%). CEQ doses of 2.5 and 40 mg/kg body weight produced prolonged postantibiotic effects (PAEs) of 2.45 to 8.55 h. Inoculum sizes had a significant influence on CEQ efficacy. Compared to the CEQ exposure and dosages in tests using standard inocula, a 4-fold dose (P = 0.006) and a 2-fold exposure time (P = 0.01) were required for a 1-log kill using large inocula of 10(8) CFU/thigh.

Gallic acid-based indanone derivative interacts synergistically with tetracycline by inhibiting efflux pump in multidrug resistant E. coli

The purpose of the present study was to study the synergy potential of gallic acid-based derivatives in combination with conventional antibiotics using multidrug resistant cultures of Escherichia coli. Gallic acid-based derivatives significantly reduced the MIC of tetracycline against multidrug resistant clinical isolate of E. coli. The best representative, 3-(3',4,'5'-trimethoxyphenyl)-4,5,6-trimethoxyindanone-1, an indanone derivative of gallic acid, was observed to inhibit ethidium bromide efflux and ATPase which was also supported by in silico docking. This derivative extended the post-antibiotic effect and decreased the mutation prevention concentration of tetracycline. This derivative in combination with TET was able to reduce the concentration of TNFα up to 18-fold in Swiss albino mice. This derivative was nontoxic and well tolerated up to 300 mg/kg dose in subacute oral toxicity study in mice. This is the first report of gallic acid-based indanone derivative as drug resistance reversal agent acting through ATP-dependent efflux pump inhibition.

A Subgroup Analysis of Patients Undergoing Autologous and Allogeneic Hematopoietic Stem Cell Transplantation (HSCT) in Deflect-1: A Double-Blind, Randomized Study of Fidaxomicin Vs. Placebo for Prophylaxis Against C. Difficile Infection

Introduction: Clostridium difficile-associated diarrhea (CDAD) is a common complication during HSCT that has been associated with increased morbidity and mortality. CDAD has been reported to occur in 6 to 30% of HSCT patients. An ideal agent for prevention of CDAD has not been established. Fidaxomicin (FDX) is bactericidal against C. difficile, has low systemic absorption, provides a prolonged post-antibiotic effect, and is currently approved for the treatment of CDAD. The efficacy and safety of low dose FDX (200mg once daily) for prevention of CDAD were evaluated in both autologous (AUTO) and allogenic (ALLO) HSCT patients receiving fluoroquinolone (FQ) prophylaxis.Methods: HSCT patients were randomized to receive FDX 200 mg once daily (QD) or placebo (PLA) from start of conditioning therapy or FQ prophylaxis until 7 days after post-transplant engraftment (ANC >500/mm3) or completion of FQ prophylaxis. Randomization was stratified by type of HSCT (AUTO vs. ALLO). Patients were contacted twice weekly for 30 days and then weekly through 60 days post-prophylaxis for symptoms; CDAD was confirmed by toxin testing or PCR. The incidence of CDAD from start of prophylaxis up to 30 days and 60 days post-treatment were primary and secondary endpoints, respectively. For the primary analysis, failures were defined as patients with confirmed CDAD, as well as those who had missing data for the primary endpoint assessment (due to death or discontinuations resulting from adverse events, protocol non-compliance, lost follow-up, or any other reasons) and those who received any CDAD-effective medication (without confirmed CDAD). Sensitivity analyses, including an analysis that defined failure as confirmed CDAD, were prospectively defined for the overall population. These same analyses were performed for the ALLO and AUTO subgroups.Results: Of 611 enrolled patients, 600 were evaluable: 352 (59%) in AUTO and 248 (41%) in ALLO subgroups. The primary analysis for the primary endpoint did not show a significant reduction in incidence of CDAD with FDX prophylaxis (28.6% FDX vs. 30.8% PLA, p = 0.28). Secondary endpoint results were similar. However, the incidence of confirmed CDAD for up to 30 days was significantly lower in AUTO, ALLO, and overall in HSCT patients receiving prophylactic FDX versus PLA (see table). There were similar trends for 60 day post-treatment results. Overall, serious adverse events (AEs) and AEs resulting in death were more frequent in the ALLO vs. AUTO subgroup. In both subgroups, no differences in drug-related serious and non-serious AEs were seen between FDX and PLA.TableIncidence of Confirmed CDAD, 30d Post-treatmentAUTOALLOTotalFDX (%)5/176 (2.8%)8/125 (6.4%)13/301 (4.3%)PLA (%)14/176 (8.0%)18/123 (14.6%)32/299 (10.7%)PLA-FDX, %5.18.26.4Wald p-value0.01630.01660.0014Incidence of Confirmed CDAD, 60d Post-treatmentFDX (%)6/176 (3.4%)11/125 (8.8%)17/301 (5.6%)PLA (%)14/176 (8.0%)18/123 (14.6%)32/299 (10.7%)PLA-FDX, %4.55.85.1Wald p-value0.03210.07590.0117Conclusions: For the primary endpoint (failure of prophylaxis due to confirmed CDAD or non-CDAD events), the efficacy of FDX and PLA were similar. However, in both AUTO and ALLO HSCT patients, prophylactic FDX significantly reduced the incidence of confirmed CDAD and was not associated with drug-related adverse events. DisclosuresDugan:Cubist/Merck & Co., Inc.: Research Funding. Winston:Cubist/Merck & Co., Inc.: Research Funding. Morris:Cubist/ Merck & Co., Inc.: Research Funding. Williams:Merck & Co., Inc.: Employment. Broyde:Merck & Co., Inc.: Employment. Sears:Merck & Co., Inc.: Employment.