Potential of the fluoroketolide RBx 14255 against Streptococcus pneumoniae, Neisseria meningitidis and Haemophilus influenzae in an experimental murine meningitis model.

BACKGROUND: RBx 14255 is a fluoroketolide in pre-clinical evaluation with potent activity against MDR Gram-positive pathogens. OBJECTIVES: To investigate the efficacy of RBx 14255 against bacterial meningitis caused by Streptococcus pneumoniae, Neisseria meningitidis or Haemophilus influenzae in an experimental murine meningitis model. METHODS: In vitro activity of RBx 14255 was evaluated against clinical isolates of S. pneumoniae, N. meningitidis and H. influenzae. The in vivo efficacy of RBx 14255 was evaluated against bacterial meningitis, induced with S. pneumoniae 3579 erm(B), S. pneumoniae MA 80 erm(B), N. meningitidis 1852 and H. influenzae B1414 in a murine meningitis model. RESULTS: RBx 14255 showed strong in vitro bactericidal potential against S. pneumoniae, N. meningitidis and H. influenzae with MIC ranges of 0.004-0.1, 0.03-0.5 and 1-4 mg/L, respectively. In a murine meningitis model, a 50 mg/kg dose of RBx 14255, q12h, resulted in significant reduction of bacterial counts in the brain compared with the pretreatment control. The concentration of RBx 14255 in brain tissue correlated well with the efficacy in this mouse model. CONCLUSIONS: RBx 14255 showed superior bactericidal activity in time-kill assays in vitro and in vivo in an experimental murine meningitis model. RBx 14255 could be a promising candidate for future drug development against bacterial meningitis.

Design, synthesis and biological evaluation of spiropyrimidinetriones oxazolidinone derivatives as antibacterial agents.

Gram-positive bacteria are among the most common human pathogens associated with clinical infections which range from mild skin infections to sepsis. Resistance towards existing class of drugs by Gram-positive bacteria including methicillin resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis (MRSE) and vancomycin resistant enterococci (VRE) is a growing concern. There is an urgent need to discover new antibiotics which are active against resistant strains of Gram positive bacteria. We report herein a novel class of spiropyrimidinetrione oxazolidinone derivatives as novel antibacterial agents. Key step towards the synthesis of title compounds involved the use of tert-amino reaction with [1,5]-hydride shift leading to the new CC bond formation. Compound 30n has demonstrated potent antibacterial activity against a panel of Gram-positive microbial strains including MRSA, MRSE, and LNZ and vancomycin resistant strains of E. faecalis. Further, molecular docking studies suggest that 30n has binding mode similar to that of LNZ in 50S RNA ribosome.

Novel fluorobenzothiazole as a dual inhibitor of gyrase B and topoisomerase IV against Gram-positive pathogens.

Aim: The development of a novel inhibitor targeting gyrase B and topoisomerase IV offers an opportunity to combat multidrug resistance. Methods: We investigated the activity of RBx 10080758 against Gram-positive bacteria in vitro and in vivo. Results: RBx 10080758 showed a potent 50% inhibitory concentration of 0.13 µM and 0.25 µM against gyrase B and topoisomerase IV, respectively, and exhibited strong whole-cell in vitro activity with MIC ranges of 0.015-0.06 and 0.015-0.03 µg/ml against Staphylococcus aureus and Streptococcus pneumoniae, respectively. In a rat thigh infection model with methicillin-resistant S. aureus, RBx 10080758 at 45 mg/kg exhibited a >3 log10 CFU reduction in thigh muscles. Conclusion: RBx 10080758 displayed potent activity against multiple multidrug-resistant Gram-positive bacteria with a dual-targeting mechanism of action.

Activity of RBx 11760, a novel biaryl oxazolidinone, against Clostridium difficile.

OBJECTIVES: RBx 11760, a novel oxazolidinone, was investigated for in vitro and in vivo activity against Clostridium difficile. METHODS: The in vitro activity of RBx 11760 and three other agents against 50 diverse C. difficile clinical isolates and other obligate anaerobic bacteria was determined. The effect of RBx 11760 on sporulation and toxin production was determined against different C. difficile isolates. We used a hamster infection model to investigate the efficacy of RBx 11760, vancomycin and metronidazole. The mechanism of action of RBx 11760 against C. difficile ATCC 43255 was determined by macromolecular synthesis inhibition. RESULTS: RBx 11760 MICs were in the range of 0.5-1 mg/L for C. difficile isolates, and it demonstrated concentration-dependent killing of C. difficile ATCC 43255 and C. difficile 6387 up to 2-4× MIC (1-2 mg/L). RBx 11760, at concentrations as low as 0.25-0.5 mg/L, resulted in a significant reduction in de novo toxin production as well as sporulation in different C. difficile isolates. In contrast, vancomycin, metronidazole and linezolid had little or no effect on toxin production and appeared to promote the formation of spores. In the hamster infection model, treatment with RBx 11760 resulted in prolonged survival of animals as compared with vancomycin or metronidazole, which correlated well with the histopathology results. Macromolecular labelling results suggest that RBx 11760 is a potent inhibitor of bacterial protein synthesis. CONCLUSIONS: RBx 11760 showed excellent in vitro and in vivo activity against C. difficile, and it could be a promising novel candidate for future drug development against C. difficile infection.

Determination of methicillin resistant Staphylococcus aureus (MRSA) using several phenotypic methods--a report from a tertiary care center at New Delhi, India.

Staphylococcus aureus is a serious current health care concern. Rapid, precise identification of MRSA is a prerequisite tool for control of hospital infection. The present study aimed at studying the antibiotic susceptibility and demographic profile of MRSA isolated from clinical specimens and also to assess the reliability of five methods of identifying methicillin resistance. A total of 112 isolates of Staphylococcus aureus isolated from critical areas of the hospital were randomly selected and subjected to various phenotypic methods for determining methicillin resistance. Determination of minimum inhibitory concentration (MIC) for oxacillin by microbroth dilution method was the 'gold standard'. The present study also focuses on the comparison of oxacillin disc diffusion and cefoxitin disc diffusion screening for determination of MRSA. The sensitivity and specificity values for latex agglutination, oxacillin salt agar screening, E-Strip, cefoxitin disc diffusion and oxacillin disc diffusion method are 98.7% and 72.5%, 94.4% and 92.5%, 93.1% and 65.0%, 86.1% and 65%, 83.3% and 90.0% respectively. No single phenotypic test is completely reliable for the detection of oxacillin resistance in S. aureus. Oxacillin salt agar screening at 6 microg/ml and PBP2' detection by latex agglutination method were the most sensitive and specific method for detecting MRSA. Amidst the disc screening methods which are most often used in the smaller laboratory set-up where agar screen may not be functionally feasible for various reasons (economic and performance) cefoxitin disc screening has good sensitivity and specificity overall and perhaps is closest to being the cheap and reliable alternative in these settings.

Azithromycin Exhibits Activity Against Pseudomonas aeruginosa in Chronic Rat Lung Infection Model.

Pseudomonas aeruginosa forms biofilms in the lungs of chronically infected cystic fibrosis patients, which are tolerant to both the treatment of antibiotics and the host immune system. Normally, antibiotics are less effective against bacteria growing in biofilms; azithromycin has shown a potent efficacy in cystic fibrosis patients chronically infected with P. aeruginosa and improved their lung function. The present study was conducted to evaluate the effect of azithromycin on P. aeruginosa biofilm. We show that azithromycin exhibited a potent activity against P. aeruginosa biofilm, and microscopic observation revealed that azithromycin substantially inhibited the formation of solid surface biofilms. Interestingly, we observed that azithromycin restricted P. aeruginosa biofilm formation by inhibiting the expression of pel genes, which has been previously shown to play an essential role in bacterial attachment to solid-surface biofilm. In a rat model of chronic P. aeruginosa lung infection, we show that azithromycin treatment resulted in the suppression of quorum sensing-regulated virulence factors, significantly improving the clearance of P. aeruginosa biofilms compared to that in the placebo control. We conclude that azithromycin attenuates P. aeruginosa biofilm formation, impairs its ability to produce extracellular biofilm matrix, and increases its sensitivity to the immune system, which may explain the clinical efficacy of azithromycin in cystic fibrosis patients.

Mode of action of Ranbezolid against staphylococci and structural modeling studies of its interaction with ribosomes.

Oxazolidinones are known to inhibit protein biosynthesis and act against a wide spectrum of gram-positive bacteria. A new investigational oxazolidinone, ranbezolid, inhibited bacterial protein synthesis in Staphylococcus aureus and Staphylococcus epidermidis. In S. epidermidis, ranbezolid showed inhibition of cell wall and lipid synthesis and a dose-dependent effect on membrane integrity. A kill-kinetics study showed that ranbezolid was bactericidal against S. epidermidis. In vitro translation of the luciferase gene done using bacterial and mammalian ribosomes indicated that ranbezolid specifically inhibited the bacterial ribosome. Molecular modeling studies revealed that both linezolid and ranbezolid fit in similar manners the active site of ribosomes, with total scores, i.e., theoretical binding affinities after consensus, of 5.2 and 6.9, respectively. The nitrofuran ring in ranbezolid is extended toward C2507, G2583, and U2584, and the nitro group forms a hydrogen bond from the base of G2583. The interaction of ranbezolid with the bacterial ribosomes clearly helps to elucidate its potent activity against the target pathogen.

Minimum inhibitory concentration of carbapenems and tigecycline against Salmonella spp.

Antimicrobial resistance in Salmonella spp. is of grave concern, more so in quinolone-resistant and extended-spectrum beta-lactamase (ESBL)-producing isolates that cause complicated infections. The MIC of azithromycin, ciprofloxacin, cefixime, cefepime, ceftriaxone, gatifloxacin, imipenem, levofloxacin, meropenem and ofloxacin (E-test strip) and tigecycline and faropenem (agar dilution) against 210 Salmonella spp. was determined. MIC(90) (defined as the antimicrobial concentration that inhibited growth of 90 % of the strains) of the carbapenems (imipenem and meropenem) for Salmonella Typhi and Salmonella Paratyphi A was 0.064 microg ml(-1). MIC(90) of faropenem was 0.25 microg ml(-1) for S. Typhi, S. Paratyphi A and Salmonella Typhimurium. The MIC(90) of azithromycin for all Salmonella spp. ranged from 8 to 16 microg ml(-1). Tigecycline showed an MIC(90) of 2 microg ml(-1) for S. Typhi, 1 microg ml(-1) for S. Paratyphi A and 4 microg ml(-1) for S. Typhimurium. We concluded that tigecycline and the carbapenems are likely to have roles in the final stage of treatment of quinolone-resistant and ESBL-producing multidrug-resistant salmonellae.

Ciprofloxacin-resistant Neisseria meningitidis, Delhi, India.

Decreased susceptibility of Neisseria meningitidis isolates to ciprofloxacin emerged from an outbreak in Delhi, India. Results of antimicrobial susceptibility testing of the meningococcal isolates to ciprofloxacin and further sequencing of DNA gyrase A quinolone-resistance-determining region confirmed the emergence of ciprofloxacin resistance in the outbreak.

Antifungal potential of disulfiram.

Disulfiram, an alcohol antagonistic drug has been on the market since 1949 with 80% bioavailability and an established safety profile. Recently it has been reported as a P-glycoprotein efflux pump modulator. Herein we report its antifungal potential. The MIC50 and MIC90 of disulfiram for yeast isolates is 4 and 8 microg/ml, respectively, and the MIC range is 1-16 micro g/ml for both fluconazole sensitive and resistant strains. Interestingly, disulfiram also showed fungicidal activity on Aspergillus spp. with MIC50 and MIC90 of 2 and 8 microg/ml, respectively.

Adverse effect of staphylococci slime on in vitro activity of glycopeptides.

Adhesion to biomaterial is assumed to be a crucial step in the development of staphylococcal foreign body infections. Production of extracellular slime has major implications for the development and implementation of therapeutic strategies. The effect of extracted slime was investigated on the activity of vancomycin, teicoplanin, linezolid, quinupristin/dalfopristin, rifampicin and ranbezolid against 10 clinical and 4 ATCC staphylococcal isolates. The slime extract caused a 2- to 16-fold increase in the MICs of vancomycin and teicoplanin, with a shift in the MIC(90) from 2 to 32 (vancomycin) and 2 to 16 (teicoplanin), whereas the MICs of linezolid and quinupristin/dalfopristin were only moderately affected. In time-kill studies, a significant decrease in bacterial killing (>3 log(10) cfu/ml) was observed with vancomycin and teicoplanin (4 x MIC) after addition of slime (5 and 20 mg/ml), whereas the effect of killing by linezolid and quinupristin/dalfopristin was very modest. The rifampicin and ranbezolid MICs and kill curves were not influenced by the addition of slime. The present study thus indicated that slime interferes with the antimicrobial effect of glycopeptide drugs (vancomycin, teicoplanin), and that for effective prevention and treatment of prosthetic device-related infections, appropriate and newer antibiotics such as ranbezolid should be considered.

Risk Factor Analysis in Clinical Isolates of ESBL and MBL (Including NDM-1) Producing Escherichia coli and Klebsiella Species in a Tertiary Care Hospital.

BACKGROUND: Extended-spectrum ß-lactamase (ESBL) and metallo-ß-lactamase (MBL) producing Gram negative organisms are emerging as a worldwide public health concern. AIM: To elucidate risk factors for infection with ESBL and MBL (also NDM-1) producing E. coli and Klebsiella spp. MATERIALS AND METHODS: A prospective observational study was conducted from November 2010 to March 2012. ESBL production was detected using ESBL E-test, MBL by MBL E-test and NDM-1 by polymerase chain reaction (PCR). Risk factors analysed includes age, sex, clinical specimen, type of infection, duration of hospital stay prior to collection of sample, admitting ward, antimicrobial susceptibility, previous antibiotics used, co-morbid illnesses like diabetes mellitus, immunodeficiency, low birth weight, respiratory/neurological/cardiac/haematological/liver diseases, malignancy, urinary or central venous catheter, ventilatory support, surgical procedures and dialysis. STATISTICAL ANALYSIS: z-test or Fisher's exact test. RESULTS: E. coli - ESBL producing isolates E. coli revealed female preponderance, equal incidence of hospital and community acquired infections, mostly from surgical wards, isolated from urine, age group among females >20-30 years and among males >28 days-1 year. They showed high resistance to cephalosporins, monobactam, penicillin but low resistance to carbapenems and aminoglycosides. Co-morbid conditions observed were surgery, urinary catheterisation, haematological disease, ventilatory support, diabetes mellitus and neurological disease. MBL producing strains were mainly from females, surgical wards, (including both NDM-1 isolates), hospital acquired infections, isolated from body fluids (NDM-1 positive), female genital tract specimen and urine (one NDM-1 positive). NDM-1 positive isolates belonged to age groups >5-10 year and >0-28 days and underwent surgery and urinary catheterisation. Klebsiella spp.- ESBL producing isolates showed female preponderance, hospital acquired infections, from surgical wards, high resistance levels to cephalosporins, fluoroquinolones, monobactam, but low levels to carbapenems, among males isolated from pus in age group >0-28 days and >28 days -1 year and among females from urine in >20-30 years, no significant difference when correlated with risk factors. MBL (NDM-1) producing isolates were mainly from females with age range 0 days to 70 years, mainly admitted to ICU/postoperative wards with urinary catheter in-situ, ventilatory support, surgery, diabetes mellitus, haematological and neurological disease. CONCLUSION: Risk factors for infections due to ESBL and MBL producing Gram Negative Bacteria (GNB) should be clearly identified to reduce their spread and to optimise antibiotic use.

Design, Synthesis, and Identification of Silicon Incorporated Oxazolidinone Antibiotics with Improved Brain Exposure.

Therapeutic options for brain infections caused by pathogens with a reduced sensitivity to drugs are limited. Recent reports on the potential use of linezolid in treating brain infections prompted us to design novel compounds around this scaffold. Herein, we describe the design and synthesis of various oxazolidinone antibiotics with the incorporation of silicon. Our findings in preclinical species suggest that silicon incorporation is highly useful in improving brain exposures. Interestingly, three compounds from this series demonstrated up to a 30-fold higher brain/plasma ratio when compared to linezolid thereby indicating their therapeutic potential in brain associated disorders.

Cissampelos pareira Linn: Natural Source of Potent Antiviral Activity against All Four Dengue Virus Serotypes.

BACKGROUND: Dengue, a mosquito-borne viral disease, poses a significant global public health risk. In tropical countries such as India where periodic dengue outbreaks can be correlated to the high prevalence of the mosquito vector, circulation of all four dengue viruses (DENVs) and the high population density, a drug for dengue is being increasingly recognized as an unmet public health need. METHODOLOGY/PRINCIPAL FINDINGS: Using the knowledge of traditional Indian medicine, Ayurveda, we developed a systematic bioassay-guided screening approach to explore the indigenous herbal bio-resource to identify plants with pan-DENV inhibitory activity. Our results show that the alcoholic extract of Cissampelos pariera Linn (Cipa extract) was a potent inhibitor of all four DENVs in cell-based assays, assessed in terms of viral NS1 antigen secretion using ELISA, as well as viral replication, based on plaque assays. Virus yield reduction assays showed that Cipa extract could decrease viral titers by an order of magnitude. The extract conferred statistically significant protection against DENV infection using the AG129 mouse model. A preliminary evaluation of the clinical relevance of Cipa extract showed that it had no adverse effects on platelet counts and RBC viability. In addition to inherent antipyretic activity in Wistar rats, it possessed the ability to down-regulate the production of TNF-α, a cytokine implicated in severe dengue disease. Importantly, it showed no evidence of toxicity in Wistar rats, when administered at doses as high as 2g/Kg body weight for up to 1 week. CONCLUSIONS/SIGNIFICANCE: Our findings above, taken in the context of the human safety of Cipa, based on its use in Indian traditional medicine, warrant further work to explore Cipa as a source for the development of an inexpensive herbal formulation for dengue therapy. This may be of practical relevance to a dengue-endemic resource-poor country such as India.

Anti-anaerobic potential of ranbezolid: insight into its mechanism of action against Bacteroides fragilis.

This study reports the anti-anaerobic properties of ranbezolid, a new investigational oxazolidinone. A time-kill kinetics study against anaerobes showed that ranbezolid was superior to linezolid and killed the anaerobic pathogens at 4-8h, except for Bacteroides fragilis where killing was observed at 24h. In addition, the time-kill kinetics study showed a concentration-dependent bactericidal potential of ranbezolid against anaerobes. Ranbezolid showed 5.39log(10) reduction and linezolid showed 1.15log(10) reduction in murine disk implant infection with B. fragilis ATCC 25285. Ranbezolid was very potent and showed fast protein synthesis inhibition against B. fragilis, a Gram-negative anaerobe. In addition, non-specific cell wall synthesis inhibition was also observed with ranbezolid. The potent and fast protein synthesis inhibition along with an additional mode of action of cell wall synthesis inhibition could be responsible for the cidal effect of ranbezolid against Gram-negative anaerobes.

Novel biaryl oxazolidinones: in vitro and in vivo activities with pharmacokinetics in an animal model.

RBx 1000075 and RBx 1000276, the new investigational oxazolidinones, have an extended spectrum of in vitro activity against Gram-positive pathogens and showed minimum inhibitory concentrations (MICs) lower than comparator drugs. MIC for 90% of the organisms (MIC(90)) values of RBx 1000075, RBx 1000276 and linezolid against the isolates tested were, respectively: methicillin-sensitive Staphylococcus aureus, 0.25, 1 and 4 microg/mL; methicillin-resistant S. aureus (MRSA), 0.5, 2 and 4 microg/mL; methicillin-sensitive Staphylococcus epidermidis, 0.25, 1 and 2 microg/mL; methicillin-resistant S. epidermidis, 0.5, 1 and 2 microg/mL; and enterococci, 0.25, 1 and 4 microg/mL. Against respiratory pathogens, MIC(90) values were: Streptococcus pneumoniae, 0.125, 0.5 and 2 microg/mL; Streptococcus pyogenes, 1, 0.5 and 2 microg/mL; and Moraxella catarrhalis, 0.5, 2 and 4 microg/mL. In vivo efficacies of RBx 1000075 and RBx 1000276 were evaluated in murine systemic infection against S. aureus (MRSA 562) and in a pulmonary infection model against S. pneumoniae ATCC 6303. In murine systemic infection, RBx 1000075 and RBx 1000276 showed efficacy against MRSA 562, exhibiting a 50% effective dose (ED(50)) of 6.25 and 9.92 mg/kg body weight for once-daily administration and 4.96 and 5.56 mg/kg body weight for twice-daily administration, respectively, whereas for linezolid the corresponding ED(50) values were 9.9 and 5.56 mg/kg body weight. In pulmonary infection with S. pneumoniae ATCC 6303, 50% survival was observed with RBx 1000075 at 50mg/kg once daily, whereas 60% survival was observed with RBx 1000276 at 50mg/kg thrice daily. The absolute oral bioavailabilities of RBx 1000075 and RBx 1000276 were 48% and 73%, with half-lives of 13.5 and 3.2h, respectively. RBx 1000075 and RBx 1000276 are promising investigational oxazolidinones against Gram-positive pathogens.

Synthesis and antibacterial activity of novel oxazolidinones with methylene oxygen- and methylene sulfur-linked substituents at C5-position.

Novel oxazolidinone derivatives of the lead compound RBx 8700, containing methylene oxygen- and methylene sulfur-linked substituents at the C5-position, were synthesized. Antibacterial screening of these compounds against a panel of resistant and susceptible Gram-positive and fastidious Gram-negative bacteria gave compounds 2 and 4 as new antibacterial agents.