Modulation of a Mycobacterial ADP-Ribosyltransferase to Augment Rifamycin Antibiotic Resistance.

The rifamycins are broad-spectrum antibiotics that are primarily utilized to treat infections caused by mycobacteria, including tuberculosis. Interestingly, various species of bacteria are known to contain an enzyme called Arr that catalyzes ADP-ribosylation of rifamycin antibiotics as a mechanism of resistance. Here, we study Arr modulation in relevant Gram-positive and -negative species. We show that a C-terminal truncation of Arr (ArrC), encoded in the genome of Mycobacterium smegmatis, activates Arr-mediated rifamycin modification. Through structural comparisons of mycobacterial Arr and human poly(ADP-ribose) polymerases (PARPs), we identify a known small molecule PARP inhibitor that can act as an adjuvant to sensitize M. smegmatis to the rifamycin antibiotic rifampin via inhibition of Arr, even in the presence of ArrC. Finally, we demonstrate that this rifampin/adjuvant combination treatment is effective at inhibiting growth of the multidrug-resistant (MDR) nontuberculosis pathogen Mycobacterium abscessus, which has become a growing cause of human infections in the clinic.

Modulation of the gut microbiota: a focus on treatments for irritable bowel syndrome.

Irritable bowel syndrome (IBS), which is characterized by recurrent abdominal pain and disordered bowel habits, is one of the most common functional bowel disorders. IBS is a substantial burden on both patient health-related quality of life and healthcare costs. Several pathophysiologic mechanisms have been postulated for the occurrence of IBS, including altered gastrointestinal motility, visceral hypersensitivity, changes in gut permeability, immune activation, gut-brain dysregulation, central nervous system dysfunction, and changes in the gut microbiota. Of note, both qualitative and quantitative differences have been observed in the gut microbiota of a population with IBS versus a healthy population. Because of the substantial interest in the gut microbiota and its role as a therapeutic target in IBS, this article provides an overview of specific interventions with the potential to modulate the gut microbiota in IBS, including elimination diets, prebiotics, probiotics, synbiotics, and nonsystemic antibiotics. Although probiotics and synbiotics are generally well tolerated, differences in the composition and concentration of different bacterial species and inclusion or exclusion of prebiotic components varies widely across studies and has prevented strong recommendations on their use in IBS. For nonsystemic antibiotics, rifaximin is indicated in the United States for the treatment of IBS with diarrhea in adults and has been shown to be efficacious and well tolerated in well-designed clinical trials. Overall, more consistent evidence is needed regarding the efficacy and safety of elimination diets, prebiotics, probiotics, and synbiotics for the treatment of patients with IBS. Furthermore, additional well-designed studies are needed that examine alterations in the gut microbiota that occur with these interventions and their potential associations with clinical symptoms of IBS.

Diagnosis of symptomatic uncomplicated diverticular disease and the role of Rifaximin in management.

Patients with diverticulosis who develop persistent abdominal pain, bloating and changes in bowel habits not associated with overt inflammation may have symptomatic uncomplicated diverticular disease (SUDD). The severity and frequency of SUDD symptoms may have an impact on daily activities and severely affect quality of life. Effective management of SUDD should follow a three part strategy: divert, tackle and maintain. Divert to make the correct diagnosis: several symptoms of SUDD are common to other conditions that require different therapeutic approaches. However, several key differences should be used to diagnose SUDD. Pain in SUDD is normally in the iliac fossa, persistent, often lasting more than 24 hrs, and is not relieved by bowel movement, as is often the case with irritable bowel syndrome. Another difference is in the timing: the prevalence of SUDD increases with age, and patients under the age of 40 years are less likely to have diverticula. It is useful to establish whether a patient has diverticulosis, especially if the patient is relatively young; lack of diverticula excludes SUDD. Cross-sectional imaging is indicated; however, recent archival image data or ultrasonography may be useful alternatives. Laboratory tests should be ordered to exclude overt inflammation. Once the diagnosis of SUDD is made, the patient should receive effective therapy to tackle the condition. This should include dietary fibre supplementation and cyclic treatment with rifaximin 400 mg twice daily for 7 days per month. Once symptom control is achieved, it should be maintained by continuing therapy for at least 12 months.

Natural plant products inhibits growth and alters the swarming motility, biofilm formation, and expression of virulence genes in enteroaggregative and enterohemorrhagic Escherichia coli.

The purpose of this study was to determine the effects of plant products on the growth, swarming motility, biofilm formation and virulence gene expression in enterohemorrhagic Escherichia coli O157:H7 and enteroaggregative E. coli strain 042 and a strain of O104:H4 serotype. Extracts of Lippia graveolens and Haematoxylon brassiletto, and carvacrol, brazilin were tested by an antimicrobial microdilution method using citral and rifaximin as controls. All products showed bactericidal activity with minimal bactericidal concentrations ranging from 0.08 to 8.1 mg/ml. Swarming motility was determined in soft LB agar. Most compounds reduced swarming motility by 7%-100%; except carvacrol which promoted motility in two strains. Biofilm formation studies were done in microtiter plates. Rifaximin inhibited growth and reduced biofilm formation, but various concentrations of other compounds actually induced biofilm formation. Real time PCR showed that most compounds decreased stx2 expression. The expression of pic and rpoS in E. coli 042 were suppressed but in E. coli O104:H4 they varied depending on compounds. In conclusion, these extracts affect E. coli growth, swarming motility and virulence gene expression. Although these compounds were bactericidal for pathogenic E. coli, sublethal concentrations had varied effects on phenotypic and genotypic traits, and some increased virulence gene expression.

Development of a Dual-Acting Antibacterial Agent (TNP-2092) for the Treatment of Persistent Bacterial Infections.

The clinical management of prosthetic joint infections and other persistent bacterial infections represents a major unmet medical need. The rifamycins are one of the most potent antibiotic classes against persistent bacterial infections, but bacteria can develop resistance to rifamycins rapidly and the clinical utility of the rifamycin class is typically limited to antibiotic combinations to minimize the development of resistance. To develop a better therapy against persistent bacterial infections, a series of rifamycin based bifunctional molecules were designed, synthesized, and evaluated with the goal to identify a dual-acting drug that maintains the potent activity of rifamycins against persistent pathogens and at the same time minimize the development of rifamycin resistance. TNP-2092 was identified as a drug candidate and is currently in an early stage of clinical development for the treatment of prosthetic joint infections.

Antimicrobial activity of different filling pastes for deciduous tooth treatment.

Guedes-Pinto paste is the filling material most employed in Brazil for endodontic treatment of deciduous teeth; however, the Rifocort® ointment has been removed. Thus, the aim of this study was to investigate the antimicrobial potential of filling pastes, by proposing three new pharmacological associations to replace Rifocort® ointment with drugs of already established antimicrobial power: Nebacetin® ointment, 2% Chlorhexidine Gluconate gel, and Maxitrol® ointment. A paste composed of Iodoform, Rifocort® ointment and Camphorated Paramonochlorophenol (CPC) was employed as the gold standard (G1). The other associations were: Iodoform, Nebacetin® ointment and CPC (G2); Iodoform, 2% Chlorhexidine Digluconate gel and CPC (G3); Iodoform, Maxitrol® ointment and CPC (G4). The associations were tested for Staphylococcus aureus (S. aureus), Streptococcus mutans (S. mutans), Streptococcus oralis (S. oralis), Enterococcus faecalis (E. faecalis), Escherichia coli (E. coli), and Bacillus subtilis (B. subtilis), using the methods of dilution on solid medium - orifice agar - and broth dilution. The results were tested using statistical analysis ANOVA and Kruskal-Wallis. They showed that all the pastes had a bacteriostatic effect on all the microorganisms, without any statistically significant difference, compared with G1. S. aureus was statistically significant (multiple comparison test of Tukey), insofar as G2 and G3 presented the worst and the best performance, respectively. All associations were bactericidal for E. coli, S. aureus, S. mutans and S. oralis. Only G3 and G4 were bactericidal for E. faecalis, whereas no product was bactericidal for B. subtilis. Thus, the tested pastes have antimicrobial potential and have proved acceptable for endodontic treatment of primary teeth.

Antimicrobial activity of different filling pastes for deciduous tooth treatment

Guedes-Pinto paste is the filling material most employed in Brazil for endodontic treatment of deciduous teeth; however, the Rifocort® ointment has been removed. Thus, the aim of this study was to investigate the antimicrobial potential of filling pastes, by proposing three new pharmacological associations to replace Rifocort® ointment with drugs of already established antimicrobial power: Nebacetin® ointment, 2% Chlorhexidine Gluconate gel, and Maxitrol® ointment. A paste composed of Iodoform, Rifocort® ointment and Camphorated Paramonochlorophenol (CPC) was employed as the gold standard (G1). The other associations were: Iodoform, Nebacetin® ointment and CPC (G2); Iodoform, 2% Chlorhexidine Digluconate gel and CPC (G3); Iodoform, Maxitrol® ointment and CPC (G4). The associations were tested for Staphylococcus aureus (S. aureus), Streptococcus mutans (S. mutans), Streptococcus oralis (S. oralis), Enterococcus faecalis (E. faecalis), Escherichia coli (E. coli), and Bacillus subtilis (B. subtilis), using the methods of dilution on solid medium – orifice agar – and broth dilution. The results were tested using statistical analysis ANOVA and Kruskal-Wallis. They showed that all the pastes had a bacteriostatic effect on all the microorganisms, without any statistically significant difference, compared with G1. S. aureus was statistically significant (multiple comparison test of Tukey), insofar as G2 and G3 presented the worst and the best performance, respectively. All associations were bactericidal for E. coli, S. aureus, S. mutans and S. oralis. Only G3 and G4 were bactericidal for E. faecalis, whereas no product was bactericidal for B. subtilis. Thus, the tested pastes have antimicrobial potential and have proved acceptable for endodontic treatment of primary teeth.

Modulatory effect of three antibiotics on uterus bovine contractility in vitro and likely therapeutic approaches in reproduction.

This in vitro study investigates the modulatory effect of three antibiotics (amoxicillin, enrofloxacin, and rifaximin) on contractility of the bovine uterine tissue in follicular and luteal phases. The effects of these antibiotics at three single doses (10(-6), 10(-5), and 10(-4) M) on their basal contractility were evaluated in isolated organ bath. The functionality of the strip throughout the experiment was evaluated by a dose of carbachol (10(-5) M); the obtained effect had to be repeatable (difference of ≤20%) that is comparable to that induced by the previous administration of the same substance. The results demonstrate the different modulatory activities of these antibiotics on uterine contractility in follicular and luteal phases. The effects induced by amoxicillin and enrofloxacin are opposite: the first relaxes and the second increases the uterine contractility in both cycle phases. Instead, the activity of rifaximin varies depending on the phase of estrous cycle: it increases in the follicular phase and relaxes in the luteal phase. The obtained data provide the hypothesis of possible implications of these drugs in the pharmacologic modulation of uterine contractions. Their action at this level, associated with their specific antimicrobial effects, could suggest using these antibiotics for the treatment of diseases related to postpartum or infections that may occur in pregnant cattle, by virtue of their effects on myometrial contractility too.

Use of rifamycin drugs and development of infection by rifamycin-resistant strains of Clostridium difficile.

The relationship between rifamycin drug use and the development of resistant strains of Clostridium difficile was studied at a large university hospital in Houston, TX, between May 2007 and September 2011. In 49 of 283 (17.3%) patients with C. difficile infection (CDI), a rifamycin-resistant strain of C. difficile was identified that compares to a rate of 8% using the same definitions in 2006-2007 (P = 0.59). The 49 patients infected by a resistant organism were matched by date of admission to 98 control patients with CDI from whom a rifamycin-susceptible C. difficile strain was isolated. Cases and controls did not differ according to demographic and clinical characteristics and showed similar but low rates of prior rifamycin use. Similar rates of rifamycin resistance were seen in cases of hospital-acquired CDI (38/112 [34%]) versus community-acquired CDI (7/20 [35%]). At a university hospital in which rifaximin was commonly used, infection by rifamycin-resistant strains of C. difficile was not shown to relate to prior use of a rifamycin drug or to acquiring the infection in the hospital, although the rate of overall resistance appeared to be rising.

Methane biogenesis during sodium azide-induced chemical hypoxia in rats.

Previous studies demonstrated methane generation in aerobic cells. Our aims were to investigate the methanogenic features of sodium azide (NaN(3))-induced chemical hypoxia in the whole animal and to study the effects of l-α-glycerylphosphorylcholine (GPC) on endogenous methane production and inflammatory events as indicators of a NaN(3)-elicited mitochondrial dysfunction. Group 1 of Sprague-Dawley rats served as the sham-operated control; in group 2, the animals were treated with NaN(3) (14 mg·kg(-1)·day(-1) sc) for 8 days. In group 3, the chronic NaN(3) administration was supplemented with daily oral GPC treatment. Group 4 served as an oral antibiotic-treated control (rifaximin, 10 mg·kg(-1)·day(-1)) targeting the intestinal bacterial flora, while group 5 received this antibiotic in parallel with NaN(3) treatment. The whole body methane production of the rats was measured by means of a newly developed method based on photoacoustic spectroscopy, the microcirculation of the liver was observed by intravital videomicroscopy, and structural changes were assessed via in vivo fluorescent confocal laser-scanning microscopy. NaN(3) administration induced a significant inflammatory reaction and methane generation independently of the methanogenic flora. After 8 days, the hepatic microcirculation was disturbed and the ATP content was decreased, without major structural damage. Methane generation, the hepatic microcirculatory changes, and the increased tissue myeloperoxidase and xanthine oxidoreductase activities were reduced by GPC treatment. In conclusion, the results suggest that methane production in mammals is connected with hypoxic events associated with a mitochondrial dysfunction. GPC is protective against the inflammatory consequences of a hypoxic reaction that might involve cellular or mitochondrial methane generation.

Repurposing screens identify rifamycins as potential broad-spectrum therapy for multidrug-resistant Acinetobacter baumannii and select agent microorganisms.

AIMS: Estimates suggest that the drug discovery and development processes take between 10 and 15 years, with costs ranging between US$500 million and $2 billion. A growing number of bacteria have become resistant to approved antimicrobials. For example, the Gram-negative bacterium Acinetobacter baumannii has become multidrug resistant (MDR) and is now an important pathogen to the US military in terms of wound infections. Industry experts have called for a 'disruptive' transformation of the drug discovery process to find new chemical entities for treating drug-resistant infections. One such attempt is drug 'repurposing' or 'repositioning' - that is, identification and development of new uses for existing or abandoned pharmacotherapies. MATERIALS & METHODS: Using a novel combination of screening technologies based on cell growth and cellular respiration, we screened 450 US FDA-approved drugs from the NIH National Clinical Collection against a dozen clinical MDR A. baumannii (MDRAb) isolates from US soldiers and Marines. We also screened the collection against a diverse set of select agent surrogate pathogens. RESULTS: Seventeen drugs showed promising antimicrobial activity against all MDRAb isolates and select agent surrogates; three of these compounds - all rifamycins - were found to be effective at preventing growth and preventing cellular respiration of MDRAb and select agent surrogate bacteria when evaluated in growth prevention assays, highlighting the potential for repurposing. CONCLUSION: We report the discovery of a class of known compounds whose repurposing may be useful in solving the current problem with MDRAb and may lead to the discovery of broad-spectrum antimicrobials.

In vivo selection of rifamycin-resistant Clostridium difficile during rifaximin therapy.

We report the selection of Clostridium difficile resistant to the rifamycin class of antibiotics in a patient within 32 h of receiving rifaximin for the treatment of recurrent C. difficile diarrhea. Resistance was associated with single nucleotide substitutions within rpoB.

Inhibition of translation by cytotrienin A--a member of the ansamycin family.

The ansamycins are a diverse and often physiologically active group of compounds that include geldanamycin and rifamycin, inhibitors of heat shock protein 90 and prokaryotic DNA-dependent RNA synthesis, respectively. Cytotrienin A is an ansamycin-type small molecule with potent antiproliferative and proapoptotic properties. Here, we report that this compound inhibits eukaryotic protein synthesis by targeting translation elongation and interfering with eukaryotic elongation factor 1A function. We also find that cytotrienin A prevents HUVEC tube formation and diminishes microvessel formation in the chorioallantoic membrane assay. These results provide a molecular understanding into cytotrienin A's previously reported properties as an anticancer apoptosis-inducing drug.

Clostridium difficile infection: update on emerging antibiotic treatment options and antibiotic resistance.

Clostridium difficile infection (CDI) is the most common cause of identifiable diarrhea in hospitalized patients. The incidence and severity of CDIs are increasing. The increased incidence and severity of the disease has sparked interest in the optimal treatment of CDI as well as the use of new therapies and drug discovery. Current treatment strategies are inadequate with decreased response rates to metronidazole, and high recurrence rates with the use of metronidazole and oral vancomycin. Although incidence rates continue to be low, in vitro resistance to antibiotics used for the treatment of CDI has been noted. Recently, important data has emerged on new anti-C. difficile antibiotics such as rifaximin, rifalazil, fidaxomicin, nitazoxanide, tigecycline and ramoplanin. The purpose of this review is to provide an update on the in vitro susceptibility and new antibiotic treatment options for CDI. This review will focus primarily on scientific studies published in the last 36 months in order to provide an up-to-date review on the topic.

New drugs and new regimens for the treatment of tuberculosis: review of the drug development pipeline and implications for national programmes.

PURPOSE OF REVIEW: The aim is to review briefly the problems related to treatment of drug-susceptible and drug-resistant tuberculosis (TB), describe recent advances in the development of new drugs and new regimens, and discuss implications for control programmes. RECENT FINDINGS: Encouraging advances in TB drug research and development have been made since the turn of the century, resulting in a large number of new products introduced into the global portfolio. SUMMARY: Currently, nine compounds at least have advanced to clinical development, including four existing drugs redeveloped for TB indication and five new chemical entities. Present clinical trials are testing new combinations of drugs for a shortened treatment of drug-susceptible TB (<6 months duration) or the safety and efficacy of new drugs in addition to an optimized background therapy for the treatment of multidrug-resistant TB. There are at least 34 compounds or projects in the discovery and preclinical stages, including eight compounds in preclinical development. This increasing development of single compounds underscores the needs for a novel approach to test for optimal drug combinations that would be proposed for treatment of TB in all its forms, and the necessary collaboration of pharmaceutical companies, academia, research institutions, donors, and regulatory authorities.

Rifaximin Redux: treatment of recurrent Clostridium difficile infections with rifaximin immediately post-vancomycin treatment.

We report our continued experience with rifaximin as a post-vancomycin treatment strategy in six patients with multiple recurrences of C. difficile infection (CDI). Four of the six patients (67%) had no further diarrhea episodes, but two patients failed shortly after or during the rifaximin treatment. C. difficile isolates from one of the two patients who failed treatment had an MIC of >256 microg/ml to rifampin. Serial therapy with vancomycin, followed by rifaximin remains an option for some patients with multiple CDI recurrences.

Moxifloxacin for the treatment of HIV-associated tuberculosis in patients with contraindications or intolerance to rifamycins.

Administration of rifampicin or rifabutin in the treatment of HIV-associated tuberculosis (TB) is made rather complex by the risk of drug-drug interactions with most antiretrovirals and/or for reasons of toxicity. While in selecting the appropriate concomitant regimens the priority usually goes to rifamycins with exclusion of interacting antiretrovirals, in some circumstances the former cannot be used and anti-TB rifamycin-free regimens must be administered. We describe here the clinical course of two patients with HIV-associated TB in whom the last generation fluorquinolone moxifloxacin (found to exert significant activity against Mycobacterium tuberculosis) successfully replaced rifamycins.

Current status of some antituberculosis drugs and the development of new antituberculous agents with special reference to their in vitro and in vivo antimicrobial activities.

Tuberculosis (TB) is a growing international health concern, since it is the leading infectious cause of death in the world today. In particular, the increasing prevalence of multidrug-resistant (MDR)-TB has greatly contributed to the increased difficulties in the control of TB. Because of the global health problems of TB, the increasing rate of MDR-TB and the high rate of a co-infection with HIV, the development of potent new anti-TB drugs without cross-resistance with known antimycobacterial agents is urgently needed. This article deals with the following areas. First, it briefly reviews some recent findings on the pharmacological status of fluoroquinolones and rifamycin derivatives. Second, it describes other types of new agents, such as oxazolidinones (linezolid, PNU-100480), nitroimidazoles (nitroimidazopyran PA-824, metronidazole), 2-pyridone, riminophenazines and diarylquinolines, which are being developed as anti-TB drugs. In addition, the future development of new antitubercular drugs is briefly discussed according to the potential pharmacological targets. New critical information on the whole genome of Mycobacterium tuberculosis (MTB) was recently elucidated and increasing knowledge on various mycobacterial virulence genes will promote the progression in the identification of genes that code for new drug targets. Using such findings on MTB genome, drug development using quantitative structure-activity relationship may be possible in the near future.