Investigational new drugs for the treatment of resistant pneumococcal infections

Antimicrobial resistance: more than 70 years of war between humans and bacteria

Development of antibiotic resistance in bacteria is one of the major issues in the present world and one of the greatest threats faced by mankind. Resistance is spread through both vertical gene transfer (parent to offspring) as well as by horizontal gene transfer like transformation, transduction and conjugation. The main mechanisms of resistance are limiting uptake of a drug, modification of a drug target, inactivation of a drug, and active efflux of a drug. The highest quantities of antibiotic concentrations are usually found in areas with strong anthropogenic pressures, for example medical source (e.g., hospitals) effluents, pharmaceutical industries, wastewater influents, soils treated with manure, animal husbandry and aquaculture (where antibiotics are generally used as in-feed preparations). Hence, the strong selective pressure applied by antimicrobial use has forced microorganisms to evolve for survival. The guts of animals and humans, wastewater treatment plants, hospital and community effluents, animal husbandry and aquaculture runoffs have been designated as "hotspots for AMR genes" because the high density of bacteria, phages, and plasmids in these settings allows significant genetic exchange and recombination. Evidence from the literature suggests that the knowledge of antibiotic resistance in the population is still scarce. Tackling antimicrobial resistance requires a wide range of strategies, for example, more research in antibiotic production, the need of educating patients and the general public, as well as developing alternatives to antibiotics (briefly discussed in the conclusions of this article).

Antibiotic Resistance Mechanisms in Bacteria: Relationships Between Resistance Determinants of Antibiotic Producers, Environmental Bacteria, and Clinical Pathogens

Emergence of antibiotic resistant pathogenic bacteria poses a serious public health challenge worldwide. However, antibiotic resistance genes are not confined to the clinic; instead they are widely prevalent in different bacterial populations in the environment. Therefore, to understand development of antibiotic resistance in pathogens, we need to consider important reservoirs of resistance genes, which may include determinants that confer self-resistance in antibiotic producing soil bacteria and genes encoding intrinsic resistance mechanisms present in all or most non-producer environmental bacteria. While the presence of resistance determinants in soil and environmental bacteria does not pose a threat to human health, their mobilization to new hosts and their expression under different contexts, for example their transfer to plasmids and integrons in pathogenic bacteria, can translate into a problem of huge proportions, as discussed in this review. Selective pressure brought about by human activities further results in enrichment of such determinants in bacterial populations. Thus, there is an urgent need to understand distribution of resistance determinants in bacterial populations, elucidate resistance mechanisms, and determine environmental factors that promote their dissemination. This comprehensive review describes the major known self-resistance mechanisms found in producer soil bacteria of the genus Streptomyces and explores the relationships between resistance determinants found in producer soil bacteria, non-producer environmental bacteria, and clinical isolates. Specific examples highlighting potential pathways by which pathogenic clinical isolates might acquire these resistance determinants from soil and environmental bacteria are also discussed. Overall, this article provides a conceptual framework for understanding the complexity of the problem of emergence of antibiotic resistance in the clinic. Availability of such knowledge will allow researchers to build models for dissemination of resistance genes and for developing interventions to prevent recruitment of additional or novel genes into pathogens.

Antibiotic Resistance Mechanisms in Bacteria: Relationships Between Resistance Determinants of Antibiotic Producers, Environmental Bacteria, and Clinical Pathogens

Emergence of antibiotic resistant pathogenic bacteria poses a serious public health challenge worldwide. However, antibiotic resistance genes are not confined to the clinic; instead they are widely prevalent in different bacterial populations in the environment. Therefore, to understand development of antibiotic resistance in pathogens, we need to consider important reservoirs of resistance genes, which may include determinants that confer self-resistance in antibiotic producing soil bacteria and genes encoding intrinsic resistance mechanisms present in all or most non-producer environmental bacteria. While the presence of resistance determinants in soil and environmental bacteria does not pose a threat to human health, their mobilization to new hosts and their expression under different contexts, for example their transfer to plasmids and integrons in pathogenic bacteria, can translate into a problem of huge proportions, as discussed in this review. Selective pressure brought about by human activities further results in enrichment of such determinants in bacterial populations. Thus, there is an urgent need to understand distribution of resistance determinants in bacterial populations, elucidate resistance mechanisms, and determine environmental factors that promote their dissemination. This comprehensive review describes the major known self-resistance mechanisms found in producer soil bacteria of the genus Streptomyces and explores the relationships between resistance determinants found in producer soil bacteria, non-producer environmental bacteria, and clinical isolates. Specific examples highlighting potential pathways by which pathogenic clinical isolates might acquire these resistance determinants from soil and environmental bacteria are also discussed. Overall, this article provides a conceptual framework for understanding the complexity of the problem of emergence of antibiotic resistance in the clinic. Availability of such knowledge will allow researchers to build models for dissemination of resistance genes and for developing interventions to prevent recruitment of additional or novel genes into pathogens.

In Vitro Activity of Sitafloxacin and Additional Newer Generation Fluoroquinolones Against Ciprofloxacin-Resistant Neisseria gonorrhoeae Isolates

Emergence of antimicrobial resistance in Neisseria gonorrhoeae is a major public health concern globally, and new antimicrobials for treatment of gonorrhea are imperative. In this study, the in vitro activity of sitafloxacin, a fluoroquinolone mainly used for respiratory tract or urogenital infections in Japan, and additional newer generation fluoroquinolones were determined against ciprofloxacin-resistant N. gonorrhoeae isolates. Minimum inhibitory concentrations (MICs) of ciprofloxacin, levofloxacin, moxifloxacin, sitafloxacin, pazufloxacin, and tosufloxacin against 47 N. gonorrhoeae isolates cultured in 2009 in Japan were determined by agar dilution method. The quinolone resistance-determining region (QRDR) of gyrA and parC was sequenced. The in vitro potency of sitafloxacin was substantially higher compared with all other tested fluoroquinolones. The MICs of sitafloxacin ranged from 0.03 to 0.5 mg/L for 35 ciprofloxacin-resistant N. gonorrhoeae isolates (ciprofloxacin MICs from 2 to 32 mg/L). No identified mutations in GyrA and ParC QRDR resulted in higher sitafloxacin MIC than 0.5 mg/L. Sitafloxacin had a high activity against N. gonorrhoeae isolates, including strains with mutations in DNA gyrase and topoisomerase IV, resulting in high-level resistance to ciprofloxacin and all other newer generation fluoroquinolones examined. However, it was still to a lower extent affected by GyrA and ParC QRDR mutations resulting in sitafloxacin MICs of up to 0.5 mg/L. This indicates that sitafloxacin should not be considered for empirical first-line monotherapy of gonorrhea. However, sitafloxacin could be valuable in a dual antimicrobial therapy and for cases with ceftriaxone resistance or allergy.

Ceftobiprole for the treatment of pneumonia: a European perspective

Ceftobiprole, a new broad spectrum, parenteral cephalosporin, exhibits potent in vitro activity against a number of Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus and penicillin-resistant Streptococcus pneumoniae, and Gram-negative pathogens associated with hospital-acquired pneumonia (HAP) and community-acquired pneumonia (CAP). Ceftobiprole has demonstrated noninferiority in two large-scale pivotal studies comparing it to ceftriaxone with or without linezolid in CAP, with clinical cure rates 86.6% versus 87.4%, or ceftazidime in HAP, with clinical cure rates of 77% versus 76%, respectively. However, ceftobiprole was inferior in the subgroup of patients undergoing mechanical ventilation. Ceftobiprole has so far demonstrated a good safety profile in preliminary studies, with similar tolerability to comparators. The most commonly observed adverse events of ceftobiprole included headache and gastrointestinal upset. It is the first cephalosporin monotherapy approved in the EU for the treatment of both CAP and HAP (excluding ventilator-associated pneumonia).

Simultaneous and Direct Determination of Vancomycin and Cephalexin in Human Plasma by Using HPLC-DAD Coupled with Second-Order Calibration Algorithms

A simple, rapid, and sensitive method for the simultaneous determination of vancomycin and cephalexin in human plasma was developed by using HPLC-DAD with second-order calibration algorithms. Instead of a completely chromatographic separation, mathematical separation was performed by using two trilinear decomposition algorithms, that is, PARAFAC-alternative least squares (PARAFAC-ALSs) and self-weight-alternative-trilinear-decomposition- (SWATLD-) coupled high-performance liquid chromatography with DAD detection. The average recoveries attained from PARAFAC-ALS and SWATLD with the factor number of 4 (N = 4) were 101 ± 5% and 102 ± 4% for vancomycin, and 96 ± 3% and 97 ± 3% for cephalexininde in real human samples, respectively. The statistical comparison between PARAFAC-ALS and SWATLD is demonstrated to be similar. The results indicated that the combination of HPLC-DAD detection with second-order calibration algorithms is a powerful tool to quantify the analytes of interest from overlapped chromatographic profiles for complex analysis of drugs in plasma.

Origins of bacterial diversity through horizontal genetic transfer and adaptation to new ecological niches

Horizontal genetic transfer (HGT) has played an important role in bacterial evolution at least since the origins of the bacterial divisions, and HGT still facilitates the origins of bacterial diversity, including diversity based on antibiotic resistance. Adaptive HGT is aided by unique features of genetic exchange in bacteria such as the promiscuity of genetic exchange and the shortness of segments transferred. Genetic exchange rates are limited by the genetic and ecological similarity of organisms. Adaptive transfer of genes is limited to those that can be transferred as a functional unit, provide a niche-transcending adaptation, and are compatible with the architecture and physiology of other organisms. Horizontally transferred adaptations may bring about fitness costs, and natural selection may ameliorate these costs. The origins of ecological diversity can be analyzed by comparing the genomes of recently divergent, ecologically distinct populations, which can be discovered as sequence clusters. Such genome comparisons demonstrate the importance of HGT in ecological diversification. Newly divergent populations cannot be discovered as sequence clusters when their ecological differences are coded by plasmids, as is often the case for antibiotic resistance; the discovery of such populations requires a screen for plasmid-coded functions. This paper reviews the features of bacterial genetics that allow HGT, the similarities between organisms that foster HGT between them, the limits to the kinds of adaptations that can be transferred, and amelioration of fitness costs associated with HGT; the paper also reviews approaches to discover the origins of new, ecologically distinct bacterial populations and the role that HGT plays in their founding.

What antimicrobial resistance has taught us about horizontal gene transfer

Horizontal gene transfer (HGT) has been responsible for the dissemination of numerous antimicrobial-resistance determinants throughout diverse bacterial species. The rapid and broad dissemination of resistance determinants by HGT, and subsequent selection for resistance imposed by the use of antimicrobials, threatens to undermine the usefulness of antimicrobials. However, vigilant surveillance of the emerging antimicrobial resistance in clinical settings and subsequent studies of resistant isolates create a powerful system for studying HGT and detecting rare events. Two of the most closely monitored phenotypes are resistance to beta-lactams and resistance to fluoroquinolones. Studies of resistance to these antimicrobials have revealed that (1) transformation occurs between different species of bacteria including some recipient species that were not previously known to be competent for natural transformation; (2) transduction may be playing an important role in generating novel methicillin-resistant Staphylococcus aureus (MRSA) strains, although the details of transferring the SCCmec element are not yet fully understood; (3) Resistance genes are probably moving to plasmids from chromosomes more rapidly than in the past; and (4) Resistance genes are aggregating upon plasmids. The linkage of numerous resistance genes on individual plasmids may underlie the persistence of resistance to specific antimicrobials even when use of those antimicrobials is discontinued. Further studies of HGT and methods for controlling HGT may be necessary to maintain the usefulness of antimicrobials.

Reduction of in-source collision-induced dissociation and thermolysis of sulopenem prodrugs for quantitative liquid chromatography/electrospray ionization mass spectrometric analysis by promoting sodium adduct formation

Six chromatographically resolved sulopenem prodrugs were monitored for their potential to undergo both in-source collision-induced dissociation (CID) and thermolysis. Initial Q1 scans for each prodrug revealed the formation of intense [Prodrug2 + H]+, [Prodrug2 + Na]+, [Prodrug + Na]+, and [Sulopenem + Na]+ ions. Non-adduct-associated sulopenem ([Sulopenem + H]+) along with several additional lower mass ions were also observed. Product ion scans of [Prodrug3 + Na]+ showed the retention of the sodium adduct in the collision cell continuing down to opening of the beta-lactam ring. In-source CID and temperature experiments were conducted under chromatographic conditions while monitoring several of the latter ion transitions (i.e., adducts, dimers and degradants/fragments) for a given prodrug. The resulting ion profiles indicated the regions of greatest stability for temperature and declustering potential (DP) that provided the highest signal intensity for each prodrug and minimized in-source degradation. The heightened stability of adduct ions, relative to their appropriate counterpart (i.e., dimer to dimer adduct and prodrug to prodrug adduct ions), was observed under elevated temperature and DP conditions. The addition of 100 microM sodium to the mobile phase further enhanced the formation of these more stable adduct ions, yielding an optimal [Prodrug + Na]+ ion signal at temperatures from 400 to 600 degrees C. A clinical liquid chromatography/tandem mass spectrometry (LC/MS/MS) assay for sulopenem prodrug PF-04064900 in buffered whole blood was successfully validated using sodium-fortified mobile phase and the [PF-04064900 + Na]+ ion for quantitation. A conservative five-fold increase in sensitivity from previously validated preclinical assays using the [PF-04064900 + H]+ precursor ion was achieved.

Multidrug-resistant Streptococcus pneumoniae infections: current and future therapeutic options

Antibacterial resistance in Streptococcus pneumoniae is increasing worldwide, affecting principally beta-lactams and macrolides (prevalence ranging between approximately 1% and 90% depending on the geographical area). Fluoroquinolone resistance has also started to emerge in countries with high level of antibacterial resistance and consumption. Of more concern, 40% of pneumococci display multi-drug resistant phenotypes, again with highly variable prevalence among countries. Infections caused by resistant pneumococci can still be treated using first-line antibacterials (beta-lactams), provided the dosage is optimised to cover less susceptible strains. Macrolides can no longer be used as monotherapy, but are combined with beta-lactams to cover intracellular bacteria. Ketolides could be an alternative, but toxicity issues have recently restricted the use of telithromycin in the US. The so-called respiratory fluoroquinolones offer the advantages of easy administration and a spectrum covering extracellular and intracellular pathogens. However, their broad spectrum raises questions regarding the global risk of resistance selection and their safety profile is far from optimal for wide use in the community. For multi-drug resistant pneumococci, ketolides and fluoroquinolones could be considered. A large number of drugs with activity against these multi-drug resistant strains (cephalosporins, carbapenems, glycopeptides, lipopeptides, ketolides, lincosamides, oxazolidinones, glycylcyclines, quinolones, deformylase inhibitors) are currently in development. Most of them are only new derivatives in existing classes, with improved intrinsic activity or lower susceptibility to resistance mechanisms. Except for the new fluoroquinolones, these agents are also primarily targeted towards methicillin-resistant Staphylococcus aureus infections; therefore, demonstration of their clinical efficacy in the management of pneumococcal infections is still awaited.

A DFT conformational analysis and VCD study on methyl tetrahydrofuran-2-carboxylate

DFT calculations were performed on (S)-methyl tetrahydrofuran-2-carboxylate to facilitate the interpretation of IR and VCD spectra. The potential energy surface could not be described unambiguously using the 6-31G* basis set in combination with different density functionals including B1LYP, B3LYP, B3P86, B3PW91, B98, BHandH, BHandHLYP, MPW1PW91 and PBE1PBE. In contrast, a uniform conformational picture could be found using the cc-pVTZ basis set. Using this large basis set and the collection of nine functionals from above, the dipole and rotational strengths were calculated, and compared to experimental values which were extracted from the experimental IR and VCD spectra for (+)-(S)-methyl tetrahydrofuran-2-carboxylate. A detailed analysis on the agreement between experiment and simulated spectra was performed by assigning the experimental bands based on the harmonic fundamentals obtained for all functionals except BHandH, which performs badly over the whole line. Assessing the dipole strengths, all tested functionals perform equally well. For the rotational strengths, differences can be observed: B3LYP, B1LYP and B98 give the highest correlation with experiment, while PBE1PBE gives the lowest correlation. Comparable conclusions are obtained using a neighborhood similarity measure.

In vitro bactericidal activity of the antiprotozoal drug miltefosine against Streptococcus pneumoniae and other pathogenic streptococci

Miltefosine (hexadecylphosphocholine), the first oral drug against visceral leishmaniasis, triggered pneumococcal autolysis at concentrations higher than 2.5 microM. Bactericidal activity was also observed in cultures of other streptococci, although these failed to undergo lysis. The autolysis elicited by miltefosine can be attributed to triggering of the pneumococcal autolysin LytA.

Intermolecular Association of Tetrahydrofuran-2-carboxylic Acid in Solution: A Vibrational Circular Dichroism Study

Carboxylic acids are known for their strong intermolecular associations. With chiral carboxylic acids, this behavior can be studied using vibrational circular dichroism (VCD). Tetrahydrofuran-2-carboxylic acid 1, a chiral building block for beta-lactam antibiotics, is studied by emphasizing the effect of the dimerization. Experimental results indicate that for solutions of 1 in CDCl3 and CS2, a complex equilibrium exists between the monomers and dimers. B3LYP/aug-cc-pVTZ calculations are performed on both monomer and dimer structures. To simulate IR and VCD spectra, populations for monomer and dimers were approximated using a semiquantitative model. A good agreement between experimental and simulated spectra is obtained by taking into account both the monomeric and the dimeric structures, weighted using the experimentally determined populations.

World Wide Web resources on antimicrobial resistance

Advances of modern technology, including the development of the Internet and the World Wide Web, have given clinicians and researches the opportunity to have immediate access to continuously updated information in various scientific fields. We compiled a list of World Wide Web resources of data from surveillance studies on antimicrobial resistance that may be useful to practitioners--especially infectious diseases specialists--as well as to scientists with a research interest in the field of antimicrobial resistance.