Comprehensive update of dalbavancin activity when tested against uncommonly isolated streptococci, Corynebacterium spp., Listeria monocytogenes, and Micrococcus spp. (1357 strains)

Dalbavancin is an investigational lipoglycopeptide having an extended serum elimination half-life allowing once-weekly dosing. Data from testing 1357 strains of uncommonly isolated species expand the dalbavancin spectrum details as follows (MIC50/90): β-haemolytic streptococcal serogroups C, F, and G (≤0.03/≤0.03 μg/mL), 7 viridans group of streptococci (≤0.03/≤0.03-0.06 μg/mL), 5 Corynebacterium spp. (0.06/0.12 μg/mL), Listeria monocytogenes (0.06/0.12 μg/mL), and Micrococcus spp. (≤0.03/≤0.03 μg/mL). Among all reported isolates, 99.8% of tested strains were inhibited at dalbavancin MIC values at ≤0.12 μg/mL. Dalbavancin remains very potent against rarer Gram-positive pathogens, using in vitro test experience with organisms cultured through 2011.

Viable screening targets related to the bacterial cell wall

The synthesis of the bacterial peptidoglycan has been recognized for over 50 years as fertile ground for antibacterial discovery. Initially, empirical screening of natural products for inhibition of bacterial growth detected many chemical classes of antibiotics whose specific mechanisms of action were eventually dissected and defined. Of the nontoxic antibiotics discovered, most were found to be inhibitors of either protein synthesis or cell wall synthesis, which led to more directed screening for inhibitors of these pathways. Directed screening and design programs for cell wall inhibitors have been undertaken since the 1960s. In that time it has become clear that, while certain steps and intermediates have yielded selective inhibitors and are established targets, other potential targets have not yielded inhibitors whose antibacterial activity is proven to be solely due to that inhibition. Why has this search been so problematic? Are the established targets still worth pursuing? This review will attempt to answer these and other questions and evaluate the viability of targets related to peptidoglycan synthesis.

Messenger functions of the bacterial cell wall-derived muropeptides

Bacterial muropeptides are soluble peptidoglycan structures central to recycling of the bacterial cell wall and messengers in diverse cell signaling events. Bacteria sense muropeptides as signals that antibiotics targeting cell-wall biosynthesis are present, and eukaryotes detect muropeptides during the innate immune response to bacterial infection. This review summarizes the roles of bacterial muropeptides as messengers, with a special emphasis on bacterial muropeptide structures and the relationship of structure to the biochemical events that the muropeptides elicit. Muropeptide sensing and recycling in both Gram-positive and Gram-negative bacteria are discussed, followed by muropeptide sensing by eukaryotes as a crucial event in the innate immune response of insects (via peptidoglycan-recognition proteins) and mammals (through Nod-like receptors) to bacterial invasion.

A carrier protein strategy yields the structure of dalbavancin

Many large natural product antibiotics act by specifically binding and sequestering target molecules found on bacterial cells. We have developed a new strategy to expedite the structural analysis of such antibiotic-target complexes, in which we covalently link the target molecules to carrier proteins, and then crystallize the entire carrier-target-antibiotic complex. Using native chemical ligation, we have linked the Lys-D-Ala-D-Ala binding epitope for glycopeptide antibiotics to three different carrier proteins. We show that recognition of this peptide by multiple antibiotics is not compromised by the presence of the carrier protein partner, and use this approach to determine the first-ever crystal structure for the new therapeutic dalbavancin. We also report the first crystal structure of an asymmetric ristocetin antibiotic dimer, as well as the structure of vancomycin bound to a carrier-target fusion. The dalbavancin structure reveals an antibiotic molecule that has closed around its binding partner; it also suggests mechanisms by which the drug can enhance its half-life by binding to serum proteins, and be targeted to bacterial membranes. Notably, the carrier protein approach is not limited to peptide ligands such as Lys-D-Ala-D-Ala, but is applicable to a diverse range of targets. This strategy is likely to yield structural insights that accelerate new therapeutic development.

MRSA new treatments on the horizon: current status

There is a choice of anti-MRSA antibiotic available with proven efficacy in the treatment of complicated skin and skin structure infection (cSSSI). Additional anti-MRSA antibiotics are in development, which have the potential to influence how such infections are managed. The emergence of resistance to current anti-MRSA agents, toxicity, and general lack of oral agents with proven efficacy for deep seated infection justify the development of new agents. However, there is a relative dearth of information specific to patients with orthopaedic-related infection. Combination therapy is often used in these patients, although there is a paucity of controlled trial data to support particular antibiotic combinations. As the choice of anti-MRSA agents increases, so does the need to identify which are best for the large variety of infections included in the group of cSSSIs. This is particular true for infections occurring in orthopaedic patients where poorly vascularised tissue, trauma or implanted prosthetic material, pose specific challenges.

Vancomycin tolerance in Gram-positive cocci

Vancomycin, a glycopeptide antimicrobial agent, represents the last line of defence against a wide range of multi-resistant Gram-positive pathogens such as enterococci, staphylococci and streptococci. However, vancomycin-resistant enterococci and staphylococci, along with vancomycin-tolerant clinical isolates, are compromising the therapeutic efficacy of vancomycin. It is conceivable that tolerance may emerge during prolonged vancomycin use. It has not been until recently, however, that the molecular basis of this tolerance began to be understood. Superoxide anions might be involved in the bactericidal activity of vancomycin in enterococci, and recent evidence suggests that the stringent response is partly responsible for vancomycin tolerance in Enterococcus faecalis. The mechanism of vancomycin tolerance in Staphylococcus aureus and Streptococcus pneumoniae is sometimes associated with a reduction of autolysin activity. Vancomycin tolerance in S. aureus and S. pneumoniae also appears to be somehow related with the two-component regulatory systems linked to cell envelope stress, although the precise molecular regulatory pathways remain poorly defined.

Actinoplanes teichomyceticus ATCC 31121 as a cell factory for producing teicoplanin

BACKGROUND

Teicoplanin is a glycopeptide antibiotic used clinically in Europe and in Japan for the treatment of multi-resistant Gram-positive infections. It is produced by fermenting Actinoplanes teichomyceticus. The pharmaceutically active principle is teicoplanin A2, a complex of compounds designated T-A2-1-A2-5 differing in the length and branching of the fatty acid moiety linked to the glucosamine residue on the heptapeptide scaffold. According to European and Japanese Pharmacopoeia, components of the drug must be reproduced in fixed amounts to be authorized for clinical use.

RESULTS

We report our studies on optimizing the fermentation process to produce teicoplanin A2 in A. teichomyceticus ATCC 31121. Robustness of the process was assessed on scales from a miniaturized deep-well microtiter system to flasks and 3-L bioreactor fermenters. The production of individual factors T-A2-1-A2-5 was modulated by adding suitable precursors to the cultivation medium. Specific production of T-A2-1, characterized by a linear C10:1 acyl moiety, is enhanced by adding methyl linoleate, trilinoleate, and crude oils such as corn and cottonseed oils. Accumulation of T-A2-3, characterized by a linear C10:0 acyl chain, is stimulated by adding methyl oleate, trioleate, and oils such as olive and lard oils. Percentages of T-A2-2, T-A2-4, and, T-A2-5 bearing the iso-C10:0, anteiso-C11:0, and iso-C11:0 acyl moieties, respectively, are significantly increased by adding precursor amino acids L-valine, L-isoleucine, and L-leucine. Along with the stimulatory effect on specific complex components, fatty acid esters, oils, and amino acids (with the exception of L-valine) inhibit total antibiotic productivity overall. By adding industrial oils to medium containing L-valine the total production is comparable, giving unusual complex compositions.

CONCLUSIONS

Since the cost and the quality of teicoplanin production depend mainly on the fermentation process, we developed a robust and scalable fermentation process by using an industrial medium in which a complex composition can be modulated by the combined addition of suitable precursors. This work was performed in the wild-type strain ATCC 31121, which has a clear genetic background. This is important for starting a rational improvement program and also helps to better control teicoplanin production during process and strain development.

Actinoplanes teichomyceticus ATCC 31121 as a cell factory for producing teicoplanin

Background

Teicoplanin is a glycopeptide antibiotic used clinically in Europe and in Japan for the treatment of multi-resistant Gram-positive infections. It is produced by fermenting Actinoplanes teichomyceticus. The pharmaceutically active principle is teicoplanin A₂, a complex of compounds designated T-A_2-1-A_2-5 differing in the length and branching of the fatty acid moiety linked to the glucosamine residue on the heptapeptide scaffold. According to European and Japanese Pharmacopoeia, components of the drug must be reproduced in fixed amounts to be authorized for clinical use.

Results

We report our studies on optimizing the fermentation process to produce teicoplanin A₂ in A. teichomyceticus ATCC 31121. Robustness of the process was assessed on scales from a miniaturized deep-well microtiter system to flasks and 3-L bioreactor fermenters. The production of individual factors T-A_2-1-A_2-5 was modulated by adding suitable precursors to the cultivation medium. Specific production of T-A_2-1, characterized by a linear C10:1 acyl moiety, is enhanced by adding methyl linoleate, trilinoleate, and crude oils such as corn and cottonseed oils. Accumulation of T-A_2-3, characterized by a linear C10:0 acyl chain, is stimulated by adding methyl oleate, trioleate, and oils such as olive and lard oils. Percentages of T-A_2-2, T-A_2-4, and, T-A_2-5 bearing the iso-C10:0, anteiso-C11:0, and iso-C11:0 acyl moieties, respectively, are significantly increased by adding precursor amino acids L-valine, L-isoleucine, and L-leucine. Along with the stimulatory effect on specific complex components, fatty acid esters, oils, and amino acids (with the exception of L-valine) inhibit total antibiotic productivity overall. By adding industrial oils to medium containing L-valine the total production is comparable, giving unusual complex compositions.

Conclusions

Since the cost and the quality of teicoplanin production depend mainly on the fermentation process, we developed a robust and scalable fermentation process by using an industrial medium in which a complex composition can be modulated by the combined addition of suitable precursors. This work was performed in the wild-type strain ATCC 31121, which has a clear genetic background. This is important for starting a rational improvement program and also helps to better control teicoplanin production during process and strain development.

Inhibition of hepatitis C virus replication by semi-synthetic derivatives of glycopeptide antibiotics

Objectives

Some semi-synthetic derivatives of glycopeptide antibiotics have been shown to exert in vitro antiviral activity against HIV and coronaviruses. Here we report and characterize the in vitro anti-hepatitis C virus (HCV) activity of several semi-synthetic derivatives of teicoplanin aglycone.

Methods

Anti-HCV activity was analysed in: (i) three different subgenomic HCV replicon systems using a luciferase or quantitative RT–PCR (qRT–PCR) assay; and (ii) an infectious HCV cell culture system by means of qRT–PCR and immunofluorescence assays.

Results

Several teicoplanin aglycone derivatives elicited selective anti-HCV activity in replicons as well as infectious cell culture systems, with LCTA-949 being the most potent derivative. LCTA-949 proved, in contrast to several directly acting antivirals for HCV, efficient in clearing cells of their replicons. When LCTA-949 was combined with HCV protease or polymerase inhibitors an overall additive effect was observed. Likewise, LCTA-949 was equipotent against wild-type replicons as well as against replicons resistant to polymerase and protease inhibitors. Following up to 4 months of selective pressure, no drug-resistant replicons were selected. When combined with the HCV NS3 protease inhibitor VX-950, LCTA-949 prevented the development of VX-950-resistant variants.

Conclusions

Semi-synthetic derivatives of teicoplanin aglycone constitute a novel class of HCV replication inhibitors that are not cross-resistant with various HCV protease and polymerase inhibitors and in particular are potent in clearing hepatoma cells of their replicons. This class of molecules also provides a good tool to obtain novel insights into the replication cycle of HCV and into cellular factors/processes that are crucial for viral replication.

Targeting bacterial membrane function: an underexploited mechanism for treating persistent infections

Persistent infections involving slow-growing or non-growing bacteria are hard to treat with antibiotics that target biosynthetic processes in growing cells. Consequently, there is a need for antimicrobials that can treat infections containing dormant bacteria. In this Review, we discuss the emerging concept that disrupting the bacterial membrane bilayer or proteins that are integral to membrane function (including membrane potential and energy metabolism) in dormant bacteria is a strategy for treating persistent infections. The clinical applicability of these approaches is exemplified by the efficacy of lipoglycopeptides that damage bacterial membranes and of the diarylquinoline TMC207, which inhibits membrane-bound ATP synthase. Despite some drawbacks, membrane-active agents form an important new means of eradicating recalcitrant, non-growing bacteria.