What if there were no new antibiotics? A look at alternatives

Quinoline-2-one derivatives as promising antibacterial agents against multidrug-resistant Gram-positive bacterial strains

This study describes the discovery of a variety of quinoline2-one derivatives with significant antibacterial action vs a spectrum of multidrug-resistant Gram-positive bacterial strains, especially methicillin-resistant Staphylococcus aureus (MRSA). Compounds 6c, 6l, and 6o exhibited significant antibacterial activity versus the Gram-positive bacterial pathogens evaluated. In comparison to the reference daptomycin, compound 6c demonstrated the most effective activity among the assessed derivatives, with MIC concentrations of 0.75 μg/mL versus MRSA and VRE and 2.50 μg/mL against MRSE. We also reported on these compounds' biofilm and dihydrofolate reductase inhibitory activities. Compound 6c showed the greatest antibiofilm action in a dose-dependent way and a substantial decrease of biofilm development in the MRSA ACL51 strain at concentrations of 0.5, 0.25, and 0.12 MIC, with reductions of 79%, 55%, and 38%, consecutively, whereas the corresponding values for vancomycin were 20%, 12%, and 9%. These findings imply that these quinoline compounds could be used to develop a new category of antibiotic representatives to prevent Gram-positive drug-resistant bacterial strains.

Recent Approaches for Downplaying Antibiotic Resistance: Molecular Mechanisms

Antimicrobial resistance (AMR) is a ubiquitous public health menace. AMR emergence causes complications in treating infections contributing to an upsurge in the mortality rate. The epidemic of AMR in sync with a high utilization rate of antimicrobial drugs signifies an alarming situation for the fleet recovery of both animals and humans. The emergence of resistant species calls for new treatments and therapeutics. Current records propose that health drug dependency, veterinary medicine, agricultural application, and vaccination reluctance are the primary etymology of AMR gene emergence and spread. Recently, several encouraging avenues have been presented to contest resistance, such as antivirulent therapy, passive immunization, antimicrobial peptides, vaccines, phage therapy, and botanical and liposomal nanoparticles. Most of these therapies are used as cutting-edge methodologies to downplay antibacterial drugs to subdue the resistance pressure, which is a featured motive of discussion in this review article. AMR can fade away through the potential use of current cutting-edge therapeutics, advancement in antimicrobial susceptibility testing, new diagnostic testing, prompt clinical response, and probing of new pharmacodynamic properties of antimicrobials. It also needs to promote future research on contemporary methods to maintain host homeostasis after infections caused by AMR. Referable to the microbial ability to break resistance, there is a great ultimatum for using not only appropriate and advanced antimicrobial drugs but also other neoteric diverse cutting-edge therapeutics.

Attenuating the virulence of the resistant superbug Staphylococcus aureus bacteria isolated from neonatal sepsis by ascorbic acid, dexamethasone, and sodium bicarbonate

Background

Infections affecting neonates caused by Staphylococcus aureus are widespread in healthcare facilities; hence, novel strategies are needed to fight this pathogen. In this study, we aimed to investigate the effectiveness of the FDA-approved medications ascorbic acid, dexamethasone, and sodium bicarbonate to reduce the virulence of the resistant Staphylococcus aureus bacteria that causes neonatal sepsis and seek out suitable alternatives to the problem of multi-drug resistance.

Methods

Tested drugs were assessed phenotypically and genotypically for their effects on virulence factors and virulence-encoding genes in Staphylococcus aureus. Furthermore, drugs were tested in vivo for their ability to reduce Staphylococcus aureus pathogenesis.

Results

Sub-inhibitory concentrations (1/8 MIC) of ascorbic acid, dexamethasone, and sodium bicarbonate reduced the production of Staphylococcus aureus virulence factors, including biofilm formation, staphyloxanthin, proteases, and hemolysin production, as well as resistance to oxidative stress. At the molecular level, qRT-PCR was used to assess the relative expression levels of crtM, sigB, sarA, agrA, hla, fnbA, and icaA genes regulating virulence factors production and showed a significant reduction in the relative expression levels of all the tested genes.

Conclusions

The current findings reveal that ascorbic acid, dexamethasone, and sodium bicarbonate have strong anti-virulence effects against Staphylococcus aureus. Thus, suggesting that they might be used as adjuvants to treat infections caused by Staphylococcus aureus in combination with conventional antimicrobials or as alternative therapies.

Discovery, synthesis, and optimization of teixobactin, a novel antibiotic without detectable bacterial resistance

Discovering new antibiotics with novel chemical scaffolds and antibacterial mechanisms presents a challenge for medicinal scientists worldwide as the ever-increasing bacterial resistance poses a serious threat to human health. A new cyclic peptide-based antibiotic termed teixobactin was discovered from a screen of uncultured soil bacteria through iChip technology in 2015. Teixobactin exhibits excellent antibacterial activity against all the tested gram-positive pathogens and Mycobacterium tuberculosis, including drug-resistant strains. Given that teixobactin targets the highly conserved lipid II and lipid III, which induces the simultaneous inhibition of both peptidoglycan and teichoic acid synthesis, the emergence of resistance is considered to be rather difficult. The novel structure, potent antibacterial activity, and highly conservative targets make teixobactin a promising lead compound for further antibiotic development. This review provides a comprehensive treatise on the advances of teixobactin in the areas of discovery processes, antibacterial activity, mechanisms of action, chemical synthesis, and structural optimizations. The synthetic methods for the key building block l-allo-End, natural teixobactin, representative teixobactin analogues, as well as the structure-activity relationship studies will be highlighted and discussed in details. Finally, some insights into new trends for the generation of novel teixobactin analogues and tips for future work and directions will be commented.

Bacteriophages as an Alternative Method for Control of Zoonotic and Foodborne Pathogens

The global increase in multidrug-resistant infections caused by various pathogens has raised concerns in human and veterinary medicine. This has renewed interest in the development of alternative methods to antibiotics, including the use of bacteriophages for controlling bacterial infections. The aim of this review is to present potential uses of bacteriophages as an alternative to antibiotics in the control of bacterial infections caused by multidrug-resistant bacteria posing a risk to humans, with particular emphasis on foodborne and zoonotic pathogens. A varied therapeutic and immunomodulatory (activation or suppression) effect of bacteriophages on humoral and cellular immune response mechanisms has been demonstrated. The antibiotic resistance crisis caused by global antimicrobial resistance among bacteria creates a compelling need for alternative safe and selectively effective antibacterial agents. Bacteriophages have many properties indicating their potential suitability as therapeutic and/or prophylactic agents. In many cases, bacteriophages can also be used in food quality control against microorganisms such as Salmonella, Escherichia coli, Listeria, Campylobacter and others. Future research will provide potential alternative solutions using bacteriophages to treat infections caused by multidrug-resistant bacteria.

The Case against Antibiotics and for Anti-Virulence Therapeutics

Although antibiotics have been indispensable in the advancement of modern medicine, there are downsides to their use. Growing resistance to broad-spectrum antibiotics is leading to an epidemic of infections untreatable by first-line therapies. Resistance is exacerbated by antibiotics used as growth factors in livestock, over-prescribing by doctors, and poor treatment adherence by patients. This generates populations of resistant bacteria that can then spread resistance genes horizontally to other bacterial species, including commensals. Furthermore, even when antibiotics are used appropriately, they harm commensal bacteria leading to increased secondary infection risk. Effective antibiotic treatment can induce bacterial survival tactics, such as toxin release and increasing resistance gene transfer. These problems highlight the need for new approaches to treating bacterial infection. Current solutions include combination therapies, narrow-spectrum therapeutics, and antibiotic stewardship programs. These mediate the issues but do not address their root cause. One emerging solution to these problems is anti-virulence treatment: preventing bacterial pathogenesis instead of using bactericidal agents. In this review, we discuss select examples of potential anti-virulence targets and strategies that could be developed into bacterial infection treatments: the bacterial type III secretion system, quorum sensing, and liposomes.

Eradication of Intracellular Salmonella Typhimurium by Polyplexes of Acid-Transforming Chitosan and Fragment DNA

Antibiotics are highly successful against microbial infections. However, current challenges include rising antibiotic resistance rates and limited efficacy against intracellular pathogens. A novel form of a nanomaterial-based antimicrobial agent is investigated for efficient treatment of an intracellular Salmonella enterica sv Typhimurium infection. A known antimicrobial polysaccharide, chitosan, is engineered to be readily soluble under neutral aqueous conditions for systemic administration. The modified biologic, named acid-transforming chitosan (ATC), transforms into an insoluble, antimicrobial compound in the mildly acidic intracellular compartment. In cell culture experiments, ATC is confirmed to have antimicrobial activity against intracellular S. Typhimurium in a concentration- and pH-dependent manner, without affecting the host cells, RAW264.7 macrophages. For improved cellular uptake and pharmacokinetic/pharmacodynamic properties, ATC is further complexed with fragment DNA (fDNA), to form nano-sized spherical polyplexes. The resulting ATC/fDNA polyplexes efficiently eradicated S. Typhimurium from RAW264.7 macrophages. ATC/fDNA polyplexes may bind with microbial wall and membrane components. Consistent with this expectation, transposon insertion sequencing of a complex random mutant S. Typhimurium library incubated with ATC does not reveal specific genomic target regions of the antimicrobial. This study demonstrates the utility of a molecularly engineered nanomaterial as an efficient and safe antimicrobial agent, particularly against an intracellular pathogen.

Alternatives to antibiotics in an era of difficult-to-treat resistance: new insights

Introduction: The rise of antibiotic resistance, the limited efficacy and the adverse events associated with antibiotics have urged the development of alternative measures to treat bacterial infections. Novel therapies which are pathogen specific and are safer to the healthy microbiome are being developed. Areas covered: This manuscript provides a compact overview of the feasibility and clinical impact of the latest novel therapies, with a focus on monoclonal antibodies (mAbs), vaccines, stem cells, bacteriophages, and liposomes. This is a follow-up of a previous manuscript (doi: 10.1080/17512433.2016.1241141); a database search (PubMed, EMBASE, Cochrane) was used to identify recently published literature (from January 2016) which was not covered in the previous publication. Expert opinion: Among non-traditional agents, monoclonal antibodies have not been as successful as in other therapeutic areas. In particular many are developed to prevent hospital-acquired infections caused by S. aureus or P. aeruginosa and, so far, results have been overall disappointing. Stem cells and bacteriophages still have a long way to go. Vaccines are always desirable to prevent infections but again there is a lack of confirmatory results. Broad spectrum liposomes have shown promising results in treating severely infected patients and could be game changers in patient management.

CAL02, a novel antitoxin liposomal agent, in severe pneumococcal pneumonia: a first-in-human, double-blind, placebo-controlled, randomised trial

BACKGROUND

Severe community-acquired pneumonia caused by Streptococcus pneumoniae is associated with high morbidity and mortality rates. CAL02, a novel antitoxin agent with an unprecedented mode of action, consists of liposomes that capture bacterial toxins known to dysregulate inflammation, cause organ damage, and impede immune defence. We aimed to assess the safety of CAL02 as an add-on therapy to antibiotics.

METHODS

This randomised, double-blind, multicentre, placebo-controlled trial was done in ten intensive care units (ICUs) in France and Belgium (but only six units enrolled patients), in patients with severe community-acquired pneumococcal pneumonia who required ICU admission and had been identified as being infected with S pneumoniae. We randomly assigned participants in two stages-the first stage randomly assigned six patients (1:1) to either low-dose CAL02 or placebo, and the second stage randomly assigned 18 patients (14:4) to either high-dose CAL02 or placebo, and stratified in four blocks (4:1, 4:1, 3:1, and 3:1), in addition to standard of care. Block randomisation was done with a computer-generated random number list. Participants, investigators, other site study personnel, the sponsor, and the sponsor's designees involved in study management and monitoring were masked to the randomisation list and treatment assignment. Patients were treated with low-dose (4 mg/kg) or high-dose (16 mg/kg) CAL02 or placebo (saline), in addition to standard antibiotic therapy. Two intravenous doses of study treatment were infused, with a 24 h interval, at a concentration of 10 mg/mL, stepwise, over a maximum of 2 h on days 1 and 2. The primary objective of the study was to assess the safety and tolerability of low-dose and high-dose CAL02 in patients with severe community-acquired pneumonia treated with standard antibiotic therapy, and the primary analysis was done on the safety population (all patients who received at least one dose of the study treatment). Efficacy was a secondary outcome. This trial is registered with ClinicalTrials.gov, number NCT02583373.

FINDINGS

Between March 21, 2016, and Jan 13, 2018, we screened 280 patients with community-acquired pneumonia. 19 patients were enrolled and randomly assigned, resulting in 13 patients in the CAL02 groups (three assigned to low-dose CAL02 and ten assigned to high-dose CAL02) and six in the placebo group. One patient randomly assigned to placebo was allocated to the wrong treatment group and received high-dose CAL02 instead of placebo. Thus, 14 patients received CAL02 (three received low-dose CAL02 and 11 received high-dose CAL02) and five patients received placebo, constituting the safety population. At baseline, the mean APACHE II score for the total study population was 21·5 (SD 4·9; 95% CI 19·3-23·7) and 11 (58%) of 19 patients had septic shock. Adverse events occurred in 12 (86%) of 14 patients in the CAL02 treatment groups combined and all five (100%) patients in the placebo group. Serious adverse events occurred in four (29%) of 14 patients in the CAL02 treatment groups combined and two (40%) of five patients in the placebo group. One non-serious adverse event (mild increase in triglycerides) in a patient in the high-dose CAL02 group was reported as related to study drug. However, analysis of the changes in triglyceride levels in the CAL02 groups compared with the placebo group revealed no correlation with administration of CAL02. No adverse events were linked to local tolerability events. All patients, apart from one who died in the low CAL02 group (death not related to the study drug) achieved clinical cure at the test of cure visit between days 15 and 22. The sequential organ failure assessment score decreased by mean 65·0% (95% CI 50·7-79·4) in the combined CAL02 groups compared with 29·2% (12·8-45·5) in the placebo group between baseline and day 8.

INTERPRETATION

The nature of adverse events was consistent with the profile of the study population and CAL02 showed a promising safety profile and tolerability. However, the difference between high-dose and low-dose CAL02 could not be assessed in this study. Efficacy was in line with the expected benefits of neutralising toxins. The results of this study support further clinical development of CAL02 and provide a solid basis for a larger clinical study.

FUNDING

Combioxin.

Developing Equipotent Teixobactin Analogues against Drug-Resistant Bacteria and Discovering a Hydrophobic Interaction between Lipid II and Teixobactin

Teixobactin, targeting lipid II, represents a new class of antibiotics with novel structures and has excellent activity against Gram-positive pathogens. We developed a new convergent method to synthesize a series of teixobactin analogues and explored structure-activity relationships. We obtained equipotent and simplified teixobactin analogues, replacing the l- allo-enduracididine with lysine, substituting oxygen to nitrogen on threonine, and adding a phenyl group on the d-phenylalanine. On the basis of the antibacterial activities that resulted from corresponding modifications of the d-phenylalanine, we propose a hydrophobic interaction between lipid II and the N-terminal of teixobactin analogues, which we map out with our analogue 35. Finally, a representative analogue from our series showed high efficiency in a mouse model of Streptococcus pneumoniae septicemia.

Self-immolative polymers with potent and selective antibacterial activity by hydrophilic side chain grafting

Self-immolative polymers, which exert potent antibacterial activity with low hemolytic toxicity to red blood cells, are triggered to unzip into small molecules by a chemical stimulus.

Cationic Poly(benzyl ether)s as Self-Immolative Antimicrobial Polymers

Self-immolative polymers (SIMPs) are macromolecules that spontaneously undergo depolymerization into small molecules when triggered by specific external stimuli. We report here the first examples of antimicrobial SIMPs with potent, rapid, and broad-spectrum bactericidal activity. Their antibacterial and hemolytic activities were examined as a function of cationic functionality. Polymers bearing primary ammonium cationic groups showed more potent bactericidal activity against Escherichia coli, relative to tertiary and quaternary ammonium counterparts, whereas the quaternary ammonium polymers showed the lowest hemolytic toxicity. These antibacterial polycations undergo end-to-end depolymerization when triggered by an externally applied stimulus. Specifically, poly(benzyl ether)s end-capped with a silyl ether group and bearing pendant allyl side chains were converted to polycations by photoinitiated thiol-ene radical addition using cysteamine HCl. The intact polycations are stable in solution, but they spontaneously unzip into their component monomers upon exposure to fluoride ions, with excellent sensitivity and selectivity. Upon triggered depolymerization, the antibacterial potency was largely retained but the hemolytic toxicity was substantially reduced. Thus, we reveal the first example of a self-immolative antibacterial polymer platform that will enable antibacterial materials to spontaneously unzip into biologically active small molecules upon the introduction of a specifically designed stimulus.

An update on the pharmacotherapeutic management of lower respiratory tract infections

INTRODUCTION

Our knowledge about lower respiratory tract infections (LRTIs) has improved substantially in the last years, but the management of respiratory infections is still a challenge and we are still far from using precision medicine in their treatment. Areas covered: The approaches developed in recent years to improve the pharmacotherapeutic management of LRTIs, such as novel diagnostic assays to facilitate medical decision-making, attempts for selecting an optimal empiric antibiotic regimen, and the role of new and possibly unproven adjunctive therapies, are described. Expert opinion: Early and appropriate antibiotics remain the cornerstone in the treatment of LRTIs. The updated trend is to apply antimicrobial stewardship principles and initiatives to optimize both the management and the outcomes of LTRIs. Biomarkers, mainly C-reactive protein (CRP) and procalcitonin (PCT), can improve the diagnostic and prognostic assessment of LRTIs and aid to guide antibiotic therapy. The widespread use of antimicrobial agents has greatly contributed to faster development of antibiotic resistance and the emergence of opportunistic pathogens, which substitute the indigenous microbiota. However, very few new antibiotics in development to overcome existing resistance and ensure continued success in the treatment of LRTIs have been approved, likely because antibiotic stewardship programs discourage the use of new agents.