Improving predictions of the risk of resistance development against new and old antibiotics

Pharmacokinetic/pharmacodynamic model-based optimization of temocillin dosing strategies for the treatment of systemic infections

BACKGROUND

Temocillin is increasingly considered as an alternative to carbapenems. However, there is no consensus on optimal dosing strategies and limited data on temocillin efficacy in systemic infections.

OBJECTIVES

We compared temocillin dosing strategies using pharmacokinetic/pharmacodynamic (PK/PD) modelling and simulation based on plasma exposure and in vitro time-kill data.

METHODS

Temocillin effects on four Escherichia coli strains were evaluated using static time-kill experiments and the hollow-fibre infection model, in which unbound plasma concentrations following intermittent and continuous infusion regimens of 4 and 6 g daily were replicated over 72 h. A PK/PD model was developed to describe the time-kill data. The PK/PD model was coupled to a population PK model of temocillin in critically ill patients to predict bacterial killing and resistance development following various dosing regimens.

RESULTS

Amplification of resistant subpopulations was observed within 24 h for all strains. The PK/PD model described the observed bacterial kill kinetics and resistance development from both experimental systems well. Simulations indicated dose-dependent bacterial killing within and beyond the currently used daily dose range, and a superiority of continuous compared with intermittent infusions. However, regrowth of resistant subpopulations was frequently observed. For two strains, bacteriostasis over 72 h was predicted only with doses that are higher than those currently licensed.

CONCLUSIONS

Continuous infusions and 6 g daily doses of temocillin kill E. coli more effectively than 4 g daily doses and intermittent infusions, and may increase efficacy in the treatment of systemic infections. However, higher daily doses may be required to suppress resistance development.

Ecological and evolutionary mechanisms driving within-patient emergence of antimicrobial resistance

The ecological and evolutionary mechanisms of antimicrobial resistance (AMR) emergence within patients and how these vary across bacterial infections are poorly understood. Increasingly widespread use of pathogen genome sequencing in the clinic enables a deeper understanding of these processes. In this Review, we explore the clinical evidence to support four major mechanisms of within-patient AMR emergence in bacteria: spontaneous resistance mutations; in situ horizontal gene transfer of resistance genes; selection of pre-existing resistance; and immigration of resistant lineages. Within-patient AMR emergence occurs across a wide range of host niches and bacterial species, but the importance of each mechanism varies between bacterial species and infection sites within the body. We identify potential drivers of such differences and discuss how ecological and evolutionary analysis could be embedded within clinical trials of antimicrobials, which are powerful but underused tools for understanding why these mechanisms vary between pathogens, infections and individuals. Ultimately, improving understanding of how host niche, bacterial species and antibiotic mode of action combine to govern the ecological and evolutionary mechanism of AMR emergence in patients will enable more predictive and personalized diagnosis and antimicrobial therapies.

Forecasting antimicrobial resistance evolution

Antimicrobial resistance (AMR) is a major global health issue. Current measures for tackling it comprise mainly the prudent use of drugs, the development of new drugs, and rapid diagnostics. Relatively little attention has been given to forecasting the evolution of resistance. Here, we argue that forecasting has the potential to be a great asset in our arsenal of measures to tackle AMR. We argue that, if successfully implemented, forecasting resistance will help to resolve the antibiotic crisis in three ways: it will (i) guide a more sustainable use (and therefore lifespan) of antibiotics and incentivize investment in drug development, (ii) reduce the spread of AMR genes and pathogenic microbes in the environment and between patients, and (iii) allow more efficient treatment of persistent infections, reducing the continued evolution of resistance. We identify two important challenges that need to be addressed for the successful establishment of forecasting: (i) the development of bespoke technology that allows stakeholders to empirically assess the risks of resistance evolving during the process of drug development and therapeutic/preventive use, and (ii) the transformative shift in mindset from the current praxis of mostly addressing the problem of antibiotic resistance a posteriori to a concept of a priori estimating, and acting on, the risks of resistance.

Characteristics and driving factors of antibiotic resistance genes in aquaculture products from freshwater ponds in China Yangtze River Delta

Antibiotic resistance genes (ARGs) are widespread in aquaculture and pose a huge threat to aquaculture organisms and human health. In this study, occurrences and relative abundances of ARGs were analysed in the guts of products cultured in freshwater ponds in the Yangtze River Delta region in China. A total of 29 ARGs were found in the gut samples, with detection frequencies ranging from 4.8% to 81%, and the relative abundances (ARGs/16S rRNA) ranging from 10-7 to 1. In addition, the human dietary intake of ARGs via aquaculture products was assessed, where the daily intake of most ARGs via aquaculture products was higher than those via PM2.5 and drinking water, but lower than that via vegetables. The relative abundances of MGE (IS613, Tp614, tnpA and int1) were significantly correlated with those of multiple ARGs, indicating the horizontal gene transfer (HGT) of ARGs among gut microorganisms. Proteobacteria, Firmicutes and Actinobacteria were the dominated microbial communities found in the guts of aquaculture products. In addition, significant correlations were found between Cyanobacteria and int1, between Nitrospira and tetE, and between sul2 and aadA2, indicating potential same hosts of these genes. In addition, results from co-correlation indicated both HGT (dominated by MGEs) of ARGs and the enrichment of ARGs in bacteria. MGEs, mostly int1, were more effective than bacteria in increasing the ARG abundance. This study could provide a better understanding of the transmission of ARGs in the aquaculture environment and improve the quality of aquaculture products and the ecology.

The potential use of nanozymes as an antibacterial agents in oral infection, periodontitis, and peri-implantitis

Several studies suggest that oral pathogenic biofilms cause persistent oral infections. Among these is periodontitis, a prevalent condition brought on by plaque biofilm. It can even result in tooth loss. Furthermore, the accumulation of germs around a dental implant may lead to peri-implantitis, which damages the surrounding bone and gum tissue. Furthermore, bacterial biofilm contamination on the implant causes soft tissue irritation and adjacent bone resorption, severely compromising dental health. On decontaminated implant surfaces, however, re-osseointegration cannot be induced by standard biofilm removal techniques such as mechanical cleaning and antiseptic treatment. A family of nanoparticles known as nanozymes (NZs) comprise highly catalytically active multivalent metal components. The most often employed NZs with antibacterial activity are those that have peroxidase (POD) activity, among other types of NZs. Since NZs are less expensive, more easily produced, and more stable than natural enzymes, they hold great promise for use in various applications, including treating microbial infections. NZs have significantly contributed to studying implant success rates and periodontal health maintenance in periodontics and implantology. An extensive analysis of the research on various NZs and their applications in managing oral health conditions, including dental caries, dental pulp disorders, oral ulcers, peri-implantitis, and bacterial infections of the mouth. To combat bacteria, this review concentrates on NZs that imitate the activity of enzymes in implantology and periodontology. With a view to the future, there are several ways that NZs might be used to treat dental disorders antibacterially.

Single-atom nanozymes with peroxidase-like activity: A review

Single-atom nanozymes (SANs) are nanomaterials-based nanozymes with atomically dispersed enzyme-like active sites. SANs offer improved as well as tunable catalytic activity. The creation of extremely effective SANs and their potential uses have piqued researchers' curiosity due to their advantages of cheap cost, variable catalytic activity, high stability, and large-scale production. Furthermore, SANs with uniformly distributed active centers and definite coordination structures offer a distinctive opportunity to investigate the structure-activity correlation and control the geometric and electrical features of metal centers. SANs have been extensively explored in photo-, thermal-, and electro-catalysis. However, SANs suffer from the following disadvantages, such as efficiency, non-mimicking of the 3-D complexity of natural enzymes, limited and narrow range of artificial SANs, and biosafety aspects. Among a quite limited range of artificial SANs, the peroxidase action of SANs has attracted significant research attention in the last five years with the aim of producing reactive oxygen species for use in cancer therapy, and water treatment among many other applications. In this review, we explore the recent progress of different SANs as peroxidase mimics, the role of the metal center in enzymatic activity, possible prospects, and underlying limitations in real-time applications.

Discovery of novel cannabidiol derivatives with augmented antibacterial agents against methicillin-resistant Staphylococcus aureus

Drug-resistant bacterium infections are a severe threat to public health and novel antimicrobial agents combating drug-resistant bacteria are an unmet medical need. Although cannabidiol (CBD) has been reported to show antibacterial effects, whether its antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) can be improved remains unclear. Herein, a series of novel CBD derivatives were designed and synthesized using various chemical approaches including amidation, Friedel-Crafts alkylation, and Negishi cross-coupling reaction for the modifications at the C-7, C-2', C-4', and C-6' positions of CBD skeleton. Derivative 21f showed augmented antibacterial activity against MRSA with a minimum inhibitory concentration of 4 μM without cytotoxic effect in microglia BV2 cells. Further mechanistic studies suggested that 21f inhibited the formation of biofilms, induced excess reactive oxygen species, and reduced bacterial metabolism, which collectively led to the acceleration of bacterial death. Findings from this study expand the understanding of CBD derivatives as promising antibacterial agents, which provides useful information for the development of cannabinoid-based antibacterial agents.

The pharmacokinetic-pharmacodynamic modelling framework as a tool to predict drug resistance evolution

Pharmacokinetic-pharmacodynamic (PKPD) models, which describe how drug concentrations change over time and how that affects pathogen growth, have proven highly valuable in designing optimal drug treatments aimed at bacterial eradication. However, the fast rise of antimicrobial resistance calls for increased focus on an additional treatment optimization criterion: avoidance of resistance evolution. We demonstrate here how coupling PKPD and population genetics models can be used to determine treatment regimens that minimize the potential for antimicrobial resistance evolution. Importantly, the resulting modelling framework enables the assessment of resistance evolution in response to dynamic selection pressures, including changes in antimicrobial concentration and the emergence of adaptive phenotypes. Using antibiotics and antimicrobial peptides as an example, we discuss the empirical evidence and intuition behind individual model parameters. We further suggest several extensions of this framework that allow a more comprehensive and realistic prediction of bacterial escape from antimicrobials through various phenotypic and genetic mechanisms.

Povidone-Iodine Fails to Eradicate Chronic Suppurative Otitis Media and Demonstrates Ototoxic Risk in Mice

HYPOTHESIS

Commercially available povidone-iodine solution can eliminate biofilms and persister cells rapidly in in vivo achievable concentrations without inducing ototoxicity.

BACKGROUND

Chronic suppurative otitis media (CSOM) is a substantial global problem. Current treatment options often induce a temporary remission without leading to a permanent cessation of symptoms secondary to the treatments' inability to eliminate persister cells. Povidone-iodine has been shown to be able to clear biofilm and planktonic cells in in vitro assays, but there are reports of ototoxic effects limiting its clinical utility.

METHODS

Bacterial and biofilm growth with quantification by spectrophotomer, murine auditory brainstem response (ABR), and distortion product otoacoustic emissions, immunohistochemistry, in vivo povidone-iodine treatment of murine CSOM, persister cell assay.

RESULTS

Commercially available 10% povidone-iodine solution is able to completely eradicate multiple clinical strains of Pseudomonas aeruginosa and Staphylococcus aureus in vitro with 10 minutes of exposure. Mice that have received a transtympanic injection of 1% povidone-iodine solution did not have significantly different auditory brainstem response or distortion product otoacoustic emission results compared with the control. Mice that received a povidone-iodine scrub or 10% povidone-iodine solution had significantly worsened hearing (25- and 13-dB increase in threshold, respectively; p < 0.05). In vivo CSOM infection recurred in all mice after the completion of treatment with 10% povidone-iodine solution, and there was no improvement in the bacterial load after treatment, indicating in vivo failure of therapy.

CONCLUSION

Povidone-iodine solution is effective at eliminating biofilm and persister cells in vitro at in vivo achievable concentrations but fails in vivo most likely because of kinetics of distribution in vivo. Even if drug distribution could be improved, the therapeutic window is likely to be too small given that the diluted solution does not have ototoxic potential, whereas while the scrub variant, which contains detergents, and the undiluted solution are ototoxic after a single treatment.

Emerging Prospects of Nanozymes for Antibacterial and Anticancer Applications

The ability of some nanoparticles to mimic the activity of certain enzymes paves the way for several attractive biomedical applications which bolster the already impressive arsenal of nanomaterials to combat deadly diseases. A key feature of such 'nanozymes' is the duplication of activities of enzymes or classes of enzymes, such as catalase, superoxide dismutase, oxidase, and peroxidase which are known to modulate the oxidative balance of treated cells for facilitating a particular biological process such as cellular apoptosis. Several nanoparticles that include those of metals, metal oxides/sulfides, metal-organic frameworks, carbon-based materials, etc., have shown the ability to behave as one or more of such enzymes. As compared to natural enzymes, these artificial nanozymes are safer, less expensive, and more stable. Moreover, their catalytic activity can be tuned by changing their size, shape, surface properties, etc. In addition, they can also be engineered to demonstrate additional features, such as photoactivated hyperthermia, or be loaded with active agents for multimodal action. Several researchers have explored the nanozyme-mediated oxidative modulation for therapeutic purposes, often in combination with other diagnostic and/or therapeutic modalities, using a single probe. It has been observed that such synergistic action can effectively by-pass the various defense mechanisms adapted by rogue cells such as hypoxia, evasion of immuno-recognition, drug-rejection, etc. The emerging prospects of using several such nanoparticle platforms for the treatment of bacterial infections/diseases and cancer, along with various related challenges and opportunities, are discussed in this review.

Single-atom Nanozymes for Biomedical Applications： Recent Advances and Challenges

Nanozymes have received extensive attention in the fields of sensing and detection, medical therapy, industry, and agriculture thanks to the combination of the catalytic properties of natural enzymes and the physicochemical properties of nanomaterials, coupled with superior stability and ease of preparation. Despite the promise of nanozymes, conventional nanozymes are constrained by their oversized size and low catalytic capacity in sophisticated practical application environments. single-atom nanozymes (SAzymes) were characterized as nanozymes with high catalytic efficiency by uniformly distributed single atoms as catalysis sites, thus effectively addressing the defects of conventional nanozymes. This paper reviews the activity improvement scheme and catalytic mechanism of SAzymes and highlights the latest research progress of SAzymes in the fields of biomedical sensing and therapy. Eventually, the challenges and future directions of SAzymes are discussed in this paper.

Gram-Selective Antibacterial Activity of Mixed-Charge 2D-MoS2

Development of nanomaterial-based antibiotics can be the most potent alternative due to the increasing resistance against conventional antibiotics. But one of the important parameters in development of antibacterial agent is...

Lanza V, Rodríguez-Beltrán J, Galán JC, San Millán A, Cantón R, Coque TM. Evolutionary Pathways and Trajectories in Antibiotic Resistance

Evolution is the hallmark of life. Descriptions of the evolution of microorganisms have provided a wealth of information, but knowledge regarding "what happened" has precluded a deeper understanding of "how" evolution has proceeded, as in the case of antimicrobial resistance. The difficulty in answering the "how" question lies in the multihierarchical dimensions of evolutionary processes, nested in complex networks, encompassing all units of selection, from genes to communities and ecosystems. At the simplest ontological level (as resistance genes), evolution proceeds by random (mutation and drift) and directional (natural selection) processes; however, sequential pathways of adaptive variation can occasionally be observed, and under fixed circumstances (particular fitness landscapes), evolution is predictable. At the highest level (such as that of plasmids, clones, species, microbiotas), the systems' degrees of freedom increase dramatically, related to the variable dispersal, fragmentation, relatedness, or coalescence of bacterial populations, depending on heterogeneous and changing niches and selective gradients in complex environments. Evolutionary trajectories of antibiotic resistance find their way in these changing landscapes subjected to random variations, becoming highly entropic and therefore unpredictable. However, experimental, phylogenetic, and ecogenetic analyses reveal preferential frequented paths (highways) where antibiotic resistance flows and propagates, allowing some understanding of evolutionary dynamics, modeling and designing interventions. Studies on antibiotic resistance have an applied aspect in improving individual health, One Health, and Global Health, as well as an academic value for understanding evolution. Most importantly, they have a heuristic significance as a model to reduce the negative influence of anthropogenic effects on the environment.

Antimicrobial Stewardship and the Infection Control Practitioner: A Natural Alliance

Antibiotic overuse and misuse has contributed to rising rates of multidrug-resistant organisms and Clostridioides difficile. Decreasing antibiotic misuse has become a national public health priority. This review outlines the goals of antimicrobial stewardship, essential members of the program, implementation strategies, approaches to measuring the program's impact, and steps needed to build a program. Highlighted is the alliance between antimicrobial stewardship programs and infection prevention programs in their efforts to improve antibiotic use, improve diagnostic stewardship for C difficile and asymptomatic bacteriuria, and decrease health care-associated infections and the spread of multidrug-resistant organisms.

Evaluation of recreational risks due to exposure of antibiotic-resistance bacteria from environmental water: A proposed framework

This research provides a framework for the human health risk assessment due to exposure of AR (antibiotic resistance) E. coli from recreational water (swimming activity). Literature-based epidemiological studies were used for f-value formulation (i.e., AR E. coli/total number of E. coli isolates) and the theoretical calculation of AR and non-AR E. coli concentrations. Risk was estimated using calculated values by considering four different dose-response (D-R) scenarios with known characteristics due to current lack of availability of D-R for AR bacteria. f-values ranged between 0.14 and 0.59 and the order of calculated theoretical values of maximum AR E. coli are as follows: ampicillin or amoxicillin (38 CFU/dip) > co-trimoxazole (19 CFU/dip) ~ tetracycline (18 CFU/dip) > ceftriaxone or cefotaxime or ceftazidime (10 CFU/dip) ~ ciprofloxacin or ofloxacin (9 CFU/dip). The risk of infection was considerably high for theoretical calculated concentration values regardless of the chosen D-R model (annual risk of infection (95th percentile) = 1, Spearman's rank correlation coefficient = -0.06 to 0.94), under the conditions studied. Further, AR levels of human gastrointestinal-tract were determined using literature-reported data in stool samples and indicated that the resistance level was very high in healthy human (range: 3.7 × 10⁷-8.4 × 10⁷ CFU/g of wet lumen content). The maximum allowable concentration values for AR E. coli and non-ARB (0.0075 CFU/dip and 2.56 CFU/dip) were found to be smaller than the USEPA recreational water quality guidelines (≤126 CFU/100 mL), which can help the USEPA and other regulatory bodies in revisiting the current guidelines. So based on the noted results, we can conclude that the maintenance of inventory of actual measured concentration of ARB in the recreational water sites is needed to prevent unwanted complication related to the treatment of infectious sustained by resistant microbes.

Antibiotic resistance: turning evolutionary principles into clinical reality

Antibiotic resistance is one of the major challenges facing modern medicine worldwide. The past few decades have witnessed rapid progress in our understanding of the multiple factors that affect the emergence and spread of antibiotic resistance at the population level and the level of the individual patient. However, the process of translating this progress into health policy and clinical practice has been slow. Here, we attempt to consolidate current knowledge about the evolution and ecology of antibiotic resistance into a roadmap for future research as well as clinical and environmental control of antibiotic resistance. At the population level, we examine emergence, transmission and dissemination of antibiotic resistance, and at the patient level, we examine adaptation involving bacterial physiology and host resilience. Finally, we describe new approaches and technologies for improving diagnosis and treatment and minimizing the spread of resistance.

Stochastic bacterial population dynamics restrict the establishment of antibiotic resistance from single cells

A better understanding of how antibiotic exposure impacts the evolution of resistance in bacterial populations is crucial for designing more sustainable treatment strategies. The conventional approach to this question is to measure the range of concentrations over which resistant strain(s) are selectively favored over a sensitive strain. Here, we instead investigate how antibiotic concentration impacts the initial establishment of resistance from single cells, mimicking the clonal expansion of a resistant lineage following mutation or horizontal gene transfer. Using two Pseudomonas aeruginosa strains carrying resistance plasmids, we show that single resistant cells have <5% probability of detectable outgrowth at antibiotic concentrations as low as one-eighth of the resistant strain's minimum inhibitory concentration (MIC). This low probability of establishment is due to detrimental effects of antibiotics on resistant cells, coupled with the inherently stochastic nature of cell division and death on the single-cell level, which leads to loss of many nascent resistant lineages. Our findings suggest that moderate doses of antibiotics, well below the MIC of resistant strains, may effectively restrict de novo emergence of resistance even though they cannot clear already-large resistant populations.

Two-dimensional nanomaterials beyond graphene for antibacterial applications: current progress and future perspectives

The marked augment of drug-resistance to traditional antibiotics underlines the crying need for novel replaceable antibacterials. Research advances have revealed the considerable sterilization potential of two-dimension graphene-based nanomaterials. Subsequently, two-dimensional nanomaterials beyond graphene (2D NBG) as novel antibacterials have also demonstrated their power for disinfection due to their unique physicochemical properties and good biocompatibility. Therefore, the exploration of antibacterial mechanisms of 2D NBG is vital to manipulate antibacterials for future applications. Herein, we summarize the recent research progress of 2D NBG-based antibacterial agents, starting with a detailed introduction of the relevant antibacterial mechanisms, including direct contact destruction, oxidative stress, photo-induced antibacterial, control drug/metallic ions releasing, and the multi-mode synergistic antibacterial. Then, the effect of the physicochemical properties of 2D NBG on their antibacterial activities is also discussed. Additionally, a summary of the different kinds of 2D NBG is given, such as transition-metal dichalcogenides/oxides, metal-based compounds, nitride-based nanomaterials, black phosphorus, transition metal carbides, and nitrides. Finally, we rationally analyze the current challenges and new perspectives for future study of more effective antibacterial agents. This review not only can help researchers grasp the current status of 2D NBG antibacterials, but also may catalyze breakthroughs in this fast-growing field.

Fluopsin C for Treating Multidrug-Resistant Infections: In vitro Activity Against Clinically Important Strains and in vivo Efficacy Against Carbapenemase-Producing Klebsiella pneumoniae

The increasing emergence of multidrug-resistant (MDR) organisms in hospital infections is causing a global public health crisis. The development of drugs with effective antibiotic action against such agents is of the highest priority. In the present study, the action of Fluopsin C against MDR clinical isolates was evaluated under in vitro and in vivo conditions. Fluopsin C was produced in cell suspension culture of Pseudomonas aeruginosa LV strain, purified by liquid adsorption chromatography and identified by mass spectrometric analysis. Bioactivity, bacterial resistance development risk against clinically important pathogenic strains and toxicity in mammalian cell were initially determined by in vitro models. In vivo toxicity was evaluated in Tenebrio molitor larvae and mice. The therapeutic efficacy of intravenous Fluopsin C administration was evaluated in a murine model of Klebsiella pneumoniae (KPC) acute sepsis, using six different treatments. The in vitro results indicated MIC and MBC below 2 μg/mL and low bacterial resistance development frequency. Electron microscopy showed that Fluopsin C may have altered the exopolysaccharide matrix and caused disruption of the cell wall of MDR bacteria. Best therapeutic results were achieved in mice treated with a single dose of 2 mg/kg and in mice treated with two doses of 1 mg/kg, 8 h apart. Furthermore, acute and chronic histopathological studies demonstrated absent nephrotoxicity and moderate hepatotoxicity. The results demonstrated the efficacy of Fluopsin C against MDR organisms in in vitro and in vivo models, and hence it can be a novel therapeutic agent for the control of severe MDR infections.

Rapid Evolution of Reduced Susceptibility against a Balanced Dual-Targeting Antibiotic through Stepping-Stone Mutations

Multitargeting antibiotics, i.e., single compounds capable of inhibiting two or more bacterial targets, are generally considered to be a promising therapeutic strategy against resistance evolution. The rationale for this theory is that multitargeting antibiotics demand the simultaneous acquisition of multiple mutations at their respective target genes to achieve significant resistance. The theory presumes that individual mutations provide little or no benefit to the bacterial host. Here, we propose that such individual stepping-stone mutations can be prevalent in clinical bacterial isolates, as they provide significant resistance to other antimicrobial agents. To test this possibility, we focused on gepotidacin, an antibiotic candidate that selectively inhibits both bacterial DNA gyrase and topoisomerase IV. In a susceptible organism, Klebsiella pneumoniae, a combination of two specific mutations in these target proteins provide an >2,000-fold reduction in susceptibility, while individually, none of these mutations affect resistance significantly. Alarmingly, strains with decreased susceptibility against gepotidacin are found to be as virulent as the wild-type Klebsiella pneumoniae strain in a murine model. Moreover, numerous pathogenic isolates carry mutations which could promote the evolution of clinically significant reduction of susceptibility against gepotidacin in the future. As might be expected, prolonged exposure to ciprofloxacin, a clinically widely employed gyrase inhibitor, coselected for reduced susceptibility against gepotidacin. We conclude that extensive antibiotic usage could select for mutations that serve as stepping-stones toward resistance against antimicrobial compounds still under development. Our research indicates that even balanced multitargeting antibiotics are prone to resistance evolution.

Development of Staphylococcus aureus tolerance to antimicrobial photodynamic inactivation and antimicrobial blue light upon sub-lethal treatment

Antimicrobial photodynamic inactivation (aPDI) and antimicrobial blue light (aBL) are considered low-risk treatments for the development of bacterial resistance and/or tolerance due to their multitargeted modes of action. In this study, we assessed the development of Staphylococcus aureus tolerance to these phototreatments. Reference S. aureus USA300 JE2 was subjected to 15 cycles of both sub-lethal aPDI (employing an exogenously administered photosensitizer (PS), i.e., rose Bengal (RB)) and sub-lethal aBL (employing endogenously produced photosensitizing compounds, i.e., porphyrins). We demonstrate substantial aPDI/aBL tolerance development and tolerance stability after 5 cycles of subculturing without aPDI/aBL exposure (the development of aPDI/aBL tolerance was also confirmed with the employment of clinical MRSA and MSSA strain as well as other representatives of Gram-positive microbes, i.e. Enterococcus faecium and Streptococcus agalactiae). In addition, a rifampicin-resistant (RIFR) mutant selection assay showed an increased mutation rate in S. aureus upon sub-lethal phototreatments, indicating that the increased aPDI/aBL tolerance may result from accumulated mutations. Moreover, qRT-PCR analysis following sub-lethal phototreatments demonstrated increased expression of umuC, which encodes stress-responsive error-prone DNA polymerase V, an enzyme that increases the rate of mutation. Employment of recA and umuC transposon S. aureus mutants confirmed SOS-induction dependence of the tolerance development. Interestingly, aPDI/aBL-tolerant S. aureus exhibited increased susceptibility to gentamicin (GEN) and doxycycline (DOX), supporting the hypothesis of genetic alterations induced by sub-lethal phototreatments. The obtained results indicate that S. aureus may develop stable tolerance to studied phototreatments upon sub-lethal aPDI/aBL exposure; thus, the risk of tolerance development should be considered significant when designing aPDI/aBL protocols for infection treatments in vitro and in clinical settings.

Cefiderocol: A Siderophore Cephalosporin with Activity Against Carbapenem-Resistant and Multidrug-Resistant Gram-Negative Bacilli

Cefiderocol is an injectable siderophore cephalosporin discovered and being developed by Shionogi & Co., Ltd., Japan. As with other β-lactam antibiotics, the principal antibacterial/bactericidal activity of cefiderocol occurs by inhibition of Gram-negative bacterial cell wall synthesis by binding to penicillin binding proteins; however, it is unique in that it enters the bacterial periplasmic space as a result of its siderophore-like property and has enhanced stability to β-lactamases. The chemical structure of cefiderocol is similar to both ceftazidime and cefepime, which are third- and fourth-generation cephalosporins, respectively, but with high stability to a variety of β-lactamases, including AmpC and extended-spectrum β-lactamases (ESBLs). Cefiderocol has a pyrrolidinium group in the side chain at position 3 like cefepime and a carboxypropanoxyimino group in the side chain at position 7 of the cephem nucleus like ceftazidime. The major difference in the chemical structures of cefiderocol, ceftazidime and cefepime is the presence of a catechol group on the side chain at position 3. Together with the high stability to β-lactamases, including ESBLs, AmpC and carbapenemases, the microbiological activity of cefiderocol against aerobic Gram-negative bacilli is equal to or superior to that of ceftazidime-avibactam and meropenem, and it is active against a variety of Ambler class A, B, C and D β-lactamases. Cefiderocol is also more potent than both ceftazidime-avibactam and meropenem versus Acinetobacter baumannii, including meropenem non-susceptible and multidrug-resistant (MDR) isolates. Cefiderocol's activity against meropenem-non-susceptible and Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacteriales is comparable or superior to ceftazidime-avibactam. Cefiderocol is also more potent than both ceftazidime-avibactam and meropenem against all resistance phenotypes of Pseudomonas aeruginosa and against Stenotrophomonas maltophilia. The current dosing regimen being used in phase III studies is 2 g administered intravenously every 8 h (q8 h) using a 3-h infusion. The pharmacokinetics of cefiderocol are best described by a three-compartment linear model. The mean plasma half-life (t½) was ~ 2.3 h, protein binding is 58%, and total drug clearance ranged from 4.6-6.0 L/h for both single- and multi-dose infusions and was primarily renally excreted unchanged (61-71%). Cefiderocol is primarily renally excreted unchanged and clearance correlates with creatinine clearance. Dosage adjustment is thus required for both augmented renal clearance and in patients with moderate to severe renal impairment. In vitro and in vivo pharmacodynamic studies have reported that as with other cephalosporins the pharmacodynamic index that best predicts clinical outcome is the percentage of time that free drug concentrations exceed the minimum inhibitory concentration (%fT > MIC). In vivo efficacy of cefiderocol has been studied in a variety of humanized drug exposure murine and rat models of infection utilizing a variety of MDR and extremely drug resistant strains. Cefiderocol has performed similarly to or has been superior to comparator agents, including ceftazidime and cefepime. A phase II prospective, multicenter, double-blind, randomized clinical trial assessed the safety and efficacy of cefiderocol 2000 mg q8 h versus imipenem/cilastatin 1000 mg q8 h, both administered intravenously for 7-14 days over 1 h, in the treatment of complicated urinary tract infection (cUTI, including pyelonephritis) or acute uncomplicated pyelonephritis in hospitalized adults. A total of 452 patients were initially enrolled in the study, with 303 in the cefiderocol arm and 149 in the imipenem/cilastatin arm. The primary outcome measure was a composite of clinical cure and microbiological eradication at the test-of-cure (TOC) visit, that is, 7 days after the end of treatment in the microbiological intent-to-treat (MITT) population. Secondary outcome measures included microbiological response per pathogen and per patient at early assessment (EA), end of treatment (EOT), TOC, and follow-up (FUP); clinical response per pathogen and per patient at EA, EOT, TOC, and FUP; plasma, urine and concentrations of cefiderocol; and the number of participants with adverse events. The composite of clinical and microbiological response rates was 72.6% (183/252) for cefiderocol and 54.6% (65/119) for imipenem/cilastatin in the MITT population. Clinical response rates per patient at the TOC visit were 89.7% (226/252) for cefiderocol and 87.4% (104/119) for imipenem/cilastatin in the MITT population. Microbiological eradication rates were 73.0% (184/252) for cefiderocol and 56.3% (67/119) for imipenem/cilastatin in the MITT population. Additionally, two phase III clinical trials are currently being conducted by Shionogi & Co., Ltd., Japan. The two trials are evaluating the efficacy of cefiderocol in the treatment of serious infections in adult patients caused by carbapenem-resistant Gram-negative pathogens and evaluating the efficacy of cefiderocol in the treatment of adults with hospital-acquired bacterial pneumonia, ventilator-associated pneumonia or healthcare-associated pneumonia caused by Gram-negative pathogens. Cefiderocol appears to be well tolerated (minor reported adverse effects were gastrointestinal and phlebitis related), with a side effect profile that is comparable to other cephalosporin antimicrobials. Cefiderocol appears to be well positioned to help address the increasing number of infections caused by carbapenem-resistant and MDR Gram-negative bacilli, including ESBL- and carbapenemase-producing strains (including metallo-β-lactamase producers). A distinguishing feature of cefiderocol is its activity against resistant P. aeruginosa, A. baumannii, S. maltophilia and Burkholderia cepacia.

The fitness costs and benefits of antibiotic resistance in drug-free microenvironments encountered in the human body

The relationship between bacterial drug resistance and growth fitness is a contentious topic, but some antibiotic resistance mutations clearly have a fitness cost in the laboratory. Whether these costs translate into deleterious effects in natural habitats is less certain however. Previously, fitness effects of resistance mutations were mostly characterized in nutrient-rich, fast-growth conditions, which bacteria rarely encounter in natural habitats. Carbon, phosphate, iron or oxygen limitations are conditions met by bacterial pathogens in various compartments of the human body. Here, we measured the fitness of four different rpoB mutations commonly found in rifampicin-resistant bacterial isolates. The fitness properties and the emergence of these and other alleles were studied in Escherichia coli populations growing under nutrient excess and in four different nutrient-limited states. Consistent with previous findings, all four mutations exhibited deleterious fitness effects under nutrient-rich conditions. In stark contrast, we found positive or neutral fitness effects under nutrient-limited conditions. Two particular rpoB alleles had a remarkable fitness increase under phosphate limitation and these alleles arose to high frequencies specifically under phosphate limitation. These findings suggest that it is not meaningful to draw general conclusions on fitness costs without considering bacterial microenvironments in humans and other animals.

Revival of old antibiotics: needs, the state of evidence and expectations

The gap between the emergence of antibiotic resistance and new antibiotic development has drawn attention to old antibiotics whose spectrum of coverage frequently comprises highly resistant bacteria. However, these antibiotics have frequently not undergone the structured process of antibiotic development of modern antibiotics, from pharmacokinetic/pharmacodynamic (PK/PD) studies establishing safe and effective dosing, establishment of susceptibility breakpoints, to clinical trials establishing clinical safety and effectiveness. In this review, we highlight the gaps for which we need old antibiotics in community- and hospital-acquired infections. Reviewing recently published and ongoing randomised controlled trials (RCTs) shows advances in our understanding of the efficacy and effectiveness of oral fosfomycin, mecillinam and nitrofurantoin for cystitis, and of trimethoprim/sulfamethoxazole for complicated skin infections caused by methicillin-resistant Staphylococcus aureus (MRSA) in the community. Summarising older evidence shows the inferiority of chloramphenicol versus modern antibiotics for severe infections. We lack studies on severe infections caused by carbapenem-resistant Gram-negative bacteria and other multidrug-resistant (MDR) bacteria in hospitalised and critically ill patients; ongoing studies assessing colistin and intravenous fosfomycin might fill in some gaps. In the re-development process of old antibiotics, we mandate modern PK/PD studies comprising special populations as well as RCTs addressing the target population of patients in need of these antibiotics powered to examine patient-relevant outcomes. Structured antibiotic re-development from the laboratory to evidence-based treatment recommendations requires public funding, multidisciplinary collaboration, international co-ordination, and methods to streamline the recruitment of critically ill patients infected by MDR bacteria.

Assessing the Risk of Antibiotic Resistance Transmission from the Environment to Humans: Non-Direct Proportionality between Abundance and Risk

The past decade has witnessed a burst of study regarding antibiotic resistance in the environment, mainly in areas under anthropogenic influence. Therefore, impacts of the contaminant resistome, that is, those related to human activities, are now recognized. However, a key issue refers to the risk of transmission of resistance to humans, for which a quantitative model is urgently needed. This opinion paper makes an overview of some risk-determinant variables and raises questions regarding research needs. A major conclusion is that the risks of transmission of antibiotic resistance from the environment to humans must be managed under the precautionary principle, because it may be too late to act if we wait until we have concrete risk values.

Multicentre open-label randomised controlled trial to compare colistin alone with colistin plus meropenem for the treatment of severe infections caused by carbapenem-resistant Gram-negative infections (AIDA): a study protocol

INTRODUCTION

The emergence of antibiotic-resistant bacteria has driven renewed interest in older antibacterials, including colistin. Previous studies have shown that colistin is less effective and more toxic than modern antibiotics. In vitro synergy studies and clinical observational studies suggest a benefit of combining colistin with a carbapenem. A randomised controlled study is necessary for clarification.

METHODS AND ANALYSIS

This is a multicentre, investigator-initiated, open-label, randomised controlled superiority 1:1 study comparing colistin monotherapy with colistin-meropenem combination therapy for infections caused by carbapenem-resistant Gram-negative bacteria. The study is being conducted in 6 centres in 3 countries (Italy, Greece and Israel). We include patients with hospital-associated and ventilator-associated pneumonia, bloodstream infections and urosepsis. The primary outcome is treatment success at day 14, defined as survival, haemodynamic stability, stable or improved respiratory status for patients with pneumonia, microbiological cure for patients with bacteraemia and stability or improvement of the Sequential Organ Failure Assessment (SOFA) score. Secondary outcomes include 14-day and 28-day mortality as well as other clinical end points and safety outcomes. A sample size of 360 patients was calculated on the basis of an absolute improvement in clinical success of 15% with combination therapy. Outcomes will be assessed by intention to treat. Serum colistin samples are obtained from all patients to obtain population pharmacokinetic models. Microbiological sampling includes weekly surveillance samples with analysis of resistance mechanisms and synergy. An observational trial is evaluating patients who met eligibility requirements but were not randomised in order to assess generalisability of findings.

ETHICS AND DISSEMINATION

The study was approved by ethics committees at each centre and informed consent will be obtained for all patients. The trial is being performed under the auspices of an independent data and safety monitoring committee and is included in a broad dissemination strategy regarding revival of old antibiotics.

TRIAL REGISTRATION NUMBER

NCT01732250 and 2012-004819-31; Pre-results.

Predicting and preventing antimicrobial resistance utilizing pharmacodynamics: Part I gram positive bacteria

INTRODUCTION

Antimicrobial resistance is a potentially inevitable consequence of widespread use of antibiotics in the healthcare system. An enhanced understanding of pharmacodynamic (PD) targets that prevent antimicrobial resistance development will improve currently availably therapies and help to guide future drug development strategies. Current in vitro methods to predict bacterial resistance to antimicrobials consist of serial dilution experiments, determination of the mutant prevention concentration (MPC), mutant selection window (MSW), and human simulated pharmacodynamics studies. Clinical trial data and real -world surveillance studies can help validate or disprove in vitro modeling.

AREAS COVERED

This review will discuss methods of predicting development of resistance and how the use of pharmacodynamics can reduce or eliminate the emergence of resistance among Staphylococcus aureus, Streptococcus pneumoniae, and Enterococcus species.

EXPERT OPINION

Pharmacodynamic targets can be used successfully to guide antimicrobial therapy to prevent resistance development. Currently, PD targets do not take into consideration horizontal resistance gene transfer and various factors may lead to different PD targets based on sites of infection. Further research is necessary to guide future drug development strategies and optimize new drug therapies.