Emergence and spread of antibiotic resistance following exposure to antibiotics

Water depollution using metal-organic frameworks-catalyzed advanced oxidation processes: A review

This paper presents a review on the environmental applications of metal-organic frameworks (MOFs), which are inorganic-organic hybrid highly porous crystalline materials, prepared from metal ion/clusters and multidentate organic ligands. The emphases are made on the enhancement of the performance of advanced oxidation processes (AOPs) (photocatalysis, Fenton reaction methods, and sulfate radical (SO₄^-)-mediated oxidations) using MOFs materials. MOFs act as adsorption and light absorbers, leading to superior performance of photocatalytic processes. More recent examples of photocatalytic degradation of dyes are presented. Additionally, it is commonly shown that Fe-based MOFs exhibited excellent catalytic performance on the Fenton-based and SO₄^•--mediated oxidations of organic pollutants (e.g., dyes, phenol and pharmaceuticals). The significantly enhanced generation of reactive species such as OH and/or SO₄^- by both homogeneous and heterogeneous catalysis was proposed as the possible mechanism for water depollution. Based on the existing literature, the challenge and future perspectives in MOF-based AOPs are addressed.

Development of de novo resistance in Salmonella Typhimurium treated with antibiotic combinations

This study was designed to evaluate the evolution of antibiotic resistance in Salmonella enterica serovar Typhimurium treated with the combination of antibiotics. The experimental evolution of antibiotic resistance of S. Typhimurium was evaluated either under single antibiotic (kanamycin, KAN; penicillin, PEN; erythromycin, ERY) or in combination of two antibiotics (KAN + PEN or KAN + ERY) as measured by fractional inhibitory concentrations (FICs), stepwise resistance selection, cross-resistance evaluation, resistance fitness and relative gene expression. KAN + PEN and KAN + ERY showed the synergistic effect against S. Typhimurium (FIC index < 0.5). KAN + ERY delayed the induction of de novo mutations in S. Typhimurium. The cross-resistance of S. Typhimurium to all antibiotics except ERY and tetracycline was observed in KAN and PEN alone. The fitness cost was lower in single antibiotic treatments than combinations. The highest relative fitness was 0.91 in PEN, followed by KAN (0.84) and ERY (0.78), indicating the low fitness costs in single antibiotic treatments. The overexpression of efflux pump-related genes (acrA and acrB), outer membrane-related gene (ompC) and adherence-related gene (csgD) were observed in the single antibiotic treatments. Our results suggest that KAN + PEN and KAN + ERY could be used as a potential therapeutic treatment by decreasing the evolution of antibiotic resistance in S. Typhimurium and reusing conventional antibiotics.

A Systematic Review and Meta-analysis of Antibiotic Treatment Duration for Bacteremia Due to Enterobacteriaceae

The duration of antibiotic therapy for bacteremia due to Enterobacteriaceae is not well defined. We sought to evaluate the clinical outcomes with shorter- versus longer-course treatment. We performed a systematic search of the PubMed and EMBASE databases through May 2018. Studies presenting comparative outcomes between patients receiving antibiotic treatment for ≤10 days ("short-course") and those treated for >10 days ("long-course") were considered eligible. Four retrospective cohort studies and one randomized controlled trial comprising 2,865 patients met the inclusion criteria. The short- and long-course antibiotic treatments did not differ in 30-day all-cause mortality (1,374 patients; risk ratio [RR] = 0.99; 95% confidence interval [CI], 0.69 to 1.43), 90-day all-cause mortality (1,750 patients; RR = 1.16; 95% CI, 0.81 to 1.66), clinical cure (1,080 patients; RR = 1.02; 95% CI, 0.96 to 1.08), or relapse at 90 days (1,750 patients; RR = 1.08; 95% CI, 0.69 to 1.67). In patients with bacteremia due to Enterobacteriaceae, the short- and long-course antibiotic treatments did not differ significantly in terms of clinical outcomes. Further well-designed studies are needed before treatment for 10 days or less is adopted in clinical practice.

Conjugated Oligo- and Polymers for Bacterial Sensing

Fast and accurate detection of bacteria and differentiation between pathogenic and commensal colonization are important keys in preventing the emergence and spread of bacterial resistance toward antibiotics. As bacteria undergo major lifestyle changes during colonization, bacterial sensing needs to be achieved on different levels. In this review, we describe how conjugated oligo- and polymers are used to detect bacterial colonization. We summarize how oligothiophene derivatives have been tailor-made for detection of biopolymers produced by a wide range of bacteria upon entering the biofilm lifestyle. We further describe how these findings are translated into diagnostic approaches for biofilm-related infections. Collectively, this provides an overview on how synthetic biorecognition elements can be used to produce fast and easy diagnostic tools and new methods for infection control.

Ozenoxacin: a review of preclinical and clinical efficacy

INTRODUCTION

Impetigo is the most common bacterial skin infection in children. Treatment is becoming complicated due to the development of antimicrobial resistance, especially in the main pathogen, Staphylococcus aureus. Ozenoxacin, a novel non-fluorinated topical quinolone antimicrobial, has demonstrated efficacy in impetigo. Areas covered: This article reviews the microbiology, pharmacodynamic and pharmacokinetic properties of ozenoxacin, and its clinical and microbiological efficacy in impetigo. Expert opinion: In an environment of increasing antimicrobial resistance and concurrent slowdown in antimicrobial development, the introduction of a new agent is a major event. Ozenoxacin is characterized by simultaneous affinity for DNA gyrase and topoisomerase IV, appears to be impervious to certain efflux pumps that confer bacterial resistance to other quinolones, shows low selection of resistant mutants, and has a mutant prevention concentration below its concentration in skin. These mechanisms protect ozenoxacin against development of resistance, while the absence of a fluorine atom in its structure confers a better safety profile versus fluoroquinolones. In vitro studies have demonstrated high potency of ozenoxacin against staphylococci and streptococci including resistant strains of S. aureus. Clinical trials of ozenoxacin in patients with impetigo reported high clinical and microbiological success rates. Preserving the activity and availability of ozenoxacin through antimicrobial stewardship is paramount.

Mutations in gyrB play an important role in ciprofloxacin-resistant Pseudomonas aeruginosa

Purpose

To investigate the main molecular resistance mechanisms to fluoroquinolones (FQs) in Pseudomonas aeruginosa and also to investigate the effect of time and concentration on mutations in resistance genes.

Materials and methods

The clinical isolates of P. aeruginosa which are sensitive to ciprofloxacin (CIP) or levofloxacin (LEV) were collected. The isolates were incubated with different concentrations of CIP or LEV for 5 days and the minimal inhibitory concentrations (MICs) of CIP, LEV and ofloxacin (OFX) were measured. The MIC of FQs to P. aeruginosa was measured by the agar dilution method. FQ resistance determining regions of gyrA, gyrB, parC and parE were amplified by PCR, and mutations in four genes were explored using sequence analysis with the Snapgene software. The relative expression levels of two efflux pumps genes (mexA and mexE) were measured by quantitative reverse transcription PCR.

Results

A total of eleven isolates were collected from the Second Hospital of Shanxi Medical University. Amino acid alterations in gyrA and gyrB were mainly detected in resistant mutants, and the percentage of strains with amino acid alterations in gyrB was significantly higher than that in gyrA (P<0.001). MICs of strains with mutations both in gyrA and gyrB were not significantly higher than those of strains with mutations only in gyrB (P>0.05). No amino acid alterations were detected in genes of parC and parE. In both gyrA and gyrB, the number of amino acid alterations increased with incubation time prolonged and increased with increasing incubation concentration.

Conclusion

CIP was more competent than LEV in making P. aeruginosa resistant to in vitro selection. Mutations occurring in gyrB played an important role in FQ resistance of P. aeruginosa in vitro selection.

Comparison of in vitro static and dynamic assays to evaluate the efficacy of an antimicrobial drug combination against Staphylococcus aureus

An easily implementable strategy to reduce treatment failures in severe bacterial infections is to combine already available antibiotics. However, most in vitro combination assays are performed by exposing standard bacterial inocula to constant concentrations of antibiotics over less than 24h, which can be poorly representative of clinical situations. The aim of this study was to assess the ability of static and dynamic in vitro Time-Kill Studies (TKS) to identify the potential benefits of an antibiotic combination (here, amikacin and vancomycin) on two different inoculum sizes of two S. aureus strains. In the static TKS (sTKS), performed by exposing both strains over 24h to constant antibiotic concentrations, the activity of the two drugs combined was not significantly different the better drug used alone. However, the dynamic TKS (dTKS) performed over 5 days by exposing one strain to fluctuating concentrations representative of those observed in patients showed that, with the large inoculum, the activities of the drugs, used alone or in combination, significantly differed over time. Vancomycin did not kill bacteria, amikacin led to bacterial regrowth whereas the combination progressively decreased the bacterial load. Thus, dTKS revealed an enhanced effect of the combination on a large inoculum not observed in sTKS. The discrepancy between the sTKS and dTKS results highlights that the assessment of the efficacy of a combination for severe infections associated with a high bacterial load could be demanding. These situations probably require the implementation of dynamic assays over the entire expected treatment duration rather than the sole static assays performed with steady drug concentrations over 24h.

Characterization of Two New Multidrug-Resistant Strains of Mycobacterium smegmatis: Tools for Routine In Vitro Screening of Novel Anti-Mycobacterial Agents

Mycobacterium tuberculosis is a pathogen of global public health concern. This threat is exacerbated by the emergence of multidrug-resistant and extremely-drug-resistant strains of the pathogen. We have obtained two distinct clones of multidrug-resistant Mycobacterium smegmatis after gradual exposure of Mycobacterium smegmatis mc² 155 to increasing concentrations of erythromycin. The resulting resistant strains of Mycobacterium smegmatis exhibited robust viability in the presence of high concentrations of erythromycin and were found to be resistant to a wide range of other antimicrobials. They also displayed a unique growth phenotype in comparison to the parental drug-susceptible Mycobacterium smegmatis mc² 155, and a distinct colony morphology in the presence of cholesterol. We propose that these two multidrug-resistant clones of Mycobacterium smegmatis could be used as model organisms at the inceptive phase of routine in vitro screening of novel antimicrobial agents targeted against multidrug-resistant Mycobacterial tuberculosis.

Sequential Combined Effect of Phages and Antibiotics on the Inactivation of Escherichia coli

The emergence of antibiotic resistance in bacteria is a global concern. The use of bacteriophages (or phages) alone or combined with antibiotics is consolidating itself as an alternative approach to inactivate antibiotic-resistant bacteria. However, phage-resistant mutants have been considered as a major threat when phage treatment is employed. Escherichia coli is one of the main responsible pathogens for moderate and serious infections in hospital and community environments, being involved in the rapid evolution of fluoroquinolones and third-generation cephalosporin resistance. The aim of this study was to evaluate the effect of combined treatments of phages and antibiotics in the inactivation of E. coli. For this, ciprofloxacin at lethal and sublethal concentrations was added at different times (0, 6, 12 and 18 h) and was tested in combination with the phage ELY-1 to inactivate E. coli. The efficacy of the combined treatment varied with the antibiotic concentration and with the time of antibiotic addition. The combined treatment prevented bacterial regrowth when the antibiotic was used at minimum inhibitory concentration (MIC) and added after 6 h of phage addition, causing less bacterial resistance than phage and antibiotic applied alone (4.0 × 10-7 for the combined treatment, 3.9 × 10-6 and 3.4 × 10-5 for the antibiotics and the phages alone, respectively). Combined treatment with phage and antibiotic can be effective in reducing the bacterial density and it can also prevent the emergence of resistant variants. However, the antibiotic concentration and the time of antibiotic application are essential factors that need to be considered in the combined treatment.

Evaluating biological plausibility in supporting evidence for action through systematic reviews in public health

OBJECTIVES

The objective of this research was to develop and test methods for accessing and evaluating information on the biological plausibility of observed associations between exposures or interventions and outcomes to generate scientific evidence for action consistent with practice in systematic reviews.

STUDY DESIGN

To undertake this research, we used the example of the observed associations between antimicrobial use in food animals and increased risks of human exposures to antimicrobial-resistant pathogens of zoonotic origin.

METHODS

We conducted a scoping search using terms related to biological plausibility or mechanism to identify key references. As recommended by these references, we also used expert consultation with researchers and a public health informationist. We used their recommendations, which included expert consultation, to identify mechanisms relevant to biological plausibility of the association we selected to test. We used the reviews conducted by the World Health Organization (WHO) Guidelines Development Group in support of reducing antimicrobial use in food animal production to populate our model for assessing biological plausibility.

RESULTS

We were able to develop a transparent model for biological plausibility based on the adverse outcome pathway used in toxicology and ecology. We were also able to populate this model using the WHO reviews.

CONCLUSIONS

This analysis of biological plausibility used transparent and validated methods to assess the evidence used in systematic reviews based on the observational studies accessed through searches of the scientific literature. Given the importance of this topic in systematic reviews and evidence-based decision-making, further research is needed to define and test the methodological approaches to access and properly evaluate information from the scientific literature.

From General to Specific: Can Pseudomonas Primary Metabolism Be Exploited for Narrow-Spectrum Antibiotics?

The spread of antimicrobial resistance is a major threat to human health, and patients requiring prolonged antibiotic exposure are in desperate need of new therapeutic strategies. It has been hypothesized that tailoring our antibiotics to inhibit molecular targets specific to pathogens might stem the spread of resistance. A prime candidate for such a strategy is Pseudomonas aeruginosa, which can be found in the lungs of nearly all adult cystic fibrosis patients and, due to chronic exposure to antibiotics, has a high rate of multidrug-resistant strains. Although much research has been done on P. aeruginosa virulence factors as narrow-spectrum targets, less attention has been paid to primary carbon metabolism being leveraged for pathogen-specific mechanisms. However, early studies show that primary metabolic pathways, although shared amongst all organisms, contain intricacies specific to Pseudomonas species that have potential for antibiotic exploitation. Here we lay out some of this work in the hopes that it inspires researchers to continue developing a knowledge base for future antibiotic discovery to build upon and include a case study of a Pseudomonas primary metabolic pathway that has been targeted by small molecules in a species-specific manner.

Enhanced Bacterial Fitness Under Residual Fluoroquinolone Concentrations Is Associated With Increased Gene Expression in Wastewater-Derived qnr Plasmid-Harboring Strains

Plasmids harboring qnr genes confer resistance to low fluoroquinolone concentrations. These genes are of significant clinical, evolutionary and environmental importance, since they are widely distributed in a diverse array of natural and clinical environments. We previously extracted and sequenced a large (∼185 Kbp) qnrB-harboring plasmid, and several small (∼8 Kbp) qnrS-harboring plasmids, from Klebsiella pneumoniae isolates from municipal wastewater biosolids, and hypothesized that these plasmids provide host bacteria a selective advantage in wastewater treatment plants (WWTPs) that often contain residual concentrations of fluoroquinolones. The objectives of this study were therefore to determine the effect of residual fluoroquinolone concentrations on the growth kinetics of qnr plasmid-harboring bacteria; and on the copy number of qnr plasmids and expression of qnr genes. Electrotransformants harboring either one of the two types of plasmids could grow at ciprofloxacin concentrations exceeding 0.5 μg ml^-1, but growth was significantly decreased at concentrations higher than 0.1 μg ml^-1. In contrast, plasmid-free strains failed to grow even at 0.05 μg ml^-1. No differences were observed in plasmid copy number under the tested ciprofloxacin concentrations, but qnr expression increased incrementally from 0 to 0.4 μg ml^-1, suggesting that the transcription of this gene is regulated by antibiotic concentration. This study reveals that wastewater-derived qnr plasmids confer a selective advantage in the presence of residual fluoroquinolone concentrations and provides a mechanistic explanation for this phenomenon.

Knowledge, attitude and practice of antibiotic use and misuse among adults in Riyadh, Saudi Arabia

Objectives:

To assess the knowledge, attitude, and practice of antibiotics (ABs) use and misuse among adults living in Riyadh, Saudi Arabia.

Methods:

In this cross-sectional study, a self-administered questionnaire was distributed to participants from March 2016 to January 2017 in the outpatient department of King Khalid University Hospital and Dental Hospital, King Saud University, Riyadh, Saudi Arabia. The questionnaire was divided into 4 sections. The first and second section inquired regarding demographic details and knowledge of ABs. The third section assessed practice of ABs and the fourth section assessed attitude of participants towards ABs use. Questionnaires were hand delivered to respondents using convenience sampling. Statistical analysis using frequency distributions and knowledge responses of AB resistance for ‘yes’ and ‘no’ were associated with participant characteristics using Chi-square test.

Results:

A total of 1966 questionnaires were completed (response rate: 93.5%). Sixty-seven percent of the respondents were unaware of the meaning of ABs resistance. Sixty-seven percent of respondents were unaware of ABs being harmful for children’s teeth and 64.9% unaware of ABs that develop allergy and death. Twenty-four percent believed that ABs worked on viruses, 31% on cold and 21% can cure cough. Almost 51% used ABs without physician prescription while 37.5% obtained ABs directly from pharmacists without physician’s prescription. Almost 42% participants discontinued ABs on alleviation of symptoms. There was significant difference in knowledge response of AB resistance and source of AB use (p=0.026), reason of AB use (p=0.038) and discontinuation of ABs (p=0.041).

Conclusion:

Adults showed insufficient knowledge and understanding regarding the safe use of ABs consumption among the population.

Impact of primary antibiotic resistance on the effectiveness of sequential therapy for Helicobacter pylori infection: lessons from a 5-year study on a large number of strains

BACKGROUND

The increasing prevalence of strains resistant to antimicrobial agents is a critical issue in the management of Helicobacter pylori (H. pylori) infection.

AIMS

(1) To evaluate the prevalence of primary resistance to clarithromycin, metronidazole and levofloxacin (2) to assess the effectiveness of sequential therapy on resistant strains (3) to identify the minimum number of subjects to enrol for evaluating the effectiveness of an eradication regimen in patients harbouring resistant strains.

METHODS

Consecutive 1682 treatment naïve H. pylori-positive patients referred for upper GI endoscopy between 2010 and 2015 were studied and resistances assessed by E-test. Sequential therapy was offered, effectiveness evaluated and analysed.

RESULTS

H. pylori-primary resistance to antimicrobials tested was high, and increased between 2010 and 2015. Eradication rates were (estimates and 95% CIs): 97.3% (95.6-98.4) in strains susceptible to clarithromycin and metronidazole; 96.1% (91.7-98.2) in strains resistant to metronidazole but susceptible to clarithromycin; 93.4% (88.2-96.4) in strains resistant to clarithromycin but susceptible to metronidazole; 83.1% (77.7-87.3) in strains resistant to clarithromycin and metronidazole. For any treatment with a 75%-85% eradication rate, some 98-144 patients with resistant strains need to be studied to get reliable information on effectiveness in these patients.

CONCLUSIONS

H. pylori-primary resistance is increasing and represents the most critical factor affecting effectiveness. Sequential therapy eradicated 83% of strains resistant to clarithromycin and metronidazole. Reliable estimates of the effectiveness of a given regimen in patients harbouring resistant strains can be obtained only by assessing a large number of strains.

Mutant Prevention Concentration and Mutant Selection Window of Micafungin and Anidulafungin in Clinical Candida glabrata Isolates

We report the mutant prevention concentration (MPC) and mutant selection window (MSW) for micafungin and anidulafungin administered to treat Candida glabrata We also determine the mutation frequency. We studied 20 echinocandin-susceptible, fluconazole-intermediate, and FKS wild-type C. glabrata isolates. Adjusted inocula were stroked directly onto Sabouraud agar plates containing different concentrations of micafungin or anidulafungin and visually inspected daily for up to 5 days of incubation. Individual colonies growing on the plates containing echinocandins at 1 mg/liter were selected for antifungal susceptibility testing. The FKS genes of the resulting individual phenotypically resistant colonies were sequenced, and the MPC, MSW, and mutation frequency were determined. Biofilm was quantified, and the growth kinetics and virulence (Galleria mellonella model) of the resulting individual FKS mutant colonies were studied. For micafungin and anidulafungin, we found similar results for the MPC (0.06 to 2 mg/liter and 0.25 to 2 mg/liter, respectively), MSW (0.015 to 2 mg/liter for both echinocandins), and mutation frequency (3.7 × 10-8 and 2.8 × 10-8, respectively). A total of 12 isolates were able to grow at 1 mg/liter on echinocandin-containing plates, yielding a total of 32 phenotypically resistant colonies; however, FKS2 mutations (ΔF658, S663P, W715L, and E655A) were observed only in 21 colonies. We did not find differences in biofilm formation, the kinetic parameters studied, or the median survival of larvae infected by wild-type isolates and the resulting individual FKS2 mutant colonies. Echinocandin concentrations lower than 2 mg/liter can lead to selection of resistance mutations in C. glabrata isolates in vitro.

Metal-mediated oxidation of fluoroquinolone antibiotics in water: A review on kinetics, transformation products, and toxicity assessment

Fluoroquinolones (FQs) are among the most potent antimicrobial agents, which have seen their increasing use as human and veterinary medicines to control bacterial infections. FQs have been extensively found in surface water and municipal wastewaters, which has raised great concerns due to their negative impacts to humans and ecological health. It is of utmost importance that FQs are treated before their release into the environment. This paper reviews oxidative removal of FQs using reactive oxygen (O₃ and OH), sulfate radicals (SO₄^-), and high-valent transition metal (Mn^VII and Fe^VI) species. The role of metals in enhancing the performance of reactive oxygen and sulfur species is presented. The catalysts can significantly enhance the production of OH and/or SO₄^- radicals. At neutral pH, the second-order rate constants (k, M^-1s^-1) of the reactions between FQs and oxidants follow the order as k(OH)>k(O₃)>k(Fe^VI)>k(Mn^VII). Moieties involved to transform target FQs to oxidized products and participation of the catalysts in the reaction pathways are discussed. Generally, the piperazinyl ring of FQs was found as the preferential attack site by each oxidant. Meanwhile, evaluation of aquatic ecotoxicity of the transformation products of FQs by these treatments is summarized.

A probabilistic approach to assess antibiotic resistance development risks in environmental compartments and its application to an intensive aquaculture production scenario

Estimating antibiotic pollution and antibiotic resistance development risks in environmental compartments is important to design management strategies that advance our stewardship of antibiotics. In this study we propose a modelling approach to estimate the risk of antibiotic resistance development in environmental compartments and demonstrate its application in aquaculture production systems. We modelled exposure concentrations for 12 antibiotics used in Vietnamese Pangasius catfish production using the ERA-AQUA model. Minimum selective concentration (MSC) distributions that characterize the selective pressure of antibiotics on bacterial communities were derived from the European Committee on Antimicrobial Susceptibility Testing (EUCAST) Minimum Inhibitory Concentration dataset. The antibiotic resistance development risk (RDR) for each antibiotic was calculated as the probability that the antibiotic exposure distribution exceeds the MSC distribution representing the bacterial community. RDRs in pond sediments were nearly 100% for all antibiotics. Median RDR values in pond water were high for the majority of the antibiotics, with rifampicin, levofloxacin and ampicillin having highest values. In the effluent mixing area, RDRs were low for most antibiotics, with the exception of amoxicillin, ampicillin and trimethoprim, which presented moderate risks, and rifampicin and levofloxacin, which presented high risks. The RDR provides an efficient means to benchmark multiple antibiotics and treatment regimes in the initial phase of a risk assessment with regards to their potential to develop resistance in different environmental compartments, and can be used to derive resistance threshold concentrations.

Inhaled Antimicrobials for Ventilator-Associated Pneumonia: Practical Aspects

Positive experience with inhaled antibiotics in pulmonary infections of patients with cystic fibrosis has paved the way for their utilization in mechanically ventilated, critically ill patients with lower respiratory tract infections. A successful antibiotic delivery depends upon the size of the generated particle and the elimination of drug impaction in the large airways and the ventilator circuit. Generated droplet size is mainly affected by the type of the nebulizer employed. Currently, jet, ultrasonic, and vibrating mesh nebulizers are marketed; the latter can deliver optimal antibiotic particle size. Promising novel drug-device combinations are able to release drug concentrations of 25- to 300-fold the minimum inhibitory concentration of the targeted pathogens into the pulmonary alveoli. The most important practical steps of nebulization include pre-assessment and preparation of the patient (suctioning, sedation, possible bronchodilation, adjustment of necessary ventilator settings); adherence to the procedure (drug preparation, avoidance of unnecessary tubing connections, interruption of heated humidification, removal of heat-moisture exchanger); inspection of the procedure (check for residual in drug chamber, change of expiratory filter, return sedation, and ventilator settings to previous status); and surveillance of the patient for adverse events (close monitoring of the patient and particularly of peak airway pressure and bronchoconstriction). Practical aspects of nebulization are very important to ensure optimal drug delivery and safe procedure for the patient. Therefore, the development of an operational checklist is a priority for every department adopting this modality.

Infection-stage adjusted dose of beta-lactams for parsimonious and efficient antibiotic treatments: A Pasteurella multocida experimental pneumonia in mice

In this study, the impact of infection stage on clinically and microbiologically efficacious doses and on antibiotic consumption was assessed during a naturally evolving infectious disease, using an original mouse model of pulmonary infection produced by air-borne contamination. When Pasteurella multocida was administered as pathogenic agent to immunocompetent mice, 60% of the animals exhibited clinical symptoms of pneumonia 2 to 4 days after bacterial contamination of the lungs. Two beta-lactam antibiotics were evaluated: amoxicillin and cefquinome, a fourth generation cephalosporin developed for food animals. First, a pharmacokinetic study was performed in infected mice to determine the exposure to amoxicillin or cefquinome required to treat clinically affected animals, based on the targeted values of PK/PD indices for beta-lactams. We then confirmed that these doses resulted in a 100% clinical cure rate in animals exhibiting clinical signs of infection and harboring a high pathogenic inoculum. More interestingly, we also showed that the same 100% clinical cure could be obtained in our model with 10-fold lower doses in animals at pre-patent stages of infection i.e. when harboring a low pathogenic inoculum. At the group level, antimicrobial drug consumption was reduced by treating animals at an early stage of the infection course with a pre-patent tailored dose. These results suggest that early treatment with a dose suitably adjusted to the stage of infection might help to reduce both overall antibiotic consumption and resistance selection pressure in the animals and in the environment.

Novel Antibiotic Resistance Determinants from Agricultural Soil Exposed to Antibiotics Widely Used in Human Medicine and Animal Farming

Antibiotic resistance has emerged globally as one of the biggest threats to human and animal health. Although the excessive use of antibiotics is recognized as accelerating the selection for resistance, there is a growing body of evidence suggesting that natural environments are "hot spots" for the development of both ancient and contemporary resistance mechanisms. Given that pharmaceuticals can be entrained onto agricultural land through anthropogenic activities, this could be a potential driver for the emergence and dissemination of resistance in soil bacteria. Using functional metagenomics, we interrogated the "resistome" of bacterial communities found in a collection of Canadian agricultural soil, some of which had been receiving antibiotics widely used in human medicine (macrolides) or food animal production (sulfamethazine, chlortetracycline, and tylosin) for up to 16 years. Of the 34 new antibiotic resistance genes (ARGs) recovered, the majority were predicted to encode (multi)drug efflux systems, while a few share little to no homology with established resistance determinants. We characterized several novel gene products, including putative enzymes that can confer high-level resistance against aminoglycosides, sulfonamides, and broad range of beta-lactams, with respect to their resistance mechanisms and clinical significance. By coupling high-resolution proteomics analysis with functional metagenomics, we discovered an unusual peptide, PPP^{AZI 4}, encoded within an alternative open reading frame not predicted by bioinformatics tools. Expression of the proline-rich PPP^{AZI 4} can promote resistance against different macrolides but not other ribosome-targeting antibiotics, implicating a new macrolide-specific resistance mechanism that could be fundamentally linked to the evolutionary design of this peptide.IMPORTANCE Antibiotic resistance is a clinical phenomenon with an evolutionary link to the microbial pangenome. Genes and protogenes encoding specialized and potential resistance mechanisms are abundant in natural environments, but understanding of their identity and genomic context remains limited. Our discovery of several previously unknown antibiotic resistance genes from uncultured soil microorganisms indicates that soil is a significant reservoir of resistance determinants, which, once acquired and "repurposed" by pathogenic bacteria, can have serious impacts on therapeutic outcomes. This study provides valuable insights into the diversity and identity of resistance within the soil microbiome. The finding of a novel peptide-mediated resistance mechanism involving an unpredicted gene product also highlights the usefulness of integrating proteomics analysis into metagenomics-driven gene discovery.

Development of antibacterial conjugates using sulfamethoxazole with monocyclic terpenes: A systematic medicinal chemistry based computational approach

BACKGROUND AND OBJECTIVE

To develop 6 conjugate agents of the moribund antibiotic sulfamethoxazole (SMZ) joined to 6 individual monoterpenes, followed by protocols of medicinal chemistry as potent antibacterials, against multidrug resistant (MDR) human gruesome pathogenic bacteria.

METHODS

Antibacterial activities of the proposed conjugates were ascertained by the 'prediction of activity spectra of substances' (PASS) program. Drug-likeness parameters and toxicity profiles of conjugates were standardized with the Lipinski rule of five, using cheminformatic tools, Molsoft, molinspiration, OSIRIS and ProTox. Antibacterial activities of individual chemicals and conjugates were examined by targeting the bacterial folic acid biosynthesis enzyme, dihydropteroate synthases (DHPSs) of bacteria, Bacillus anthracis, Escherichia coli, Staphylococcus aureus, Streptococcus pneumoniae and Mycobacterium tuberculosis, with 3D structures of DHPSs from protein data bank.

RESULTS

According to the PASS program, biological spectral values of conjugate-2, conjugate-5 and conjugate-6 were ascertained effective with 'probably active' or 'Pa' value > 0.5, for anti-infective and antituberculosic activities. Using molecular docking against 5 cited bacterial DHPSs, effective docking scores of 6 monoterpenes in the specified decreasing order (kcal/mol): -9.72 (eugenol against B. anthracis), -9.61 (eugenol against S. pneumoniae), -9. 42 (safrol, against B. anthracis), -9.39 (thymol, against M. tuberculosis), -9.34 (myristicin, against S. pneumoniae) and -9.29 (thymol, against B. anthracis); whereas the lowest docking score of SMZ was -8.46kcal/mol against S. aureus DHPS. Similarly, effective docking scores of conjugates were as specified (kcal/mol.): -10.80 (conjugate-4 consisting SMZ+safrol, against M. tuberculosis), -10.78 (conjugate-5 consisting SMZ+thymol, against M. tuberculosis), -10.60 (conjugate-5 against B. anthracis), -10.26 (conjugate-2 consisting SMZ+ eugenol, against M. tuberculosis), -10.25 (conjugate-5, against S. aureus) and -10.19 (conjugate-2 against S. pneumoniae. Conjugates-2 and -5 were the most effective antibacterials based on Lipinski rule of five with lethal doses 3471 and 3500mg/kg, respectively and toxicity class levels.

CONCLUSIONS

Conjugate-2 and conjugate-5 were more effective than individual monoterpenes and SMZ, against pathogenic bacteria. Synthesis, characterization and in vitro antibacterial study with acute toxicity testing for Wister rat model of the conjugate-5 could land at success in the recorded computational trial and it could be promoted for synthesis in the control of MDR bacteria.

The use of minimum selectable concentrations (MSCs) for determining the selection of antimicrobial resistant bacteria

The use of antimicrobial compounds is indispensable in many industries, especially drinking water production, to eradicate microorganisms. However, bacterial growth is not unusual in the presence of disinfectant concentrations that would be typically lethal, as bacterial populations can develop resistance. The common metric of population resistance has been based on the Minimum Inhibitory Concentration (MIC), which is based on bacteria lethality. However, sub-lethal concentrations may also select for resistant bacteria due to the differences in bacterial growth rates. This study determined the Minimal Selective Concentrations (MSCs) of bacterial populations exposed to free chlorine and monochloramine, representing a metric that possibly better reflects the selective pressures occurring at lower disinfectant levels than MIC. Pairs of phylogenetically similar bacteria were challenged to a range of concentrations of disinfectants. The MSCs of free chlorine and monochloramine were found to range between 0.021 and 0.39 mg L^-1, which were concentrations 1/250 to 1/5 than the MICs of susceptible bacteria (MIC _susc ). This study indicates that sub-lethal concentrations of disinfectants could result in the selection of resistant bacterial populations, and MSCs would be a more sensitive indicator of selective pressure, especially in environmental systems.

Tet(C) Gene Transfer between Chlamydia suis Strains Occurs by Homologous Recombination after Co-infection: Implications for Spread of Tetracycline-Resistance among Chlamydiaceae

Chlamydia suis is a swine pathogen that has also recently been found to cause zoonotic infections of the human eye, pharynx, and gastrointestinal tract. Many strains contain a tetracycline class C gene [tet(C)] cassette that confers tetracycline resistance. The cassette was likely originally acquired by horizontal gene transfer from a Gram-negative donor after the introduction of tetracycline into animal feed in the 1950s. Various research groups have described the capacity for different Chlamydia species to exchange DNA by homologous recombination. Since over 90% of C. suis strains are tetracycline resistant, they represent a potential source for antibiotic-resistance spread within and between Chlamydiaceae species. Here, we examined the genetics of tet(C)-transfer among C. suis strains. Tetracycline-sensitive C. suis strain S45 was simultaneously or sequentially co-infected with tetracycline-resistant C. suis strains in McCoy cells. Potential recombinants were clonally purified by a harvest assay derived from the classic plaque assay. C. suis strain Rogers132, lacking transposases IS200 and IS605, was the most efficient donor, producing two unique recombinants detected in three of the 56 (5.4%) clones screened. Recombinants were found to have a minimal inhibitory concentration (MIC) of 8-16 μg/mL for tetracycline. Resistance remained stable over 10 passages as long as recombinants were initially grown in tetracycline at twice the MIC of S45 (0.032 μg/mL). Genomic analysis revealed that tet(C) had integrated into the S45 genome by homologous recombination at two unique sites depending on the recombinant: a 55 kb exchange between nrqF and pckG, and a 175 kb exchange between kdsA and cysQ. Neither site was associated with inverted repeats or motifs associated with recombination hotspots. Our findings show that cassette transfer into S45 has low frequency, does not require IS200/IS605 transposases, is stable if initially grown in tetracycline, and results in multiple genomic configurations. We provide a model for stable cassette transfer to better understand the capability for cassette acquisition by Chlamydiaceae species that infect humans, a matter of public health importance.

A Bioengineered Three-Dimensional Cell Culture Platform Integrated with Microfluidics To Address Antimicrobial Resistance in Tuberculosis

Antimicrobial resistance presents one of the most significant threats to human health, with the emergence of totally drug-resistant organisms. We have combined bioengineering, genetically modified bacteria, longitudinal readouts, and fluidics to develop a transformative platform to address the drug development bottleneck, utilizing Mycobacterium tuberculosis as the model organism. We generated microspheres incorporating virulent reporter bacilli, primary human cells, and an extracellular matrix by using bioelectrospray methodology. Granulomas form within the three-dimensional matrix, and mycobacterial stress genes are upregulated. Pyrazinamide, a vital first-line antibiotic for treating human tuberculosis, kills M. tuberculosis in a three-dimensional culture but not in a standard two-dimensional culture or Middlebrook 7H9 broth, demonstrating that antibiotic sensitivity within microspheres reflects conditions in patients. We then performed pharmacokinetic modeling by combining the microsphere system with a microfluidic plate and demonstrated that we can model the effect of dynamic antibiotic concentrations on mycobacterial killing. The microsphere system is highly tractable, permitting variation of cell content, the extracellular matrix, sphere size, the infectious dose, and the surrounding medium with the potential to address a wide array of human infections and the threat of antimicrobial resistance.

Antimicrobial resistance is a major global threat, and an emerging concept is that infection should be studied in the context of host immune cells. Tuberculosis is a chronic infection that kills over a million people every year and is becoming progressively more resistant to antibiotics. Recent major studies of shorter treatment or new vaccination approaches have not been successful, demonstrating that transformative technologies are required to control tuberculosis. We have developed an entirely new system to study the infection of host cells in a three-dimensional matrix by using bioengineering. We showed that antibiotics that work in patients are effective in this microsphere system but not in standard infection systems. We then combined microspheres with microfluidics to model drug concentration changes in patients and demonstrate the effect of increasing antibiotic concentrations on bacterial survival. This system can be widely applied to address the threat of antimicrobial resistance and develop new treatments.

Efficacy of High-Dose Meropenem (Six Grams per Day) in Treatment of Experimental Murine Pneumonia Induced by Meropenem-Resistant Pseudomonas aeruginosa

High-dose meropenem (MEPM; 6 g/day) has been approved as a treatment for purulent meningitis; however, little is known regarding its in vivo efficacy in refractory lower respiratory tract infections. The purpose of this study was to evaluate the efficacy of MEPM at 6 g/day in a murine model of severe pneumonia caused by MEPM-resistant Pseudomonas aeruginosa Experimental pneumonia induced by MEPM-resistant P. aeruginosa was treated with normal-dose MEPM (150 mg/kg of body weight, simulating a 3-g/day regimen in humans) or high-dose MEPM (500 mg/kg, simulating a 6-g/day regimen in humans). Mice treated with high-dose MEPM showed significantly restored survival relative to that of untreated mice and tended to show a survival rate higher than that of mice treated with normal-dose MEPM. The viable bacterial counts (of two clinical isolates) in the lungs decreased significantly in mice treated with high-dose MEPM from those for untreated mice (P < 0.001) or mice treated with normal-dose MEPM (P, <0.01 and <0.05). The number of inflammatory cells in the bronchoalveolar lavage fluid (BALF) was also significantly lower in mice treated with high-dose MEPM than in untreated mice. The free MEPM concentration in the epithelial lining fluid (ELF) exceeded 16 μg/ml for 85 min in mice treated with high-dose MEPM, but not for mice treated with normal-dose MEPM. Our results demonstrate that high-dose MEPM (6 g/day) might provide better protection against pneumonia caused by MEPM-resistant strains of P. aeruginosa than the dose normally administered (less than 3 g/day).

Antibiotic Resistant Superbugs: Assessment of the Interrelationship of Occurrence in Clinical Settings and Environmental Niches

The increasing threat to global health posed by antibiotic resistance remains of serious concern. Human health remains at higher risk due to several reported therapeutic failures to many life threatening drug resistant microbial infections. The resultant effects have been prolonged hospital stay, higher cost of alternative therapy, increased mortality, etc. This opinionated review considers the two main concerns in integrated human health risk assessment (i.e., residual antibiotics and antibiotic resistant genes) in various compartments of human environment, as well as clinical dynamics associated with the development and transfer of antibiotic resistance (AR). Contributions of quorum sensing, biofilms, enzyme production, and small colony variants in bacteria, among other factors in soil, water, animal farm and clinical settings were also considered. Every potential factor in environmental and clinical settings that brings about AR needs to be identified for the summative effects in overall resistance. There is a need to embrace coordinated multi-locational approaches and interrelationships to track the emergence of resistance in different niches in soil and water versus the hospital environment. The further integration with advocacy, legislation, enforcement, technological innovations and further research input and recourse to WHO guidelines on antibiotic policy would be advantageous towards addressing the emergence of antibiotic resistant superbugs.

Asymptotic profile in selection-mutation equations: Gauss versus Cauchy distributions

In this paper, we study the asymptotic (large time) behaviour of a selection-mutation-competition model for a population structured with respect to a phenotypic trait when the rate of mutation is very small. We assume that the reproduction is asexual, and that the mutations can be described by a linear integral operator. We are interested in the interplay between the time variable t and the rate ε of mutations. We show that depending on α > 0 , the limit ε → 0 with t = ε - α can lead to population number densities which are either Gaussian-like (when α is small) or Cauchy-like (when α is large).

Impact of untreated urban waste on the prevalence and antibiotic resistance profiles of human opportunistic pathogens in agricultural soils from Burkina Faso

This study examined the long-term effects of the landfill disposal of untreated urban waste for soil fertilization on the prevalence and antibiotic resistance profiles of various human opportunistic pathogens in soils from Burkina Faso. Samples were collected at three sites in the periphery of Ouagadougou during two campaigns in 2008 and 2011. At each site, amendment led to changes in physico-chemical characteristics as shown by the increase in pH, CEC, total C, total N, and metal contents. Similarly, the numbers of total heterotrophic bacteria were higher in the amended fields than in the control ones. No sanitation indicators, i.e., coliforms, Staphylococci, and Enterococci, were detected. Pseudomonas aeruginosa and Burkholderia cepacia complex (Bcc) were detected at a low level in one amended field. Stenotrophomonas maltophilia was detected from both campaigns at the three sites in the amended fields and only once in an unamended field. Diversity analysis showed some opportunistic pathogen isolates to be closely related to reference clinical strains responsible for nosocomial- or community-acquired infections in Northern countries. Antibiotic resistance tests showed that P. aeruginosa and Bcc isolates had a wild-type phenotype and that most S. maltophilia isolates had a multi-drug resistance profile with resistance to 7 to 15 antibiotics. Then we were able to show that amendment led to an increase of some human opportunistic pathogens including multi-drug resistant isolates. Although the application of untreated urban waste increases both soil organic matter content and therefore soil fertility, the consequences of this practice on human health should be considered.

Occurrences and Characterization of Antibiotic-Resistant Bacteria and Genetic Determinants of Hospital Wastewater in a Tropical Country

Wastewater discharged from clinical isolation and general wards at two hospitals in Singapore was examined to determine the emerging trends of antibiotic resistance (AR). We quantified the concentrations of 12 antibiotic compounds by analysis using liquid chromatography-tandem mass spectrometry (LC-MS/MS), antibiotic-resistant bacteria (ARB), the class 1 integrase gene (intI1), and 16 antibiotic resistance genes (ARGs) that confer resistance to 10 different clinically relevant antibiotics. A subset of 119 antibiotic-resistant isolates were phylogenetically classified and tested for the presence of ARGs encoding resistance to β-lactam antibiotics (bla_NDM, bla_KPC, bla_SHV, bla_CTX-M), amikacin [aac(6')-Ib], co-trimoxazole (sul1, sul2, dfrA), ciprofloxacin (qnrA, qnrB), and the intI1 gene. Among these resistant isolates, 80.7% were detected with intI1 and 66.4% were found to carry at least 1 of the tested ARGs. Among 3 sampled locations, the clinical isolation ward had the highest concentrations of ARB and the highest levels of ARGs linked to resistance to β-lactam (bla_KPC), co-trimoxazole (sul1, sul2, dfrA), amikacin [aac(6')-Ib], ciprofloxacin (qnrA), and intI1 We found strong positive correlations (P < 0.05) between concentrations of bacteria resistant to meropenem, ceftazidime, amikacin, co-trimoxazole, and ciprofloxacin and abundances of bla_KPC, aac(6')-Ib, sul1, sul2, dfrA, qnrA, and intI1 genes.

Growth Behavior of E. coli, Enterococcus and Staphylococcus Species in the Presence and Absence of Sub-inhibitory Antibiotic Concentrations: Consequences for Interpretation of Culture-Based Data

Culture-based approaches are used to monitor, e.g., drinking water or bathing water quality and to investigate species diversity and antibiotic resistance levels in environmental samples. For health risk assessment, it is important to know whether the growing cultures display the actual abundance of, e.g., clinically relevant antibiotic resistance phenotypes such as vancomycin-resistant Enterococcus faecium/Enterococcus faecalis (VRE) or methicillin-resistant Staphylococcus aureus. In addition, it is important to know whether sub-inhibitory antibiotic concentrations, which are present in surface waters, favor the growth of antibiotic-resistant strains. Therefore, clinically relevant bacteria were isolated from different water sources and the growth behavior of 58 Escherichia coli, 71 Enterococcus, and 120 Staphylococcus isolates, belonging to different species and revealing different antibiotic resistance patterns, was studied with respect to "environmental" antibiotic concentrations. The finding that VRE could only be detected after specific enrichment can be explained by their slow growth compared to non-resistant strains. Interpreting their absence in standardized culture-based methods as nonexistent might be a fallacy. Sub-inhibitory antibiotic concentrations that were detected in sewage and receiving river water did not specifically promote antibiotic-resistant strains. Generally, those antibiotics that influenced cell metabolism directly led to slightly reduced growth rates and less than maximal optical densities after 48 h of incubation.

Inhalable Antimicrobials for Treatment of Bacterial Biofilm-Associated Sinusitis in Cystic Fibrosis Patients: Challenges and Drug Delivery Approaches

Bacterial biofilm-associated chronic sinusitis in cystic fibrosis (CF) patients caused by Pseudomonas aeruginosa infections and the lack of available treatments for such infections constitute a critical aspect of CF disease management. Currently, inhalation therapies to combat P. aeruginosa infections in CF patients are focused mainly on the delivery of antimicrobials to the lower respiratory tract, disregarding the sinuses. However, the sinuses constitute a reservoir for P. aeruginosa growth, leading to re-infection of the lungs, even after clearing an initial lung infection. Eradication of P. aeruginosa from the respiratory tract after a first infection has been shown to delay chronic pulmonary infection with the bacteria for up to two years. The challenges with providing a suitable treatment for bacterial sinusitis include: (i) identifying a suitable antimicrobial compound; (ii) selecting a suitable device to deliver the drug to the sinuses and nasal cavities; and (iii) applying a formulation design, which will mediate delivery of a high dose of the antimicrobial directly to the site of infection. This review highlights currently available inhalable antimicrobial formulations for treatment and management of biofilm infections caused by P. aeruginosa and discusses critical issues related to novel antimicrobial drug formulation design approaches.

Direct Photolysis of Fluoroquinolone Antibiotics at 253.7 nm: Specific Reaction Kinetics and Formation of Equally Potent Fluoroquinolone Antibiotics

Three fluoroquinolone-to-fluoroquinolone antibiotic transformations were monitored during UV-C irradiation processes. In particular, the following reactions were observed: enrofloxacin-to-ciprofloxacin, difloxacin-to-sarafloxacin, and pefloxacin-to-norfloxacin. The apparent molar absorptivity and fluence-based pseudo-first-order rate constants for transformation of the six fluoroquinolones by direct photolysis at 253.7 nm were determined for the pH 2-12 range. These parameters were deconvoluted to calculate specific molar absorptivity and fluence-based rate constants for cationic, zwitterionic, and anionic fluoroquinolone species. For a typical disinfection fluence of 40 mJ/cm(2), the apparent transformation efficiencies were inflated by 2-8% when fluoroquinolone products were not considered; moreover, the overall transformation efficiencies at 400 mJ/cm(2) varied by up to 40% depending on pH. The three product antibiotics, namely ciprofloxacin, sarafloxacin, and norfloxacin, were found to be equally or more potent than the parent fluoroquinolones using an Escherichia coli-based assay. UV treatment of a solution containing difloxacin was found to increase antimicrobial activity due to formation of sarafloxacin. These results highlight the importance of considering antibiotic-to-antibiotic transformations in UV-based processes.

[Dosing regimens of antibiotics in neonates: Variations in clinical practice and what should be done?]

There is wide variation in neonatal dosages of antibiotics in clinical practice, both nationally and internationally. This reflects the lack of evaluation of drugs in this therapeutic class, although widely prescribed. Given this situation, optimization of antibiotic prescription is required to ensure efficacy and safety of neonatal treatment and reduce microbial resistance. Rational prescription should be based on the knowledge of developmental pharmacokinetics and pharmacodynamics. Rigorous studies, conducted in collaboration between neonatologists and pharmacologists, are essential to develop and validate evidence-based neonatal dosage regimens.

Inhaled Antibiotics for Gram-Negative Respiratory Infections

Gram-negative organisms comprise a large portion of the pathogens responsible for lower respiratory tract infections, especially those that are nosocomially acquired, and the rate of antibiotic resistance among these organisms continues to rise. Systemically administered antibiotics used to treat these infections often have poor penetration into the lung parenchyma and narrow therapeutic windows between efficacy and toxicity. The use of inhaled antibiotics allows for maximization of target site concentrations and optimization of pharmacokinetic/pharmacodynamic indices while minimizing systemic exposure and toxicity. This review is a comprehensive discussion of formulation and drug delivery aspects, in vitro and microbiological considerations, pharmacokinetics, and clinical outcomes with inhaled antibiotics as they apply to disease states other than cystic fibrosis. In reviewing the literature surrounding the use of inhaled antibiotics, we also highlight the complexities related to this route of administration and the shortcomings in the available evidence. The lack of novel anti-Gram-negative antibiotics in the developmental pipeline will encourage the innovative use of our existing agents, and the inhaled route is one that deserves to be further studied and adopted in the clinical arena.

Methodology in improving antibiotic implementation policies

The basic requirements of antibiotic prescribing are components of methodology; knowledge, logical reasoning, and analysis. Antimicrobial drugs are valuable but limited resources, different from other drugs and they are among the most commonly prescribed drugs all over the world. They are the only drugs which do not intentionally affect the patient. They affect the pathogens which invade the host. The emergence and spread of antibiotic-resistant pathogens are accelerated by heavy antibiotic usage. The effective antimicrobial stewardship and infection control program have been shown to limit the emergence of antimicrobial-resistant bacteria. In this respect, education for antibiotic prescribing could be designed by going through the steps of scientific methodology. A defined leadership and a coordinated multidisciplinary approach are necessary for optimizing the indication, selection, dosing, route of administration, and duration of antimicrobial therapy. In scenarios, knowledge is also as important as experience for critical decision making as is designated. In this setting, the prevalence and resistance mechanisms of antimicrobials, and their interactions with other drugs need to be observed. In this respect, infectious disease service should play an important role in improving antimicrobial use by giving advice on the appropriate use of antimicrobial agents, and implementing evidence-based guidelines.

Simultaneous assessment of the pharmacokinetics of a pleuromutilin, lefamulin, in plasma, soft tissues and pulmonary epithelial lining fluid

BACKGROUND

Lefamulin is a pleuromutilin antibiotic under evaluation for the treatment of bacterial infections, including respiratory tract infections. Currently, there are no high-quality pharmacokinetic data on drug tissue concentrations of lefamulin available.

METHODS

A single dose of intravenous lefamulin (150 mg) was given to 12 healthy men. The registered EudraCT number for this study was 2010-021938-54. Lefamulin concentrations were simultaneously measured in plasma, skeletal muscle tissue, subcutaneous adipose tissue and epithelial lining fluid (ELF) over 24 h, and corresponding pharmacokinetic parameters were calculated. Microdialysis was used to measure unbound lefamulin concentrations in skeletal muscle tissue and subcutaneous adipose tissue, which were similar to unbound lefamulin concentrations in plasma. Bronchoalveolar lavage was performed 1, 2, 4 and 8 h post-dose to determine lefamulin concentrations in ELF.

RESULTS

Unbound lefamulin levels showed a 5.7-fold higher exposure in ELF compared with that in plasma, demonstrating good penetration to the target site.

CONCLUSIONS

Lefamulin may be an addition to the therapeutic armamentarium for the treatment of infections. Simultaneous measurements of unbound drug concentration can guide target attainment for future therapeutic trials.

Multidrug Resistant CTX-M-Producing Escherichia coli: A Growing Threat among HIV Patients in India

Extended Spectrum β-Lactamases (ESBLs) confer resistance to third-generation cephalosporins and CTX-M types have emerged as the most prominent ESBLs worldwide. This study was designed to determine the prevalence of CTX-M positive ESBL-producing urinary E. coli isolates from HIV patients and to establish the association of multidrug resistance, phylogeny, and virulence profile with CTX-M production. A total of 57 ESBL producers identified among 76 E. coli strains isolated from HIV patients from South India were screened for bla_CTX-M, AmpC production, multidrug resistance, and nine virulence associated genes (VAGs), fimH, pap, afa/dra, sfa/foc, iutA, fyuA, iroN, usp, and kpsMII. The majority (70.2%) of the ESBL producers harbored bla_CTX-M and were AmpC coproducers. Among the CTX-M producers, 47.5% were found to be UPEC, 10% harbored as many as 7 VAGs, and 45% possessed kpsMII. Multidrug resistance (CIP^RSXT^RGEN^R) was significantly more common among the CTX-M producers compared to the nonproducers (70% versus 41.2%). However, 71.4% of the multidrug resistant CTX-M producers exhibited susceptibility to nitrofurantoin thereby making it an effective alternative to cephalosporins/fluoroquinolones. The emergence of CTX-M-producing highly virulent, multidrug resistant uropathogenic E. coli is of significant public health concern in countries like India with a high burden of HIV/AIDS.

Emergence of Hyper-Resistant Escherichia coli MG1655 Derivative Strains after Applying Sub-Inhibitory Doses of Individual Constituents of Essential Oils

The improvement of food preservation by using essential oils (EOs) and their individual constituents (ICs) is attracting enormous interest worldwide. Until now, researchers considered that treatments with such antimicrobial compounds did not induce bacterial resistance via a phenotypic (i.e., transient) response. Nevertheless, the emergence of genotypic (i.e., stable) resistance after treatment with these compounds had not been previously tested. Our results confirm that growth of Escherichia coli MG1655 in presence of sub-inhibitory concentrations of the ICs carvacrol, citral, and (+)-limonene oxide do not increase resistance to further treatments with either the same IC (direct resistance) or with other preservation treatments (cross-resistance) such as heat or pulsed electric fields (PEF). Bacterial mutation frequency was likewise lower when those IC's were applied; however, after 10 days of re-culturing cells in presence of sub-inhibitory concentrations of the ICs, we were able to isolate several derivative strains (i.e., mutants) displaying an increased minimum inhibitory concentration to those ICs. Furthermore, when compared to the wild type (WT) strain, they also displayed direct resistance and cross-resistance. Derivative strains selected with carvacrol and citral also displayed morphological changes involving filamentation along with cell counts at late-stationary growth phase that were lower than the WT strain. In addition, co-cultures of each derivative strain with the WT strain resulted in a predominance of the original strain in absence of ICs, indicating that mutants would not out-compete WT cells under optimal growth conditions. Nevertheless, growth in the presence of ICs facilitated the selection of these resistant mutants. Thus, as a result, subsequent food preservation treatments of these bacterial cultures might be less effective than expected for WT cultures. In conclusion, this study recommends that treatment with ICs at sub-inhibitory concentrations should be generally avoided, since it could favor the emergence of hyper-resistant strains. To ascertain the true value of EOs and their ICs in the field of food preservation, further research thus needs to be conducted on the induction of increased transient and stable bacterial resistance via such antimicrobial compounds, as revealed in this study.

Does High-Dose Antimicrobial Chemotherapy Prevent the Evolution of Resistance?

High-dose chemotherapy has long been advocated as a means of controlling drug resistance in infectious diseases but recent empirical studies have begun to challenge this view. We develop a very general framework for modeling and understanding resistance emergence based on principles from evolutionary biology. We use this framework to show how high-dose chemotherapy engenders opposing evolutionary processes involving the mutational input of resistant strains and their release from ecological competition. Whether such therapy provides the best approach for controlling resistance therefore depends on the relative strengths of these processes. These opposing processes typically lead to a unimodal relationship between drug pressure and resistance emergence. As a result, the optimal drug dose lies at either end of the therapeutic window of clinically acceptable concentrations. We illustrate our findings with a simple model that shows how a seemingly minor change in parameter values can alter the outcome from one where high-dose chemotherapy is optimal to one where using the smallest clinically effective dose is best. A review of the available empirical evidence provides broad support for these general conclusions. Our analysis opens up treatment options not currently considered as resistance management strategies, and it also simplifies the experiments required to determine the drug doses which best retard resistance emergence in patients.

The evolution of antimicrobial resistant pathogens threatens much of modern medicine. For over one hundred years, the advice has been to ‘hit hard’, in the belief that high doses of antimicrobials best contain resistance evolution. We argue that nothing in evolutionary theory supports this as a good rule of thumb in the situations that challenge medicine. We show instead that the only generality is to either use the highest tolerable drug dose or the lowest clinically effective dose; that is, one of the two edges of the therapeutic window. This approach suggests treatment options not currently considered, and simplifies the experiments required to identify the dose that best retards resistance evolution.

Quinolone resistant Aeromonas spp. as carriers and potential tracers of acquired antibiotic resistance in hospital and municipal wastewater

Members of the genus Aeromonas are recognized carriers of antibiotic resistance in aquatic environments. However, their importance on the spread of resistance from hospital effluents to the environment is poorly understood. Quinolone resistant Aeromonas spp. (n = 112) isolated from hospital effluent (HE) and from raw (RWW) and treated wastewater (TWW) of the receiving urban wastewater treatment plant (UWTP) were characterized. Species identification and genetic intraspecies diversity were assessed based on the 16S rRNA, cpn60 and gyrB genes sequence analysis. The antibiotic resistance phenotypes and genotypes (qnrA, qnrB, qnrC, qnrD, qnrS, qnrVC; qepA; oqxAB; aac(6′)-Ib-cr; blaOXA; incU) were analyzed in function of the origin and taxonomic group. Most isolates belonged to the species Aeromonas caviae and Aeromonas hydrophila (50% and 41%, respectively). The quinolone and the beta-lactamase resistance genes aac(6′)-Ib-cr and blaOXA, including gene blaOXA-101, identified for the first time in Aeromonas spp., were detected in 58% and 56% of the isolates, respectively, with identical prevalence in HE and UWTP wastewater. In contrast, the gene qnrS2 was observed mainly in isolates from the UWTP (51%) and rarely in HE isolates (3%), suggesting that its origin is not the clinical setting. Bacterial groups and genes that allow the identification of major routes of antibiotic resistance dissemination are valuable tools to control this problem. In this study, it was concluded that members of the genus Aeromonas harboring the genes aac(6′)-Ib-cr and blaOXA are relevant tracers of antibiotic resistance dissemination in wastewater habitats, while those yielding the gene qnrS2 allow the traceability from non-clinical sources.

Going beyond the Control of Quorum-Sensing to Combat Biofilm Infections

Most bacteria attach to surfaces where they form a biofilm, cells embedded in a complex matrix of polymers. Cells in biofilms are much better protected against noxious agents than free-living cells. As a consequence it is very difficult to control pathogens with antibiotics in biofilm infections and novel targets are urgently needed. One approach aims at the communication between cells to form and to maintain a biofilm, a process called quorum-sensing. Water soluble small-sized molecules mediate this process and a number of antagonists of these compounds have been found. In this review natural compounds and synthetic drugs which do not interfere with the classical quorum-sensing compounds are discussed. For some of these compounds the targets are still not known, but others interfere with the formation of exopolysaccharides, virulence factors, or cell wall synthesis or they start an internal program of biofilm dispersal. Some of their targets are more conserved among pathogens than the receptors for quorum sensing autoinducers mediating quorum-sensing, enabling a broader application of the drug. The broad spectrum of mechanisms, the diversity of bioactive compounds, their activity against several targets, and the conservation of some targets among bacterial pathogens are promising aspects for several clinical applications of this type of biofilm-controlling compound in the future.

Microspectrometric insights on the uptake of antibiotics at the single bacterial cell level

Bacterial multidrug resistance is a significant health issue. A key challenge, particularly in Gram-negative antibacterial research, is to better understand membrane permeation of antibiotics in clinically relevant bacterial pathogens. Passing through the membrane barrier to reach the required concentration inside the bacterium is a pivotal step for most antibacterials. Spectrometric methodology has been developed to detect drugs inside bacteria and recent studies have focused on bacterial cell imaging. Ultimately, we seek to use this method to identify pharmacophoric groups which improve penetration, and therefore accumulation, of small-molecule antibiotics inside bacteria. We developed a method to quantify the time scale of antibiotic accumulation in living bacterial cells. Tunable ultraviolet excitation provided by DISCO beamline (synchrotron Soleil) combined with microscopy allows spectroscopic analysis of the antibiotic signal in individual bacterial cells. Robust controls and measurement of the crosstalk between fluorescence channels can provide real time quantification of drug. This technique represents a new method to assay drug translocation inside the cell and therefore incorporate rational drug design to impact antibiotic uptake.