The effect of combining antibiotics on resistance: A systematic review and meta-analysis

When and under which conditions antibiotic combination therapy decelerates rather than accelerates resistance evolution is not well understood. We examined the effect of combining antibiotics on within-patient resistance development across various bacterial pathogens and antibiotics. We searched CENTRAL, EMBASE and PubMed for (quasi)-randomised controlled trials (RCTs) published from database inception to November 24th, 2022. Trials comparing antibiotic treatments with different numbers of antibiotics were included. A patient was considered to have acquired resistance if, at the follow-up culture, a resistant bacterium (as defined by the study authors) was detected that had not been present in the baseline culture. We combined results using a random effects model and performed meta-regression and stratified analyses. The trials' risk of bias was assessed with the Cochrane tool. 42 trials were eligible and 29, including 5054 patients, were qualified for statistical analysis. In most trials, resistance development was not the primary outcome and studies lacked power. The combined odds ratio (OR) for the acquisition of resistance comparing the group with the higher number of antibiotics with the comparison group was 1.23 (95% CI 0.68-2.25), with substantial between-study heterogeneity (I 2 =77%). We identified tentative evidence for potential beneficial or detrimental effects of antibiotic combination therapy for specific pathogens or medical conditions. The evidence for combining a higher number of antibiotics compared to fewer from RCTs is scarce and overall, is compatible with both benefit or harm. Trials powered to detect differences in resistance development or well-designed observational studies are required to clarify the impact of combination therapy on resistance.

Recent advances in the exploration of oxazolidinone scaffolds from compound development to antibacterial agents and other bioactivities

Bacterial infections cause a variety of life-threatening diseases, and the continuous evolution of drug-resistant bacteria poses an increasing threat to current antimicrobial regimens. Gram-positive bacteria (GPB) have a wide range of genetic capabilities that allow them to adapt to and develop resistance to practically all existing antibiotics. Oxazolidinones, a class of potent bacterial protein synthesis inhibitors with a unique mechanism of action involving inhibition of bacterial ribosomal translation, has emerged as the antibiotics of choice for the treatment of drug-resistant GPB infections. In this review, we discussed the oxazolidinone antibiotics that are currently on the market and in clinical development, as well as an updated synopsis of current advances on their analogues, with an emphasis on innovative strategies for structural optimization of linezolid, structure-activity relationship (SAR), and safety properties. We also discussed recent efforts aimed at extending the activity of oxazolidinones to gram-negative bacteria (GNB), antitumor, and coagulation factor Xa. Oxazolidinone antibiotics can accumulate in GNB by a conjugation to siderophore-mediated β-lactamase-triggered release, making them effective against GNB.

Linezolid-associated serotonin toxicity: a systematic review

PURPOSE

This systematic review aims to evaluate the existing evidence associating linezolid to serotonin toxicity when used as monotherapy or when co-administered with other serotonergic agents.

METHODS

A systematic literature search using PubMed (till March 2023), IDWeek meetings (2003-2023), the European Congress of Clinical Microbiology and Infectious Disease Annual Meetings (2001-2023), and the American College of Clinical Pharmacy (1999-2023) identified studies and abstracts related to linezolid and serotonin toxicity.

RESULTS

A total of 84 studies were included. The data collected in retrospective/observational studies compared the incidence of serotonin toxicity with linezolid monotherapy at 0.0050% and linezolid combination therapy at 0.0134%. All cases which discontinued linezolid and serotonergic agent/s at signs and symptoms of toxicity found symptom resolution; 75% of cases reported serotonin toxicity resolution within 24-48 h after discontinuation.

CONCLUSION

Linezolid therapy when optimal should not be deferred due to the risk of serotonin syndrome. The data collected reveals a low prevalence of serotonin toxicity in both linezolid monotherapy and linezolid concurrent with other serotonergic agents.

Oral minocycline plus rifampicin versus oral linezolid for complicated skin and skin structure infections caused by methicillin-resistant Staphylococcus aureus: The AIDA open label, randomized, controlled Phase 4 trial

BACKGROUND

The need for oral, cost-effective treatment for complicated skin and skin structure infections (cSSSIs) due to methicillin-resistant Staphylococcus aureus (MRSA) was addressed by the non-inferiority comparisons of oral minocycline plus rifampicin with linezolid.

METHODS

In the AIDA multicenter, open label, randomized, controlled clinical trial, hospitalized adults with cSSSI and documented MRSA were randomly assigned at a 2:1 ratio to either oral 600 mg rifampicin qd plus 100 mg minocycline bid or oral 600 mg linezolid bid for 10 days. The primary endpoint was the clinical cure rate in the clinically evaluable (CE) population at the test-of-cure visit (14 days). Non-inferiority was confirmed if the lower confidence limit (CI) did not fall below the accepted error margin of 15%. The study is registered with EudraCT number 2014-001276-56.

FINDINGS

123 patients recruited between November 2014 and January 2017 were randomly assigned to treatment (81 patients to minocycline plus rifampicin and 42 patients to linezolid). Cure rates were 78.% (46/59, 90% CI 67.3-86.5) and 68.6% (24/35, 90% CI 53.4-81.3), respectively (P = 0.337). The percent difference in cure rates was 9.4% (90% CI -7.2 to 26.8%). Minocycline plus rifampicin combination was deemed non-inferior to linezolid as the lower CI was -7.2% i.e. smaller than the accepted error margin of -15%. Although statistically not significant, the overall rate of adverse events was higher in the linezolid group (47.6%, 20/42 versus 38.3%, 31/81).

INTERPRETATION

Oral minocycline plus rifampicin was non-inferior to oral linezolid treatment providing alternative oral treatment for cSSSI.

FUNDING

The EU Seventh Research Framework Programme.

Current pharmacotherapy for methicillin-resistant Staphylococcus aureus (MRSA) pneumonia

INTRODUCTION

Currently, several antibiotics are active against methicillin-resistant Staphylococcus aureus (MRSA) and can be used for the treatment of pneumonia. They show great variability in terms of antibiotic class, indication, pharmacodynamic/pharmacokinetic properties, type of available formulations, spectrum of activity against bacteria other than MRSA, and toxicity profile.

AREAS COVERED

In this narrative review, the authors discuss the characteristics of currently available agents for the treatment of MRSA pneumonia.

EXPERT OPINION

The availability of different agents with anti-MRSA activity, and approved for the treatment of pneumonia can allow a personalized approach for any given patient based on the severity of the disease, the setting of occurrence, the patient's baseline risk of toxicity and drug interactions, and the possibility of oral therapy whenever early discharge or outpatient treatment are possible. Although some gray areas still remain, like the lack of high certainty evidence on the efficacy of some old agents and on the precise role of companion agents with toxin inhibitory activity in the case of necrotizing pneumonia, the frequent availability of different treatment choices, each with peculiar characteristics, is already allowing an important step toward a precision medicine approach for the treatment of MRSA pneumonia.

Synthesis, microbiological evaluation and structure activity relationship analysis of linezolid analogues with different C5-acylamino substituents

Antimicrobial resistance and lack of new antibiotics to treat multidrug-resistant (MDR) bacteria is a significant public health problem. There is a discovery void and the pipeline of new classes of antibiotics in clinical development is almost empty. Therefore, it is important to understand the structure activity relationships (SAR) of current chemical classes as that can help the drug discovery community in their efforts to develop new antibiotics by modifying existing antibiotic classes. We studied the SAR of the C5-acylaminomethyl moiety of the linezolid, an oxazolidinone antibiotic, by synthesizing 25 compounds containing various aromatic, heteroaromatic and aliphatic substitutions. Our findings suggest that this position is highly important for the function of this antibiotic class, since only smaller non-polar fragments are tolerated at this position while larger and polar ones lead to a decrease in activity compared to linezolid. Our findings have led us to construct a structure activity relationship, around the C5-acylaminomethyl moiety of linezolid, that provides valuable insight into the function of the oxazolidinone class of antibiotics.

Molecular analysis of an increase in trimethoprim/sulfamethoxazole-resistant MRSA reveals multiple introductions into a tertiary care hospital, Germany 2012-19

OBJECTIVES

Increasing spread of resistance could jeopardize the use of antifolates against MRSA infections.

METHODS

We compared the prevalence of phenotypic trimethoprim/sulfamethoxazole resistance in 20 534 clinical Staphylococcus aureus isolates (19 096 MSSA and 1438 MRSA) of non-redundant patients at Heidelberg University Hospital over 8 years and performed WGS on trimethoprim/sulfamethoxazole-resistant MRSA.

RESULTS

From 2012 to 2019, trimethoprim/sulfamethoxazole resistance in MSSA (674/19 096; 3.5%) ranged between 1.5% and 7.2% and in MRSA (135/1438; 9.4%) between 0.5% and 20.2%, reaching a peak in 2016 and 2018, respectively (Ptrend < 0.001). Trimethoprim/sulfamethoxazole resistance was more likely in outpatients than inpatients (P = 0.005), younger patients (P < 0.001), skin and soft tissue infections (SSTIs) (MRSA only, P = 0.05), submissions from pulmonology (MRSA only, P = 0.001), the upper respiratory tract (MSSA only, P < 0.001) and general surgery (MSSA only, P = 0.001). WGS of 76 trimethoprim/sulfamethoxazole-resistant MRSA revealed that 59% belonged to major pandemic CA-MRSA clones (ST22, ST8, ST398, ST772, ST30), 47% harboured Panton-Valentine leucocidin (PVL), 97% SCCmec IV/V, 71% dfrG and 28% dfrA. SNP-based phylogeny of trimethoprim/sulfamethoxazole-resistant MRSA core genomes favoured independent introduction over clonal expansion as the source, most prominently of dfrA+ trimethoprim/sulfamethoxazole-resistant ST22 MRSA from the Gaza Strip.

CONCLUSIONS

The presented results support that trimethoprim/sulfamethoxazole-resistant S. aureus, formerly associated with SSTI from outpatients and S. aureus in the (sub)tropics, is on the rise in the temperate zone, potentially due to migration. Closer monitoring of trimethoprim/sulfamethoxazole resistance in S. aureus is recommended to safeguard the effectiveness of antifolate compounds.

Environmental hotspots for antibiotic resistance genes

Bacterial resistance toward broad-spectrum antibiotics has become a major concern in recent years. The threat posed by the infectious bacteria and the pace with which resistance determinants are transmitted needs to be deciphered. Soil and water contain unique and diverse microbial communities as well as pools of naturally occurring antibiotics resistant genes. Overuse of antibiotics along with poor sanitary practices expose these indigenous microbial communities to antibiotic resistance genes from other bacteria and accelerate the process of acquisition and dissemination. Clinical settings, where most antibiotics are prescribed, are hypothesized to serve as a major hotspot. The predisposition of the surrounding environments to a pool of antibiotic-resistant bacteria facilitates rapid antibiotic resistance among the indigenous microbiota in the soil, water, and clinical environments via horizontal gene transfer. This provides favorable conditions for the development of more multidrug-resistant pathogens. Limitations in detecting gene transfer mechanisms have likely left us underestimating the role played by the surrounding environmental hotspots in the emergence of multidrug-resistant bacteria. This review aims to identify the major drivers responsible for the spread of antibiotic resistance and hotspots responsible for the acquisition of antibiotic resistance genes.

Investigator-initiated Randomized Controlled Trials in Infectious Diseases: Better Value for Money for Registration Trials of New Antimicrobials

Randomized controlled trials (RCTs) conducted by the industry are expensive, especially trials conducted for registration of new drugs for multidrug-resistant (MDR) bacteria. Lower-cost investigator-initiated trials have recently been successful in recruiting patients with severe infections caused by MDR bacteria. In this viewpoint, we contrast the aims, methods, and resulting costs of industry-led and investigator-initiated trials and ask whether contemporary registration trial costs are justified. Contract research organizations, delivering and monitoring industry-sponsored trials at a significant cost, have little incentive to make trials more efficient or less expensive. The value of universal monitoring of all trial data is questionable. We propose that clinical trial networks play a more influential role in RCT design and planning, lead adaptive risk-based trial monitoring, and work with the industry to maximize efficient recruitment and lower costs in registration trials for the approval of new antimicrobials.

The First Report on Pharmacokinetic/Pharmacodynamic Study of Trimethoprim/Sulfamethoxazole against Staphylococcus aureus with a Neutropenic Murine Thigh Infection Model

INTRODUCTION

With an increase in the incidence of Staphylococcus aureus infections in the healthcare settings and in the community, trimethoprim/sulfamethoxazole (TMP/SMX) has been suggested as a convenient treatment option. However, the appropriate dosage regimen of TMP/SMX is unclear.

OBJECTIVE

This study aimed to examine the pharmacokinetics/pharmacodynamics (PK/PD) of TMP/SMX against S. aureus using a neutropenic murine thigh infection model.

METHODS

Five S. aureus isolates with TMP/SMX (1:5 fixed ratio) minimum inhibitory concentrations (MICs) of 0.032-64 μg/mL were tested. The antimicrobial efficacy of TMP/SMX (1-689 mg/kg/day: dose shown as SMX dosage) was calculated as the change in bacterial density after 24 h of treatment. The plasma concentrations of TMP/SMX were detected using high-performance liquid chromatography.

RESULTS

After TMP/SMX single dose (130 mg/kg), the half-life, area under the blood concentration curve (AUC0-∞), and the protein binding ratio of SMX were 1.5 h, 718.2 μg h/mL, and 73.0 ± 8.3%, respectively. The free AUC/MIC and free %time (%T) above the MIC of SMX were better correlated with the in vivo antimicrobial activity than Cmax/MIC (free AUC/MIC, R2 = 0.69; free %T > MIC, R2 = 0.71; free Cmax/MIC, R2 = 0.53). The distributed doses (2-3 times per day) of TMP/SMX (130, 260, and 390 mg/kg/day) showed higher antimicrobial activity than the single dosage. However, TMP/SMX did not show its antimicrobial activity at <100% free %T > MIC.

CONCLUSIONS

The TMP/SMX treatment demonstrated that the free AUC/MIC of SMX was the better predictor of the PK/PD index of TMP/SMX.

A Narrative Review of Early Oral Stepdown Therapy for the Treatment of Uncomplicated Staphylococcus aureus Bacteremia: Yay or Nay?

Historically, intravenous (IV) antibiotics have been the cornerstone of treatment for uncomplicated Staphylococcus aureus bacteremia (SAB). However, IV antibiotics are expensive, increase the rates of hospital readmission, and can be associated with catheter-related complications. As a result, the potential role of oral antibiotics in the treatment of uncomplicated SAB has become a subject of interest. This narrative review article aims to summarize key arguments for and against the use of oral antibiotics to complete treatment of uncomplicated SAB and evaluates the available evidence for specific oral regimens. We conclude that evidence suggests that oral step-down therapy can be an alternative for select patients who meet the criteria for uncomplicated SAB and will comply with medical treatment and outpatient follow-up. Of the currently studied regimens discussed in this article, linezolid has the most support, followed by fluoroquinolone plus rifampin.

Phenazine Antibiotic-Inspired Discovery of Bacterial Biofilm-Eradicating Agents

Bacterial biofilms are surface-attached communities of slow-growing and non-replicating persister cells that demonstrate high levels of antibiotic tolerance. Biofilms occur in nearly 80 % of infections and present unique challenges to our current arsenal of antibiotic therapies, all of which were initially discovered for their abilities to target rapidly dividing, free-floating planktonic bacteria. Bacterial biofilms are credited as the underlying cause of chronic and recurring bacterial infections. Innovative approaches are required to identify new small molecules that operate through bacterial growth-independent mechanisms to effectively eradicate biofilms. One source of inspiration comes from within the lungs of young cystic fibrosis (CF) patients, who often endure persistent Staphylococcus aureus infections. As these CF patients age, Pseudomonas aeruginosa co-infects the lungs and utilizes phenazine antibiotics to eradicate the established S. aureus infection. Our group has taken a special interest in this microbial competition strategy and we are investigating the potential of phenazine antibiotic-inspired compounds and synthetic analogues thereof to eradicate persistent bacterial biofilms. To discover new biofilm-eradicating agents, we have established an interdisciplinary research program involving synthetic medicinal chemistry, microbiology and molecular biology. From these efforts, we have identified a series of halogenated phenazines (HPs) that potently eradicate bacterial biofilms, and future work aims to translate these preliminary findings into ground-breaking clinical advances for the treatment of persistent biofilm infections.

Linezolid use in German acute care hospitals: results from two consecutive national point prevalence surveys

Background

Linezolid belongs to a reserve group of antibiotics. In recent years, reports on linezolid resistance in gram-positive cocci have become more frequent. Overuse of linezolid is a relevant factor for resistance development. The objective of this study was to describe current prescription practices of linezolid in German hospitals and identify targets for antimicrobial stewardship interventions.

Methods

We analyzed all linezolid prescriptions from the datasets of the consecutive national point prevalence surveys performed in German hospitals in 2011 and 2016. In both surveys, data on healthcare-associated infections and antimicrobial use were collected following the methodology of the European Centre for Disease Prevention and Control.

Results

Overall, the percentage of linezolid among all documented antimicrobials increased significantly from 2011 to 2016 (p < 0.01). In 2011, 0.3% (119 of 41,539) patients received linezolid, in 2016 this proportion was significantly higher (0.4%; 255 of 64,412 patients; p < 0.01). In 2016, intensive care units (ICUs) were the wards most frequently prescribing linezolid. The largest proportion of patients receiving linezolid were non-ICU patients. Roughly 38% of linezolid prescriptions were for treatment of skin/soft tissue and respiratory tract infections. In 2016, linezolid was administered parenterally in 70% (n = 179) of cases. Multivariable analysis showed that the ward specialty ICU posed an independent risk factor, while Northern and Southwestern regions in Germany were independent protective factors for a high rate of linezolid prescriptions.

Conclusions

In conclusion, we detected potentials for improving linezolid prescription practices in German hospitals. Given the emergence of linezolid resistance, optimization of linezolid use must be a target of future antimicrobial stewardship activities.

Efficacy of cotrimoxazole (Sulfamethoxazole-Trimethoprim) as a salvage therapy for the treatment of bone and joint infections (BJIs)

INTRODUCTION

Cotrimoxazole (Sulfamethoxazole-Trimethoprim, SXT) has interesting characteristics for the treatment of bone and joint infection (BJI): a broad spectrum of activity with adequate bone diffusion and oral and intravenous formulations. However, its efficacy and safety in BJIs are poorly documented and its use remains limited.

METHODS

We conducted a retrospective study in 2 reference centers for BJIs from 2013 to 2018 among patients treated with SXT for a BJI. Data were collected from patient's medical charts. Outcomes and adverse events were evaluated at day (D)7, D45 and D90.

RESULTS

We analyzed 51 patients with a mean age of 60 ± 20 (SD) years of which 76% presented with an orthopedic device infection (ODI). Gram-negative bacilli (GNB) were involved in 47% of BJIs (n = 24). Moreover, they were often polymicrobial infections (41%). Doses of SXT ranged from 800/160mg bid (61%; n = 31) to 800/160mg tid (39%; n = 20). Median SXT treatment duration was 45 days (IQR 40-45). SXT was part of a dual therapy in 84% of patients (n = 43), associated mainly with fluoroquinolones (n = 17) or rifampicin (n = 14). Outcome was favorable at D7 in 98% (n = 50), at D45 in 88.2% (n = 45) and at D90 in 78.4% (n = 40). The second agent combined with SXT was not an independent factor of favorable outcome (p = 0.97). Adverse events were reported in 8% (n = 4) of patients, with a median of 21 days (IQR 20-30) from SXT initiation and led to discontinuation (n = 3).

CONCLUSION

SXT appears to be effective for treatment of BJIs as a salvage therapy, even in GNB or polymicrobial infection, including ODI. Further data are needed to confirm SXT efficacy as an alternative oral regimen in BJIs.

Efficacy of Azithromycin in a Mouse Pneumonia Model against Hospital-Acquired Methicillin-Resistant Staphylococcus aureus

The use of macrolides against pneumonia has been reported to improve survival; however, little is known about their efficacy against methicillin-resistant Staphylococcus aureus (MRSA) pneumonia. In this study, we investigated the effect of azithromycin (AZM) and compared it with that of vancomycin (VCM) and daptomycin (DAP) in a murine model of MRSA pneumonia. Mice were infected with MRSA by intratracheal injection and then treated with AZM, VCM, or DAP. The therapeutic effect of AZM, in combination or not with the other drugs, was compared in vivo, whereas the effect of AZM on MRSA growth and toxin mRNA expression was evaluated in vitro. In vivo, the AZM-treated group showed significantly longer survival and fewer bacteria in the lungs 24 h after infection than the untreated group, as well as the other anti-MRSA drug groups. No significant decrease in cytokine levels (interleukin-6 [IL-6] and macrophage inflammatory protein-2 [MIP-2]) in bronchoalveolar lavage fluid or toxin expression levels (α-hemolysin [Hla] and staphylococcal protein A [Spa]) was observed following AZM treatment. In vitro, AZM suppressed the growth of MRSA in late log phase but not in stationary phase. No suppressive effect against toxin production was observed following AZM treatment in vitro In conclusion, contrary to the situation in vitro, AZM was effective against MRSA growth in vivo in our pneumonia model, substantially improving survival. The suppressive effect on MRSA growth at the initial stage of pneumonia could underlie the potential mechanism of AZM action against MRSA pneumonia.

Randomized Noninferiority Trial of Cefoperazone-Sulbactam versus Cefepime in the Treatment of Hospital-Acquired and Healthcare-Associated Pneumonia

Cefoperazone, a third-generation cephamycin with broad-spectrum antibacterial activity and the ability to permeate bacterial cell membranes, is active against commonly encountered multidrug-resistant pathogens for hospital-acquired pneumonia (HAP) and health care-associated pneumonia (HCAP). To clarify the clinical effects of cefoperazone-sulbactam in the treatment of HAP and HCAP, we conducted an open-label, randomized, noninferiority trial that recruited patients aged ≥18 years suffering HAP/HCAP. Participants were randomly assigned to the cefoperazone-sulbactam (2 g of each per 12 h) or cefepime (2 g per 12 h) arm. Clinical and microbiological responses were evaluated at early posttherapy and test-of-cure visits. Recruited patients were allocated to subpopulations for intent-to-treat (n = 154), per-protocol (n = 147), and safety (n = 166) analyses. Intent-to-treat analysis demonstrated that (i) at the early posttherapy visit, 87.3% of patients receiving cefoperazone-sulbactam and 84.3% of patients receiving cefepime achieved clinical improvement or cure (risk difference of 3.0%; 95% confidence interval [CI], -9.0% to 15.0%), and (ii) at the test-of-cure visit, 73.1% of patients receiving cefoperazone-sulbactam and 56.8% of patients receiving cefepime were assessed as cured (risk difference of 16.3%; 95% CI, 0.0% to 33.0%). These results indicated the noninferiority of cefoperazone-sulbactam to cefepime, which was confirmed by per-protocol analysis. The chest radiographic consolidation/infiltration resolution rate, microbiological eradiation rate, and percentage of adverse events were comparable in both groups. Serious adverse events were rare, and none was judged to be related to the study drugs. Cefoperazone-sulbactam at 2 g every 12 h was noninferior to cefepime at 2 g every 2 h for patients with HCAP.

What Is the Evidence for Co-trimoxazole, Clindamycin, Doxycycline, and Minocycline in the Treatment of Methicillin-Resistant Staphylococcus aureus (MRSA) Pneumonia?

Objective: To review the evidence for trimethoprim-sulfamethoxazole (TMP-SMX), clindamycin, doxycycline, and minocycline in the treatment of methicillin-resistant Staphylococcus aureus (MRSA) pneumonia. Data Source: MEDLINE, PubMed, EMBASE, Google, Google Scholar, Cochrane Central Register of Controlled Trials from 1946 to May 20, 2019. The search was performed with the keywords methicillin-resistant Staphylococcus aureus, MRSA, Staphylococcus aureus, pneumonia, trimethoprim, sulfamethoxazole drug combination, trimethoprim, sulfamethoxazole, TMP-SMX, co-trimoxazole, clindamycin, doxycycline, and minocycline. Data Extraction: Studies reporting the use of the above antibiotics for MRSA pneumonia treatment with clinical outcomes were included. Search parameters were limited to English language and human studies only. Data Synthesis: The search yielded 16 relevant articles: 6 TMP-SMX, 8 clindamycin, zero doxycycline, and 2 minocycline. For TMP-SMX, prospective randomized trials showed variable results; however, these studies were not specifically designed to assess MRSA pneumonia treatment. Retrospective studies with clindamycin suggested that it could be used as monotherapy or in combination with other anti-MRSA antibiotics. There was no evidence for doxycycline use, but 2 small retrospective reviews appeared to support minocycline as a treatment option. Relevance to Patient Care and Clinical Practice: These antibiotics are often used in clinical practice as potential treatment options for MRSA pneumonia. This article reviews the evidence for the clinical efficacy and safety of these agents. Conclusions: There are limited data to support use of TMP-SMX, clindamycin, doxycycline, or minocycline in MRSA pneumonia treatment. Randomized controlled trials are required to determine the effectiveness of these antibiotics. Clinicians should base their decision to use these agents on a case-by-case basis depending on clinical status and susceptibility results.

Network meta-analysis and pharmacoeconomic evaluation of antibiotics for the treatment of patients infected with complicated skin and soft structure infection and hospital-acquired or ventilator-associated penumonia

Background

Infections due to methicillin-resistant Staphylococcus aureus (MRSA) cause serious health risks and significant economic burdens and the preferred drugs are still controversial.

Methods

We performed a network meta-analysis (NMA) to compare the efficacy and safety of antibiotics used to treat inpatients with complicated skin and soft structure infections (cSSSI) or hospital-acquired or ventilator-associated pneumonia (HAP/VAP). We also developed a decision tree model to assess the cost-effectiveness of antibiotics.

Results

Forty-nine randomized controlled trials met the inclusion criteria (34 for cSSSI, 15 for HAP/VAP) and compared the efficacy and safety of 16 antibiotics. For cSSSI, NMA indicated that for clinical cure, linezolid was superior than vancomycin (odds ratio (OR) 1.55, 95% confidence interval (CI) 1.19–2.02), while tedizolid (OR 1.39, CI 0.70–2.76) was similar to vancomycin. In terms of safety, there were no significant differences between any two interventions on total adverse events. Based on drug and hospital costs in America, the incremental cost-effectiveness ratios (ICERs) per life-year saved for linezolid and tedizolid compared with vancomycin were US$2833 and US$5523. For HAP/VAP, there were no significant effects either for clinical cure or for safety endpoints between linezolid and vancomycin in NMA. ICERs per life-year saved for linezolid compared with vancomycin were US$2185.

Conclusion

In these clinical trials, considering efficacy, safety, and cost-effectivenes, linezolid and tedizolid showed their superiority in MRSA cSSSI; while linezolid might be recommended to treat MRSA pneumonia. Although vancomycin was not cost-effective in pharmacoeconomic evaluation, it is still the first-line treatment for MRSA infection in the clinical practice. This study might provide new insights of therapeutic choices for patients with MRSA infections whilst awaiting the arrival of higher quality evidence.

Electronic supplementary material

The online version of this article (10.1186/s13756-019-0518-2) contains supplementary material, which is available to authorized users.

Alterations of Salmonella enterica Serovar Typhimurium Antibiotic Resistance under Environmental Pressure

Microbial horizontal gene transfer is a continuous process that shapes bacterial genomic adaptation to the environment and the composition of concurrent microbial ecology. This includes the potential impact of synthetic antibiotic utilization in farm animal production on overall antibiotic resistance issues; however, the mechanisms behind the evolution of microbial communities are not fully understood. We explored potential mechanisms by experimentally examining the relatedness of phylogenetic inference between multidrug-resistant Salmonella enterica serovar Typhimurium isolates and pathogenic Salmonella Typhimurium strains based on genome-wide single-nucleotide polymorphism (SNP) comparisons. Antibiotic-resistant S Typhimurium isolates in a simulated farm environment barely lost their resistance, whereas sensitive S Typhimurium isolates in soils gradually acquired higher tetracycline resistance under antibiotic pressure and manipulated differential expression of antibiotic-resistant genes. The expeditious development of antibiotic resistance and the ensuing genetic alterations in antimicrobial resistance genes in S Typhimurium warrant effective actions to control the dissemination of Salmonella antibiotic resistance.IMPORTANCE Antibiotic resistance is attributed to the misuse or overuse of antibiotics in agriculture, and antibiotic resistance genes can also be transferred to bacteria under environmental stress. In this study, we report a unidirectional alteration in antibiotic resistance from susceptibility to increased resistance. Highly sensitive Salmonella enterica serovar Typhimurium isolates from organic farm systems quickly acquired tetracycline resistance under antibiotic pressure in simulated farm soil environments within 2 weeks, with expression of antibiotic resistance-related genes that was significantly upregulated. Conversely, originally resistant S Typhimurium isolates from conventional farm systems lost little of their resistance when transferred to environments without antibiotic pressure. Additionally, multidrug-resistant S Typhimurium isolates genetically shared relevancy with pathogenic S Typhimurium isolates, whereas susceptible isolates clustered with nonpathogenic strains. These results provide detailed discussion and explanation about the genetic alterations and simultaneous acquisition of antibiotic resistance in S Typhimurium in agricultural environments.

Evaluation of linezolid or trimethoprim/sulfamethoxazole in combination with rifampicin as alternative oral treatments based on an in vitro pharmacodynamic model of staphylococcal biofilm

Combinations of linezolid (LZD) or trimethoprim/sulfamethoxazole (SXT) plus rifampicin (RIF) are alternative oral treatments for staphylococcal prosthetic joint infections (PJIs) when fluoroquinolones are not possible to use, but there is limited evidence regarding their activity. This study evaluated the efficacy of LZD and SXT, alone and in combination with RIF, against Staphylococcus aureus in an in vitro pharmacokinetic/pharmacodynamic biofilm model. Using the CDC Biofilm Reactor^® system, simulated regimens of LZD (600 mg every 12 h), SXT (160/800 mg every 8 h) and levofloxacin (LVX) (750 mg/day), alone and in combination with RIF (600 mg/day), were evaluated against one methicillin-susceptible S. aureus (MSSA) and one methicillin-resistant S. aureus (MRSA) strain. Antibiotic efficacy was evaluated by the decrease in planktonic bacterial counts from medium and biofilm-embedded bacteria from coupons over 56 h. Resistant strains were screened. In both strains, SXT alone was ineffective and LZD presented low activity, but no resistance emerged. Combinations with RIF significantly increased the antibiofilm efficacy against MSSA (Δlog CFU/mL 56h-0h: SXT + RIF, -2.9 and LZD + RIF, -3.1), but RIF-resistant strains appeared with SXT + RIF. Against MRSA, LZD + RIF (-3.1) protected against the emergence of resistance and was more effective than SXT + RIF (-0.6; P <0.05), in which RIF-resistant strains were again detected. LVX + RIF confirmed its high efficacy against biofilm-embedded bacteria, this being the most effective therapy (-5.1 against MSSA). The emergence of RIF-resistant strains with SXT + RIF poses serious concerns for its use in clinical practice. Interestingly, LZD + RIF appears to be an appropriate alternative for PJI caused by LVX-resistant S. aureus.

Trimethoprim/sulfamethoxazole versus vancomycin in the treatment of healthcare/ventilator-associated MRSA pneumonia: a case-control study

Objectives

Therapeutic options available to treat MRSA pneumonia are limited. Trimethoprim/sulfamethoxazole is an attractive treatment because of its bactericidal anti-MRSA activity, oral and parenteral formulations and good penetration to the lung tissue. We aimed to compare the efficacy and safety of trimethoprim/sulfamethoxazole with vancomycin in the treatment of healthcare/ventilator-associated MRSA pneumonia.

Methods

We carried out a retrospective case-control study of all consecutive hospitalized adult patients diagnosed with MRSA pneumonia at Beilinson Hospital during 2010-15 and treated with either vancomycin or trimethoprim/sulfamethoxazole. The primary outcomes were all-cause mortality at 30 days and clinical failure at the end of treatment. In order to reduce bias affecting the decision to use a specific antibiotic and as a sensitivity analysis, a propensity-score model for choosing between vancomycin and trimethoprim/sulfamethoxazole was used.

Results

We identified 42 patients with MRSA pneumonia treated with trimethoprim/sulfamethoxazole and 39 treated with vancomycin. There were no significant differences in the baseline characteristics between the groups. Vancomycin-treated patients showed significantly higher 30 day mortality on both multivariate analysis (HR = 5.28; 95% CI = 1.50-18.60; P  < 0.05) and sensitivity analysis with propensity score [vancomycin 13/24 (54.1%) versus trimethoprim/sulfamethoxazole 4/24 (16.7%); P  < 0.05], and higher clinical failure rates [vancomycin 23/39 (59%) versus trimethoprim/sulfamethoxazole 15/42 (35.7%); P  < 0.05], also in the sensitivity analysis with propensity score [vancomycin 14/24 (58.3%) versus trimethoprim/sulfamethoxazole 6/24 (25%); P  < 0.05]. The rates of side effects in both arms were comparable.

Conclusions

Trimethoprim/sulfamethoxazole appears to be superior to vancomycin in the treatment of MRSA pneumonia. A large-scale randomized controlled trial is needed to evaluate these findings.

Response Adjusted for Days of Antibiotic Risk (RADAR): evaluation of a novel method to compare strategies to optimize antibiotic use

OBJECTIVES

The Response Adjusted for Days of Antibiotic Risk (RADAR) statistic was proposed to improve the efficiency of trials comparing antibiotic stewardship strategies to optimize antibiotic use. We studied the behaviour of RADAR in a non-inferiority trial in which a β-lactam monotherapy strategy (n = 656) was non-inferior to fluoroquinolone monotherapy (n = 888) for patients with moderately severe community-acquired pneumonia.

METHODS

Patients were ranked according to clinical outcome, using five or eight categories, and antibiotic use. RADAR was calculated as the probability that the β-lactam group had a more favourable ranking than the fluoroquinolone group. To investigate the sensitivity of RADAR to detrimental clinical outcome we simulated increasing rates of 90-day mortality in the β-lactam group and performed the RADAR and non-inferiority analysis.

RESULTS

The RADAR of the β-lactam group compared with the fluoroquinolone group was 60.3% (95% CI 57.9%-62.7%) using five and 58.4% (95% CI 56.0%-60.9%) using eight clinical outcome categories, all in favour of β-lactam. Sample sizes for RADAR were 38% (250/653) and 89% (580/653) of the non-inferiority sample size calculation, using five or eight clinical outcome categories, respectively. With simulated mortality rates, loss of non-inferiority of the β-lactam group occurred at a relative risk of 1.125 in the conventional analysis, whereas using RADAR the β-lactam group lost superiority at a relative risk of mortality of 1.25 and 1.5, with eight and five clinical outcome categories, respectively.

CONCLUSIONS

RADAR favoured β-lactam over fluoroquinolone therapy for community-acquired pneumonia. Although RADAR required fewer patients than conventional non-inferiority analysis, the statistic was less sensitive to detrimental outcomes.

Are antibiotic-resistant pathogens more common in subsequent episodes of diabetic foot infection?

BACKGROUND

After antibiotic therapy of an initial diabetic foot infection (DFI), pathogens isolated from subsequent episodes might become more resistant to commonly prescribed antibiotics. If so, this might require a modification of the current recommendations for the selection of empiric antibiotic therapy. This study investigated whether the Infectious Diseases Society of America (IDSA) DFI guideline recommendations should be modified based on the number of past DFI episodes.

METHODS

This was a single-centre retrospective cohort survey of DFI patients seen during the years 2010 to 2016.

RESULTS

A total 1018 episodes of DFI in 482 adult patients were identified. These patients were followed-up for a median of 3.3 years after the first DFI episode. The total number of episodes was 2257 and the median interval between recurrent episodes was 7.6 months. Among the recurrent DFIs, the causative pathogens were the same as in the previous episode in only 43% of cases (158/365). Staphylococcus aureus was the predominant pathogen in all episodes (range 1 to 13 episodes) and was not more prevalent with the increasing number of episodes. DFIs were treated with systemic antibiotics for a median duration of 20 days (interquartile range 11-35 days). Overall, there was no significant increase in the incidence of antibiotic resistance to methicillin, rifampicin, clindamycin, or ciprofloxacin over the episodes (Pearson's Chi-square test p-values of 0.76, 1.00, 0.06, and 0.46, respectively; corresponding p-values for trend of 0.21, 0.27, 0.38, and 0.08, respectively).

CONCLUSIONS

After the successful treatment of a DFI, recurrent episodes are frequent. A history of a previous DFI episode did not predict a greater likelihood of any antibiotic-resistant isolate in subsequent episodes. Thus, broadening the spectrum of empiric antibiotic therapy for recurrent episodes of DFI does not appear necessary.

Comparing the cost-effectiveness of linezolid to trimethoprim/sulfamethoxazole plus rifampicin for the treatment of methicillin-resistant Staphylococcus aureus infection: a healthcare system perspective

OBJECTIVE

Few industry-independent studies have been conducted to compare the relative costs and benefits of drugs to treat methicillin-resistant Staphylococcus aureus (MRSA) infection. We performed a stochastic cost-effectiveness analysis comparing two treatment strategies-linezolid versus trimethoprim-sulfamethoxazole plus rifampicin-for the treatment of MRSA infection.

METHODS

We used cost and effectiveness data from a previously conducted clinical trial, complementing with other data from published literature, to compare the two regimens from a healthcare system perspective. Effectiveness was expressed in terms of quality-adjusted life-years (QALYs). Several sensitivity analyses were performed using Monte Carlo simulation, to measure the effect of potential parameter changes on the base-case model results, including potential differences related to type of infection and drug toxicity.

RESULTS

Treatment of MRSA infection with trimethoprim-sulfamethoxazole plus rifampicin and linezolid were found to cost on average €146 and €2536, and lead to a gain of 0.916 and 0.881 QALYs, respectively. Treatment with trimethoprim-sulfamethoxazole plus rifampicin was found to be more cost-effective than linezolid in the base case and remained dominant over linezolid in most alternative scenarios, including different types of MRSA infection and potential disadvantages in terms of toxicity. With a willingness-to-pay threshold of €0, €50 000 and €200 000 per QALY gained, trimethoprim-sulfamethoxazole plus rifampicin was dominant in 100%, 96% and 85% of model iterations. A 95% discount on the current purchasing price of linezolid would be needed when it goes off-patent for it to represent better value for money compared with trimethoprim-sulfamethoxazole plus rifampicin.

CONCLUSIONS

Combined treatment of trimethoprim-sulfamethoxazole plus rifampicin is more cost-effective than linezolid in the treatment of MRSA infection.

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.

Promoting Antibacterial Drug Development: Select Policies and Challenges

BACKGROUND

The development pipeline for antibacterial drugs has not met the demand of hospitals and healthcare providers struggling to cope with increasing problems of antibacterial resistance. Although the challenges associated with antibacterial drug development have been known for some time, previous efforts to address them have not been sufficient. There remains an urgent need for targeted incentives to foster antibacterial drug development while encouraging prudent use.

OBJECTIVE

We examine the effects of two types of incentives, a 5-year delay in competition from generics and a lump-sum US$50 million prize payment upon successful US Food and Drug Administration approval, on antibacterial drug company returns.

METHODS

We use the decision-tree framework developed in a study for the US Department of Health and Human Services, which models the drug company's decision process as a revenue maximizer under uncertainty.

RESULTS

Our results show that, to maximize societal benefit, such incentives need to take into consideration the indication(s) the new antibacterial drug is designed to treat as well as the drug development stage.

CONCLUSIONS

Optimal policies should maximize the difference between societal benefit, primarily measured as the reduction in public health burden from the development of a new antibacterial drug that treats an infectious disease while ensuring prudent use, and social cost. Here, we show that the two types of policies examined under-incentivize early-stage developers (i.e., do not achieve the desired outcome) and over-incentivize late-stage developers (i.e., achieve the desired outcome but at a cost that is higher than needed) ceteris paribus.

Antimicrobial activity of ceftaroline against methicillin-resistant Staphylococcus aureus (MRSA) isolates collected in 2013-2014 at the Geneva University Hospitals

Ceftaroline is a broad-spectrum antibiotic with activity against methicillin-resistant Staphylococcus aureus (MRSA) strains. Ceftaroline susceptibility of an MRSA set archived between 1994 and 2003 in the Geneva University Hospitals detected a high percentage (66 %) of ceftaroline resistance in clonotypes ST228 and ST247 and correlated with mutations in PBP2a. The ceftaroline mechanism of action is based on the inhibition of PBP2a; thus, the identification of PBP2a mutations of recently circulating clonotypes in our institution was investigated. We analyzed ceftaroline susceptibility in MRSA isolates (2013 and 2014) and established that resistant strains correlated with PBP2a mutations and specific clonotypes. Ninety-six MRSA strains were analyzed from independent patients and were isolated from blood cultures (23 %), deep infections (38.5 %), and superficial (skin or wound) infections (38.5 %). This sample showed a ceftaroline minimum inhibitory concentration (MIC) range between 0.25 and 2 μg/ml and disk diameters ranging from 10 to 30 mm, with a majority of strains showing diameters ≥20 mm. Based on the European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints, 76 % (73/96) of isolates showed susceptibility to ceftaroline. Nevertheless, we still observed 24 % (23/96) of resistant isolates (MIC = 2 μg/ml). All resistant isolates were assigned to clonotype ST228 and carried the N146K mutation in PBP2a. Only two ST228 isolates showed ceftaroline susceptibility. The decreasing percentage of ceftaroline-resistant isolates in our hospital can be explained by the decline of ST228 clonotype circulating in our hospital since 2008. We present evidence that ceftaroline is active against recent MRSA strains from our hospital; however, the presence of PBP2a variants in particular clonotypes may affect ceftaroline efficacy.

Old antibiotics for multidrug-resistant pathogens: from in vitro activity to clinical outcomes

Antimicrobial resistance is a major and emerging threat worldwide. New antimicrobials have been unable to meet the resistance challenge, and treatment options are limited for a growing number of resistant pathogens. More and more clinicians are relying on older antimicrobials for the treatment of multidrug-resistant (MDR) bacteria. Some older antimicrobials have maintained excellent in vitro activity against highly resistant pathogens. In some instances, use of older agents is limited by unfavourable pharmacokinetic/pharmacodynamic characteristics and/or toxicities. In general, clinical data pertaining to the use of older agents for the treatment of MDR pathogens are scarce. Research efforts should be focused on the evaluation of older agents for the treatment of MDR pathogens as well as evaluating how these agents perform in complex patient populations with various and multiple co-morbid conditions.

In vitro synergistic effects of various combinations of vancomycin and non-beta-lactams against Staphylococcus aureus with reduced susceptibility to vancomycin

The aim of our study was to determine the potential for synergistic effect of vancomycin combined with a non-beta-lactam agent and of combinations of orally available non-beta-lactam agents against vancomycin-intermediate S. aureus (VISA) and heterogeneous VISA (hVISA). Three VISA isolates, three hVISA isolates, and two vancomycin-susceptible S. aureus (VSSA) isolates were used. The combinations included vancomycin and one of clindamycin, ciprofloxacin, gentamicin, rifampicin, or trimethoprim/sulfamethoxazole. Pairwise combinations among five non-beta-lactam agents were also tested for synergy. Synergy was determined using time-kill curves at 24h. Vancomycin combined with either ciprofloxacin or gentamicin showed synergy against some isolates of VISA, hVISA and VSSA. Vancomycin combined with trimethoprim/sulfamethoxazole showed synergy against VISA and hVISA. Among orally available non-beta-lactam agents, only ciprofloxacin combined with either clindamycin or trimethoprim/sulfamethoxazole showed synergy against one isolate of VISA.

Rapid molecular determination of methicillin resistance in staphylococcal bacteraemia improves early targeted antibiotic prescribing: a randomized clinical trial

Empiric therapy of methicillin-susceptible Staphylococcus aureus (MSSA) infections with vancomycin is associated with poorer outcome than targeted therapy with β-lactams. Our objective was to evaluate whether rapid determination of methicillin resistance shortens the time from Gram stain to targeted antimicrobial therapy in staphylococcal bacteraemia, thereby reducing vancomycin overuse. This was a single-centre open parallel RCT. Gram-positive cocci in clusters in positive blood culture underwent real-time PCR for rapid species and methicillin resistance determination parallel to conventional microbiology. Patients were randomized 1:1 so that clinicians would be informed of PCR results (intervention group) or not (control group). Eighty-nine patients (intervention 48, control 41) were analysed. MRSA was identified in seven patients, MSSA in 46, and CoNS in 36. PCR results were highly concordant (87/89) with standard microbiology. Median time (hours) from Gram stain to transmission of methicillin-susceptibility was 3.9 (2.8-4.3) vs. 25.4 (24.4-26-7) in intervention vs. control groups (p <0.001). Median time (hours) from Gram stain to targeted treatment was similar for 'all staphylococci' [6 (3.8-10) vs. 8 (1-36) p 0.13] but shorter in the intervention group when considering S. aureus only [5 (3-7) vs. 25.5 (3.8-54) p <0.001]. When standard susceptibility testing was complete, 41/48 (85.4%) patients in the intervention group were already receiving targeted therapy compared with 23/41 (56.1%) in the control group (p 0.004). There was no significant effect on clinical outcomes. Rapid determination of methicillin resistance in staphylococcal bacteraemia is accurate and reduces significantly the time to targeted antibiotic therapy in the subgroup of S. aureus, thereby avoiding unnecessary exposure to vancomycin.

Assessment of free fatty acids and cholesteryl esters delivered in liposomes as novel class of antibiotic

BACKGROUND

Healthcare associated infections (HAI) with multidrug-resistant (MDR) bacteria continue to be a global threat, highlighting an urgent need for novel antibiotics. In this study, we assessed the potential of free fatty acids and cholesteryl esters that form part of the innate host defense as novel antibacterial agents for use against MDR bacteria.

METHODS

Liposomes of six different phospholipid mixtures were employed as carrier for six different fatty acids and four different cholesteryl esters. Using a modified MIC assay based on DNA quantification with the fluoroprobe Syto9, formulations were tested against Gram-positive and Gram-negative bacteria implicated in HAI. Formulations with MIC values in the low μg/mL range were further subjected to determination of minimal bactericidal activity, hemolysis assay with sheep erythrocytes, and cytotoxicity testing with the human liver cell line HepG2. The potential for synergistic activity with a standard antibiotic was also probed.

RESULTS

Palmitic acid and stearic acid prepared in carrier 4 (PA4 and SA4, respectively) were identified as most active lipids (MIC against MDR Staphylococcus epidermidis was 0.5 and 0.25 μg/mL, respectively; MIC against vancomycin resistant Enterococcus faecalis (VRE) was 2 and 0.5 μg/mL, respectively). Cholesteryl linoleate formulated with carrier 3 (CL3) exhibited activity against the S. epidermidis strain (MIC 1 μg/mL) and a Pseudomonas aeruginosa strain (MIC 8 μg/mL) and lowered the vancomycin MIC for VRE from 32-64 μg/mL to as low as 4 μg/mL. At 90 μg/mL PA4, SA4, and CL3 effected less than 5 % hemolysis over 3 h and PA4 and CL3 did not exhibit significant cytotoxic activity against HepG2 cells when applied at 100 μg/mL over 48 h.

CONCLUSIONS

Our results showed that selected fatty acids and cholesteryl esters packaged with phospholipids exhibit antibacterial activity against Gram-positive and Gram-negative bacteria and may augment the activity of antibiotics. Bactericidal activity could be unlinked from hemolytic and cytotoxic activity and the type of phospholipid carrier greatly influenced the activity. Thus, fatty acids and cholesteryl esters packaged in liposomes may have potential as novel lipophilic antimicrobial agents.

Silver(I) complexes with phthalazine and quinazoline as effective agents against pathogenic Pseudomonas aeruginosa strains

Five silver(I) complexes with aromatic nitrogen-containing heterocycles, phthalazine (phtz) and quinazoline (qz), were synthesized, characterized and analyzed by single-crystal X-ray diffraction analysis. Although different AgX salts reacted with phtz, only dinuclear silver(I) complexes of the general formula {[Ag(X-O)(phtz-N)]2(μ-phtz-N,N')2} were formed, X=NO3(-) (1), CF3SO3(-) (2) and ClO4(-) (3). However, reactions of qz with an equimolar amount of AgCF3SO3 and AgBF4 resulted in the formation of polynuclear complexes, {[Ag(CF3SO3-O)(qz-N)]2}n (4) and {[Ag(qz-N)][BF4]}n (5). Complexes 1-5 were evaluated by in vitro antimicrobial studies against a panel of microbial strains that lead to many skin and soft tissue, respiratory, wound and nosocomial infections. The obtained results indicate that all tested silver(I) complexes have good antibacterial activity with MIC (minimum inhibitory concentration) values in the range from 2.9 to 48.0μM against the investigated strains. Among the investigated strains, these complexes were particularly efficient against pathogenic Pseudomonas aeruginosa (MIC=2.9-29μM) and had a marked ability to disrupt clinically relevant biofilms of strains with high inherent resistance to antibiotics. On the other hand, their activity against the fungus Candida albicans was moderate. In order to determine the therapeutic potential of silver(I) complexes 1-5, their antiproliferative effect on the human lung fibroblastic cell line MRC5, has been also evaluated. The binding of complexes 1-5 to the genomic DNA of P. aeruginosa was demonstrated by gel electrophoresis techniques and well supported by molecular docking into the DNA minor groove. All investigated complexes showed an improved cytotoxicity profile in comparison to the clinically used AgNO3.

Antimicrobial resistance: one world, one fight!

The lack of new antibiotic classes calls for a cautious use of existing agents. Yet, every 10 min, almost two tons of antibiotics are used around the world, all too often without any prescription or control. The use, overuse and misuse of antibiotics select for resistance in numerous species of bacteria which then renders antimicrobial treatment ineffective. Almost all countries face increased antimicrobial resistance (AMR), not only in humans but also in livestock and along the food chain. The spread of AMR is fueled by growing human and animal populations, uncontrolled contamination of fresh water supplies, and increases in international travel, migration and trade. In this context of global concern, 68 international experts attending the fifth edition of the World HAI Resistance Forum in June 2015 shared their successes and failures in the global fight against AMR. They underlined the need for a “One Health” approach requiring research, surveillance, and interventions across human, veterinary, agricultural and environmental sectors. This strategy involves concerted actions on several fronts. Improved education and increased public awareness are a well-understood priority. Surveillance systems monitoring infections need to be expanded to include antimicrobial use, as well as the emergence and spread of AMR within clinical and environmental samples. Adherence to practices to prevent and control the spread of infections is mandatory to reduce the requirement of antimicrobials in general care and agriculture. Antibiotics need to be banned as growth promoters for farm animals in countries where it has not yet been done. Antimicrobial stewardship programmes in animal husbandry have proved to be efficient for minimising AMR, without compromising productivity. Regarding the use of antibiotics in humans, new tools to provide highly specific diagnoses of pathogens can decrease diagnostic uncertainty and improve clinical management. Finally, infection prevention and control measures – some of them as simple as hand hygiene – are essential and should be extended beyond healthcare settings. Aside from regulatory actions, all people can assist in AMR reduction by limiting antibiotic use for minor illnesses. Together, we can all work to reduce the burden of AMR.

Randomized, placebo-controlled, double-blind clinical trial to evaluate the efficacy of polyhexanide for topical decolonization of MRSA carriers

OBJECTIVES

The objective of this study was to evaluate the efficacy of polyhexanide (Prontoderm(®)) in eliminating MRSA carriage.

METHODS

In a 1900 bed teaching hospital, MRSA-colonized patients were randomized into a double-blind, placebo-controlled superiority trial between January 2011 and July 2014. Patients were treated with either polyhexanide or placebo applied to the anterior nares (thrice daily) and skin (once daily) for 10 days. The primary outcome was MRSA decolonization at day 28 (D28) after the end of treatment assessed by ITT responder and PP analyses (microbiological follow-up ± 7 days and topical treatment ≥ 5 days). Secondary outcomes included safety, emergence of resistance and MRSA genotype changes. Registered trial number ISRCTN02288276.

RESULTS

Of 2590 patients screened, 146 (polyhexanide group, 71; placebo group, 75) were included. ITT analysis showed that 24/71 (33.8%) patients in the polyhexanide group versus 22/75 (29.3%) in the placebo group were MRSA-free at D28 (risk difference, 4.5%; 95% CI, -10.6% to 19.5%; P = 0.56). PP analysis confirmed the results with 19/53 (35.8%) decolonized polyhexanide-treated patients versus 17/56 (30.4%) in the placebo arm (risk difference, 5.5%; 95% CI, -12.2% to 23%; P = 0.54). Nine serious adverse events occurred in the polyhexanide group versus 12 in the placebo group; none was attributable to study medication. Emergence of polyhexanide resistance or cross-resistance between polyhexanide and chlorhexidine was not observed. No case of exogenous recolonization by a genotypically different MRSA strain was documented.

CONCLUSIONS

This study suggests that under real-life conditions, a single polyhexanide decolonization course is not effective in eradicating MRSA carriage.

Predominance of dfrG as determinant of trimethoprim resistance in imported Staphylococcus aureus

To investigate the global occurrence of trimethoprim-sulfamethoxazole resistance and the genetic mechanisms of trimethoprim resistance, we analysed Staphylococcus aureus from travel-associated skin and soft-tissue infections treated at 13 travel clinics in Europe. Thirty-eight per cent (75/196) were trimethoprim-resistant and 21% (41/196) were resistant to trimethoprim-sulfamethoxazole. Among methicillin-resistant S. aureus, these proportions were 30% (7/23) and 17% (4/23), respectively. DfrG explained 92% (69/75) of all trimethoprim resistance in S. aureus. Travel to South Asia was associated with the highest risk of acquiring trimethoprim-sulfamethoxazole-resistant S. aureus. We conclude that globally dfrG is the predominant determinant of trimethoprim resistance in human S. aureus infection.

Trimethoprim-sulfamethoxazole versus vancomycin for severe infections caused by meticillin resistant Staphylococcus aureus: randomised controlled trial

OBJECTIVE

To show non-inferiority of trimethoprim-sulfamethoxazole compared with vancomycin for the treatment of severe infections due to meticillin resistant Staphylococcus aureus (MRSA).

DESIGN

Parallel, open label, randomised controlled trial.

SETTING

Four acute care hospitals in Israel.

PARTICIPANTS

Adults with severe infections caused by MRSA susceptible to trimethoprim-sulfamethoxazole and vancomycin. Patients with left sided endocarditis, meningitis, chronic haemodialysis, and prolonged neutropenia were excluded.

INTERVENTIONS

Trimethoprim-sulfamethoxazole 320 mg/1600 mg twice daily versus vancomycin 1 g twice daily for a minimum of seven days and then by indication.

MAIN OUTCOME MEASURES

The primary efficacy outcome was treatment failure assessed at day 7, consisting of death, persistence of haemodynamic instability or fever, stable or worsening Sequential Organ Failure Assessment score, and persistence of bacteraemia. The primary safety outcome was all cause mortality at day 30. Non-inferiority was defined by a difference of less than 15% for treatment failure.

RESULTS

252 patients were included in the trial, of whom 91 (36%) had bacteraemia. No significant difference in treatment failure was seen for trimethoprim-sulfamethoxazole (51/135, 38%) versus vancomycin (32/117, 27%)-risk ratio 1.38 (95% confidence interval 0.96 to 1.99). However, trimethoprim-sulfamethoxazole did not meet the non-inferiority criterion-absolute difference 10.4% (95% confidence interval -1.2% to 21.5%). For patients with bacteraemia, the risk ratio was 1.40 (0.91 to 2.16). In a multivariable logistic regression analysis, trimethoprim-sulfamethoxazole was significantly associated with treatment failure (adjusted odds ratio 2.00, 1.09 to 3.65). The 30 day mortality rate was 32/252 (13%), with no significant difference between arms. Among patients with bacteraemia, 14/41 (34%) treated with trimethoprim-sulfamethoxazole and 9/50 (18%) with vancomycin died (risk ratio 1.90, 0.92 to 3.93).

CONCLUSIONS

High dose trimethoprim-sulfamethoxazole did not achieve non-inferiority to vancomycin in the treatment of severe MRSA infections. The difference was particularly marked for patients with bacteraemia. Trial registration Clinical trials NCT00427076.

Vancomycin in the treatment of methicillin-resistant Staphylococcus aureus - a clinician's guide to the science informing current practice

Clinicians treating an infection assess a patient in terms of disease manifestation, causative organism and available antibiotic options with the aim of devising a therapeutic strategy under the creed of 'first, do no harm'. It is often only when treatment is failing or options are limited, as in the scenario of multidrug-resistant organisms, that consideration is given to the interplay that occurs between the microbe and the host. The emergence of Staphylococcus aureus with reduced susceptibility to vancomycin provides a prime example of these dynamic interactions. This review shall explore these concepts in relation to vancomycin for the treatment of methicillin-resistant S. aureus, with the aim of providing an informed approach to the utilization of this drug.