The Effectiveness of Combination Therapy for Treating Methicillin-Susceptible Staphylococcus aureus Bacteremia: A Systematic Literature Review and a Meta-Analysis

Management of methicillin-resistant Staphylococcus aureus bloodstream infections: a comprehensive narrative review of available evidence focusing on current controversies and the challenges ahead

INTRODUCTION

Bloodstream infections (BSIs) caused by Staphylococcus aureus are common worldwide, representing one of the most relevant issues in clinical infectious diseases practice. In particular, BSIs by methicillin-resistant S. aureus (MRSA-BSI) are still today a challenge since mortality burden remains elevated although decades of research.

AREAS COVERED

The following topics regarding MRSA-BSI were reviewed and discussed by resorting to best available evidence retrieved from PubMed/MEDLINE up to October 2024: i) epidemiology; ii) microbiology; iii) classification, with a focus on complicated and not complicated forms; iv) the structured approach to the patient; v) pharmacokinetics and pharmacodynamics of the main antimicrobial options; vi) controversies regarding the best therapeutic approach.

EXPERT OPINION

Despite ongoing efforts to better stratify and manage MRSA-BSI, there is no universally accepted classification system accurately distinguishing between uncomplicated/low risk and complicated/high risk forms. Biomarkers such as interleukin(IL)-10 hold promise in order to enable a more precise stratification, premise for an appropriate treatment plan. There is a theoretical rationale for implementing a combination therapy including a beta-lactam agent upfront, especially for patients considered at higher risk of unfavorable outcomes, but further data are necessary, and the same applies to newer adjuvants. Novel microbiological techniques may help in guiding antimicrobial duration.

Alisol A 24-Acetate combats Methicillin-Resistant Staphylococcus aureus infection by targeting the mevalonate biosynthesis

Infections caused by Methicillin-resistant Staphylococcus aureus (MRSA) have emerged as one of the most pressing global public health challenges. In concert with global rise of antimicrobial resistance at alarming rate, there is an urgent need for alternative strategies to combat MRSA. Here, the high throughput screening indicated that the Alisol A 24-acetate (AA) effectively inhibits the mevalonate (MVA) synthesis in MRSA. The mechanistic analysis revealed that AA competitively inhibits the 3-hydroxy-3-methyl glutaryl coenzyme A reductase (HMGR) protein to blockade the MVA pathway, thereby disrupting the bacterial membrane integrity and functions. Further investigations showed that this disruption consequently restores the β-lactam susceptibility in MRSA by retarding the expression of PBP2a protein and dampens the virulence of MRSA by reducing the exotoxins secretion. In addition to the effect on MRSA, AA has been found to exert host-acting activity to reduce the MRSA-induced inflammation. The promising anti-MRSA activity of AA was further confirmed in vivo. Collectively, the current study highlighted the potential of AA as a proposing drug for combating MRSA and emphasize the MVA pathway as an ideal therapeutic target for MRSA treatment.

Exploring combination treatment options for persistent methicillin-susceptible Staphylococcus aureus bacteremia

PURPOSE

This review explores the management of persistent methicillin-susceptible Staphylococcus aureus bacteremia (SAB), emphasizing the importance of timely intervention due to SAB's association with metastatic dissemination, relapse, and mortality.

SUMMARY

The literature analysis first delves into risk factors for persistent SAB, highlighting the need for effective treatment strategies. The subsequent focus is on combination strategies for persistent SAB. Daptomycin, ertapenem, ceftaroline, fosfomycin, rifampin, and gentamicin are explored as adjuncts to cefazolin or antistaphylococcal penicillins. Daptomycin combination therapy is assessed through in vivo and clinical studies, indicating potential benefits, especially with higher-risk sources of infection. Ertapenem combination therapy has been demonstrated to have a synergistic effect with cefazolin, presenting a viable salvage option. Rifampin's ability to penetrate biofilm is examined, with discussion of inconclusive evidence on mortality benefits. The review also considers stewardship implications, discussing concerns such as resistance emergence, adverse events, and increased costs associated with combination therapy. Mathematical models suggest combination therapy as an effective approach to prevent resistance. Adverse events vary with each combination, and duration of therapy remains diverse across studies in the absence of well-established dosing guidelines.

CONCLUSION

The review provides a thorough exploration of the literature on treatment of persistent SAB, underscoring the need for evidence-based guidelines, further studies, and clinical judgment in tailoring treatment strategies. The multifaceted analysis contributes valuable insights for clinicians managing this challenging condition.

Efficacy and safety of antistaphylococcal penicillin or cephazolin-based combinations versus monotherapy for methicillin-susceptible Staphylococcus aureus infective endocarditis: A propensity score analysis of nationwide prospective cohort

OBJECTIVES

We aimed to evaluate the usefulness of antistaphylococcal penicillin (ASP) or cephazolin-based combinations versus monotherapy in patients with native-valve infective endocarditis (IE) caused by methicillin-susceptible Staphylococcus aureus (MSSA).

METHODS

Post-hoc analysis of a multicentre prospective cohort. We include patients from 2008 to 2022 with definite native-valve, left-side IE due to MSSA treated primarily with ASP/cephazolin. Patients were categorized according to whether they initially received monotherapy or combination therapy for more than 72 h. A propensity score-matched cohort was planned.

RESULTS

Out of 420 included cases, 94 (22.4%) received monotherapy and 326 (77.6%) combination. Median combination duration was 14 days (interquartile range 10-20). Sixty-eight combination cases were matched with 68 monotherapy controls. Baseline characteristics were well balanced. There were no differences in in-hospital or one-year mortality between groups (OR 0.85, 95%CI 0.33-2.18 and HR 0.68, 95%CI 0.35-1.31, respectively). Endocarditis relapses and persistent bacteraemia rates were similar (0% vs 1.5%, p = 1.000; and 19.1% vs 13.2%, p = 0.352, respectively). Drug-related adverse events were more frequent in the combination group (15.0% vs 1.1%, p < 0.001).

CONCLUSIONS

Antibiotic combinations for patients with native valve left-sided MSSA endocarditis did not improve patient's outcomes. Drug-related adverse events were more frequent in combination patients.

Combination Therapy Is Not Associated with Decreased Mortality in Infectious Endocarditis: A Systematic Review and Meta-Analysis

Untreated infective endocarditis (IE) is uniformly fatal. The practice of combination antibiotic therapy for IE is recommended by treatment guidelines but largely unsupported by high-quality evidence. This study aimed to assess the efficacy of combination antibiotic therapy compared to monotherapy in IE through a systematic review and meta-analysis. We systematically searched MEDLINE, Embase, Cochrane, Web of Science, and CINAHL from inception to 29 July 2024. Studies reporting mortality outcomes of combination therapy versus monotherapy in adult patients with IE were included. Non-English papers and studies with less than 10 patients in the combination therapy group were excluded. Two reviewers independently assessed the studies and extracted relevant data. Summaries of odds ratios (ORs) with 95% confidence intervals (CIs) were evaluated using random-effects models. Out of 4545 studies identified, 32 studies (involving 2761 patients) met the inclusion criteria for the meta-analysis. There was no significant difference in the risk of all-cause mortality between the monotherapy and combination therapy groups (OR = 0.90; 95% CI = 0.67-1.20). Similar results were observed in subgroup analyses based on mortality time points, bacterial species, publication date, and type of study. Studies conducted in Europe reported a statistically significant decrease in overall mortality risk with combination therapy (OR = 0.67; 95% CI = 0.51-0.89), though this result was driven entirely by a single outlier study. Combination antibiotic therapy in patients with IE was not associated with reduced mortality.

A review of chemical signaling mechanisms underlying quorum sensing and its inhibition in Staphylococcus aureus

Staphylococcus aureus is a significant bacterium responsible for multiple infections and is a primary cause of fatalities among patients in hospital environments. The advent of pathogenic bacteria such as methicillin-resistant S. aureus revealed the shortcomings of employing antibiotics to treat bacterial infectious diseases. Quorum sensing enhances S. aureus's survivability through signaling processes. Targeting the key components of quorum sensing has drawn much interest nowadays as a promising strategy for combating infections caused by bacteria. Concentrating on the accessory gene regulator quorum-sensing mechanism is the most commonly suggested anti-virulence approach for S.aureus. Quorum quenching is a common strategy for controlling illnesses triggered by microorganisms since it reduces the pathogenicity of bacteria and improves bacterial biofilm susceptibility to antibiotics, thus providing an intriguing prospect for drug discovery. Quorum sensing inhibition reduces selective stresses and constrains the emergence of antibiotic resistance while limiting bacterial pathogenicity. This review examines the quorum sensing mechanisms involved in S. aureus, quorum sensing targets and gene regulation, environmental factors affecting quorum sensing, quorum sensing inhibition, natural products as quorum sensing inhibitory agents and novel therapeutical strategies to target quorum sensing in S. aureus as drug developing technique to augment conventional antibiotic approaches.

Emerging strategies and therapeutic innovations for combating drug resistance in Staphylococcus aureus strains: A comprehensive review

In recent years, antibiotic therapy has encountered significant challenges due to the rapid emergence of multidrug resistance among bacteria responsible for life-threatening illnesses, creating uncertainty about the future management of infectious diseases. The escalation of antimicrobial resistance in the post-COVID era compared to the pre-COVID era has raised global concern. The prevalence of nosocomial-related infections, especially outbreaks of drug-resistant strains of Staphylococcus aureus, have been reported worldwide, with India being a notable hotspot for such occurrences. Various virulence factors and mutations characterize nosocomial infections involving S. aureus. The lack of proper alternative treatments leading to increased drug resistance emphasizes the need to investigate and examine recent research to combat future pandemics. In the current genomics era, the application of advanced technologies such as next-generation sequencing (NGS), machine learning (ML), and quantum computing (QC) for genomic analysis and resistance prediction has significantly increased the pace of diagnosing drug-resistant pathogens and insights into genetic intricacies. Despite prompt diagnosis, the elimination of drug-resistant infections remains unattainable in the absence of effective alternative therapies. Researchers are exploring various alternative therapeutic approaches, including phage therapy, antimicrobial peptides, photodynamic therapy, vaccines, host-directed therapies, and more. The proposed review mainly focuses on the resistance journey of S. aureus over the past decade, detailing its resistance mechanisms, prevalence in the subcontinent, innovations in rapid diagnosis of the drug-resistant strains, including the applicants of NGS and ML application along with QC, it helps to design alternative novel therapeutics approaches against S. aureus infection.

Daptomycin Plus Oxacillin for Persistent Methicillin-Susceptible Staphylococcus aureus Bacteremia

BACKGROUND

The preferred antibiotic salvage regimen for persistent methicillin-susceptible Staphylococcus aureus bacteremia (MSSAB) is unclear. Ertapenem with cefazolin or an antistaphylococcal penicillin has been primarily described, but identifying alternative carbapenem-sparing options may support antibiotic stewardship efforts and decrease the risk of antibiotic-associated Clostridioides difficile infection.

OBJECTIVE

We sought to evaluate the effectiveness and safety of daptomycin plus oxacillin (D/O) for persistent MSSAB.

METHODS

This was a single-center, retrospective cohort of patients with persistent MSSAB who received D/O between January 1, 2014, and January 1, 2023. Adult patients were included if they had blood cultures positive for MSSA ≥72 hours and received D/O combination for ≥48 hours. Patients were excluded if they were pregnant, incarcerated, or received another antibiotic considered to have excellent activity against MSSA. The primary outcome was time to MSSA bacteremia clearance post-daptomycin initiation. Secondary outcomes included microbiological cure, hospital length of stay, 90-day all-cause mortality, MSSA bacteremia-related mortality, 90-day readmission for MSSAB, and incidence of antibiotic-associated adverse effects. Time to MSSAB clearance post-D/O initiation was plotted using Kaplan-Meier estimation.

RESULTS

Seven unique patient encounters were identified including 4 with endocarditis. Despite a median MSSA bacteremia duration of 7.8 days, median clearance was 2 days post-daptomycin initiation. All achieved microbiological cure, and no adverse effects were reported. Ninety-day all-cause mortality, MSSAB-related mortality, and 90-day readmission for MSSAB occurred in 28.6%, 14.3%, and 14.3% of patients, respectively.

CONCLUSIONS AND RELEVANCE

D/O was an effective, well-tolerated salvage regimen in this cohort and may represent a carbapenem-sparing option for persistent MSSAB.

Safety and effectiveness of fifth generation cephalosporins for the treatment of methicillin-resistant staphylococcus aureus bloodstream infections: a narrative review exploring past, present, and future

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infection (BSI) is a major issue in healthcare, since it is often associated with endocarditis or deep site foci. Relevant morbidity and mortality associated with MRSA-BSIs forced the development of new antibiotic strategies; in particular, this review will focus the attention on fifth-generation cephalosporins (ceftaroline/ceftobiprole), that are the only ß-lactams active against MRSA.

AREAS COVERED

The review discusses the available randomized controlled trials and real-world observational studies conducted on safety and effectiveness of ceftaroline/ceftobiprole for the treatment of MRSA-BSIs. Finally, a proposal of MRSA-BSI treatment flowchart, based on fifth-generation cephalosporins, is described.

EXPERT OPINION

The use of anti-MRSA cephalosporins is an acceptable choice either in monotherapy or combination therapy for the treatment of MRSA-BSIs due to their relevant effectiveness and safety. Particularly, their use may be advisable in combination therapy in case of severe infections (including endocarditis or persistent bacteriemia) or in monotherapy in subjects at higher risk of drugs-induced toxicity with older regimens. On the contrary, caution should be taken in case of suspected/ascertained central nervous system infections due to inconsistent data regarding penetration of these drugs in cerebrospinal fluid and brain tissues.

Methicillin Resistant Staphylococcus aureus: Molecular Mechanisms Underlying Drug Resistance Development and Novel Strategies to Combat

Antimicrobial resistance (AMR) represents a major threat to global health. Infection caused by Methicillin-resistant Staphylococcus aureus (MRSA) is one of the well-recognized global public health problem globally. In some regions, as many as 90% of S. aureus infections are reported to be MRSA, which cannot be treated with standard antibiotics. WHO reports indicated that MRSA is circulating in every province worldwide, significantly increasing the risk of death by 64% compared to drug-sensitive forms of the infection which is attributed to its antibiotic resistance. The emergence and spread of antibiotic-resistant MRSA strains have contributed to its increased prevalence in both healthcare and community settings. The resistance of S. aureus to methicillin is due to expression of penicillin-binding protein 2a (PBP2a), which renders it impervious to the action of β-lactam antibiotics including methicillin. The other is through the production of beta-lactamases. Although the treatment options for MRSA are limited, there are promising alternatives to antibiotics to combat the infections. Innovative therapeutic strategies with wide range of activity and modes of action are yet to be explored. The review highlights the global challenges posed by MRSA, elucidates the mechanisms underlying its resistance development, and explores mitigation strategies. Furthermore, it focuses on alternative therapies such as bacteriophages, immunotherapy, nanobiotics, and antimicrobial peptides, emphasizing their synergistic effects and efficacy against MRSA. By examining these alternative approaches, this review provides insights into the potential strategies for tackling MRSA infections and combatting the escalating threat of AMR. Ultimately, a multifaceted approach encompassing both conventional and novel interventions is imperative to mitigate the impact of MRSA and ensure a sustainable future for global healthcare.

Effectiveness of adjunctive rifampicin for treatment of Staphylococcus aureus bacteraemia: a systematic review and meta-analysis of randomized controlled trials

OBJECTIVES

To assess whether the addition of rifampicin to conventional treatment of Staphylococcus aureus bacteraemia (SAB) reduces bacteriological or clinical failure or death.

DATA SOURCES

PubMed, Embase and Cochrane CENTRAL databases were searched from inception to 31 December 2022. Reference lists and PubMed citations of eligible studies were checked.

REVIEW METHODS

Two study authors independently identified randomized controlled trials (RCTs) involving adult participants with SAB, in which an intervention group received adjunctive rifampicin and the control group received usual care with or without a placebo. Dichotomous data (bacteriological and clinical failure and deaths) were analysed and pooled across studies using risk ratio (RR) with 95% confidence intervals (CI) using a Mantel-Haenszel random-effect model. The key variable of interest being whether rifampicin was used.

RESULTS

Six RCTs including 894 participants-of which 758 (85%) were from one trial-met the inclusion criteria. The addition of rifampicin to conventional treatment of SAB significantly reduced bacteriological failure by 59% (RR 0.41, 95% CI 0.21-0.81, I2 = 0%, number need to treat 27). However, it did not reduce clinical failure (RR 0.70, 95% CI 0.47-1.03, I2 = 0%) or deaths (RR 0.96, 95% CI 0.70-1.32, I2 = 0%). Further, it did not reduce the duration of bacteraemia, or the length of hospital stay. Adjunctive rifampicin reduced SAB recurrences (1% versus 4%, P = 0.01). Emergence of rifampicin resistance during treatment was uncommon (<1%).

CONCLUSION

Although adjunctive rifampicin reduced the risk of bacteriological failure and recurrences, we found no mortality benefit to support its use in SAB.

Cloxacillin plus fosfomycin versus cloxacillin alone for methicillin-susceptible Staphylococcus aureus bacteremia: a randomized trial

Treatment failure occurs in about 25% of patients with methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia. We assessed whether cloxacillin plus fosfomycin achieves better treatment success than cloxacillin alone in hospitalized adults with MSSA bacteremia. We conducted a multicenter, open-label, phase III-IV superiority randomized clinical trial. We randomly assigned patients (1:1) to receive 2 g of intravenous cloxacillin alone every 4 h or with 3 g of intravenous fosfomycin every 6 h for the initial 7 days. The primary endpoint was treatment success at day 7, a composite endpoint with the following criteria: patient alive, stable or with improved quick Sequential Organ Failure Assessment score, afebrile and with negative blood cultures for MSSA, adjudicated by an independent committee blinded to treatment allocation. We randomized 215 patients, of whom 105 received cloxacillin plus fosfomycin and 110 received cloxacillin alone. We analyzed the primary endpoint with the intention-to-treat approach in 214 patients who received at least 1 day of treatment. Treatment success at day 7 after randomization was achieved in 83 (79.8%) of 104 patients receiving combination treatment versus 82 (74.5%) of 110 patients receiving monotherapy (risk difference 5.3%; 95% confidence interval (CI), -5.95-16.48). Secondary endpoints, including mortality and adverse events, were similar in the two groups except for persistent bacteremia at day 3, which was less common in the combination arm. In a prespecified interim analysis, the independent committee recommended stopping recruitment for futility prior to meeting the planned randomization of 366 patients. Cloxacillin plus fosfomycin did not achieve better treatment success at day 7 of therapy than cloxacillin alone in MSSA bacteremia. Further trials should consider the intrinsic heterogeneity of the infection by using a more personalized approach. ClinicalTrials.gov registration: NCT03959345 .

Targeted Therapy of Severe Infections Caused by Staphylococcus aureus in Critically Ill Adult Patients: A Multidisciplinary Proposal of Therapeutic Algorithms Based on Real-World Evidence

(1) Introduction: To develop evidence-based algorithms for targeted antibiotic therapy of infections caused by Staphylococcus aureus in critically ill adult patients. (2) Methods: A multidisciplinary team of four experts had several rounds of assessment for developing algorithms concerning targeted antimicrobial therapy of severe infections caused by Staphylococcus aureus in critically ill patients. The literature search was performed by a researcher on PubMed-MEDLINE (until August 2022) to provide evidence for supporting therapeutic choices. Quality and strength of evidence was established according to a hierarchical scale of the study design. Two different algorithms were created, one for methicillin-susceptible Staphylococcus aureus (MSSA) and the other for methicillin-resistant Staphylococcus aureus (MRSA). The therapeutic options were categorized for each different site of infection and were selected also on the basis of pharmacokinetic/pharmacodynamic features. (3) Results: Cefazolin or oxacillin were the agents proposed for all of the different types of severe MSSA infections. The proposed targeted therapies for severe MRSA infections were different according to the infection site: daptomycin plus fosfomycin or ceftaroline or ceftobiprole for bloodstream infections, infective endocarditis, and/or infections associated with intracardiac/intravascular devices; ceftaroline or ceftobiprole for community-acquired pneumonia; linezolid alone or plus fosfomycin for infection-related ventilator-associated complications or for central nervous system infections; daptomycin alone or plus clindamycin for necrotizing skin and soft tissue infections. (4) Conclusions: We are confident that targeted therapies based on scientific evidence and optimization of the pharmacokinetic/pharmacodynamic features of antibiotic monotherapy or combo therapy may represent valuable strategies for treating MSSA and MRSA infections.