Daptomycin in combination with other antibiotics for the treatment of complicated methicillin-resistant Staphylococcus aureus bacteremia

Early Initiation of Ceftaroline-Based Combination Therapy for Methicillin-resistant Staphylococcus aureus Bacteremia

Purpose

Monotherapy with vancomycin or daptomycin remains guideline-based care for methicillin-resistant Staphylococcus aureus bacteremia (MRSA-B) despite concerns regarding efficacy. Limited data support potential benefit of combination therapy with ceftaroline as initial therapy. We present an assessment of outcomes of patients initiated on early combination therapy for MRSA-B.

Methods

This was a single-center, retrospective study of adult patients admitted with MRSA-B between July 1, 2017 and April 31, 2023. During this period, there was a change in institutional practice from routine administration of monotherapy to initial combination therapy for most patients with MRSA-B. Combination therapy included vancomycin or daptomycin plus ceftaroline within 72 hours of index blood culture and monotherapy was vancomycin or daptomycin alone. The primary outcome was a composite of persistent bacteremia, 30-day all-cause mortality, and 30-day bacteremia recurrence. Time to microbiological cure and safety outcomes were assessed. All outcomes were assessed using propensity score-weighted logistic regression.

Results

Of 213 patients included, 118 received monotherapy (115 vancomycin, 3 daptomycin) and 95 received combination therapy with ceftaroline (76 vancomycin, 19 daptomycin). The mean time from MRSA-positive molecular diagnostic blood culture result to combination therapy was 12.1 hours. There was no difference between groups for the primary composite outcome (OR 1.58, 95% CI 0.60, 4.18). Time to microbiological cure was longer with combination therapy (mean difference 1.50 days, 95% CI 0.60, 2.41). Adverse event rates were similar in both groups.

Conclusions

Early initiation of ceftaroline-based combination therapy did not improve outcomes for patients with MRSA-B in comparison to monotherapy therapy.

Contemporary pharmacologic treatments of MRSA for hospitalized adults: rationale for vancomycin versus non-vancomycin therapies as first line agents

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) remains an important pathogen in the hospital setting and causes significant morbidity and mortality each year. Since the initial discovery over 60 years ago, vancomycin has remained a first-line treatment for many different types of MRSA infections. However, significant concerns related to target attainment and nephrotoxicity have spurred efforts to develop more effective agents in the last two decades.

AREAS COVERED

Newer anti-MRSA antibiotics that have been approved since 2000 include linezolid, daptomycin, and ceftaroline. As clinical evidence has accumulated, these newer agents have become more frequently used, and some are now recommended as co-first-line options (along with vancomycin) in clinical practice guidelines. For this review, a scoping review of the literature was conducted to support our findings and recommendations.

EXPERT OPINION

Vancomycin remains an important standard of care for MRSA infections but is limited with respect to nephrotoxicity and rapid target attainment. Newer agents such as linezolid, daptomycin, and ceftaroline have specific indications for treating different types of MRSA infections; however, newer agents also have unique attributes which require consideration during therapy.

Outcomes of Daptomycin Plus Ceftaroline Versus Alternative Therapy for Persistent Methicillin-resistant Staphylococcus aureus (MRSA) Bacteraemia

OBJECTIVES

This study aimed to evaluate both efficacy and safety of combination therapy with daptomycin plus ceftaroline (DAP/CPT) versus alternative therapy in the treatment of persistent methicillin-resistant Staphylococcus aureus bacteraemia (MRSAB).

METHODS

This retrospective, single-centre study investigated adult patients who underwent a change in antibiotic therapy for persistent MRSAB. Daptomycin plus ceftaroline was compared with alternative therapy after initial treatment with vancomycin or DAP monotherapy was modified. The primary outcome was in-hospital mortality, and several secondary efficacy and safety outcomes were evaluated.

RESULTS

A total of 68 patients with persistent MRSAB had initial therapy switched to DAP/CPT (n = 43) or alternative therapy (n = 25). In-hospital mortality was similar with DAP/CPT versus alternative therapy (16.3% vs. 16%; P = 1.0). On average, the total duration of bacteraemia was numerically 1 day less in patients switched to DAP/CPT (11.4 days vs. 12.5 days; P = 0.5). Daptomycin plus ceftaroline was de-escalated in 81% of patients after receiving combination therapy for an average of 12.5 days. Secondary outcomes, including rates of adverse events and emergence of antimicrobial resistance, were similar between the two groups.

CONCLUSIONS

Switching to DAP/CPT after approximately 1 week of persistent MRSA bacteraemia may result in similar clinical outcomes when compared with alternative therapy. Rates of adverse events and emergence of antimicrobial resistance were low without a statistically significant difference observed between DAP/CPT and alternative therapy. These findings, as well as the impact of earlier switch or prolonged treatment with the combination, require further investigation.

Escalation of antimicrobial resistance among MRSA part 2: focus on infections and treatment

INTRODUCTION

MRSA is associated with causing a variety of infections including skin and skin structure infections, catheter and device-related (e.g. central venous catheter, prosthetic heart valve) infections, infectious endocarditis, blood stream infections, bone, and joint infections (e.g. osteomyelitis, prosthetic joint, surgical site), central nervous system infections (e.g. meningitis, brain/spinal cord abscess, ventriculitis, hydrocephalus), respiratory tract infections (e.g. hospital-acquired pneumonia, ventilator-associated pneumonia), urinary tract infections, and gastrointestinal infections. The emergence and spread of multidrug resistant (MDR) MRSA clones has limited therapeutic options. Older agents such as vancomycin, linezolid and daptomycin and a variety of newer MRSA antimicrobials and combination therapy are available to treat serious MRSA infections.

AREAS COVERED

The authors discuss infections caused by MRSA as well as common older and newer antimicrobials and combination therapy for MRSA infections. A literature search of MRSA was performed via PubMed (up to September 2022), using the keywords: antimicrobial resistance; β-lactams; multidrug resistance, Staphylococcus aureus, vancomycin; glycolipopeptides.

EXPERT OPINION

Innovation, discovery, and development of new and novel classes of antimicrobial agents are critical to expand effective therapeutic options. The authors encourage the judicious use of antimicrobials in accordance with antimicrobial stewardship programs along with infection-control measures to minimize the spread of MRSA.

Successful Treatment of Vancomycin-Resistant Enterococcus species Bone and Joint Infection with Daptomycin Plus Beta Lactam Agents

Bone and joint infections (BJI) caused by vancomycin-resistant Enterococcus spp. (VRE) are difficult to treat due to limited antibiotic options. Although linezolid can be used for VRE treatment, it is often discontinued due to time-dependent bone marrow suppression. Daptomycin, a lipopeptide antibiotic agent with rapid bactericidal activity, is another available therapeutic option for VRE infections. We report a case of VRE BJI successfully treated with a high dose of daptomycin plus β-lactam agents. An 84-year-old man received linezolid for the treatment of VRE BJI. After 2 weeks of therapy, the patient experienced bleeding events associated with linezolid-induced bone marrow toxicity and linezolid was discontinued. Next, high-dose daptomycin therapy combined with a β-lactam agent was selected to treat the remaining VRE BJI. During daptomycin treatment, microbiological eradication was achieved, and the patient clinically improved without evidence of adverse events. We highlight the need for daptomycin use for the treatment of VRE infections, especially in cases where linezolid is ineffective.

The Potential of Antibiotics and Nanomaterial Combinations as Therapeutic Strategies in the Management of Multidrug-Resistant Infections: A Review

Antibiotic resistance has become a major public health concern around the world. This is exacerbated by the non-discovery of novel drugs, the development of resistance mechanisms in most of the clinical isolates of bacteria, as well as recurring infections, hindering disease treatment efficacy. In vitro data has shown that antibiotic combinations can be effective when microorganisms are resistant to individual drugs. Recently, advances in the direction of combination therapy for the treatment of multidrug-resistant (MDR) bacterial infections have embraced antibiotic combinations and the use of nanoparticles conjugated with antibiotics. Nanoparticles (NPs) can penetrate the cellular membrane of disease-causing organisms and obstruct essential molecular pathways, showing unique antibacterial mechanisms. Combined with the optimal drugs, NPs have established synergy and may assist in regulating the general threat of emergent bacterial resistance. This review comprises a general overview of antibiotic combinations strategies for the treatment of microbial infections. The potential of antibiotic combinations with NPs as new entrants in the antimicrobial therapy domain is discussed.

Implantable drug delivery systems for the treatment of osteomyelitis

Osteomyelitis is an infection of the bone tissue and bone marrow which is becoming increasingly difficult to treat due to the infection causing pathogens associated. Staphylococcus aureus is one of the main bacteria that causes this infection, which has a broad spectrum of antibiotic resistance making it extremely difficult to treat. Conventional metal implants used in orthopaedic applications often have the drawback of implant induced osteomyelitis as well as the requirement of a second surgery to remove the implant once it is no longer required. Recently, attention has been focused on the design and fabrication of biodegradable implants for the treatment of bone infection. The main benefit of biodegradable implants over polymethylmethacrylate (PMMA) based non-degradable systems is that they do not require a second surgery for removal and so making degradable implants safer and easier to use. The main purpose of a biodegradable implant is to provide the necessary support and conductivity to allow the bone to regenerate whilst themselves degrading at a rate that is compatible with the rate of formation of new bone. They must be highly biocompatible to ensure there is no inflammation or irritation within the surrounding tissue. During this review, the latest research into antibiotic loaded biodegradable implants will be explored. Their benefits and drawbacks will be compared with those non-degradable PMMA beads, which is the stable material used within antibiotic loaded implants. Biodegradable implants most frequently used are based on biodegradable natural and synthetic polymers. Implants can take the form of many different structures; the most commonly fabricated structure is a scaffold. Other structures that will be explored within this review are hydrogels, nanoparticles and surface coatings, all with their own benefits/drawbacks.

Staphylococcus aureus Carotenoids Modulate the Thermotropic Phase Behavior of Model Systems That Mimic Its Membrane Composition

Staphylococcus aureus (S. aureus) is a pathogenic gram-positive bacterium that normally resides in the skin and nose of the human body. It is subject to fluctuations in environmental conditions that may affect the integrity of the membrane. S. aureus produces carotenoids, which act as antioxidants. However, these carotenoids have also been implicated in modulating the biophysical properties of the membrane. Here, we investigate how carotenoids modulate the thermotropic phase behavior of model systems that mimic the phospholipid composition of S. aureus. We found that carotenoids depress the main phase transition of DMPG and CL, indicating that they strongly affect cooperativity of membrane lipids in their gel phase. In addition, carotenoids modulate the phase behavior of mixtures of DMPG and CL, indicating that they may play a role in modulation of lipid domain formation in S. aureus membranes.

Comparing the Outcomes of Ceftaroline plus Vancomycin or Daptomycin Combination Therapy versus Vancomycin or Daptomycin Monotherapy in Adults with Methicillin-Resistant Staphylococcus aureus Bacteremia—A Meta-Analysis

Introduction: Combination therapy with daptomycin plus ceftaroline to treat methicillin-resistant Staphylococcus aureus bacteremia has been reported to reduce methicillin-resistant Staphylococcus aureus bacteremia-related mortality. The purpose of the current meta-analysis was to compare the clinical outcome of methicillin-resistant Staphylococcus aureus bacteremia in patients treated with daptomycin or vancomycin plus ceftaroline combination therapy versus daptomycin or vancomycin monotherapy. Methods: Studies were included if they directly compared the efficacy of daptomycin or vancomycin plus ceftaroline combination therapy with that of daptomycin or vancomycin monotherapy in the treatment of methicillin-resistant Staphylococcus aureus bacteremia in adult patients. Results: One randomized controlled trial and five retrospective studies were included in the meta-analysis. The combination therapy group had an in-hospital mortality, duration of bacteremia, and adverse event rate similar to those patients who had monotherapy. There was less bacteremia recurrence in the combination group. Initial combination therapy with ceftaroline for the treatment of methicillin-resistant Staphylococcus aureus bacteremia showed a trend of reducing the risk of in-hospital mortality in the current meta-analysis. Conclusions: Randomized controlled trials are needed to further study the role of initial combination therapy with daptomycin or vancomycin plus ceftaroline in the treatment of methicillin-resistant Staphylococcus aureus bacteremia.

Does a New Antibiotic Scheme Improve the Outcome of Staphylococcus aureus-Caused Acute Prosthetic Joint Infections (PJI) Treated with Debridement, Antibiotics and Implant Retention (DAIR)?

One of the most commonly used treatments for acute prosthetic joint infection (PJI) is DAIR (debridement, antibiotics and implant retention), which comprises the debridement and the retention of the implant, followed by antibiotic treatment. The efficacy of DAIR remains unclear, as the literature has demonstrated variable success rates, ranging from 26% to 92%. The Staphylococcus aureus is one of the most closely related causative microorganisms, especially with acute and late-acute PJI; it has been identified as one of the most significant predictors of DAIR failure. The current guidelines consider the use of vancomycin as the therapy of choice, but it requires the close control of possible side effects. The aim of this study is to determine if a new combination of antibiotics (a highly bactericidal initial combination followed by an antibiofilm scheme) decreases the failure of DAIR-treated acute prosthetic joint infection (PJI) caused by Staphylococcus aureus. A retrospective analysis of cases of orthopedic infections during a nine-year period (2011–2019) was performed. A total of 45 acute PJI cases caused by S. aureus were diagnosed. The results of two antibiotic schemes were compared: a novel scheme comprising 5 days of daptomycin (10 mg/kg/24 h) + cloxacillin (2 g/6 h) followed by levofloxacin (500 mg/24 h) + rifampicin (600 mg/24 h), versus a traditional, less bactericidal scheme of vancomycin (1000 mg/12 h) plus rifampicin (600 mg/24 h) or levofloxacin (500 mg/24 h) plus rifampicin (600 mg/24 h). Twenty-two out of the twenty-four patients treated with the new scheme (91.6%) were free of infection after 24.8 months of mean follow-up, whereas fourteen out of twenty-one patients (66.6%) were free of infection after 46.6 months of follow-up. This difference was statistically significant (p = 0.036). Demographic comparisons demonstrated homogeneous features, except the Charlson score, which was higher in the novel scheme group (p = 0.047). The combination of high-dose daptomycin and cloxacillin, followed by levofloxacin plus rifampicin, together with surgical treatment, shows better results when compared with other antibiotic schemes for treating acute PJI caused by S. aureus in which DAIR was performed.

Clinical Outcomes With Definitive Treatment of Methicillin-Resistant Staphylococcus aureus Bacteremia With Retained Daptomycin and Ceftaroline Combination Therapy vs De-escalation to Monotherapy With Vancomycin, Daptomycin, or Ceftaroline

Background

Lower mortality has been observed with combination therapy compared to monotherapy for methicillin-resistant Staphylococcus aureus (MRSA) bacteremia; however, there is a lack of evidence for continued combination therapy over de-escalation to monotherapy following bacteremia clearance.

Methods

This was a single-center, retrospective study evaluating patients with MRSA bacteremia hospitalized from November 1, 2011, through July 31, 2019. Patients who received three to ten days of combination therapy followed by de-escalation to monotherapy were directly compared to patients retained on combination therapy. The primary composite outcome included inpatient infection-related mortality, 60-day readmission, and 60-day bacteremia recurrence.

Results

A total of 286 patients with MRSA bacteremia were identified, with 146 patients omitted based on exclusion criteria. The study population included 66 in the combination therapy group and 74 in the monotherapy group. Study population was 51% female (n = 71) and 78% white (n = 109) with median age of 46 years (IQR 34.5-61). No significant difference was observed in the primary composite outcome (21% combination therapy group vs 24% monotherapy group; P =.66), with retained observations after controlling for confounders. Within this outcome, there was no significant difference in 60-day readmission (20% combination therapy group vs 18% monotherapy group; P =.75), bacteremia recurrence (3% combination therapy group vs 7% monotherapy group; P =.45), or inpatient infection-related mortality (2% combination therapy group vs 5% monotherapy group; P = 1.00).

Conclusions

No difference was found in the composite outcome of 60-day bacteremia recurrence, readmission, or inpatient infection-related mortality for patients with MRSA bacteremia retained on combination therapy versus those de-escalated to monotherapy.

The Pharmacodynamics Study of Insect Defensin DLP4 Against Toxigenic Staphylococcus hyicus ACCC 61734 in Vitro and Vivo

Staphylococcus hyicus (S. hyicus), as the main pathogen of exudative epidermitis (EE) in piglet, can cause a wide variety of diseases, ranging from bovine mastitis, chicken arthritis and even human sepsis, which has brought serious threats to animals and human. The potential threat of S. hyicus infection to both public and animal health has aroused great concern. The aim of our study was to explore the efficacy of insect defensin DLP4 against S. hyicus ACCC 61734 in vitro and in vivo. The in vitro efficacies of DLP4 against S. hyicus ACCC 61734 showed high antibacterial activity (0.92 μM), a long postantibiotic effect (9.54 h), a synergistic effect with ceftriaxone, penicillin and amoxicillin, a stable bacteriostatic effect, and intracellular bacteriostatic activity against S. hyicus ACCC 61734 in HaCaT cells. Besides, the antibacterial mechanism of DLP4 against S. hyicus ACCC 61734 was explored for the first time, which indicated that the antibacterial effect of DLP4 was related to its ability to destroy cell wall and generate membrane vesicles. The in vivo therapeutic effect of DLP4 was evaluated through mouse abscess model, and the results showed that DLP4 could effectively alleviate the mouse skin abscess by inhibiting bacterial proliferation and regulating cytokines. This study first demonstrated that DLP4 may be a promising therapeutic agent against S. hyicus ACCC 61734 infection.

Carotenogenesis of Staphylococcus aureus: New insights and impact on membrane biophysical properties

Staphyloxanthin (STX) is a saccharolipid derived from a carotenoid in Staphylococcus aureus involved in oxidative-stress tolerance and antimicrobial peptide resistance. STX influences the biophysical properties of the bacterial membrane and has been associated to the formation of lipid domains in the regulation of methicillin-resistance. In this work, a targeted metabolomics and biophysical characterization study was carried out to investigate the biosynthetic pathways of carotenoids, and their impact on the membrane biophysical properties. Five different S. aureus strains were investigated, including three wild-type strains containing the crtM gene related to STX biosynthesis, a crtM-deletion mutant, and a crtMN plasmid-complemented variant. LC-DAD-MS/MS analysis of extracts allowed the identification of 34 metabolites related to carotenogenesis in S. aureus at different growth phases (8, 24 and 48 h), showing the progression of these metabolites as the bacteria advances into the stationary phase. For the first time, 22 members of a large family of carotenoids were identified, including STX and STX-homologues, as well as Dehydro-STX and Dehydro-STX-homologues. Moreover, thermotropic behavior of the CH₂ stretch of lipid acyl chains in live cells by FTIR, show that the presence of STX increases acyl chain order at the bacterial growth temperature. Indeed, the cooperative melting event of the bacterial membrane, which occurs around 15 °C in the native strains, shifts with increased carotenoid content. These results show the diversity biosynthetic of carotenoids in S. aureus, and their influence on membrane biophysical properties.

Chemotherapeutic Strategies for Combating Staphylococcus aureus Infections

Staphylococcus aureus is a prominent human pathogen that causes nosocomial and community acquired infections. The accelerating emergence and prevalence of staphylococcal infections have grotesque health consequences which are mostly due to its anomalous capability to acquire drug resistance and scarcity of novel classes of antibacterials. Many combating therapies are centered on primary targets of S. aureus which are cell envelope, ribosomes and nucleic acids. This review describes various chemotherapeutic strategies for combating S. aureus infections which includes monotherapy, combination drug therapy, phage endolysin therapy, lysostaphins and antibacterial drones. Monotherapy has dwindled in due course of time but combination therapy, endolysin therapy, lysostaphin and antibacterial drones are emerging alternatives which efficiently conquer the shortcomings of monotherapy. Combinations of more than one antibiotic agents or combination of adjuvant with antibiotics provide a synergistic approach to combat infections causing pathogenic strains. Phage endolysin therapy and lysostaphin are also presents as possible alternatives to conventional antibiotic therapies. Antibacterial Drones goes a step further by specifically targeting the virulence genes in bacteria giving them a certain advantage over existing antibacterial strategies. But the challenge remains on the better understanding of these strategies for executing and implementing them in health sector. In this day and age, most of the S. aureus strains are resistant to ample number of antibiotics, so there is an urgent need to overcome such multidrug resistant strains for the welfare of our community.

Vancomycin or Daptomycin Plus a β-Lactam Versus Vancomycin or Daptomycin Alone for Methicillin-Resistant Staphylococcus aureus Bloodstream Infections: A Systematic Review and Meta-Analysis

Aims: Several in vitro and in vivo studies demonstrated that adding a β-lactam to vancomycin (VAN) or daptomycin (DAP) can provide synergy against methicillin-resistant Staphylococcus aureus (MRSA). However, the results from clinical studies were controversial. The objective of this systematic review and meta-analysis was to compare the efficacy and safety of using VAN or DAP plus a β-lactam (combination therapy) and using VAN or DAP alone (monotherapy) in MRSA bloodstream infections. Methods: We included randomized controlled trials and observational studies evaluating whether combination therapy can improve clinical and microbiological outcomes and safety compared to monotherapy with VAN or DAP in MRSA-related bacteremia. Results: Literature search identified 3 randomized clinical trials and 10 observational studies involving at least 1,796 patients. There were no significant associations between the combination therapy and risk of mortality within 30 days (risk ratios [RRs], 1.10, 95% confidence interval [CI], 0.82-1.46), in-hospital mortality (RR, 0.59, 95% CI, 0.31-1.13) and mortality within 60-90 days (RR, 0.91, 95% CI, 0.64-1.29). There was also no evidence that there was a difference in length of hospital stay between the combination therapy and monotherapy (mean difference, -0.41 days, 95% CI, -3.41 to 2.59). However, compared with monotherapy, combination therapy seemed to have a shorter duration of bacteremia(mean difference, -1.06 days, 95% CI, -1.53 to -0.60), a lower risk of persistent bacteremia (RR, 0.63, 95% CI, 0.51-0.79) and a lower risk of bacteremia recurrence within 60-90 days (RR, 0.61, 95% CI, 0.40-0.92). There were no statistically significant differences in the total number of adverse events, including acute kidney injury (AKI) (RR, 1.52, 95% CI, 0.84-2.73), thrombocytopenia (RR, 1.13, 95% CI, 0.74-1.73), and diarrhea (RR, 1.36, 95% CI, 0.70-2.65), between patients with combination therapy and monotherapy. In subgroup analysis, when the analysis was limited to the studies comparing using DAP plus ceftaroline with monotherapy, we found that the former had a lower risk of mortality within 30 days. In addition, a subgroup analysis limited to randomized clinical trials showed that the combination therapy was associated with a higher risk of AKI compared with using VAN or DAP alone. Conclusions: Although adding a β-lactam to standard therapy seemed to experience a higher clearance compared with monotherapy in patients with MRSA bacteremia, the combination therapy did not increase survival benefits. Based on the available evidence, the combination therapy was not supported as the routine management of MRSA-related bacteremia, and both its harms and benefits should be taken into account.

Verification of a Novel Approach to Predicting Effects of Antibiotic Combinations: In Vitro Dynamic Model Study with Daptomycin and Gentamicin against Staphylococcus aureus

To explore whether susceptibility testing with antibiotic combinations at pharmacokinetically derived concentration ratios is predictive of the antimicrobial effect, a Staphylococcus aureus strain was exposed to daptomycin and gentamicin alone or in combination in multiple dosing experiments. The susceptibility of the S. aureus strain to daptomycin and gentamicin in combination was tested at concentration ratios equal to the ratios of 24 h areas under the concentration–time curve (AUC₂₄s) of antibiotics simulated in an in vitro dynamic model in five-day treatments. The MICs of daptomycin and gentamicin decreased in the presence of each other; this led to an increase in the antibiotic AUC₂₄/MIC ratios and the antibacterial effects. Effects of single and combined treatments were plotted against the AUC₂₄/MIC ratios of daptomycin or gentamicin, and a significant sigmoid relationship was obtained. Similarly, when the effects of single and combined treatments were related to the total exposure of both drugs (the sum of AUC₂₄/MIC ratios (∑AUC₂₄/MIC)), a significant sigmoid relationship was obtained. These findings suggest that (1) the effects of antibiotic combinations can be predicted by AUC₂₄/MICs using MICs of each antibacterial determined at pharmacokinetically derived concentration ratios; (2) ∑AUC₂₄/MIC is a reliable predictor of the antibacterial effects of antibiotic combinations.

Ceftobiprole for Treatment of MRSA Blood Stream Infection: A Case Series

While methicillin-resistant Staphylococcus aureus (MRSA) bacteremia has poor outcomes, we describe our experience with Ceftobiprole mainly as a combination therapy for the treatment of MRSA bacteremia. All the cases of MRSA bacteremia in our center at the King Abdulaziz Medical City (KAMC), Riyadh, that had undergone Ceftobiprole treatment were included. We had six cases of MRSA bacteremia between 2018 and 2019, secondary to different infectious syndromes including endocarditis. There was a severe infection that required intensive care unit (ICU) admission in four cases. Ceftobiprole is used in combination with vancomycin in four cases. On day 14, all cases had a favorable outcome with microbiological and clinical improvement. However, three patients died after months of suffering from bacteremia from unrelated causes for the infection. The clinical outcome in our series of treatment of MRSA bacteremia using Ceftobiprole was favorable. Further studies for the evaluation of the use of Ceftobiprole in MRSA bacteremia should be encouraged.

Antibiotics and Innate Immunity: A Cooperative Effort Toward the Successful Treatment of Infections

Despite the common ancestry of antimicrobial and immunological science, a divergence driven by artificially construed paradigms in microbiology has placed limits on how we understand the mechanisms of antibiotics in vivo. We summarize recent updates on data that shed light on how antibiotics interact with components of innate immunity.

Evaluation of anti-infective potencies of formulated aloin A ointment and aloin A isolated from Aloe barbadensis Miller

Introduction

Isolated bioactive components of plants or their raw extract are utilized as complementary or alternate remedy in copious illnesses. The current research was aimed at assessing the activity of aloin A isolated from Aloe barbadensis Miller and its formulated ointment against six (6) selected clinical isolates.

Methods

The column chromatography was utilized in isolating aloin A from chloroform/methanol solvent polarity. The characterization of the isolated compound was performed by spectroscopy techniques corresponding to UV, IR, ¹H- and ¹³C-NMR spectroscopy. It was formulated as ointment using polyethylene glycol (PEG) and both the ointment and the isolated compound were probed for in vitro antimicrobial activity.

Results

Aloin A has been isolated from chloroform/methanol solvent mixture. The structure has been explicated as (10S)-10-β-d-glucopyranosyl-1,8-dihydroxy-3-(hydroxymethyl)-9(10H)-anthracenone(1S)-1,5-anhydro-1-[(9S)-4,5-dihydroxy-2-(hydroxymethyl)-10-oxo-9,10-dihydro-9-anthracenyl]-d-glucitol. The minimum inhibitory concentration (MIC) of the isolated aloin A on the pathogens ranged from 2.5 to 5.0 mg/ml and 0.32 to 5.0 mg/ml for both aloin A and the formulated ointment respectively. It was further revealed that the activity of aloin A showed dose dependence against all the test microorganisms. There was no significant difference in the activity of the drug against K. pneumoniae, S. aureus, E. coli, C. albicans and T. flavus (P > 0.05) when the concentration was raised from 2.5 to 5 mg/ml, however, there was significant difference (P ˂ 0.05) in activity against P. aeruginosa. The formulated ointment exhibited dose dependent activity against all test microorganisms. At low concentrations, the ointment showed no significant difference in diameter zone of inhibition against all test microorganisms (P > 0.05) except P. aeruginosa which exhibited a highly significant difference (P < 0.05).

Conclusion

Both the isolated aloin A and its formulated ointment demonstrated substantial inhibition of growth of the pathogenic strains. These findings sturdily suggest that aloin A is a nascent drug that could be explored as skin and wound transmittable agent.

In vitro activity of ceftaroline in combination with other antimicrobials active against Staphylococcus spp

INTRODUCTION

We evaluated the in vitro activity of the combination of ceftaroline with daptomycin, linezolid and vancomycin against methicillin-resistant Staphylococcus aureus and coagulase-negative Staphylococcus (CNS).

MATERIAL AND METHODS

We analysed 70 staphylococcal strains (31 S. aureus and 39 CNS) with the Etest using the MIC:MIC ratio method and calculation of fractional inhibitory concentration indexes.

RESULTS

The combination of ceftaroline with daptomycin showed an additive effect (53.2%) and synergy (6.6%) against methicillin-susceptible S. aureus, and an additive effect (81.2%) against methicillin-resistant S. aureus (MRSA). This combination also showed an additive effect against 33% of linezolid-susceptible CNS and was not synergistic against linezolid-resistant CNS. The combination of ceftaroline with vancomycin was synergistic (87%) and ceftaroline with linezolid was additive (37%) against MRSA.

CONCLUSIONS

The combinations of ceftaroline with daptomycin, vancomycin or linezolid showed additive and/or synergistic effects against methicillin-resistant Staphylococcus.

Multicenter Cohort of Patients With Methicillin-Resistant Staphylococcus aureus Bacteremia Receiving Daptomycin Plus Ceftaroline Compared With Other MRSA Treatments

Background

Daptomycin and ceftaroline (DAP-CPT) have been used for persistent methicillin-resistant Staphylococcus aureus bacteremia (MRSAB), but have rarely been compared with other therapies. This study provides an exploratory analysis of patients placed on DAP-CPT vs standard of care (SOC) for MRSAB.

Methods

This is a retrospective, matched cohort study MRSAB patients at 4 hospitals in the United States. Patients receiving DAP-CPT for ≥72 hours at any point in therapy were matched 2:1 when possible, 1:1 otherwise, to SOC, first by infection source, then age and renal function. SOC was empiric treatment with vancomycin or daptomycin and any subsequent combination antibiotic(s), except for DAP-CPT.

Results

Fifty-eight patients received DAP-CPT with 113 matched SOC. Ninety-six percent of SOC received vancomycin, and 56% (63/113) escalated therapy at least once in the treatment course. Twenty-four patients received DAP-CPT within 72 hours of index culture; 2 (8.3%) died within 30 days vs 14.2% (16/113) with SOC (P > .05). Subgroup analysis identified numerically lower mortality in DAP-CPT patients with a Charlson comorbidity index ≥3, endovascular source, and receipt of DAP-CPT within 72 hours of index culture. The median MRSAB duration was 9.3 vs 4.8 days for DAP-CPT and SOC, respectively. DAP-CPT was initiated on day 6 on average; after receipt of DAP-CPT, MRSAB duration was 3.3 days.

Conclusions

DAP-CPT treatment is often delayed in MRSAB. Combination therapy may be more beneficial if initiated earlier, particularly in patients at higher risk for mortality. Blinded, randomized, prospective studies are needed to eliminate selection bias inherent in retrospective analyses when examining DAP-CPT vs SOC.

Pharmacodynamics of ClpP-Activating Antibiotic Combinations against Gram-Positive Pathogens

It is often difficult to cure endocarditis, osteomyelitis, and device-associated infections caused by Gram-positive pathogens, despite therapy with clinically appropriate antibiotics. This may be due to antibiotic tolerance or resistance development. Acyldepsipeptides (ADEPs) are a class of bactericidal compounds active against a variety of clinically important Gram-positive bacteria, including staphylococci, streptococci, and enterococci. ADEPs activate caseinolytic protease P (ClpP), killing high-density, nondividing cultures of bacteria that are tolerant to approved classes of antibiotics. Acyldepsipeptide analog 4 (ADEP4) was active against a panel of drug-resistant Gram-positive pathogens in MIC assays, with no preexisting resistance detected. Killing of stationary-phase cultures was observed when ADEP4 was combined with multiple classes of approved antibiotics. Additionally, a hollow-fiber infection model was used to assess the effects of ADEP4 antibiotic combinations on bacterial killing and resistance development. These studies were performed on high-density cultures of methicillin-resistant S. aureus (MRSA), methicillin-susceptible S. aureus (MSSA), and vancomycin-resistant Enterococcus faecalis (VRE). None of the approved antibiotics linezolid, ampicillin, and oxacillin tested alone had bactericidal activity under these conditions. ADEP4 initially caused killing, but regrowth of the culture was apparent within 96 h due to resistance. Combinations of ADEP4 with linezolid or oxacillin caused substantially improved killing of MRSA or MSSA cultures, respectively, and no regrowth due to resistance was observed. The combination of ADEP4 and ampicillin eradicated cultures of VRE to the limit of detection within 52 h. These data suggest that combining ClpP activators with traditional antibiotics may be a good strategy to treat complicated Gram-positive infections.

Multi-strain Tn-Seq reveals common daptomycin resistance determinants in Staphylococcus aureus

Antibiotic-resistant Staphylococcus aureus remains a leading cause of antibiotic resistance-associated mortality in the United States. Given the reality of multi-drug resistant infections, it is imperative that we establish and maintain a pipeline of new compounds to replace or supplement our current antibiotics. A first step towards this goal is to prioritize targets by identifying the genes most consistently required for survival across the S. aureus phylogeny. Here we report the first direct comparison of multiple strains of S. aureus via transposon sequencing. We show that mutant fitness varies by strain in key pathways, underscoring the importance of using more than one strain to differentiate between core and strain-dependent essential genes. We treated the libraries with daptomycin to assess whether the strain-dependent differences impact pathways important for survival. Despite baseline differences in gene importance, several pathways, including the lipoteichoic acid pathway, consistently promote survival under daptomycin exposure, suggesting core vulnerabilities that can be exploited to resensitize daptomycin-nonsusceptible isolates. We also demonstrate the merit of using transposons with outward-facing promoters capable of overexpressing nearby genes for identifying clinically-relevant gain-of-function resistance mechanisms. Together, the daptomycin vulnerabilities and resistance mechanisms support a mode of action with wide-ranging effects on the cell envelope and cell division. This work adds to a growing body of literature demonstrating the nuanced insights gained by comparing Tn-Seq results across multiple bacterial strains.

Antibiotic-resistant Staphylococcus aureus kills thousands of people every year in the United States alone. To stay ahead of the looming threat of multidrug-resistant infections, we must continue to develop new antibiotics and find ways to make our current repertoire of antibiotics more effective, including by finding pairs of compounds that perform best when administered together. In the age of next-generation sequencing, we can now use transposon sequencing to find potential targets for new antibiotics on a genome-wide scale, identified as either essential genes or genes that positively influence survival in the presence of an antibiotic. In this work, we created a compendium of genes that are essential across a range of S. aureus strains, as well as those that are important for growth in the presence of the antibiotic daptomycin. The results will be a resource for researchers working to develop the next generation of antibiotic therapies.

Adjunctive ceftaroline in combination with daptomycin or vancomycin for complicated methicillin-resistant Staphylococcus aureus bacteremia after monotherapy failure

Background:

Methicillin-resistant Staphylococcus aureus bacteremia (MRSA-B) may fail to improve with standard monotherapy, particularly in patients with multifocal infection, incomplete source control, or persistent bacteremia. Synergy observed in vitro between ceftaroline (CPT) and daptomycin (DAP) or vancomycin (VAN) may translate into clinical benefit. Here, we describe our experience with DAP/CPT and VAN/CPT for complicated MRSA-B after monotherapy failure.

Methods:

Single-center, retrospective review of consecutive patients treated with DAP/CPT or VAN/CPT for MRSA-B after monotherapy failure from 1 January 2016 to 30 November 2018.

Results:

We identified 11 instances of combination therapy in 10 patients (DAP/CPT = 6, VAN/CPT = 5) with 1 patient receiving VAN/CPT followed by DAP/CPT. Rates of multifocal infection, incomplete source control, persistent bacteremia, and infective endocarditis were high (100%, 80%, 60%, and 60%, respectively). Combination therapy was initiated most commonly for persistent bacteremia (60%). When patients were persistently bacteremic, median preceding duration was 13 days and median time to clearance was 3 days. Total microbiologic cure rate was 100%. There were zero instances of bacteremia relapse at 30 days (30D) or 60 days (60D). All-cause 30D and 60D mortality rates were 11.1% and 33.3%, respectively.

Conclusions:

Combination therapy demonstrated success in diverse cases of refractory MRSA-B, including instances of persistent bacteremia paired with incomplete source control. Optimal timing and therapeutic cadence for combination therapy remain unclear. Our findings suggest that DAP/CPT and VAN/CPT can be considered for complicated MRSA bacteremia when other treatment options fail or are unavailable. We propose persistent bacteremia with incomplete source control to be a clinical niche particularly worthy of further investigation.

Successful treatment with daptomycin and ceftaroline of MDR Staphylococcus aureus native valve endocarditis: a case report

OBJECTIVES

The best therapeutic approach for treating MRSA endocarditis remains unknown, particularly in cases of high vancomycin MICs. We report here a case of daptomycin-non-susceptible, ceftaroline-resistant and fosfomycin-resistant MRSA native left valve endocarditis that was successfully treated with valve repair and a combination of high-dose daptomycin and ceftaroline.

METHODS

Antimicrobial testing of the clinical strain was performed using Etest and microdilution broth methods. Time-kill and chequerboard methodologies were used to test the activity of antibiotic combinations.

RESULTS

By Etest, the MIC of vancomycin was 2 mg/L, the MIC of daptomycin was 2 mg/L, the MIC of fosfomycin was 1024 mg/L and the MIC of ceftaroline was 1.5 mg/L. At the standard inoculum (105 cfu/mL), the three combinations of daptomycin plus ceftaroline, cloxacillin or fosfomycin were synergistic and bactericidal. However, when these combinations were tested using a higher inoculum (108 cfu/mL), all combinations were synergistic, but only daptomycin plus ceftaroline had bactericidal activity.

CONCLUSIONS

These results confirmed a synergistic effect between daptomycin plus ceftaroline and increased bactericidal activity against MRSA, suggesting that this combination may be effective for the treatment of invasive MRSA infection. Our experience highlights the potential clinical use of synergy testing to guide difficult treatment decisions in patients with MDR MRSA infection.

Methicillin-resistant Staphylococcus aureus in solid organ transplantation-Guidelines from the American Society of Transplantation Infectious Diseases Community of Practice

These updated guidelines from the American Society of Transplantation Infectious Diseases Community of Practice review the epidemiology, diagnosis, prevention, and management of methicillin-resistant Staphylococcus aureus (MRSA) infections in solid organ transplantation. Despite an increasing armamentarium of antimicrobials active against MRSA, improved diagnostic tools, and overall declining rates of infection, MRSA infections remain a substantial cause of morbidity and mortality in solid organ transplant recipients. Pre- and post-transplant MRSA colonization is a significant risk factor for post-transplant MRSA infection. The preferred initial treatment of MRSA bacteremia remains vancomycin. Hand hygiene, chlorhexidine bathing in the ICU, central-line bundles that focus on reducing unnecessary catheter use, disinfection of patient equipment, and the environment along with antimicrobial stewardship are all aspects of an infection prevention approach to prevent MRSA transmission and decrease healthcare-associated infections.

Treatments and limitations for methicillin-resistant Staphylococcus aureus: A review of current literature

Methicillin-resistant Staphylococcus aureus (MRSA) has remained a major threat to healthcare; in both hospital and community settings over the past five decades. With the current use of antibiotics for a variety of infections, including MRSA, emerging resistance is a major concern. Currently available treatments have restrictions limiting their use. These issues include, but are not limited to, side effects, cross-resistance, lack of understanding of pharmacokinetics and clinical pharmacodynamics, gradual increment in minimal inhibitory concentration over the period (MIC creep) and ineffectiveness in dealing with bacterial biofilms. Despite availability of various therapeutic options for MRSA, the clinical cure rates remain low with high morbidity and mortality. Given these challenges with existing treatments, there is a need for development of novel agents for MRSA. Along with prompt infection control strategies and strict implementation of antibiotic stewardship, cautious use of newer anti-MRSA agents will be of utmost importance. This article reviews the treatments and limitations of MRSA management and highlights the future path.

Methicillin-Resistant Staphylococcus aureus Prosthetic Valve Endocarditis: Pathophysiology, Epidemiology, Clinical Presentation, Diagnosis, and Management

Staphylococcus aureus prosthetic valve endocarditis (PVE) remains among the most morbid bacterial infections, with mortality estimates ranging from 40% to 80%. The proportion of PVE cases due to methicillin-resistant Staphylococcus aureus (MRSA) has grown in recent decades, to account for more than 15% of cases of S. aureus PVE and 6% of all cases of PVE. Because no large studies or clinical trials for PVE have been published, most guidelines on the diagnosis and management of MRSA PVE rely upon expert opinion and data from animal models or related conditions (e.g., coagulase-negative Staphylococcus infection). We performed a review of the literature on MRSA PVE to summarize data on pathogenic mechanisms and updates in epidemiology and therapeutic management and to inform diagnostic strategies and priority areas where additional clinical and laboratory data will be particularly useful to guide therapy. Major updates discussed in this review include novel diagnostics, indications for surgical management, the utility of aminoglycosides in medical therapy, and a review of newer antistaphylococcal agents used for the management of MRSA PVE.

Population-Based Study of Risk of AKI with Levetiracetam

BACKGROUND AND OBJECTIVES

Regulatory agencies warn about the risk of AKI with levetiracetam use on the basis of information from case reports. We conducted this study to determine whether new levetiracetam use versus nonuse is associated with a higher risk of AKI.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This was a population-based retrospective cohort study of adults with epilepsy in Ontario, Canada. Patients who received a new outpatient prescription for levetiracetam between January 1, 2004 and March 1, 2017 were matched to two nonusers on stage of CKD, recorded seizure in the prior 90 days, and logit of a propensity score for levetiracetam use. The primary outcome was a hospital encounter (emergency department visit or hospitalization) with AKI within 30 days of cohort entry. Secondary outcomes were AKI within 180 days and change in the concentration of serum creatinine. We assessed the primary outcome using health care diagnosis codes. We evaluated the change in the concentration of serum creatinine in a subpopulation with laboratory measurements.

RESULTS

We matched 3980 levetiracetam users to 7960 nonusers (mean age 55 years, 51% women). Levetiracetam use was not significantly associated with a higher risk of AKI within 30 days (13 [0.33%] events in levetiracetam users and 21 [0.26%] events in nonusers [odds ratio, 1.24; 95% confidence interval, 0.62 to 2.47]). Similarly, there was no significant association with AKI within 180 days (odds ratio, 0.70; 95% confidence interval, 0.43 to 1.13). The change in the concentration of serum creatinine did not significantly differ between levetiracetam users and nonusers.

CONCLUSIONS

In this population-based study levetiracetam use was not associated with a higher risk of AKI.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2018_12_11_Yau_Podcast.mp3.

Treatment strategies for persistent methicillin-resistant Staphylococcus aureus bacteraemia

WHAT IS KNOWN AND OBJECTIVE

Treatment of methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia is a long-standing challenge to health care, often complicated by metastatic infections, treatment failure and mortality. When MRSA bacteraemia persists despite adequate initial treatment, current Infectious Diseases Society of America guidelines recommend evaluation and removal of possible sources of infection. In addition, a change in therapy may be considered. The objective of this review was to explore the therapeutic options for the treatment of persistent MRSA bacteraemia.

METHODS

A literature search of PubMed, MEDLINE and Google Scholar was performed using the following search terms: [methicillin-resistant Staphylococcus aureus OR MRSA] AND [bacteraemia OR bloodstream infection] AND [persistent OR persistence OR refractory OR treatment failure OR salvage] AND treatment. We evaluated relevant, adult, English-language, peer-reviewed studies published between 1985 and May 2018. In vitro and animal studies were considered as supportive of in vivo data.

RESULTS AND DISCUSSION

Randomized, controlled trials are lacking. However, case series and case reports support multiple treatment options including high-dose daptomycin in combination with an antistaphylococcal β-lactam, ceftaroline, trimethoprim-sulfamethoxazole (TMP-SMX) or fosfomycin; ceftaroline alone or in combination with vancomycin or TMP-SMX; linezolid alone or in combination with a carbapenem, or telavancin.

WHAT IS NEW AND CONCLUSION

Given the heterogeneity of the data, a preferred regimen has not emerged. Prescribers must take into consideration recent exposure, source control, and available synergy and clinical data. Further comparative trials are needed to establish a preferred regimen and the creation of a universal treatment algorithm.

Daptomycin versus placebo as an adjunct to beta-lactam therapy in the treatment of Staphylococcus aureus bacteremia: study protocol for a randomized controlled trial

BACKGROUND

Staphylococcus aureus bacteremia is associated with significant morbidity and mortality. To treat this infection, the current standard of care includes intravenous anti-staphylococcal beta-lactam antibiotics and obtaining adequate source control. Combination therapy with an aminoglycoside or rifampin, despite early promise, can no longer be routinely recommended due to an absence of proven benefit and risk of harm. Daptomycin is a rapidly acting bactericidal antibiotic that is approved for the treatment of Staphylococcus aureus bacteremia as monotherapy but has not been shown to be superior to the current standard of care. As demonstrated in vitro, the addition of daptomycin to beta-lactam therapy may result in enhanced anti-staphylococcal activity. Our objective is to assess the efficacy and safety of prescribing the combination of daptomycin with cefazolin or cloxacillin for the treatment of methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia in adults. We hypothesize that adjunctive therapy with daptomycin will reduce the duration of bacteremia in this population.

METHODS

The DASH-RCT trial is a randomized, double blind, placebo-controlled trial designed per the Standard Protocol Items: Recommendation for Interventional Trials (SPIRIT) and Consolidated Standards of Reporting Trials (CONSORT) guidelines. We recruit adults with confirmed MSSA bacteremia, at the McGill University Health Center. Patients are eligible if they are 18 years or older, can receive cefazolin or cloxacillin monotherapy, and are enrolled within 72 h of the first blood culture being drawn. Exclusion criteria include anaphylaxis to study drugs, having polymicrobial bacteremia, anticipated hospital admission for < 5 days, and healthcare team refusal. While receiving standard of care, study patients are randomized to a 5-day course of adjunctive daptomycin or placebo. The trial began in December 2016 and is expected to end in December 2018, after recruiting an estimated 102 patients.

DISCUSSION

The DASH-RCT will compare the use of daptomycin as an adjunct to an anti-staphylococcal beta-lactam versus placebo in the treatment of MSSA bacteremia. We believe that a short course of dual therapy will result in earlier eradication of bacteremia and that subsequent research could evaluate effects on metastatic infection, relapse, and/or mortality. Ongoing issues in the trial include a delay between presentation of infection, enrollment in the trial, and the potential for unrecognized deep foci of infection at diagnosis.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT02972983 . Registered on 25 November 2016. Trial protocol: http://individual.utoronto.ca/leet/dash/dashprotocol.pdf.

Impact of cefazolin co-administration with vancomycin to reduce development of vancomycin-intermediate Staphylococcus aureus

OBJECTIVE

Development of antimicrobial resistance during monotherapy of complicated methicillin-resistant Staphylococcus aureus bacteremia is problematic due to cross-resistance between vancomycin (VAN) and daptomycin, the only approved agents for this condition. Our objective was to demonstrate that development of resistance under conditions of suboptimal VAN (200 mg q 12 h) exposure in S. aureus can be attenuated by addition of cefazolin (CFZ).

METHODS

Two strains of S. aureus, 1 methicillin-susceptible Staphylococcus aureus (MSSA) (RN9120) and 1 methicillin-resistant S. aureus (MRSA) (JH1), were evaluated. The organisms were exposed to subtherapeutic VAN concentrations in a 1-compartment pharmacokinetic/pharmacodynamic model combined with recycling in the presence and absence of CFZ. Changes in MIC to glyco/lipopeptides and β-lactams along with susceptibility to human cathelicidin LL-37 killing were studied. Population analysis profiles (PAPs) were performed to detect changes in VAN heteroresistance.

RESULTS

VAN MIC of both organisms increased from 1 to 4 mg/L within 144 h under subtherapeutic VAN exposure. Increase in VAN MIC was associated with increased glyco/lipopeptides MICs. Additionally, increased survival in LL-37 killing assays from 40% to >90% accompanied the increase in VAN MIC. Addition of CFZ prevented the emergence of VAN-intermediate S. aureus. PAPs demonstrated an attenuation of VAN area under the curve shift (reduced organism selection with higher MICs values) when suboptimal VAN exposure was accompanied with CFZ compared to VAN alone (MSSA 17.81 versus 36.027, MRSA -0.35 versus 17.92, respectively). Given the emerging data on the clinical benefits of β-lactam adjunctive therapy in refractory MRSA bacteremia, additional studies on a larger collection of clinical isolates are needed to establish the utility of VAN plus CFZ for treatment of MRSA bacteremia.

Morbidity, mortality, and management of methicillin-resistant S. aureus bacteremia in the USA: update on antibacterial choices and understanding

Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia is associated with significant healthcare costs, morbidity, and mortality in the United States. Complications of MRSA bacteremia include infective endocarditis, osteomyelitis, and sepsis, all of which are difficult to treat. Time to effective therapy and antibacterial choice greatly affect patient outcomes. Vancomycin and daptomycin remain first-line therapies; however, reports of vancomycin-associated treatment failure and reduced daptomycin susceptibility highlight the need to define alternative strategies for MRSA bacteremia treatment. In addition, several patient- and pathogen-specific factors influence the outcomes of MRSA bacteremia. It is, therefore, critical to explore the interaction between host- and pathogen-specific factors and its effect on MRSA bacteremia pathogenesis and mortality. This review discusses the factors that drive the development of MRSA bacteremia and examines alternative treatment strategies.

Antibiotic resistance in Staphylococcus aureus. Current status and future prospects

The major targets for antibiotics in staphylococci are (i) the cell envelope, (ii) the ribosome and (iii) nucleic acids. Several novel targets emerged from recent targeted drug discovery programmes including the ClpP protease and FtsZ from the cell division machinery. Resistance can either develop by horizontal transfer of resistance determinants encoded by mobile genetic elements viz plasmids, transposons and the staphylococcal cassette chromosome or by mutations in chromosomal genes. Horizontally acquired resistance can occur by one of the following mechanisms: (i) enzymatic drug modification and inactivation, (ii) enzymatic modification of the drug binding site, (iii) drug efflux, (iv) bypass mechanisms involving acquisition of a novel drug-resistant target, (v) displacement of the drug to protect the target. Acquisition of resistance by mutation can result from (i) alteration of the drug target that prevents the inhibitor from binding, (ii) derepression of chromosomally encoded multidrug resistance efflux pumps and (iii) multiple stepwise mutations that alter the structure and composition of the cell wall and/or membrane to reduce drug access to its target. This review focuses on development of resistance to currently used antibiotics and examines future prospects for new antibiotics and informed use of drug combinations.

Pharmacokinetic/pharmacodynamic parameters for treatment optimization of infection due to antibiotic resistant bacteria: a summary for practical purposes in children and adults

In the last years, there has been a tremendous increase in the incidence of bacterial infections due to resistant strains, especially multi-drug resistant Gram-negative bacilli. In Europe, a north to south and a west to east gradient was noticed, with more than one third of the K. pneumonia isolates being resistant to carbapenems in few countries. New antibiotics are lacking and, as a consequence, pharmacokinetic/pharmacodynamic parameters, normalized to pathogen minimal inhibitory concentration, are used with increased frequency to treat infections due to difficult-to-treat pathogens. These parameters are available at least for the adult population, but sparse in many different publications. This review wants to provide a comprehensive and 'easy to read' text for everyday practice, briefly summarizing the presently available knowledge on pharmacokinetic/pharmacodynamic parameters (normalized for minimal inhibitory concentration values) of different class drugs, that can be applied for an effective antibacterial treatment infections due to antibiotic-resistant pathogens.

Beta-lactam combination therapy for the treatment of Staphylococcus aureus and Enterococcus species bacteremia: A summary and appraisal of the evidence

Staphylococcal bacteremia and enterococcal bacteremia are prevalent in hospitalized or recently instrumented patients, and are associated with significant morbidity and mortality. They are often difficult to treat due to the pathogenicity of the organisms, poor response to antibiotics, and increasing development of multidrug resistance. Therefore, there has been increasing interest in combination therapy for the treatment of these infections. The aim of this review was to summarize and assess the evidence supporting combination beta-lactam therapy for both Staphylococcus aureus and Enterococcus species blood stream infections. Currently, there is promising in vitro data but little clinical evidence supporting combination beta-lactam therapy for this indication. Further clinical investigations are needed to elucidate the potential benefits of beta-lactam combination therapy over monotherapy for Gram-positive bacteremia, although combination therapy may be useful in refractory cases of bacteremia that do not respond to standard antibiotic therapy.

In vitro activity of daptomycin combinations with rifampicin, gentamicin, fosfomycin and fusidic acid against MRSA strains

OBJECTIVES

Although new antimicrobial agents designed to treat infections with limited therapeutic options have been introduced in the past few years, resistant Gram positive cocci have continued to emerge and spread. Daptomycin is a cyclic lipopeptide antibiotic that has rapid bactericidal activity against broad spectrum of Gram positive bacteria, including methicillin resistant Staphylococcus aureus (MRSA). Antibiotics are sometimes used in combination in an attempt to prevent or delay the in vivo emergence of drug-resistant subpopulations of pathogenic organisms. The aim of the study was to evaluate in vitro activity of daptomycin combinations with rifampicin, gentamicin, fosfomycin, and fusidic acid against MRSA strains.

METHODS

In total, 25 strains were tested. The minimum inhibitory concentrations of all antibiotics were determined using a microbroth dilution assay. The in vitro activities of antibiotics in combination were assessed using the microbroth checkerboard technique. With this method, the fractional inhibitory concentration index was interpreted as follows: synergism ≤0.5; additive/indifference >0.5-≤4; antagonism >4.

RESULTS

According to the MIC values, all strains (100%) were susceptible to daptomycin, 16% (4/25) to rifampicin, 20% (5/25) to gentamicin, 44% (11/25) to fosfomycin, and 72% (18/25) to fusidic acid. Synergistic interaction of daptomycin in combinations with rifampicin, gentamicin, fosfomycin, and fusidic acid were found as 12%, 68%, 100% and 16%, respectively. No antagonism was observed.

CONCLUSION

The combination of daptomycin with fosfomycin may be a promising alternative therapy of MRSA infections.

Daptomycin Improves Outcomes Regardless of Vancomycin MIC in a Propensity-Matched Analysis of Methicillin-Resistant Staphylococcus aureus Bloodstream Infections

Vancomycin remains the mainstay treatment for methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infections (BSIs) despite increased treatment failures. Daptomycin has been shown to improve clinical outcomes in patients with BSIs caused by MRSA isolates with vancomycin MICs of >1 mg/liter, but these studies relied on automated testing systems. We evaluated the outcomes of BSIs caused by MRSA isolates for which vancomycin MICs were determined by standard broth microdilution (BMD). A retrospective, matched cohort of patients with MRSA BSIs treated with vancomycin or daptomycin from January 2010 to March 2015 was completed. Patients were matched using propensity-adjusted logistic regression, which included age, Pitt bacteremia score, primary BSI source, and hospital of care. The primary endpoint was clinical failure, which was a composite endpoint of the following metrics: 30-day mortality, bacteremia with a duration of ≥7 days, or a change in anti-MRSA therapy due to persistent or worsening signs or symptoms. Secondary endpoints included MRSA-attributable mortality and the number of days of MRSA bacteremia. Independent predictors of failure were determined through conditional backwards-stepwise logistic regression with vancomycin BMD MIC forced into the model. A total of 262 patients were matched. Clinical failure was significantly higher in the vancomycin cohort than in the daptomycin cohort (45.0% versus 29.0%; P = 0.007). All-cause 30-day mortality was significantly higher in the vancomycin cohort (15.3% versus 6.1%; P = 0.024). These outcomes remained significant when stratified by vancomycin BMD MIC. There was no significant difference in the length of MRSA bacteremia. Variables independently associated with treatment failure included vancomycin therapy (adjusted odds ratio [aOR] = 2.16, 95% confidence interval [CI] = 1.24 to 3.76), intensive care unit admission (aOR = 2.46, 95% CI = 1.34 to 4.54), and infective endocarditis as the primary source (aOR = 2.33, 95% CI = 1.16 to 4.68). Treatment of MRSA BSIs with daptomycin was associated with reduced clinical failure and 30-day mortality; these findings were independent of vancomycin BMD MIC.

Bacteremia due to Methicillin-Resistant Staphylococcus aureus: New Therapeutic Approaches

This article reviews recent clinical evidence for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia. Vancomycin remains the initial antibiotic of choice for the treatment of patients with MRSA bacteremia and endocarditis due to isolates with vancomycin minimum inhibitory concentration ≤2 μg/mL, whereas daptomycin is an effective alternative, and ceftaroline seems promising. Treatment options for persistent MRSA bacteremia or bacteremia due to vancomycin-intermediate or vancomycin-resistant strains include daptomycin, ceftaroline, and combination therapies. There is a critical need for high-level evidence from clinical trials to allow optimally informed decisions in the treatment of MRSA bacteremia and endocarditis.

Effectiveness of sequential intravenous-to-oral antibiotic switch therapy in hospitalized patients with gram-positive infection: the SEQUENCE cohort study

Switching from intravenous to oral antibiotic therapy may improve inpatient management and reduce hospital stays and the complications of intravenous treatment. We aimed to assess the effectiveness of intravenous-to-oral antibiotic switch therapy and an early discharge algorithm in hospitalized patients with gram-positive infection. We performed a prospective cohort study with a retrospective comparison cohort, recruited from eight tertiary, acute-care Spanish referral hospitals. All patients included had culture-confirmed methicillin-resistant gram-positive infection, or methicillin-susceptible gram-positive infection and beta-lactam allergy and had received intravenous treatment with glycopeptides, lipopeptides, or linezolid. The study comprised two cohorts: the prospective cohort to assess the effectiveness of a sequential intravenous-to-oral antibiotic switch algorithm and early discharge, and a retrospective cohort in which the algorithm had not been applied, used as the comparator. A total of 247 evaluable patients were included; 115 in the prospective and 132 in the retrospective cohort. Forty-five retrospective patients (34 %) were not changed to oral antibiotics, and 87 (66 %) were changed to oral antibiotics without following the proposed algorithm. The duration of hospitalization was significantly shorter in the prospective cohort compared to the retrospective group that did not switch to oral drugs (16.7 ± 18.7 vs 23 ± 13.4 days, P  < 0.001). No differences were observed regarding the incidence of catheter-related bacteraemia (4.4 % vs 2.6 %, P = 0.621). Our results suggest that an intravenous-to-oral antibiotic switch strategy is effective for reducing the length of hospital stay in selected hospitalized patients with gram-positive infection.

Daptomycin: an evidence-based review of its role in the treatment of Gram-positive infections

Infections caused by Gram-positive pathogens remain a major public health burden and are associated with high morbidity and mortality. Increasing rates of infection with Gram-positive bacteria and the emergence of resistance to commonly used antibiotics have led to the need for novel antibiotics. Daptomycin, a cyclic lipopeptide with rapid bactericidal activity against a wide range of Gram-positive bacteria including methicillin-resistant Staphylococcus aureus, has been shown to be effective and has a good safety profile for the approved indications of complicated skin and soft tissue infections (4 mg/kg/day), right-sided infective endocarditis caused by S. aureus, and bacteremia associated with complicated skin and soft tissue infections or right-sided infective endocarditis (6 mg/kg/day). Based on its pharmacokinetic profile and concentration-dependent bactericidal activity, high-dose (>6 mg/kg/day) daptomycin is considered an important treatment option in the management of various difficult-to-treat Gram-positive infections. Although daptomycin resistance has been documented, it remains uncommon despite the increasing use of daptomycin. To enhance activity and to minimize resistance, daptomycin in combination with other antibiotics has also been explored and found to be beneficial in certain severe infections. The availability of daptomycin via a 2-minute intravenous bolus facilitates its outpatient administration, providing an opportunity to reduce risk of health care-associated infections, improve patient satisfaction, and minimize health care costs. Daptomycin, not currently approved for use in the pediatric population, has been shown to be widely used for treating Gram-positive infections in children.

Phytochemical Composition and Antibacterial Activity of Hydroalcoholic Extracts of Pterospartum tridentatum and Mentha pulegium against Staphylococcus aureus Isolates

Pterospartum tridentatum and Mentha pulegium are largely used in Portuguese folk medicine to treat several human disorders and inflammatory processes but without any consistent evidence for those beneficial pointed properties. Thus, the aim of the current work is to evaluate its benefits and phytochemicals related to those beneficial properties. A distinct polyphenol profile between P. tridentatum and M. pulegium was found. Taxifolin, myricetin, ginestin, ginestein, and ginestein derivatives, biochanin A-glucoside, and biochanin A were identified in P. tridentatum, whilst in M. pulegium the luteolin-7-rutinoside, diosmin, and apigenin and respective derivatives were most representative polyphenols. These variations had implications in the antiradical and antibacterial activity and the P. tridentatum exhibited the highest antibacterial activity against methicillin-resistant and methicillin-sensitive Staphylococcus aureus MSSA, which was mainly dose-dependent. This antibacterial activity seems to be related to high content of flavonols, flavones, and isoflavones, which can act synergistically with each other against this type of bacteria. Our results showed consistent evidence that Pterospartum tridentatum and Mentha pulegium are an important reservoir of phytochemicals with antiradical activity and antibacterial capacity and thus they might be used in a preventive way or in a combined pharmaceutical and antibiotic therapy against pathogenic bacteria.