Synergy of daptomycin with oxacillin and other beta-lactams against methicillin-resistant Staphylococcus aureus

Antibacterial efficacy of antimicrobial peptide-functionalized hydrogel particles combined with vancomycin and oxacillin antibiotics

The rise of antibiotic resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), requires novel approaches to combat infections. Medical devices like implants and wound dressings are frequently used in conjunction with antibiotics, motivating the development of antibacterial biomaterials capable of exhibiting combined antibacterial effects with conventional antibiotics. This study explores the synergistic antibacterial effects of combining antimicrobial peptide (AMP) functionalized hydrogel particles with conventional antibiotics, vancomycin (VCM) and oxacillin (OXA), against Staphylococcus aureus and MRSA. The AMP employed, RRPRPRPRPWWWW-NH2, has previously demonstrated broad-spectrum activity and enhanced stability when attached to hydrogel substrates. Here, checkerboard assays revealed additive and synergistic interactions between the free AMP and both VCM and OXA against Staphylococcus aureus and MRSA. Notably, the AMP-OXA combination displayed a significant synergistic effect against MRSA, with a 512-fold reduction in OXA's minimum inhibitory concentration (MIC) when combined with free AMP. The observed synergism against MRSA was retained upon covalent AMP immobilization onto the hydrogel particles; however, at a lower rate with a 64-fold reduction in OXA MIC. Despite this, the OXA-AMP hydrogel particle combinations retained considerable synergistic potential against MRSA, a strain resistant to OXA, highlighting the potential of AMP-functionalized materials for enhancing antibiotic efficacy. These findings underscore the importance of developing antimicrobial biomaterials for future medical devices to fight biomaterial-associated infections and reverse antimicrobial resistance.

Structural and kinetic analysis of the monofunctional Staphylococcus aureus PBP1

Staphylococcus aureus, an ESKAPE pathogen, is a major clinical concern due to its pathogenicity and manifold antimicrobial resistance mechanisms. The commonly used β-lactam antibiotics target bacterial penicillin-binding proteins (PBPs) and inhibit crosslinking of peptidoglycan strands that comprise the bacterial cell wall mesh, initiating a cascade of effects leading to bacterial cell death. S. aureus PBP1 is involved in synthesis of the bacterial cell wall during division and its presence is essential for survival of both antibiotic susceptible and resistant S. aureus strains. Here, we present X-ray crystallographic data for S. aureus PBP1 in its apo form as well as acyl-enzyme structures with distinct classes of β-lactam antibiotics representing the penicillins, carbapenems, and cephalosporins, respectively: oxacillin, ertapenem and cephalexin. Our structural data suggest that the PBP1 active site is readily accessible for substrate, with little conformational change in key structural elements required for its covalent acylation of β-lactam inhibitors. Stopped-flow kinetic analysis and gel-based competition assays support the structural observations, with even the weakest performing β-lactams still having comparatively high acylation rates and affinities for PBP1. Our structural and kinetic analysis sheds insight into the ligand-PBP interactions that drive antibiotic efficacy against these historically useful antimicrobial targets and expands on current knowledge for future drug design and treatment of S. aureus infections.

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.

Hyphae-specific genes: Possible molecular targets for magnetic iron oxide nanoparticles alone and combined with visible light in Candida albicans

Candida albicans readily develops resistance to fluconazole. Magnetic iron oxide nanoparticles (denoted as MION) and antimicrobial photodynamic therapy are attracting attention as therapeutic agents. This study aims to investigate the inhibitory efficacy of MION alone and combined with visible light against C. albicans and expression analysis of hyphal wall protein 1 (HWP1) and agglutinin-like sequence 1 (ALS1) genes in C. albicans. Antifungal susceptibility testing, photodynamic activity assay, reactive oxygen species (ROS) production assay and gene expression analysis were determined in C. albicans treated with MION alone and combined with visible light. MION at 1 × minimum inhibitory concentration (MIC) level (500 μg/mL) exhibited antifungal activity against C. albicans isolates. Further, 1 × MIC levels of MION alone and combined with visible light displayed remarkable fungicidal effects at 24 and 48 h after treatment. The MION combined with visible light caused the highest levels of ROS production by all C. albicans isolates. The relative RT-PCR data showed significant downregulation of HWP1 and ALS1 genes which are the key virulence genes in C. albicans. Differences in gene expression of  HWP1 and ALS1 were more significant in MION combined with visible light treatments than MION alone. Our study sheds a novel light on facile development of effective treatment of C. albicans especially fluconazole-resistant C. albicans infections. The hyphae-specific genes HWP1 and ALS1 could be probable molecular targets for MION alone and combined with visible light in C. albicans.

In vitro activity of fidaxomicin and combinations of fidaxomicin with other antibiotics against Clostridium perfringens strains isolated from dogs and cats

BACKGROUND

Previous studies have demonstrated that fidaxomicin, a macrocyclic lactone antibiotic used to treat recurrent Clostridioides difficile-associated diarrhea, also displays potent in vitro bactericidal activity against Clostridium perfringens strains isolated from humans. However, to date, there is no data on the susceptibility to fidaxomicin of C. perfringens strains of animal origin. On the other hand, although combination therapy has become popular in human and veterinary medicine, limited data are available on the effects of antibiotic combinations on C. perfringens. We studied the in vitro response of 21 C. perfringens strains obtained from dogs and cats to fidaxomicin and combinations of fidaxomicin with six other antibiotics.

RESULTS

When tested by an agar dilution method, fidaxomicin minimum inhibitory concentrations (MICs) ranged between 0.004 and 0.032 µg/ml. Moreover, the results of Etest-based combination assays revealed that the incorporation of fidaxomicin into the test medium at a concentration equivalent to half the MIC significantly increased the susceptibility of isolates to metronidazole and erythromycin in 71.4% and 61.9% of the strains, respectively, and the susceptibility to clindamycin, imipenem, levofloxacin, and vancomycin in 42.9-52.4% of the strains. In contrast, ¼ × MIC concentrations of fidaxomicin did not have any effect on levofloxacin and vancomycin MICs and only enhanced the effects of clindamycin, erythromycin, imipenem, and metronidazole in ≤ 23.8% of the tested strains.

CONCLUSIONS

The results of this study demonstrate that fidaxomicin is highly effective against C. perfringens strains of canine and feline origin. Although fidaxomicin is currently considered a critically important antimicrobial that has not yet been licensed for veterinary use, we consider that the results reported in this paper provide useful baseline data to track the possible emergence of fidaxomicin resistant strains of C. perfringens in the veterinary setting.

A Potential Nontraditional Approach To Combat tmexCD1-toprJ1-Mediated Tigecycline Resistance: Melatonin as a Synergistic Adjuvant of Tigecycline

The emergence of TMexCD1-TOprJ1, a novel transferable resistance-nodulation-division (RND)-type efflux pump conferring resistance to tigecycline, is now a serious public health issue in the world. Here, we found that melatonin synergistically enhanced the antibacterial efficacy of tigecycline against tmexCD1-toprJ1-positive Klebsiella pneumoniae by disrupting the proton driving force and efflux function to promote the accumulation of tigecycline into cells, damaging cell membrane integrity and causing the leakage of cell contents. The synergistic effect was further validated by a murine thigh infection model. The results revealed that the melatonin/tigecycline combination is a potential therapy to combat resistant bacteria carrying the tmexCD1-toprJ1 gene.

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.

Growth Arrest of Staphylococcus aureus Induces Daptomycin Tolerance via Cell Wall Remodelling

Almost all bactericidal drugs require bacterial replication and/or metabolic activity for their killing activity. When these processes are inhibited by bacteriostatic antibiotics, bacterial killing is significantly reduced. One notable exception is the lipopeptide antibiotic daptomycin, which has been reported to efficiently kill growth-arrested bacteria. However, these studies employed only short periods of growth arrest (<1 h), which may not fully represent the duration of growth arrest that can occur in vivo. We found that a growth inhibitory concentration of the protein synthesis inhibitor tetracycline led to a time-dependent induction of daptomycin tolerance in S. aureus, with an approximately 100,000-fold increase in survival after 16 h of growth arrest, relative to exponential-phase bacteria. Daptomycin tolerance required glucose and was associated with increased production of the cell wall polymers peptidoglycan and wall-teichoic acids. However, while the accumulation of peptidoglycan was required for daptomycin tolerance, only a low abundance of wall teichoic acid was necessary. Therefore, whereas tolerance to most antibiotics occurs passively due to a lack of metabolic activity and/or replication, daptomycin tolerance arises via active cell wall remodelling. IMPORTANCE Understanding why antibiotics sometimes fail to cure infections is fundamental to improving treatment outcomes. This is a major challenge when it comes to Staphylococcus aureus because this pathogen causes several different chronic or recurrent infections. Previous work has shown that a lack of replication, as often occurs during infection, makes bacteria tolerant of most bactericidal antibiotics. However, one antibiotic that has been reported to kill nonreplicating bacteria is daptomycin. In this work, we show that the growth arrest of S. aureus does in fact lead to daptomycin tolerance, but it requires time, nutrients, and biosynthetic pathways, making it distinct from other types of antibiotic tolerance that occur in nonreplicating bacteria.

Synergistic Antibiotic Activity of Ricini Semen Extract with Oxacillin against Methicillin-Resistant Staphylococcus aureus

Resistant bacteria are emerging as a critical problem in the treatment of bacterial infections by neutralizing antibiotic activity. The development of new traditional mechanisms of antibiotics is not the optimal solution. A more reasonable approach may be to use relatively safe, plant-based compounds in combination with conventional antibiotics in an effort to increase their efficacy or restore their activity against resistant bacteria. We present our study of mixing Ricini Semen extract, or its constituent fatty acids, with oxacillin and testing the effects of each on the growth of methicillin-resistant Staphylococcus aureus. Changes in the cell membrane fluidity of methicillin-resistant S. aureus were found to be a major component of the mechanism of synergistic antibiotic activity of Ricini Semen extract and its constituent fatty acids. In our model, changes in cellular membrane fluidity disrupted the normal function of bacterial signaling membrane proteins BlaR1 and MecR1, which are known to detect oxacillin, and resulted in the incomplete expression of penicillin-binding proteins 2a and β-lactamase. Utilizing the mechanism presented in this study presents the possibility of developing a method for treating antibiotic-resistant bacteria using traditional antibiotics with plant-based compounds.

MRSA compendium of epidemiology, transmission, pathophysiology, treatment, and prevention within one health framework

Staphylococcus aureus is recognized as commensal as well as opportunistic pathogen of humans and animals. Methicillin resistant strain of S. aureus (MRSA) has emerged as a major pathogen in hospitals, community and veterinary settings that compromises the public health and livestock production. MRSA basically emerged from MSSA after acquiring SCCmec element through gene transfer containing mecA gene responsible for encoding PBP-2α. This protein renders the MRSA resistant to most of the β-lactam antibiotics. Due to the continuous increasing prevalence and transmission of MRSA in hospitals, community and veterinary settings posing a major threat to public health. Furthermore, high pathogenicity of MRSA due to a number of virulence factors produced by S. aureus along with antibiotic resistance help to breach the immunity of host and responsible for causing severe infections in humans and animals. The clinical manifestations of MRSA consist of skin and soft tissues infection to bacteremia, septicemia, toxic shock, and scalded skin syndrome. Moreover, due to the increasing resistance of MRSA to number of antibiotics, there is need to approach alternatives ways to overcome economic as well as human losses. This review is going to discuss various aspects of MRSA starting from emergence, transmission, epidemiology, pathophysiology, disease patterns in hosts, novel treatment, and control strategies.

Daptomycin synergistic properties from in vitro and in vivo studies: a systematic review

INTRODUCTION

Daptomycin is a bactericidal lipopeptide antibiotic approved for the treatment of systemic infections (i.e. skin and soft tissue infections, bloodstream infections, infective endocarditis) caused by Gram-positive cocci. It is often prescribed in association with a partner drug to increase its bactericidal effect and to prevent the emergence of resistant strains during treatment; however, its synergistic properties are still under evaluation.

METHODS

We performed a systematic review to offer clinicians an updated overview of daptomycin synergistic properties from in vitro and in vivo studies. Moreover, we reported all in vitro and in vivo data evaluating daptomycin in combination with other antibiotic agents, subdivided by antibiotic classes, and a summary graph presenting the most favourable combinations at a glance.

RESULTS

A total of 92 studies and 1087 isolates (723 Staphylococcus aureus, 68 Staphylococcus epidermidis, 179 Enterococcus faecium, 105 Enterococcus faecalis, 12 Enterococcus durans) were included. Synergism accounted for 30.9% of total interactions, while indifferent effect was the most frequently observed interaction (41.9%). Antagonistic effect accounted for 0.7% of total interactions. The highest synergistic rates against S. aureus were observed with daptomycin in combination with fosfomycin (55.6%). For S. epidermidis and Enterococcus spp., the most effective combinations were daptomycin plus ceftobiprole (50%) and daptomycin plus fosfomycin (63.6%) or rifampicin (62.8%), respectively.

FUTURE PERSPECTIVES

We believe this systematic review could be useful for the future updates of guidelines on systemic infections where daptomycin plays a key role.

Proteomic Correlates of Enhanced Daptomycin Activity following β-Lactam Preconditioning in Daptomycin-Resistant, Methicillin-Resistant Staphylococcus aureus

Clinical treatment options for daptomycin (DAP)-resistant (DAP-R), methicillin-resistant Staphylococcus aureus (MRSA) infections are relatively limited. Current therapeutic strategies often take advantage of potential synergistic activity of DAP plus β-lactams; however, the mechanisms underlying their combinatorial efficacy are likely complex and remain incompletely understood. We recently showed that in vitro β-lactam passaging can resensitize DAP-R strains to a DAP-susceptible (DAP-S) phenotype. To further investigate the implications of selected β-lactam pretreatments on DAP plus β-lactam combination efficacy, we utilized DAP-R strain D712. We studied six such combinations, featuring β-lactams with a broad range of penicillin-binding protein-targeting profiles (PBP-1 to -4), using DAP-R strain D712. Of note, preconditioning with each β-lactam antibiotic (sequential exposures), followed by DAP exposure, yielded significantly enhanced in vitro activity compared to either DAP treatment alone or simultaneous exposures to both antibiotics. To explore the underpinnings of these outcomes, proteomic analyses were performed, with or without β-lactam preconditioning. Relative proteomic quantitation comparing β-lactam pretreatments (versus untreated controls) identified differential modulation of several well-known metabolic, cellular, and biosynthetic processes, i.e., the autolytic and riboflavin biosynthetic pathways. Moreover, these differential proteomic readouts with β-lactam preconditioning were not PBP target specific. Taken together, these studies suggest that the cellular response to β-lactam preconditioning in DAP-R MRSA leads to distinct and complex changes in the proteome that appear to resensitize such strains to DAP-mediated killing.

β-Lactam-Induced Cell Envelope Adaptations, Not Solely Enhanced Daptomycin Binding, Underlie Daptomycin-β-Lactam Synergy in Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a serious clinical threat due to innate virulence properties, high infection rates, and the ability to develop resistance to multiple antibiotics, including the lipopeptide daptomycin (DAP). The acquisition of DAP resistance (DAP-R) in MRSA has been linked with several characteristic alterations in the cell envelope. Clinical treatment of DAP-R MRSA infections has generally involved DAP-plus-β-lactam combinations, although definable synergy of such combinations varies in a strain-dependent as well as a β-lactam-dependent manner. We investigated distinct β-lactam-induced cell envelope adaptations of nine clinically derived DAP-susceptible (DAP-S)/DAP-R strain pairs following in vitro exposure to a panel of six standard β-lactams (nafcillin, meropenem, cloxacillin, ceftriaxone, cefaclor, or cefoxitin), which differ in their penicillin-binding protein (PBP)-targeting profiles. In general, in both DAP-S and DAP-R strains, exposure to these β-lactams led to (i) a decreased positive surface charge; (ii) decreased cell membrane (CM) fluidity; (iii) increased content and delocalization of anionic phospholipids (i.e., cardiolipin), with delocalization being more pronounced in DAP-R strains; and (iv) increased DAP binding in DAP-S (but not DAP-R) strains. Collectively, these results suggest that β-lactam-induced alterations in at least three major cell envelope phenotypes (surface charge, membrane fluidity, and cardiolipin content) could underlie improved DAP activity, not mediated solely by an increase in DAP binding. (Note that for ease of presentation, we utilize the terminology "DAP-R" instead of "DAP nonsusceptibility.").

Adjunctive Daptomycin in the Treatment of Methicillin-susceptible Staphylococcus aureus Bacteremia: A Randomized, Controlled Trial

BACKGROUND

Bloodstream infections (BSIs) with methicillin-susceptible Staphylococcus aureus (MSSA) are associated with significant morbidity and mortality. Our objective in this study was to determine the efficacy of synergistic treatment with daptomycin when given with either cefazolin or cloxacillin for the treatment of MSSA BSI.

METHODS

A randomized, double-blind, placebo-controlled trial was performed at 2 academic hospitals in Montreal, Canada. Patients aged ≥18 years with MSSA BSI receiving either cefazolin or cloxacillin monotherapy were considered for inclusion. In addition to the standard-of-care treatment, participants received a 5-day course of adjunctive daptomycin or placebo. The primary outcome was the duration of MSSA BSI in days.

RESULTS

Of 318 participants screened, 115 were enrolled and 104 were included in the intention-to-treat analysis (median age, 67 years; 34.5% female). The median duration of bacteremia was 2.04 days among patients who received daptomycin vs 1.65 days in those who received placebo (absolute difference, 0.39 days; P = .40). In a modified intention-to-treat analysis that involved participants who remained bacteremic at the time of enrollment, we found a median duration of bacteremia of 3.06 days among patients who received daptomycin vs 3.0 days in those who received placebo (absolute difference, 0.06 days; P = .77). Ninety-day mortality in the daptomycin arm was 18.9% vs 17.7% in the placebo arm (P = 1.0).

CONCLUSIONS

Among patients with MSSA BSIs, the administration of adjunctive daptomycin therapy to standard-of-care treatment did not shorten the duration of bacteremia and should not be routinely considered.

CLINICAL TRIALS REGISTRATION

NCT02972983.

Current Paradigms of Combination therapy in Methicillin-Resistant Staphylococcus aureus (MRSA) Bacteremia: Does it Work, Which Combination and For Which Patients?

The last several years have seen an emergence of literature documenting the utility of combination antimicrobial therapy, particularly in the salvage of refractory MRSA bacteremia. Recent clinical data are shaping conundrums of which regimens may be more beneficial, which can be potentially harmful, and which subset of patients stand to benefit from more aggressive treatment regimens than called for by current standards. In addition, the incorporation of combination therapy for MRSA bacteremia should be accompanied by the reminder that antimicrobial therapy does not need to be uniform for the entire duration, with an early intensive phase in high inoculum infections (e.g. with combination therapy), followed by a consolidation phase (i.e. monotherapy). This review and perspective consolidates the recent data on this subject and directs future goals in filling the knowledge gaps to methodically move forward towards improving patient outcomes.

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.

Review: Lessons Learned From Clinical Trials Using Antimicrobial Peptides (AMPs)

Antimicrobial peptides (AMPs) or host defense peptides protect the host against various pathogens such as yeast, fungi, viruses and bacteria. AMPs also display immunomodulatory properties ranging from the modulation of inflammatory responses to the promotion of wound healing. More interestingly, AMPs cause cell disruption through non-specific interactions with the membrane surface of pathogens. This is most likely responsible for the low or limited emergence of bacterial resistance against many AMPs. Despite the increasing number of antibiotic-resistant bacteria and the potency of novel AMPs to combat such pathogens, only a few AMPs are in clinical use. Therefore, the current review describes (i) the potential of AMPs as alternatives to antibiotics, (ii) the challenges toward clinical implementation of AMPs and (iii) strategies to improve the success rate of AMPs in clinical trials, emphasizing the lessons we could learn from these trials.

The Emerging Role of β-Lactams in the Treatment of Methicillin-Resistant Staphylococcus aureus Bloodstream Infections

Methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infections (BSI) are associated with substantial morbidity and mortality. Monotherapy with first-line antimicrobials such as vancomycin (VAN; glycopeptide) and daptomycin (DAP; lipopeptide) are inadequate in some cases due to reduced antibiotic susceptibilities or therapeutic failure. In recent years, β-lactam antibiotics have emerged as a potential option for combination therapy with VAN and DAP that may meet an unmet therapeutic need for MRSA BSI. Ceftaroline (CPT), the only commercially available β-lactam in the United States with intrinsic in vitro activity against MRSA, has been increasingly studied in the setting of VAN and DAP failures. Novel combinations of first-line agents (VAN and DAP) with β-lactams have been the subject of many recent investigations due to in vitro findings such as the "seesaw effect," where β-lactam susceptibility may be improved in the presence of decreased glycopeptide and lipopeptide susceptibility. The combination of CPT and DAP, in particular, has become the focus of many scientific evaluations, due to intrinsic anti-MRSA activities and potent in vitro synergistic activity against various MRSA strains. This article reviews the available literature describing these innovative therapeutic approaches for MRSA BSI, focusing on preclinical and clinical studies, and evaluates the potential benefits and limitations of each strategy.

A copper-dependent compound restores ampicillin sensitivity in multidrug-resistant Staphylococcus aureus

Multi-drug resistant Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA), has become a worldwide, major health care problem. While initially restricted to clinical settings, drug resistant S. aureus is now one of the key causative agents of community-acquired infections. We have previously demonstrated that copper dependent inhibitors (CDIs), a class of antibiotics that are only active in the presence of copper ions, are effective bactericidal agents against MRSA. A second-generation CDI, APT-6K, exerted bactericidal activity at nanomolar concentrations. At sub-bactericidal concentrations, it effectively synergized with ampicillin to reverse drug resistance in multiple MRSA strains. APT-6K had a favorable therapeutic index when tested on eukaryotic cells (TI: > 30) and, unlike some previously reported CDIs, did not affect mitochondrial activity. These results further establish inhibitors that are activated by the binding of transition metal ions as a promising class of antibiotics, and for the first time, describe their ability to reverse existing drug resistance against clinically relevant antibiotics.

The Potential Role of Sulbactam and Cephalosporins Plus Daptomycin Against Daptomycin-Nonsusceptible VISA and H-VISA Isolates: An in Vitro Study

This study assesses the synergistic effect of the combination of cephalosporins and sulbactam with daptomycin against daptomycin-nonsusceptible, vancomycin-intermediate resistant Staphylococcus aureus (VISA) or heterogeneous vancomycin-intermediate S. aureus (h-VISA) isolates. The in vitro activity of daptomycin against daptomycin-nonsusceptible VISA/h-VISA isolates after adding cephalosporins with or without sulbactam was evaluated. The MIC of daptomycin against the VISA/h-VISA isolates was reduced after adding cephalosporins to daptomycin. Except for one VISA and two h-VISA isolates, the other VISA/h-VISA isolates became daptomycin-susceptible (MICs 1 mg/L). After adding sulbactam to each daptomycin/cephalosporin combination, the MIC of daptomycin against the VISA/h-VISA isolates decreased for 5 (33.3%), 6 (40.0%), 6 (40.0%), and 6 (40.0%) isolates with the cefazolin, cefmetazole, cefotaxime, and cefepime combinations, respectively. Synergism using the checkerboard method was noted in 100% of cefazolin and cefotaxime combinations and 87% and 80% of cefmetazole and cefepime combinations for all the VISA and h-VISA isolates. With the addition of sulbactam, synergism was noted in 100% of cefazolin, cefmetazole, and cefotaxime combinations and 93% of the cefepime combinations for all the VISA and h-VISA isolates. Almost all the FICs for the three-drug combinations were lower than those for the two-drug combinations. Using time-killing methods, a synergistic effect against five h-VISA isolates was observed. A synergistic effect of daptomycin, sulbactam, and each cephalosporin was observed for all VISA isolates. In conclusion, the activity of daptomycin against daptomycin-nonsusceptible VISA/h-VISA isolates can be enhanced by adding cephalosporins, and partially further promoted by sulbactam.

Ceftobiprole: drug evaluation and place in therapy

Introduction: Ceftobiprole is a fifth-generation cephalosporin with a broad spectrum of antimicrobial activity, including also methicillin-resistant Staphylococcus aureus (MRSA). Ceftobiprole is approved for the treatment of community-acquired pneumonia (CAP) and hospital-acquired pneumonia (HAP), excluding ventilator-associated pneumonia, in several European and non-European countries. Areas covered: In this narrative review, we discuss the current place in therapy of ceftobiprole, both within and outside approved indications. An inductive MEDLINE/PubMed search of the available literature was conducted. Expert opinion: There are three main reasons which render ceftobiprole an attractive option for the empirical and targeted treatment of CAP and HAP: (i) its broad spectrum of activity; (ii) its activity against MRSA; (iii) its good safety profile. For these indications, ceftobiprole should be employed thoughtfully, in those scenarios in which its intrinsic advantages could be maximized. The use of ceftobiprole outside approved indications could be justified in specific scenarios, such as when other approved alternatives are ineffective, when the risk of toxicity due to other agents is unacceptable, and for salvage therapy. In the near future, ongoing phase 3 studies and further observational experiences could both enlarge the current panel of approved indications and enrich our knowledge on the use of ceftobiprole for off-label indications.

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.

Sub-inhibitory membrane damage undermines Staphylococcus aureus virulence

We investigated antibacterial properties of a recently described membrane-active lipopeptide, C₁₀OOc₁₂O (decanoyl-ornithyl-ornithyl-dodecanoyl-ornithyl-amide) against Gram-positive bacteria (GPB). Minimal inhibitory concentrations (MICs) and kinetics were compared in culture media and plasma. Chemo-sensitization to antibiotics was determined using the checkerboard assay. Membrane damages were estimated using diverse membrane potential sensitive dyes. ATP levels and relevant enzymes activities were measured using commercial bioassay kits. While relatively weakly active in simple culture media, sub-MIC levels (~ten-fold) of C₁₀OOc₁₂O have significantly improved the antibacterial function of Human plasma. Mechanistic studies indicated that C₁₀OOc₁₂O-treated bacteria have sustained mild membrane damage(s) in association with rapid (within 2 min) but low (<10%) dissipation of the trans-membrane potential; Intracellular ATP levels were transiently reduced (~20%) whereas extracellular ATP increased only at MIC values; Sub-inhibitory concentrations were sufficient for inhibiting major agr-regulated virulence factors (lipase and α-toxin) and for sensitizing MRSA USA300 to the antibiotic oxacillin to the point of reverting the bacteria status from oxacillin-resistant to oxacillin-sensitive (i.e., oxacillin MIC was reduced from 32 to 0.1 mg/l). These findings argue that by means of mild depolarization, C₁₀OOc₁₂O affects the quorum sensing regulator in a manner that transiently weakens bacterial defenses, thereby enforcing studies that support the potential usefulness of fighting S. aureus (and possibly other GPB) infections, by targeting its virulence.

Ceftobripole: Experience in staphylococcal bacteremia

Ceftobiprole is a new cephalosporin with an extended spectrum activity against the majority of microorganisms isolated in bacteremia including methicillin-susceptible (MSSA) and -resistant S. aureus (MRSA). This antibiotic has demonstrated a potent activity against MRSA in animal models of endocarditis in monotherapy but particularly in combination with daptomycin, suggesting that this combination could be a future option to improve the outcome of staphylococcal endovascular infections. In addition, the extended-spectrum ceftobiprole activity, including coagulase-negative staphylococci, Enterococcus faecalis, Enterobacteriaceae and Pseudomonas aeruginosa represents an advantage for use as empirical therapy in bacteremia potentially caused by a broad spectrum of microorganisms, such as in catheter-related bacteremia.

Daptomycin

Daptomycin is a cyclic lipopeptide antibiotic used for the treatment of Gram-positive infections including complicated skin and skin structure infections, right-sided infective endocarditis, bacteraemia, meningitis, sepsis and urinary tract infections. Daptomycin has distinct mechanisms of action, disrupting multiple aspects of cell membrane function and inhibiting protein, DNA and RNA synthesis. Although daptomycin resistance in Gram-positive bacteria is uncommon, there are increasing reports of daptomycin resistance in Staphylococcus aureus, Enterococcus faecium and Enterococcus faecalis. Such resistance is seen largely in the context of prolonged treatment courses and infections with high bacterial burdens, but may occur in the absence of prior daptomycin exposure. Furthermore, use of inadequate treatment regimens, irregular drug supply and poor drug quality have also been recognized as other important risk factors for emergence of daptomycin-resistant strains. Antimicrobial susceptibility testing of Gram-positive bacteria, communication between clinicians and laboratories, establishment of internet-based reporting systems, development of better and more rapid diagnostic methods and continuous monitoring of drug resistance are urgent priorities.

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.

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.

Future trends in the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infection: An in-depth review of newer antibiotics active against an enduring pathogen

Methicillin-resistant Staphylococcus aureus (MRSA) continues to be a major public health problem. Vancomycin and teicoplanin have been in clinical use for several decades but their drawbacks are well described. In the last 10 years, several antibiotics have been made available for clinical use. Daptomycin and linezolid have been extensively used during this period. Other agents such as ceftaroline, ceftobiprole, dalbavancin, oritavancin, tedizolid and telavancin have been approved by regulatory agencies since 2009. Many others, such as the newer tetracyclines, fluoroquinolones, oxazolidinones and pleuromutilins, are in various stages of development. In addition, an ongoing multicentre trial is investigating the role of combination of vancomycin or daptomycin with β-lactam antibiotics. This review discusses the role of the newer antibiotics, reflecting the views of the 6th MRSA Consensus Conference meeting of the International Society of Chemotherapy MRSA Working Group that took place in 2016.

Ceftaroline for Severe Methicillin-Resistant Staphylococcus aureus Infections: A Systematic Review

Ceftaroline is approved by the Food and Drug Administration for acute bacterial skin and skin-structure infections and community-acquired bacterial pneumonia, including cases with concurrent bacteremia. Use for serious methicillin-resistant Staphylococcus aureus (MRSA) infections has risen for a multitude of reasons. The aim of this article is to review the literature evaluating clinical outcomes and safety of ceftaroline prescribed for serious MRSA infections. We conducted a literature search in Ovid (Medline) and PubMed for reputable case reports, clinical trials, and reviews focusing on the use of ceftaroline for treatment of MRSA infections. Twenty-two manuscripts published between 2010 and 2016 met inclusion criteria. Mean clinical cure was 74% across 379 patients treated with ceftaroline for severe MRSA infections. Toxicities were infrequent. Ceftaroline treatment resulted in clinical and microbiologic cure for severe MRSA infections. Close monitoring of hematological parameters is necessary with prolonged courses of ceftaroline.

Molecular Bases Determining Daptomycin Resistance-Mediated Resensitization to β-Lactams (Seesaw Effect) in Methicillin-Resistant Staphylococcus aureus

Antimicrobial resistance is recognized as one of the principal threats to public health worldwide, yet the problem is increasing. Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) strains are among the most difficult to treat in clinical settings due to the resistance of MRSA to nearly all available antibiotics. The cyclic anionic lipopeptide antibiotic daptomycin (DAP) is the clinical mainstay of anti-MRSA therapy. The decreased susceptibility to DAP (DAP resistance [DAP^r]) reported in MRSA is frequently accompanied by a paradoxical decrease in β-lactam resistance, a process known as the "seesaw effect." Despite the observed discordance in resistance phenotypes, the combination of DAP and β-lactams has been proven to be clinically effective for the prevention and treatment of infections due to DAP^r MRSA strains. However, the mechanisms underlying the interactions between DAP and β-lactams are largely unknown. In the study described here, we studied the role of mprF with DAP-induced mutations in β-lactam sensitization and its involvement in the effective killing by the DAP-oxacillin (OXA) combination. DAP-OXA-mediated effects resulted in cell wall perturbations, including changes in peptidoglycan insertion, penicillin-binding protein 2 (PBP 2) delocalization, and reduced membrane amounts of PBP 2a, despite the increased transcription of mecA through mec regulatory elements. We have found that the VraSR sensor-regulator is a key component of DAP resistance, triggering mutated mprF-mediated cell membrane (CM) modifications that result in impairment of PrsA location and chaperone functions, both of which are essential for PBP 2a maturation, the key determinant of β-lactam resistance. These observations provide for the first time evidence that synergistic effects between DAP and β-lactams involve PrsA posttranscriptional regulation of CM-associated PBP 2a.

Resistance to Non-glycopeptide Agents in Serious Staphylococcus aureus Infections

The role of vancomycin in the treatment of serious Staphylococcus aureus infections, both methicillin-susceptible and methicillin-resistant, is becoming increasingly ineffective due to increasing MIC and failure. The development of reduced vancomycin susceptibility by S. aureus to glycopeptides highlights the need for clinicians to reexamine the roles of non-glycopeptide therapy. As the use of these alternative non-glycopeptides antimicrobials increases, it will become pertinent to monitor the rates of resistance. Large surveillance programs have provided data for resistance against S. aureus for the non-glycopeptides (daptomycin, ceftaroline, tigecycline, linezolid, and tedizolid). The current published literatures suggest that worldwide resistance rates to these non-glycopeptides for serious MRSA infections are still low. Implementation of antimicrobial stewardship programs will be crucial in prevention of resistance of these antimicrobials against S. aureus.

Staphylococcus aureus inactivates daptomycin by releasing membrane phospholipids

Daptomycin is a bactericidal antibiotic of last resort for serious infections caused by methicillin-resistant Staphylococcus aureus (MRSA)^1,2. Although resistance is rare, treatment failure can occur in more than 20% of cases^3,4 and so there is a pressing need to identify and mitigate factors that contribute to poor therapeutic outcomes. Here, we show that loss of the Agr quorum-sensing system, which frequently occurs in clinical isolates, enhances S. aureus survival during daptomycin treatment. Wild-type S. aureus was killed rapidly by daptomycin, but Agr-defective mutants survived antibiotic exposure by releasing membrane phospholipids, which bound and inactivated the antibiotic. Although wild-type bacteria also released phospholipid in response to daptomycin, Agr-triggered secretion of small cytolytic toxins, known as phenol soluble modulins, prevented antibiotic inactivation. Phospholipid shedding by S. aureus occurred via an active process and was inhibited by the β-lactam antibiotic oxacillin, which slowed inactivation of daptomycin and enhanced bacterial killing. In conclusion, S. aureus possesses a transient defence mechanism that protects against daptomycin, which can be compromised by Agr-triggered toxin production or an existing therapeutic antibiotic.

In Vitro and In Vivo Synergy of the Oxadiazole Class of Antibacterials with β-Lactams

The oxadiazole antibacterials target the bacterial cell wall and are bactericidal. We investigated the synergism of ND-421 with the commonly used β-lactams and non-β-lactam antibiotics by the checkerboard method and by time-kill assays. ND-421 synergizes well with β-lactam antibiotics, and it also exhibits a long postantibiotic effect (4.7 h). We also evaluated the in vivo efficacy of ND-421 in a murine neutropenic thigh infection model alone and in combination with oxacillin. ND-421 has in vivo efficacy by itself in a clinically relevant infection model (1.49 log10 bacterial reduction for ND-321 versus 0.36 log10 for linezolid with NRS119) and acts synergistically with β-lactam antibiotics in vitro and in vivo, and the combination of ND-421 with oxacillin is efficacious in a mouse neutropenic thigh methicillin-resistant Staphylococcus aureus (MRSA) infection model (1.60 log10 bacterial reduction). The activity of oxacillin was potentiated in the presence of ND-421, as the strain would have been resistant to oxacillin otherwise.

Diminished Susceptibility to Daptomycin Accompanied by Clinical Failure in a Patient With Methicillin-Resistant Staphylococcus aureus Bacteremia

We cared for a patient with methicillin-resistant Staphylococcus aureus bacteremia who experienced clinical failure with daptomycin. The failure was accompanied by progressive elevation of the daptomycin minimum inhibitory concentration during treatment. DNA fingerprinting confirmed that the minimum inhibitory concentration elevation occurred within the same strain of methicillin-resistant Staphylococcus aureus. This observation provides important new information to clinicians who adopt this promising drug for treatment of serious infections caused by methicillin-resistant Staphylococcus aureus.

Daptomycin-β-Lactam Combinations in a Rabbit Model of Daptomycin-Nonsusceptible Methicillin-Resistant Staphylococcus aureus Endocarditis

Beta-lactams enhance the in vitro activity of daptomycin against methicillin-resistant strains of Staphylococcus aureus Experiments were performed in a rabbit model of aortic valve endocarditis caused by methicillin-resistant daptomycin-nonsusceptible S. aureus strain CB5054 to determine if a cephalosporin, ceftriaxone, administered as a once-daily dose of 100 mg/kg of body weight, or a carbapenem, ertapenem, administered as a once-daily dose of 40 mg/kg, improved the efficacy of daptomycin, administered as a once-daily dose of 12 mg/kg. Daptomycin was ineffective alone in reducing organism densities compared to untreated controls in vegetations and spleen, but densities were 1.4 log10 CFU/g lower in kidney. The combination of daptomycin plus ceftriaxone or daptomycin plus ertapenem reduced bacterial densities in all tissues compared to single agents, with 0.6 to 1.0 log10 CFU/g fewer organisms in vegetations, 1.5 to 2.5 log10 CFU/g fewer organisms in spleen, and 1.8 to 2.5 log10 CFU/g fewer organisms in kidney, although differences were statistically significant only in spleen for daptomycin plus ceftriaxone and in kidney for daptomycin plus ertapenem. Drug exposures in rabbits were less than those achievable in humans, which may have limited the in vivo activity, particularly in vegetations.

Daptomycin in Combination with Ceftolozane-Tazobactam or Cefazolin against Daptomycin-Susceptible and -Nonsusceptible Staphylococcus aureus in an In Vitro, Hollow-Fiber Model

Ceftolozane-tazobactam (TOL-TAZ) is a novel cephalosporin/beta-lactamase inhibitor with activity against several Gram-negative pathogens. Daptomycin (DAP) has demonstrated synergistic activity with beta-lactams against methicillin-resistant Staphylococcus aureus (MRSA) isolates with reduced lipopeptide and glycopeptide susceptibilities. Our objective was to determine if DAP and TOL-TAZ possess synergy in hollow-fiber pharmacokinetic/pharmacodynamic (PK/PD) models. One isogenic pair of daptomycin-susceptible and daptomycin-nonsusceptible MRSA strains was evaluated. DAP, TOL-TAZ, and cefazolin (CFZ) MIC determinations were performed. DAP MIC determinations were also performed in the presence of subinhibitory concentrations of TOL-TAZ and CFZ. Ninety-six-hour in vitro models were run, simulating DAP at 10 mg/kg of body weight/day; TOL-TAZ at 1,500 mg every 8 h; TOL at 1,000 mg every 8 h; and DAP combined with TOL-TAZ (DAP+TOL-TAZ), DAP+TOL, DAP+TAZ, and DAP+CFZ at 2,000 mg every 8 h. DAP MICs were 0.5 and 4 μg/ml for strains R8845 and R8846, respectively. In the presence of CFZ, R8845 and R8846 DAP MICs were reduced 8-fold and 16-fold, respectively. TOL and TAZ had no effect on DAP MICs. PK/PD models demonstrated bactericidal activity with DAP+CFZ against both strains. The combination of DAP+TOL-TAZ was bactericidal against R8845 but was not bactericidal against daptomycin-nonsusceptible strain R8846. DAP+TOL and DAP+TAZ were not bactericidal. No other regimens were bactericidal. DAP+TOL-TAZ did not demonstrate synergistic activity against daptomycin-nonsusceptible S. aureus but prevented daptomycin-nonsusceptible MRSA emergence. Because DAP+TOL or TAZ alone did not prevent daptomycin-nonsusceptible MRSA emergence, the combination TOL-TAZ may be necessary for synergy with DAP. DAP+CFZ demonstrated enhancement against both strains. The combination of DAP+CFZ warrants further clinical study.

A Novel Way of Treating Multidrug-resistant Enterococci

Context:

Daptomycin is the only antibiotic available with in vitro bactericidal activity against vancomycin-resistant enterococci (VRE). Its increased use has resulted in cases of decreased daptomycin efficacy. Recent in vitro studies have shown effective use of beta (β)-lactam and daptomycin antibiotics, as a combination therapy, in the treatment of VRE. We describe a case of effective treatment in a patient with VRE infection using dual ampicillin and daptomycin therapy that shows bench-to-bedside application of the abovementioned finding.

Case Report:

A 76-year-old gentleman with a history of bilateral arthroplasty was admitted with a swollen left knee. Blood cultures were positive for Enterococcus faecium. Left knee joint aspiration showed leukocytosis and alpha defensins. Extensive imaging did not show any other source of infection. Culture sensitivity results showed multidrug-resistant enterococci sensitive to daptomycin. The patient was started on intravenous (IV) daptomycin. His left knee prosthesis was explanted and a spacer was placed. The patient continued to be bacteremic for 10 days after removing the knee prosthesis. The patient was trialed on combination IV ampicillin and daptomycin. His blood culture turned negative 2 days later. The patient was discharged home to continue 6 weeks of IV ampicillin and daptomycin.

Conclusion:

The exact mechanism of the daptomycin/ampicillin synergy effect is unclear. Current hypothesis suggests that ampicillin causes a reduction in the net positive charge of the bacterial surface, possibly by releasing lipoteichoic acid (LTA) from the cell wall. This process increases the ability of the cationic daptomycin/calcium complex to bind to the cell wall more effectively. Our case shows the clinical application of the same. A prospective randomized control trial to explore the effectiveness of dual antibiotic therapy in vivo is needed. If proven, daptomycin/β-lactam can become a standard of care to treat VRE and decrease daptomycin nonsusceptibility.

CAMERA2 - combination antibiotic therapy for methicillin-resistant Staphylococcus aureus infection: study protocol for a randomised controlled trial

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia is a serious infection resulting in 20-50 % 90-day mortality. The limitations of vancomycin, the current standard therapy for MRSA, make treatment difficult. The only other approved drug for treatment of MRSA bacteraemia, daptomycin, has not been shown to be superior to vancomycin. Surprisingly, there has been consistent in-vitro and in-vivo laboratory data demonstrating synergy between vancomycin or daptomycin and an anti-staphylococcal β-lactam antibiotic. There is also growing clinical data to support such combinations, including a recent pilot randomised controlled trial (RCT) that demonstrated a trend towards a reduction in the duration of bacteraemia in patients treated with vancomycin plus flucloxacillin compared to vancomycin alone. Our aim is to determine whether the addition of an anti-staphylococcal penicillin to standard therapy results in improved clinical outcomes in MRSA bacteraemia.

METHODS/DESIGN

We will perform an open-label, parallel-group, randomised (1:1) controlled trial at 29 sites in Australia, New Zealand, Singapore, and Israel. Adults (aged 18 years or older) with MRSA grown from at least one blood culture and able to be randomised within 72 hours of the index blood culture collection will be eligible for inclusion. Participants will be randomised to vancomycin or daptomycin (standard therapy) given intravenously or to standard therapy plus 7 days of an anti-staphylococcal β-lactam (flucloxacillin, cloxacillin, or cefazolin). The primary endpoint will be a composite outcome at 90 days of (1) all-cause mortality, (2) persistent bacteraemia at day 5 or beyond, (3) microbiological relapse, or (4) microbiological treatment failure. The recruitment target of 440 patients is based on an expected failure rate for the primary outcome of 30 % in the control arm and the ability to detect a clinically meaningful absolute decrease of 12.5 %, with a two-sided alpha of 0.05, a power of 80 %, and assuming 10 % of patients will not be evaluable for the primary endpoint.

DISCUSSION

Key potential advantages of adding anti-staphylococcal β-lactams to standard therapy for MRSA bacteraemia include their safety profile, low cost, and wide availability.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02365493 . Registered 24 February 2015.

When sepsis persists: a review of MRSA bacteraemia salvage therapy

MRSA bacteraemia (MRSAB), including infective endocarditis, carries a high mortality rate, with up to 50% of patients failing initial therapy with vancomycin and requiring salvage therapy. Persistent MRSAB can be difficult to successfully eliminate, especially when source control is not possible due to an irremovable focus or the bacteraemia still persists despite surgical intervention. Although vancomycin and daptomycin are the only two antibiotics approved by the US FDA for the treatment of patients with MRSAB as monotherapy, the employment of novel strategies is required to effectively treat patients with persistent MRSAB and these may frequently involve combination drug therapy. Treatment strategies that are reviewed in this manuscript include vancomycin combined with a β-lactam, daptomycin-based therapy, ceftaroline-based therapy, linezolid-based therapy, quinupristin/dalfopristin, telavancin, trimethoprim/sulfamethoxazole-based therapy and fosfomycin-based therapy. We recommend that combination antibiotic therapy be considered for use in MRSAB salvage treatment.

Penicillin Binding Protein 1 Is Important in the Compensatory Response of Staphylococcus aureus to Daptomycin-Induced Membrane Damage and Is a Potential Target for β-Lactam-Daptomycin Synergy

The activity of daptomycin (DAP) against methicillin-resistant Staphylococcus aureus (MRSA) is enhanced in the presence of β-lactam antibiotics. This effect is more pronounced with β-lactam antibiotics that exhibit avid binding to penicillin binding protein 1 (PBP1). Here, we present evidence that PBP1 has a significant role in responding to DAP-induced stress on the cell. Expression of the pbpA transcript, encoding PBP1, was specifically induced by DAP exposure whereas expression of pbpB, pbpC, and pbpD, encoding PBP2, PBP3, and PBP4, respectively, remained unchanged. Using a MRSA COL strain with pbpA under an inducible promoter, increased pbpA transcription was accompanied by reduced susceptibility to, and killing by, DAP in vitro. Exposure to β-lactams that preferentially inactivate PBP1 was not associated with increased DAP binding, suggesting that synergy in the setting of anti-PBP1 pharmacotherapy results from increased DAP potency on a per-molecule basis. Combination exposure in an in vitro pharmacokinetic/pharmacodynamic model system with β-lactams that preferentially inactivate PBP1 (DAP-meropenem [MEM] or DAP-imipenem [IPM]) resulted in more-rapid killing than did combination exposure with DAP-nafcillin (NAF) (nonselective), DAP-ceftriaxone (CRO) or DAP-cefotaxime (CTX) (PBP2 selective), DAP-cefaclor (CEC) (PBP3 selective), or DAP-cefoxitin (FOX) (PBP4 selective). Compared to β-lactams with poor PBP1 binding specificity, exposure of S. aureus to DAP plus PBP1-selective β-lactams resulted in an increased frequency of septation and cell wall abnormalities. These data suggest that PBP1 activity may contribute to survival during DAP-induced metabolic stress. Therefore, targeted inactivation of PBP1 may enhance the antimicrobial efficiency of DAP, supporting the use of DAP-β-lactam combination therapy for serious MRSA infections, particularly when the β-lactam undermines the PBP1-mediated compensatory response.

Controlling bacterial infections by inhibiting proton-dependent processes

Bacterial resistance to antibiotics is recognized as one of the greatest threats in modern healthcare, taking a staggering toll worldwide. New approaches for controlling bacterial infections must be designed, eventually combining multiple strategies for complimentary therapies. This review explores an old/new paradigm for multi-targeted antibacterial therapy, focused at disturbing bacterial cytoplasmic membrane functions at sub minimal inhibitory concentrations, namely through superficial physical alterations of the bilayer, thereby perturbing transmembrane signals transduction. Such a paradigm may have the advantage of fighting the infection while avoiding many of the known resistance mechanisms. This article is part of a Special Issue entitled: Antimicrobial peptides edited by Karl Lohner and Kai Hilpert.

Clinical pharmacological approach for balancing the use of daptomycin and linezolid in comparison with that of vancomycin in the treatment of MRSA-related infections

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most challenging bacterial pathogens responsible for severe infections among hospitalized patients. In recent years there is increasing evidence that the clinical efficacy of vancomycin is progressively decreasing. Although daptomycin and linezolid are valuable alternatives to vancomycin for the treatment of MRSA-related bloodstream infections and pneumonia, respectively, a great deal of debate exists about their role in daily clinical practice due to cost-effectiveness issues. In this article we put into perspective the importance of pharmacokinetic/pharmacodynamic (PK/PD) considerations based on recent experimental and clinical data to argue whether they could be helpful in identifying clinical conditions in which these agents could be advantageous as compared to vancomycin.

Treatment of methicillin-resistant Staphylococcus aureus infections: Importance of high vancomycin minumum inhibitory concentrations

Staphylococcus aureus (SA) infections remain a major cause of morbidity and mortality despite the availability of numerous effective anti-staphylococcal antibiotics. This organism is responsible for both nosocomial and community-acquired infections ranging from relatively minor skin and soft tissue infections to life-threatening systemic infections. The increasing incidence of methicillin-resistant strains has granted an increasing use of vancomycin causing a covert progressive increase of its minimum inhibitory concentration (MIC) (dubbed the MIC “creep”). In this way, the emergence of vancomycin-intermediate SA (VISA) strains and heteroresistant-VISA has raised concern for the scarcity of alternative treatment options. Equally alarming, though fortunately less frequent, is the emergence of vancomycin-resistant SA. These strains show different mechanisms of resistance but have similar problems in terms of therapeutic approach. Ultimately, various debate issues have arisen regarding the emergence of SA strains with a minimum inhibitory concentration sitting on the superior limit of the sensitivity range (i.e., MIC = 2 μg/mL). These strains have shown certain resilience to vancomycin and a different clinical behaviour regardless of vancomycin use, both in methicillin-resistant SA and in methicillin-sensitive SA. The aim of this text is to revise the clinical impact and consequences of the emergence of reduced vancomycin susceptibility SA strains, and the different optimal treatment options known.

Impact of the combination of daptomycin and trimethoprim-sulfamethoxazole on clinical outcomes in methicillin-resistant Staphylococcus aureus infections

Complicated Staphylococcus aureus infections, including bacteremia, are often associated with treatment failures, prolonged hospital stays, and the emergence of resistance to primary and even secondary therapies. Daptomycin is commonly used as salvage therapy after vancomycin failure for the treatment of methicillin-resistant S. aureus (MRSA) infections. Unfortunately, the emergence of daptomycin resistance, especially in deep-seated infections, has been reported, prompting the need for alternative or combination therapy. Numerous antibiotic combinations with daptomycin have been investigated clinically and in vitro. Of interest, the combination of daptomycin and trimethoprim-sulfamethoxazole (TMP-SMX) has proved to be rapidly bactericidal in vitro to strains that are both susceptible and nonsusceptible to daptomycin. However, to date, there is limited clinical evidence supporting the use of this combination. This was a multicenter, retrospective case series of patients treated with the combination of daptomycin and TMP-SMX for at least 72 h. The objective of this study was to describe the safety and effectiveness of this regimen in clinical practice. The most commonly stated reason that TMP-SMX was added to daptomycin was persistent bacteremia and/or progressive signs and symptoms of infection. After the initiation of combination therapy, the median time to clearance of bacteremia was 2.5 days. Microbiological eradication was demonstrated in 24 out of 28 patients, and in vitro synergy was demonstrated in 17 of the 17 recovered isolates. Further research with this combination is necessary to describe the optimal role and its impact on patient outcomes.

Antimicrobial salvage therapy for persistent staphylococcal bacteremia using daptomycin plus ceftaroline

PURPOSE

Guidelines recommend daptomycin combination therapy as an option for methicillin-resistant Staphylococcus aureus (MRSA) bacteremia after vancomycin failure. Recent data suggest that combining daptomycin with a β-lactam may have unique benefits; however, there are very limited clinical data regarding the use of ceftaroline with daptomycin.

METHODS

All 26 cases from the 10 medical centers in which ceftaroline plus daptomycin was used for treatment of documented refractory staphylococcal bacteremia from March 2011 to November 2012 were included. In vitro (synergy studies, binding assays, cathelicidin LL-37 killing assays), and in vivo (virulence assays using a murine subcutaneous infection model) studies examining the effects of ceftaroline with daptomycin were also performed.

FINDINGS

Daptomycin plus ceftaroline was used in 26 cases of staphylococcal bacteremia (20 MRSA, 2 vancomycin-intermediate S aureus, 2 methicillin-susceptible S aureus [MSSA], 2 methicillin-resistant S epidermidis). Bacteremia persisted for a median of 10 days (range, 3-23 days) on previous antimicrobial therapy. After daptomycin plus ceftaroline was started, the median time to bacteremia clearance was 2 days (range, 1-6 days). In vitro studies showed ceftaroline synergy against MRSA and enhanced MRSA killing by cathelicidin LL-37 and neutrophils. Ceftaroline also induced daptomycin binding in MSSA and MRSA to a comparable degree as nafcillin. MRSA grown in subinhibitory concentrations of ceftaroline showed attenuated virulence in a murine subcutaneous infection model.

IMPLICATIONS

Ceftaroline plus daptomycin may be an option to hasten clearance of refractory staphylococcal bacteremia. Ceftaroline offers dual benefit via synergy with both daptomycin and sensitization to innate host defense peptide cathelicidin LL37, which could attenuate virulence of the pathogen.

Comparative efficacies of cloxacillin-daptomycin and the standard cloxacillin-rifampin therapies against an experimental foreign-body infection by methicillin-susceptible Staphylococcus aureus

We compared the efficacies of daptomycin (doses equivalent to 8 to 10 mg/kg of body weight/day in humans) and cloxacillin alone with those of cloxacillin-rifampin and cloxacillin-daptomycin combinations, using a tissue cage methicillin-susceptible Staphylococcus aureus (MSSA) infection model. Monotherapies were less effective than combinations (P<0.05), and daptomycin resistance emerged. Cloxacillin-daptomycin proved as effective as cloxacillin-rifampin and prevented the appearance of resistance; this combination may be an alternative anti-MSSA therapy, which may offer greater benefits in the early treatment of prosthetic joint infections (PJI).