Ceftobiprole: an extended-spectrum anti-methicillin-resistant Staphylococcus aureus cephalosporin

In Vitro activity of ceftobiprole against 20,255 recent clinical bacterial isolates in Canada (CANWARD 2015-2023)

BACKGROUND

Ceftobiprole is a fifth-generation cephalosporin active against methicillin-resistant Staphylococcus aureus (MRSA). In this study, we determined the in vitro activities of ceftobiprole and comparator agents against 20,225 common Gram-positive and Gram-negative bacteria isolated from patients who presented for care at 16 tertiary-care hospitals across Canada between 2015 and 2023.

METHODS

Minimum inhibitory concentrations (MICs) were determined using the Clinical and Laboratory Standards Institute (CLSI) reference M07 broth microdilution method. MICs were interpreted using CLSI M100 breakpoints where available. As CLSI does not publish MIC breakpoints for ceftobiprole, ceftobiprole MICs were interpreted using United States Food and Drug Administration (FDA), European Committee on Antimicrobial Susceptibility Testing (EUCAST), and Health Canada breakpoints.

RESULTS

Ceftobiprole inhibited 100 % of MRSA at ≤ 4 μg/ml; 100 % of methicillin-susceptible S. aureus (MSSA) and 99.8% of MRSA at ≤ 2 μg/ml; 100 % of Streptococcus pneumoniae and Streptococcus pyogenes at ≤ 0.5 μg/ml; and 97.9 % of ESBL-negative Escherichia coli, 97.4 % of ESBL-negative Klebsiella pneumoniae, 97.8 % of Proteus mirabilis, 89.3 % of Serratia marcescens, 78.2 % of Enterobacter cloacae, 55.7 % of Klebsiella oxytoca at ≤ 0.25 μg/ml. Ceftobiprole was inactive against ESBL-positive E. coli and ESBL-positive K. pneumoniae.

CONCLUSIONS

Ceftobiprole demonstrated potent in vitro activity against MRSA, MSSA, S. pneumoniae, S. pyogenes, ESBL-negative E. coli and K. pneumoniae, and P. mirabilis isolated from clinical specimens of patients seeking care at Canadian tertiary-care hospitals.

Treatment of MRSA Infection: Where are We?

Staphylococcus aureus is a leading cause of septicemia, endocarditis, pneumonia, skin and soft tissue infections, bone and joint infections, and hospital-acquired infections. In particular, methicillin-resistant Staphylococcus aureus (MRSA) is associated with high morbidity and mortality, and continues to be a major public health problem. The emergence of multidrug-resistant MRSA strains along with the wide consumption of antibiotics has made anti-MRSA treatment a huge challenge. Novel treatment strategies (e.g., novel antimicrobials and new administrations) against MRSA are urgently needed. In the past decade, pharmaceutical companies have invested more in the research and development (R&D) of new antimicrobials and strategies, spurred by favorable policies. All research articles were collected from authentic online databases, including Google Scholar, PubMed, Scopus, and Web of Science, by using different combinations of keywords, including 'anti-MRSA', 'antibiotic', 'antimicrobial', 'clinical trial', 'clinical phase', clinical studies', and 'pipeline'. The information extracted from articles was compared to information provided on the drug manufacturer's website and Clinical Trials.gov (https://clinicaltrials.gov/) to confirm the latest development phase of anti-MRSA agents. The present review focuses on the current development status of new anti-MRSA strategies concerning chemistry, pharmacological target(s), indications, route of administration, efficacy and safety, pharmacokinetics, and pharmacodynamics, and aims to discuss the challenges and opportunities in developing drugs for anti-MRSA infections.

Current state of the art in rapid diagnostics for antimicrobial resistance

Antimicrobial resistance (AMR) is a fundamental global concern analogous to climate change threatening both public health and global development progress. Infections caused by antimicrobial-resistant pathogens pose serious threats to healthcare and human capital. If the increasing rate of AMR is left uncontrolled, it is estimated that it will lead to 10 million deaths annually by 2050. This global epidemic of AMR necessitates radical interdisciplinary solutions to better detect antimicrobial susceptibility and manage infections. Rapid diagnostics that can identify antimicrobial-resistant pathogens to assist clinicians and health workers in initiating appropriate treatment are critical for antimicrobial stewardship. In this review, we summarize different technologies applied for the development of rapid diagnostics for AMR and antimicrobial susceptibility testing (AST). We briefly describe the single-cell technologies that were developed to hasten the AST of infectious pathogens. Then, the different types of genotypic and phenotypic techniques and the commercially available rapid diagnostics for AMR are discussed in detail. We conclude by addressing the potential of current rapid diagnostic systems being developed as point-of-care (POC) diagnostic tools and the challenges to adapt them at the POC level. Overall, this review provides an insight into the current status of rapid and POC diagnostic systems for AMR.

The Continuing Threat of Methicillin-Resistant Staphylococcus aureus

Staphylococcus aureus has been an exceptionally successful pathogen, which is still relevant in modern age-medicine due to its adaptability and tenacity. This bacterium may be a causative agent in a plethora of infections, owing to its abundance (in the environment and in the normal flora) and the variety of virulence factors that it possesses. Methicillin-resistant S. aureus (MRSA) strains—first described in 1961—are characterized by an altered penicillin-binding protein (PBP2a/c) and resistance to all penicillins, cephalosporins, and carbapenems, which makes the β-lactam armamentarium clinically ineffective. The acquisition of additional resistance determinants further complicates their eradication; therefore, MRSA can be considered as the first representative of multidrug-resistant bacteria. Based on 230 references, the aim of this review is to recap the history, the emergence, and clinical features of various MRSA infections (hospital-, community-, and livestock-associated), and to summarize the current advances regarding MRSA screening, typing, and therapeutic options (including lipoglycopeptides, oxazolidinones, anti-MRSA cephalosporins, novel pleuromutilin-, tetracycline- and quinolone-derivatives, daptomycin, fusidic acid, in addition to drug candidates in the development phase), both for an audience of clinical microbiologists and infectious disease specialists.

PBP 4 Mediates High-Level Resistance to New-Generation Cephalosporins in Staphylococcus aureus

Staphylococcus aureus is an important cause of both hospital- and community-associated methicillin-resistant S. aureus (MRSA) infections worldwide. β-Lactam antibiotics are the drugs of choice to treat S. aureus infections, but resistance to these and other antibiotics make treatment problematic. High-level β-lactam resistance of S. aureus has always been attributed to the horizontally acquired penicillin binding protein 2a (PBP 2a) encoded by the mecA gene. Here, we show that S. aureus can also express high-level resistance to β-lactams, including new-generation broad-spectrum cephalosporins that are active against methicillin-resistant strains, through an uncanonical core genome-encoded penicillin binding protein, PBP 4, a nonessential enzyme previously considered not to be important for staphylococcal β-lactam resistance. Our results show that PBP 4 can mediate high-level resistance to β-lactams.

Skin and soft-tissue infections: a critical review and the role of telavancin in their treatment

Skin and soft-tissue infections (SSTIs) are an important cause of morbidity and mortality among hospitalized patients and a major therapeutic challenge for clinicians. Although uncomplicated SSTIs are managed successfully on an outpatient basis, more serious infections extending to the subcutaneous tissue, fascia, or muscle require complex management. Early diagnosis, selection of appropriate antimicrobials, and timely surgical intervention are key to successful treatment. Surgical-site infections, an important category of SSTI, occur in approximately half a million patients in North America annually. SSTIs are also a potential source for life-threatening bacteremia and metastatic abscesses. Gram-positive organisms, such as Staphylococcus aureus and Streptococcus pyogenes, are the dominant organisms isolated early in the infectious process, whereas gram-negative organisms are found in chronic wounds. Methicillin-resistant S. aureus (MRSA) is a potential bloodstream invader that requires aggressive antimicrobial treatment and surgery. Recent concerns regarding vancomycin activity include heteroresistance in MRSA and increase in the minimum inhibitory concentrations (>1 or 2 µg/mL); however, alternative agents, such as telavancin, daptomycin, linezolid, ceftaroline, dalbavancin, oritavancin, and tedizolid, are now available for the treatment of severe MRSA infections. Here, we present a review of the epidemiology, etiology, and available treatment options for the management of SSTIs.

New antibiotics against gram-positives: present and future indications

Gram-positive cocci are the most frequent aetiology of community and nosocomially bacterial acquired infections. The prevalence of multidrug-resistant gram-positive bacteria is increasing and is associated with high morbidity and mortality. New antibiotics will be available in the European market during the next months. This revision is focused on lipoglycopeptides, new cephalosporins active against methicillin-resistant Staphylococcus aureus (MRSA) and the new oxazolidinone, tedizolid. The purpose of this review is to describe their in vitro activity, pharmacokinetic and pharmacodynamic characteristics, and experience from clinical trials.

Ceftobiprole- and ceftaroline-resistant methicillin-resistant Staphylococcus aureus

The role of mecA mutations in conferring resistance to ceftobiprole and ceftaroline, cephalosporins with anti-methicillin-resistant Staphylococcus aureus (MRSA) activity, was determined with MRSA strains COL and SF8300. The SF8300 ceftaroline-passaged mutant carried a single mecA mutation, E447K (E-to-K change at position 447), and expressed low-level resistance. This mutation in COL conferred high-level resistance to ceftobiprole but only low-level resistance to ceftaroline. The COL ceftaroline-passaged mutant, which expressed high-level resistance to ceftobiprole and ceftaroline, had mutations in pbp2, pbp4, and gdpP but not mecA.

[Resistance to "last resort" antibiotics in Gram-positive cocci: The post-vancomycin era]

New therapeutic alternatives have been developed in the last years for the treatment of multidrug-resistant Gram-positive infections. Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) are considered a therapeutic challenge due to failures and lack of reliable antimicrobial options. Despite concerns related to the use of vancomycin in the treatment of severe MRSA infections in specific clinical scenarios, there is a paucity of solid clinical evidence that support the use of alternative agents (when compared to vancomycin). Linezolid, daptomycin and tigecycline are antibiotics approved in the last decade and newer cephalosporins (such as ceftaroline and ceftobiprole) and novel glycopeptides (dalvavancin, telavancin and oritavancin) have reached clinical approval or are in the late stages of clinical development. This review focuses on discussing these newer antibiotics used in the "post-vancomycin" era with emphasis on relevant chemical characteristics, spectrum of antimicrobial activity, mechanisms of action and resistance, as well as their clinical utility.

TcaR-ssDNA complex crystal structure reveals new DNA binding mechanism of the MarR family proteins

The teicoplanin-associated locus regulator (TcaR) regulates gene expression of proteins on the intercellular adhesion (ica) locus involved in staphylococci poly-N-acetylglucosamine biosynthesis. The absence of TcaR increases poly-N-acetylglucosamine production and promotes biofilm formation. Until recently, the mechanism of multiple antibiotic resistance regulator family protein members, such as TcaR, was restricted to binding double-stranded DNA. However, we recently found that TcaR strongly interacts with single-stranded DNA, which is a new role for this family of proteins. In this study, we report Staphylococcus epidermidis TcaR–single-stranded DNA complex structures. Our model suggests that TcaR and single-stranded DNA form a 6₁-symmetry polymer composed of TcaR dimers with single-stranded DNA that wraps outside the polymer and 12 nt per TcaR dimer. Single-stranded DNA binding to TcaR involves a large conformational change at the DNA binding lobe. Several point mutations involving the single-stranded DNA binding surface validate interactions between single-stranded DNA and TcaR. Our results extend the novel role of multiple antibiotic resistance regulator family proteins in staphylococci.

Structural analysis of the antibiotic-recognition mechanism of MarR proteins

Staphylococci cause a wide range of diseases in humans and animals, and the proteins of the multiple antibiotic-resistance repressor (MarR) family in staphylococci function as regulators of protein expression and confer resistance to multiple antibiotics. Diverse mechanisms such as biofilm formation, drug transport, drug modification etc. are associated with this resistance. In this study, crystal structures of the Staphylococcus aureus MarR homologue SAR2349 and its complex with salicylate and the aminoglycoside antibiotic kanamycin have been determined. The structure of SAR2349 shows for the first time that a MarR protein can interact directly with different classes of ligands simultaneously and highlights the importance and versatility of regulatory systems in bacterial antibiotic resistance. The three-dimensional structures of TcaR from S. epidermidis in complexes with chloramphenicol and with the aminoglycoside antibiotic streptomycin were also investigated. The crystal structures of the TcaR and SAR2349 complexes illustrate a general antibiotic-regulated resistance mechanism that may extend to other MarR proteins. To reveal the regulatory mechanism of the MarR proteins, the protein structures of this family were further compared and three possible mechanisms of regulation are proposed. These results are of general interest because they reveal a remarkably broad spectrum of ligand-binding modes of the multifunctional MarR proteins. This finding provides further understanding of antimicrobial resistance mechanisms in pathogens and strategies to develop new therapies against pathogens.

Functional studies of ssDNA binding ability of MarR family protein TcaR from Staphylococcus epidermidis

The negative transcription regulator of the ica locus, TcaR, regulates proteins involved in the biosynthesis of poly-N-acetylglucosamine (PNAG). Absence of TcaR increases PNAG production and promotes biofilm formation in Staphylococci. Previously, the 3D structure of TcaR in its apo form and its complex structure with several antibiotics have been analyzed. However, the detailed mechanism of multiple antibiotic resistance regulator (MarR) family proteins such as TcaR is unclear and only restricted on the binding ability of double-strand DNA (dsDNA). Here we show by electrophoretic mobility shift assay (EMSA), electron microscopy (EM), circular dichroism (CD), and Biacore analysis that TcaR can interact strongly with single-stranded DNA (ssDNA), thereby identifying a new role in MarR family proteins. Moreover, we show that TcaR preferentially binds 33-mer ssDNA over double-stranded DNA and inhibits viral ssDNA replication. In contrast, such ssDNA binding properties were not observed for other MarR family protein and TetR family protein, suggesting that the results from our studies are not an artifact due to simple charge interactions between TcaR and ssDNA. Overall, these results suggest a novel role for TcaR in regulation of DNA replication. We anticipate that the results of this work will extend our understanding of MarR family protein and broaden the development of new therapeutic strategies for Staphylococci.

Cost-effectiveness analysis of linezolid, daptomycin, and vancomycin in methicillin-resistant Staphylococcus aureus: complicated skin and skin structure infection using Bayesian methods for evidence synthesis

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) complicated skin and skin structure infection (cSSSI) is a prominent infection encountered in hospital and outpatient settings that is associated with high resource use for the health-care system.

OBJECTIVE

A decision analytic (DA) model was developed to evaluate the cost-effectiveness analysis (CEA) of linezolid, daptomycin, and vancomycin in MRSA cSSSI.

METHODS

Bayesian methods for evidence synthesis were used to generate efficacy and safety parameters for a DA model using published clinical trials. CEA was done from the US health-care perspective. Efficacy was defined as a successfully treated patient at the test of cure without any adverse reaction. Primary outcome was the incremental cost-effectiveness ratio between linezolid and vancomycin, daptomycin and vancomycin, and linezolid and daptomycin in MRSA cSSSI. Univariate and probabilistic sensitivity analyses were performed to test the robustness of the model.

RESULTS

The total direct costs of linezolid, daptomycin, and vancomycin were $18,057, $20,698, and $23,671, respectively. The cost-effectiveness ratios for linezolid, daptomycin, and vancomycin were $37,604, $44,086, and $52,663 per successfully treated patient, respectively. Linezolid and daptomycin were dominant strategies compared to vancomycin. However, linezolid was dominant when compared to daptomycin. The model was sensitive to the duration of daptomycin and linezolid treatment.

CONCLUSION

Linezolid and daptomycin are potentially cost-effective based on the assumptions of the DA model; however, linezolid appears to be more cost-effective compared to daptomycin and vancomycin for MRSA cSSSIs.

Newer beta-lactam antibiotics: doripenem, ceftobiprole, ceftaroline, and cefepime

This article reviews the new beta-lactam (β-lactam) antibiotics doripenem, ceftobiprole, and ceftaroline. It covers pharmacokinetic and pharmacodynamic properties, dosing, in vitro activities, safety, and clinical trial results. Doripenem (Doribax) has been approved by the US Food and Drug Administration (FDA) for the treatment of complicated intra-abdominal and urinary tract infections. Ceftaroline has received FDA approval for the treatment of skin and soft tissue infections and community acquired pneumonia. Ceftobiprole has not received FDA approval. The article also reviews recent data suggesting increased overall mortality with Cefepime (Maxipime) use compared with other beta-lactam antibiotics and the potential risk for neurotoxicity in the setting of renal failure.

Telavancin, a new lipoglycopeptide antimicrobial, in complicated skin and soft tissue infections

Telavancin, a novel lipoglycopeptide with rapid concentration-dependent bactericidal effects, is a semisynthetic derivative of the glycopeptide, vancomycin. Telavancin has a dual mechanism of action, ie, inhibition of peptidoglycan polymerization and disruption of the bacterial membrane. It has linear pharmacokinetics, rapid bactericidal killing, and broad spectrum activity against Gram positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant S. aureus. Phase II and III clinical trials for complicated skin and skin structure infections have shown telavancin to have similar efficacy and tolerability to that of vancomycin and standard anti-staphylococcal β-lactams plus vancomycin. In Phase II trials, there was a significant difference in eradication of MRSA between groups, ie, telavancin therapy 92% and standard therapy (vancomycin, nafcillin, oxacillin, or cloxacillin) 68% (P < 0.05). In Phase III trials, among clinically evaluable patients who had MRSA isolated at baseline, the overall therapeutic response was higher in patients treated with telavancin than in patients treated with vancomycin (89.9% versus 84.7%; 95% CI −0.3, 10.5). Also, the efficacy of telavancin was not inferior to that of vancomycin for the treatment of complicated skin and skin structure infections in the clinical trials.

Eradication of drug resistant Staphylococcus aureus by liposomal oleic acids

Staphylococcus aureus (S. aureus) represents a major threat to a broad range of healthcare and community associated infections. This bacterium has rapidly evolved resistance to multiple drugs throughout its antibiotic history and thus it is imperative to develop novel antimicrobial strategies to enrich the currently shrinking therapeutic options against S. aureus. This study evaluated the antimicrobial activity and therapeutic efficacy of oleic acid (OA) in a liposomal formulation as an innate bactericide against methicillin-resistant S. aureus (MRSA). In vitro studies showed that these OA-loaded liposomes (LipoOA) could rapidly fuse into the bacterial membranes, thereby significantly improving the potency of OA to kill MRSA compared with the use of free OA. Further in vivo tests demonstrated that LipoOA were highly effective in curing skin infections caused by MRSA bacteria and preserving the integrity of the infected skin using a mouse skin model. Moreover, a preliminary skin toxicity study proved high biocompatibility of LipoOA to normal skin tissues. These findings suggest that LipoOA hold great potential to become a new, effective, and safe antimicrobial agent for the treatment of MRSA infections.

New therapeutic choices for infections caused by methicillin-resistant Staphylococcus aureus

In recent years, a marked increase in the incidence of infections caused by methicillin-resistant Staphylococcus aureus (MRSA) has occurred in many countries. This review addresses the effectiveness and limitations of drugs classically used for the treatment of MRSA, e.g. vancomycin, and also newer anti-MRSA antimicrobials, e.g. second-generation glycolipopeptides, tigecycline, and beta-lactams.

Gram-negative bloodstream infections

Gram-negative bloodstream infection (BSI) is both dangerous and challenging. The incidence of Gram-negative BSI rises with age in both men and women, but there are still some gender differences in terms of aetiology and acquisition. Clinical elements such as organ dysfunction are helpful in determining prognosis. During the last few years we have observed dramatic increases in resistance among Gram-negative organisms, including those causing bloodstream infections. Gram-negative pathogens producing extended-spectrum beta-lactamases are now common, and are associated with high rates of inadequate empirical treatment and mortality. In addition, carbapenem resistance is increasing, leaving clinicians with limited therapeutic options. Better knowledge of local epidemiology can help to optimize therapies. The use of cefepime has been questioned based on a recent meta-analysis showing increased mortality in patients treated with the drug. However, an analysis performed by the US Food and Drug Administration has not confirmed these results. Unfortunately, antimicrobial development has not kept pace with resistance, particularly for Gram-negative pathogens. We need therefore to better utilize current antibiotics and undertake rigorous infection control measures to prevent these life-threatening infections.

Newer beta-lactam antibiotics: doripenem, ceftobiprole, ceftaroline, and cefepime

This article reviews the new beta-lactam (beta-lactam) antibiotics doripenem, ceftobiprole, and ceftaroline. It covers pharmacokinetic and pharmacodynamic properties, dosing, in vitro activities, safety, and clinical trial results. Doripenem (Doribax) has been approved by the US Food and Drug Administration (FDA) for the treatment of complicated intra-abdominal and urinary tract infections. At this writing, ceftobiprole is under review by the FDA for approval based on results of phase 3 clinical trials, whereas at least one phase 3 clinical trial of ceftaroline has been completed. The article also reviews recent data suggesting increased overall mortality with Cefepime (Maxipime) use compared with other beta-lactam antibiotics and the potential risk for neurotoxicity in the setting of renal failure.

Three decades of beta-lactamase inhibitors

Since the introduction of penicillin, beta-lactam antibiotics have been the antimicrobial agents of choice. Unfortunately, the efficacy of these life-saving antibiotics is significantly threatened by bacterial beta-lactamases. beta-Lactamases are now responsible for resistance to penicillins, extended-spectrum cephalosporins, monobactams, and carbapenems. In order to overcome beta-lactamase-mediated resistance, beta-lactamase inhibitors (clavulanate, sulbactam, and tazobactam) were introduced into clinical practice. These inhibitors greatly enhance the efficacy of their partner beta-lactams (amoxicillin, ampicillin, piperacillin, and ticarcillin) in the treatment of serious Enterobacteriaceae and penicillin-resistant staphylococcal infections. However, selective pressure from excess antibiotic use accelerated the emergence of resistance to beta-lactam-beta-lactamase inhibitor combinations. Furthermore, the prevalence of clinically relevant beta-lactamases from other classes that are resistant to inhibition is rapidly increasing. There is an urgent need for effective inhibitors that can restore the activity of beta-lactams. Here, we review the catalytic mechanisms of each beta-lactamase class. We then discuss approaches for circumventing beta-lactamase-mediated resistance, including properties and characteristics of mechanism-based inactivators. We next highlight the mechanisms of action and salient clinical and microbiological features of beta-lactamase inhibitors. We also emphasize their therapeutic applications. We close by focusing on novel compounds and the chemical features of these agents that may contribute to a "second generation" of inhibitors. The goal for the next 3 decades will be to design inhibitors that will be effective for more than a single class of beta-lactamases.

New treatments for methicillin-resistant Staphylococcus aureus

PURPOSE OF REVIEW

Methicillin-resistant Staphylococcus aureus (MRSA) is a dynamic pathogen. Rates of MRSA are increasing worldwide. In some centers, MRSA is becoming less susceptible to vancomycin, and these strains have been associated with worse clinical outcomes. Intermediate or fully resistant vancomycin strains of MRSA have emerged clinically, whereas MRSA acquired in the community has become epidemic. The purpose of this manuscript is to provide clinicians with an evidence-based review on new treatments for MRSA.

RECENT FINDINGS

Linezolid, daptomycin and tigecycline have been approved during the last decade to treat infections due to MRSA. Although these agents are extremely valuable in the fight against MRSA, each one has limitations. New lypoglycopeptides (telavancin, dalbavancin and oritavancin) are in advanced phase of clinical development. Similarly, new broad-spectrum cephalosporins active against MRSA (e.g. ceftobiprole and ceftaroline) and a new dihydrofolate reductase inhibitor (iclaprim) are in or have completed phase 3 studies.

SUMMARY

Here, we review the most relevant information on new drugs to treat MRSA. New studies with available agents and upcoming studies with investigational drugs will help to better understand the role of each compound in the treatment of patients infected with MRSA and assist the clinician in keeping pace with this challenging pathogen.

Waves of resistance: Staphylococcus aureus in the antibiotic era

Staphylococcus aureus is notorious for its ability to become resistant to antibiotics. Infections that are caused by antibiotic-resistant strains often occur in epidemic waves that are initiated by one or a few successful clones. Methicillin-resistant S. aureus (MRSA) features prominently in these epidemics. Historically associated with hospitals and other health care settings, MRSA has now emerged as a widespread cause of community infections. Community or community-associated MRSA (CA-MRSA) can spread rapidly among healthy individuals. Outbreaks of CA-MRSA infections have been reported worldwide, and CA-MRSA strains are now epidemic in the United States. Here, we review the molecular epidemiology of the epidemic waves of penicillin- and methicillin-resistant strains of S. aureus that have occurred since 1940, with a focus on the clinical and molecular epidemiology of CA-MRSA.

Ceftobiprole: a new beta-lactam antibiotic

The increasing threat of antimicrobial resistance in general, and that of methicillin-resistant Staphylococcus aureus (MRSA) in particular, is raising significant medical, economical and public health challenges worldwide, both within hospitals and throughout the community. These considerations, along with the extensive time and costs associated with the development and approval of new therapeutic agents, represent some of the major reasons why understanding the advantages and limitations of new antibiotics, ensuring their judicious use and maximising their active shelf life should become global priorities. On March 18, 2008, the Food and Drug Administration issued an approvable letter for ceftobiprole, a broad-spectrum beta-lactam antibiotic active against MRSA and other clinically relevant Gram-positive and Gram-negative pathogens. Ceftobiprole is currently available only for parenteral administration, and besides its remarkable antimicrobial spectrum, this antibiotic possesses additional desirable characteristics, such as low propensity to select for resistance, efficacy in animal models of disease and good safety profile. Furthermore, in recently completed clinical trials, ceftobiprole demonstrated non-inferiority to comparator compounds such as vancomycin, and emerged as a promising clinical option of monotherapy for the treatment of complicated skin and skin structure infections and community-acquired pneumonia. Here, we discuss some of the most important clinically relevant findings on ceftobiprole obtained from in vitro studies, animal models of disease and recently completed phase III clinical trials.

Activities of ceftobiprole and other cephalosporins against extracellular and intracellular (THP-1 macrophages and keratinocytes) forms of methicillin-susceptible and methicillin-resistant Staphylococcus aureus

Staphylococcus aureus is an opportunistic intracellular organism. Although they poorly accumulate in eukaryotic cells, beta-lactams show activity against intracellular methicillin (methicillin)-susceptible S. aureus (MSSA) if the exposure times and the drug concentrations are sufficient. Intraphagocytic methicillin-resistant S. aureus (MRSA) strains are susceptible to penicillins and carbapenems because the acidic pH favors the acylation of PBP 2a by these beta-lactams through pH-induced conformational changes. The intracellular activity (THP-1 macrophages and keratinocytes) of ceftobiprole, which shows almost similar in vitro activities against MRSA and MSSA in broth, was examined against a panel of hospital-acquired and community-acquired MRSA strains (MICs, 0.5 to 2.0 mg/liter at pH 7.4 and 0.25 to 1.0 mg/liter at pH 5.5) and was compared with its activity against MSSA isolates. The key pharmacological descriptors {relative maximal efficacy (E(max)), relative potency (the concentration causing a reduction of the inoculum halfway between E(0) and E(max) [EC(50)]), and static concentration (C(s))} were measured. All strains showed sigmoidal dose-responses, with E(max) being about a 1 log(10) CFU decrease from the postphagocytosis inoculum, and EC(50) and C(s) being 0.2 to 0.3x and 0.6 to 0.9x the MIC, respectively. Ceftobiprole effectively competed with Bocillin FL (a fluorescent derivative of penicillin V) for binding to PBP 2a at both pH 5.5 and pH 7.4. In contrast, cephalexin, cefuroxime, cefoxitin, or ceftriaxone (i) were less potent in PBP 2a competitive binding assays, (ii) showed only partial restoration of the activity against MRSA in broth at acidic pH, and (iii) were collectively less effective against MRSA in THP-1 macrophages and were ineffective in keratinocytes. The improved activity of ceftobiprole toward intracellular MRSA compared with the activities of conventional cephalosporins can be explained, at least in part, by its greater ability to bind to PBP 2a not only at neutral but also at acidic pH.