An association between reduced susceptibility to daptomycin and reduced susceptibility to vancomycin in Staphylococcus aureus

Staphylococcus aureus response and adaptation to vancomycin

Antibiotic resistance is an increasing challenge for the human pathogen Staphylococcus aureus. Methicillin-resistant S. aureus (MRSA) clones have spread globally, and a growing number display decreased susceptibility to vancomycin, the favoured antibiotic for treatment of MRSA infections. These vancomycin-intermediate S. aureus (VISA) or heterogeneous vancomycin-intermediate S. aureus (hVISA) strains arise from accumulation of a variety of point mutations, leading to cell wall thickening and reduced vancomycin binding to the cell wall building block, Lipid II, at the septum. They display only minor changes in vancomycin susceptibility, with varying tolerance between cells in a population, and therefore, they can be difficult to detect. In this review, we summarize current knowledge of VISA and hVISA. We discuss the role of genetic strain background or epistasis for VISA development and the possibility of strains being 'transient' VISA with gene expression changes mediated by, for example, VraTSR, GraXSR, or WalRK signal transduction systems, leading to temporary vancomycin tolerance. Additionally, we address collateral susceptibility to other antibiotics than vancomycin. Specifically, we estimate how mutations in rpoB, encoding the β-subunit of the RNA polymerase, affect overall protein structure and compare changes with rifampicin resistance. Ultimately, such in-depth analysis of VISA and hVISA strains in terms of genetic and transcriptional changes, as well as changes in protein structures, may pave the way for improved detection and guide antibiotic therapy by revealing strains at risk of VISA development. Such tools will be valuable for keeping vancomycin an asset also in the future.

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.

Evolutionary history of Staphylococcus aureus influences antibiotic resistance evolution

Antibiotic resistance often confers a fitness cost to the resistant cell and thus raises key questions of how resistance is maintained in the absence of antibiotics and, if lost, whether cells are genetically primed for re-evolving resistance. To address these questions, we have examined vancomycin-intermediate Staphylococcus aureus (VISA) strains that arise during vancomycin therapy. VISA strains harbor a broad spectrum of mutations, and they are known to be unstable both in patients and in the laboratory. Here, we show that loss of resistance in VISA strains is correlated with a fitness increase and is attributed to adaptive mutations, leaving the initial VISA-adaptive mutations intact. Importantly, upon a second exposure to vancomycin, such revertants evolve significantly faster to become VISA, and they reach higher resistance levels than vancomycin-naive cells. Further, we find that sub-lethal concentrations of vancomycin stabilize the VISA phenotype, as do the human β-defensin 3 (hBD-3) and the bacteriocin nisin that both, like vancomycin, bind to the peptidoglycan building block, lipid II. Thus, factors binding lipid II may stabilize VISA both in vivo and in vitro, and in case resistance is lost, mutations remain that predispose to resistance development. These findings may explain why VISA infections often are re-occurring and suggest that previous vancomycin adaptation should be considered a risk factor when deciding on antimicrobial chemotherapy.

Effectiveness and Safety of Linezolid Versus Vancomycin, Teicoplanin, or Daptomycin against Methicillin-Resistant Staphylococcus aureus Bacteremia: A Systematic Review and Meta-Analysis

Vancomycin (VCM) and daptomycin (DAP) are standard therapies for methicillin-resistant Staphylococcus aureus (MRSA) bacteremia, despite concerns regarding clinical utility and growing resistance. Linezolid (LZD) affords superior tissue penetration to VCM or DAP and has been successfully used as salvage therapy for persistent MRSA bacteremia, indicating its utility as a first-choice drug against MRSA bacteremia. In a systematic review and meta-analysis, we compared the effectiveness and safety of LZD with VCM, teicoplanin (TEIC), or DAP in patients with MRSA bacteremia. We evaluated all-cause mortality as the primary effectiveness outcome, clinical and microbiological cure, hospital length of stay, recurrence, and 90-day readmission rates as secondary effectiveness outcomes, and drug-related adverse effects as primary safety outcomes. We identified 5328 patients across 2 randomized controlled trials (RCTs), 1 pooled analysis of 5 RCTs, 1 subgroup analysis (1 RCT), and 5 case-control and cohort studies (CSs). Primary and secondary effectiveness outcomes were comparable between patients treated with LZD versus VCM, TEIC, or DAP in RCT-based studies and CSs. There was no difference in adverse event incidence between LZD and comparators. These findings suggest that LZD could be a potential first-line drug against MRSA bacteremia as well as VCM or DAP.

Effect of Antibiotic Exposure on Staphylococcus epidermidis Responsible for Catheter-Related Bacteremia

Coagulase-negative staphylococci (CoNS) and especially Staphylococcus epidermidis are responsible for health care infections, notably in the presence of foreign material (e.g., venous or central-line catheters). Catheter-related bacteremia (CRB) increases health care costs and mortality. The aim of our study was to evaluate the impact of 15 days of antibiotic exposure (ceftobiprole, daptomycin, linezolid and vancomycin) at sub-inhibitory concentration on the resistance, fitness and genome evolution of 36 clinical strains of S. epidermidis responsible for CRB. Resistance was evaluated by antibiogram, the ability to adapt metabolism by the Biofilm Ring test^® and the in vivo nematode virulence model. The impact of antibiotic exposure was determined by whole-genome sequencing (WGS) and biofilm formation experiments. We observed that S. epidermidis strains presented a wide variety of virulence potential and biofilm formation. After antibiotic exposure, S. epidermidis strains adapted their fitness with an increase in biofilm formation. Antibiotic exposure also affected genes involved in resistance and was responsible for cross-resistance between vancomycin, daptomycin and ceftobiprole. Our data confirmed that antibiotic exposure modified bacterial pathogenicity and the emergence of resistant bacteria.

Vancomycin plus ceftaroline for persistent methicillin-resistant Staphylococcus aureus bacteremia

STUDY OBJECTIVE

The preferred antibiotic salvage regimen for persistent methicillin-resistant Staphylococcus aureus bacteremia (MRSAB) is unclear. We sought to evaluate the effectiveness and safety of vancomycin plus ceftaroline for persistent MRSAB. The primary outcome was time to MRSAB clearance post-ceftaroline initiation. Secondary outcomes included microbiological cure, hospital length of stay, 90-day readmission for MRSAB, 90-day all-cause mortality, MRSAB-related mortality, and incidence of antibiotic-associated adverse effects.

DESIGN

Single-center, retrospective cohort study between January 1, 2016, and December 31, 2021.

SETTING

State University of New York Upstate University Hospital, a 748-bed tertiary care, academic medical center in Syracuse, NY.

PATIENTS

Adult patients were included if they had blood cultures positive for MRSA ≥72 h, received vancomycin monotherapy initially, and received vancomycin plus ceftaroline for ≥24 h. Patients were excluded if they received other anti-MRSA antibiotics, were pregnant, or were incarcerated. Of the 178 patients identified, 30 unique patients were evaluated.

MEASUREMENTS AND MAIN RESULTS

Patients were medically complex with a median Pitt bacteremia score of 3, 63.3% (19/30) were admitted to the intensive care unit, and 66.7% (20/30) had infective endocarditis. Vancomycin-associated acute kidney injury was observed in 10% (3/30) of patients, which resulted in dose adjustments. No patients experienced ceftaroline-associated neutropenia or Clostridioides difficile infection, but 6.7% (2/30) developed a rash attributed to ceftaroline. Median time to MRSAB clearance post-ceftaroline initiation was 2.6 days. Microbiologic cure occurred in nearly all patients 96.7% (29/30). Median hospital length of stay was 19.5 days, and 6.7% (2/30) of patients had 90-day readmission for MRSAB. 90-day all-cause mortality and MRSAB-related mortality occurred in 26.7% (8/30) and 13.3% (4/30) of patients, respectively.

CONCLUSIONS

Vancomycin plus ceftaroline may represent an effective and well-tolerated salvage regimen option for persistent MRSAB.

Bacterial cell membranes and their role in daptomycin resistance: A review

Lipids play a major role in bacterial cells. Foremost, lipids are the primary constituents of the cell membrane bilayer, providing structure and separating the cell from the surrounding environment. This makes the lipid bilayer a prime target for antimicrobial peptides and membrane-acting antibiotics such as daptomycin. In response, bacteria have evolved mechanisms by which the membrane can be adapted to resist attack by these antimicrobial compounds. In this review, we focus on the membrane phospholipid changes associated with daptomycin resistance in enterococci, Staphylococcus aureus, and the Viridans group streptococci.

Persistent Methicilin-Resistant Staphylococcus aureus Bacteremia: Resetting the Clock for Optimal Management

A positive follow-up blood culture for methicillin-resistant Staphylococcus aureus (MRSA) while on seemingly appropriate therapy is a common and ominous development. However, the definition and management of persistent MRSA bacteremia is unstandardized. In this Opinion Paper, we identify the presence of bacteremia for > 1 calendar day as a "worry point" that should trigger an intensive diagnostic evaluation to identify metastatic infection sites. Next, we define the duration of MRSA bacteremia that likely constitutes antibiotic failure and outline a potential management algorithm for such patients. Finally, we propose pragmatic clinical trial designs to test treatment strategies for persistent MRSA bacteremia.

Adaptive laboratory evolution and independent component analysis disentangle complex vancomycin adaptation trajectories

Human infections with methicillin-resistant Staphylococcus aureus (MRSA) are commonly treated with vancomycin, and strains with decreased susceptibility, designated as vancomycin-intermediate S. aureus (VISA), are associated with treatment failure. Here, we profiled the phenotypic, mutational, and transcriptional landscape of 10 VISA strains adapted by laboratory evolution from one common MRSA ancestor, the USA300 strain JE2. Using functional and independent component analysis, we found that: 1) despite the common genetic background and environmental conditions, the mutational landscape diverged between evolved strains and included mutations previously associated with vancomycin resistance (in vraT, graS, vraFG, walKR, and rpoBCD) as well as novel adaptive mutations (SAUSA300_RS04225, ssaA, pitAR, and sagB); 2) the first wave of mutations affected transcriptional regulators and the second affected genes involved in membrane biosynthesis; 3) expression profiles were predominantly strain-specific except for sceD and lukG, which were the only two genes significantly differentially expressed in all clones; 4) three independent virulence systems (φSa3, SaeR, and T7SS) featured as the most transcriptionally perturbed gene sets across clones; 5) there was a striking variation in oxacillin susceptibility across the evolved lineages (from a 10-fold increase to a 63-fold decrease) that also arose in clinical MRSA isolates exposed to vancomycin and correlated with susceptibility to teichoic acid inhibitors; and 6) constitutive expression of the VraR regulon explained cross-susceptibility, while mutations in walK were associated with cross-resistance. Our results show that adaptation to vancomycin involves a surprising breadth of mutational and transcriptional pathways that affect antibiotic susceptibility and possibly the clinical outcome of infections.

Identifying patient-level risk factors associated with non-β-lactam resistance outcomes in invasive MRSA infections in the United States using chain graphs

Background

MRSA is one of the most common causes of hospital- and community-acquired infections. MRSA is resistant to many antibiotics, including β-lactam antibiotics, fluoroquinolones, lincosamides, macrolides, aminoglycosides, tetracyclines and chloramphenicol.

Objectives

To identify patient-level characteristics that may be associated with phenotype variations and that may help improve prescribing practice and antimicrobial stewardship.

Methods

Chain graphs for resistance phenotypes were learned from invasive MRSA surveillance data collected by the CDC as part of the Emerging Infections Program to identify patient level risk factors for individual resistance outcomes reported as MIC while accounting for the correlations among the resistance traits. These chain graphs are multilevel probabilistic graphical models (PGMs) that can be used to quantify and visualize the complex associations among multiple resistance outcomes and their explanatory variables.

Results

Some phenotypic resistances had low connectivity to other outcomes or predictors (e.g. tetracycline, vancomycin, doxycycline and rifampicin). Only levofloxacin susceptibility was associated with healthcare-associated infections. Blood culture was the most common predictor of MIC. Patients with positive blood culture had significantly increased MIC of chloramphenicol, erythromycin, gentamicin, lincomycin and mupirocin, and decreased daptomycin and rifampicin MICs. Some regional variations were also observed.

Conclusions

The differences in resistance phenotypes between patients with previous healthcare use or positive blood cultures, or from different states, may be useful to inform first-choice antibiotics to treat clinical MRSA cases. Additionally, we demonstrated multilevel PGMs are useful to quantify and visualize interactions among multiple resistance outcomes and their explanatory variables.

Addition of daptomycin to levofloxacin increased the efficacy of levofloxacin monotherapy against a methicillin-susceptible Staphylococcus aureus strain in experimental meningitis and prevented development of resistance in vitro

Introduction. Daptomycin and levofloxacin were tested as monotherapies and in combination against the antibiotic-susceptible S. aureus strain MSSA 1112 in a rabbit meningitis model and the effect of the combination on induction of resistance was determined in vitro.

Hypothesis/Gap Statement. Treatment combination might be more efficacious than the monotherapies regarding antibacterial efficacy in vivo and development of resistance.

Aim. To demonstrate a synergy of the antibiotic combination daptomycin and levofloxacin in experimental meningitis, and also its ability to reduce the emergence of resistance against the antibiotics in vitro.

Methodology. Changes of the susceptibility to fluoroquinolones and daptomycin were determined by the measurement of the MIC and mutations were detected by whole genome sequence comparison of the mutants with the parent strain MSSA 1112. Meningitis was induced by intracisternal inoculation of 105 c.f.u. (colony forming unit) of MSSA 1112 and treatment was started 10 h later by injection of daptomycin (15 mg kg−1) and levofloxacin (10 mg kg−1) standard doses. Cerebrospinal fluid (CSF) samples were repeatedly collected during therapy in order to determine killing rates and results of bactericidal activity were expressed in Δlog10c.f.u. ml-1 over 8 h.

Results. The combination of daptomycin with levofloxacin was significantly (P<0.001) superior to levofloxacin monotherapy and increased the antibacterial activity of daptomycin. In vitro, MSSA 1112 was cycled over 6 days with either increasing concentrations of levofloxacin or daptomycin or with a combination of levofloxacin with half of the MIC of daptomycin or daptomycin with half of the MIC of levofloxacin leading to mutations in target genes as identified by whole genome sequence analysis. Addition of low concentration of daptomycin (0.25 mg l−1) reduced levofloxacin-induced resistance in vitro. Addition of levofloxacin in low concentration (0.125 mg l−1) did not influence daptomycin-induced resistance.

Conclusion. These findings highlight the lack of reciprocal interference of antibiotics in combination with regard to the development of resistance.

Cell Membrane Adaptations Mediate β-Lactam-Induced Resensitization of Daptomycin-Resistant (DAP-R) Staphylococcus aureus In Vitro

The reversal of daptomycin resistance in MRSA to a daptomycin-susceptible phenotype following prolonged passage in selected β-lactams occurs coincident with the accumulation of multiple point mutations in the mprF gene. MprF regulates surface charge by modulating the content and translocation of the positively charged cell membrane phospholipid, lysyl-phosphatidylglycerol (LPG). The precise cell membrane adaptations accompanying such β-lactam-induced mprF perturbations are unknown. This study examined key cell membrane metrics relevant to antimicrobial resistance among three daptomycin-resistant MRSA clinical strains, which became daptomycin-susceptible following prolonged exposure to cloxacillin ('daptomycin-resensitized'). The causal role of such secondary mprF mutations in mediating daptomycin resensitization was confirmed through allelic exchange strategies. The daptomycin-resensitized strains derived either post-cloxacillin passage or via allelic exchange (vs. their respective daptomycin-resistant strains) showed the following cell membrane changes: (i) enhanced BODIPY-DAP binding; (ii) significant reductions in LPG content, accompanied by significant increases in phosphatidylglycerol content (p < 0.05); (iii) no significant changes in positive cell surface charge; (iv) decreased cell membrane fluidity (p < 0.05); (v) enhanced carotenoid content (p < 0.05); and (vi) lower branched chain fatty acid profiles (antiso- vs. iso-), resulting in increases in saturated fatty acid composition (p < 0.05). Overall, the cell membrane characteristics of the daptomycin-resensitized strains resembled those of parental daptomycin-susceptible strains. Daptomycin resensitization with selected β-lactams results in both definable genetic changes (i.e., mprF mutations) and a number of key cell membrane phenotype modifications, which likely facilitate daptomycin activity.

Optimizing the Dosing Regimens of Daptomycin Based on the Susceptible Dose-Dependent Breakpoint against Vancomycin-Resistant Enterococci Infection

Daptomycin, a lipopeptide antibiotic, is one of the therapeutic options used for the treatment of vancomycin-resistant enterococci (VRE). Recently, the Clinical and Laboratory Standards Institute (CLSI) M100 30th edition has removed the susceptibility (S) breakpoint for Enterococcus faecium and replaced it with a susceptible dose-dependent (SDD) breakpoint of ≤4 μg/mL, with a suggested dosage of 8–12 mg/kg/day. Herein, we aimed to determine the minimum inhibitory concentration (MIC) values of daptomycin against clinical VRE isolates and to study the appropriate daptomycin dosing regimens among critically ill patients based on the new susceptibility CLSI breakpoint. The MIC determination of daptomycin was performed using E-test strips among clinical VRE strains isolated from patients at the Phramongkutklao Hospital. We used Monte Carlo simulation to calculate the probability of target attainment (PTA) and the cumulative fraction of response (CFR) of the ratio of the free area under the curve to MIC (fAUC_0–24/MIC) > 27.4 and fAUC_0–24/MIC > 20 for survival and microbiological response, respectively, at the first day and steady state. Further, we determined that the simulated daptomycin dosing regimen met the minimum concentration (Cmin) requirements for safety of being below 24.3 mg/L. All of the 48 VRE isolates were E. faecium strains, and the percentiles at the 50th and 90th MIC of daptomycin were 1 and 1.5 μg/mL, respectively. At MIC ≤ 2 μg/mL, a daptomycin dosage of 12 mg/kg/day achieved the PTA target of survival and microbiological response at the first 24 h time point and steady state. For a MIC of 4 μg/mL, none of the dosage regimens achieved the PTA target. For CFR, a dosage of 8–12 mg/kg/day could achieve the 90% CFR target at the first day and steady state. All dosing regimens had a low probability of Cmin being greater than 24.3 mg/L. In conclusion, the MIC of VRE against daptomycin is quite low, and loading and maintenance doses with 8 mg/kg/day were determined to be optimal and safe.

Vancomycin-resistant Enterococcus in solid organ transplant recipients: Guidelines from the American Society of Transplantation Infectious Diseases Community of Practice

These updated guidelines from the Infectious Diseases Community of Practice of the American Society of Transplantation address vancomycin-resistant enterococci (VRE) infections in SOT candidates and recipients. VRE are an important cause of infection and have been named by the CDC as a serious public threat. Typically, a commensal of the gastrointestinal tract, VRE may become pathogenic after abdominal organ manipulation like transplantation. This guideline reviews the microbiology, antimicrobial resistance mechanisms, epidemiology, and clinical manifestations of VRE infection in the context of solid organ transplantation. Treatment regimens including combination therapies and novel investigational agents are also reviewed. Finally, an updated appraisal of infection control measures relevant to VRE infection and colonization is presented.

Combating a Master Manipulator: Staphylococcus aureus Immunomodulatory Molecules as Targets for Combinatorial Drug Discovery

Staphylococcus aureus is a bacterial pathogen that can cause significant disease burden and mortality by counteracting host defenses through producing virulence factors to survive the immune responses evoked by infection. This emerging drug-resistant pathogen has led to a decline in the efficacy of traditional antimicrobial therapy. To combat these threats, precision antimicrobial therapeutics have been created to target key virulence determinants of specific pathogens. Here we review the benefits of, progresses in, and roadblocks to the development of precision antimicrobial therapeutics using combinatorial chemistry.

Treatment strategies for persistent methicillin-resistant Staphylococcus aureus bacteraemia

WHAT IS KNOWN AND OBJECTIVE

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

METHODS

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

RESULTS AND DISCUSSION

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

WHAT IS NEW AND CONCLUSION

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

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

OBJECTIVE

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

METHODS

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

RESULTS

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

Vancomycin and daptomycin minimum inhibitory concentrations as a predictor of outcome of methicillin-resistant Staphylococcus aureus bacteraemia

OBJECTIVES

The aim of this study was to determine the persistence of the adverse prognostic effect of elevated vancomycin minimum inhibitory concentration (MIC) in methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia in a setting with low vancomycin use.

METHODS

A retrospective study focusing on episodes of bacteraemia due to MRSA diagnosed from January 2010 through December 2015 was designed. The main outcome measures were 30-day mortality and treatment failure. Multivariate logistic regression analysis was used to identify variables associated with patient mortality and treatment outcome.

RESULTS

In total, 79 MRSA bacteraemia episodes were included. The vancomycin MIC was >1.0μg/mL in 53 episodes (67.1%). The presence of high vancomycin MIC was not associated with a higher mortality rate or treatment success. A daptomycin MIC≥0.5μg/mL was present in 16 (26.2%) of 61 episodes for which the daptomycin MIC was obtained and was associated with 30-day mortality in the multivariate analysis (odds ratio=4.72, 95% confidence interval 1.19-18.71). None of the antimicrobials used were associated with a lower risk of treatment failure or mortality.

CONCLUSIONS

The pernicious effect of high vancomycin MIC disappears in the absence of a predominant use of this antibiotic. However, a high daptomycin MIC in MRSA bacteraemia is associated with higher mortality in patients with bacteraemia, irrespective of antimicrobial treatment choice.

Current and future treatment options for community-associated MRSA infection

INTRODUCTION

Community-associated MRSA (CA-MRSA) represents a global epidemic which beautifully encapsulates the fascinating ability of bacterial organisms to adapt quickly on an evolutionary basis to the extreme selective pressure of antibiotic exposure. In stark contrast to Healthcare-associated MRSA (HA-MRSA), it has become apparent that CA-MRSA is less straight forward of a challenge in terms of controlling its transmission, and has forced clinicians to adjust empiric management of clinical syndromes such as skin and soft tissue infection (SSTI) as well as pneumonia.

AREAS COVERED

This review details the history and epidemiology of CA-MRSA, while covering both current and future treatment options that are and may be available to clinicians. The authors reviewed both historic and more recent literature on this ever-evolving topic.

EXPERT OPINION

While development of new anti-MRSA agents should be encouraged, the importance of antimicrobial stewardship in the battle to stay ahead of the curve with regards to the ongoing control of the MRSA epidemic should be emphasised.

Increasing rate of daptomycin non-susceptible strains of Staphylococcus aureus in patients with atopic dermatitis

Introduction

Daptomycin is a cyclic lipopeptide that is bactericidal against Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA), vancomycin-intermediate S. aureus (VISA) and vancomycin-resistant S. aureus (VRSA) strains. Daptomycin exerts its antimicrobial effect by a calcium-dependent interaction with the cytoplasmic membrane resulting in depolarization, ion loss and rapid cell death. Unfortunately, loss of daptomycin susceptibility in S. aureus in the clinical setting has been noted.

Aim

To evaluate the susceptibility profile to daptomycin among S. aureus strains isloted from patients with atopic dermatitis (AD). Another point was to correlate the results obtained by broth microdilution method and Etest, which is commonly applied in clinical setting.

Material and methods

One hundred patients with the diagnosis of atopic dermatitis were microbiologically assessed for the carriage of S. aureus. Antimicrobial susceptibility tests were performed using broth-microdilution (BMD) and Etests for daptomycin.

Results

Staphylococcus aureus strains were isolated from the majority of our patients, either from the skin (73%) or the anterior nares (75%). Six of the 100 nasal swabs (6%) and 5 of the 100 skin swabs (5%) were positive for methicillin-resistant Staphylococcus aureus (MRSA). A total of 81 of 148 (54.7%) daptomycin non-susceptible isolates of S. aureus were identified by BMD. Only 19 of 81 were also classified as non-susceptible by Etest.

Conclusions

Clinicians and microbiologists should be aware of the possibility of the emergence of daptomycin non-susceptibility (or increase in minimal inhibitory concentration) during prolonged therapy and closely monitor the susceptibility of persisting isolates that might be recovered during therapy.

Emergence of Daptomycin-Nonsusceptible Methicillin-Resistant Staphylococcus aureus Clinical Isolates Among Daptomycin-Naive Patients in Korea

This study was conducted to assess emergence of daptomycin-nonsusceptible (DAP-NS) phenotype in DAP-naive patients with invasive Staphylococcus aureus (ISA) infections in Korea. A total of 208 S. aureus clinical isolates were selected from a previous prospective study on ISA infections and evaluated for DAP-NS. Although DAP has never been introduced in Korea, five DAP-NS S. aureus strains (2.4%) were identified among 208 S. aureus strains collected from ISA infections. The DAP-NS phenotype was observed only in methicillin-resistant S. aureus (MRSA) strains, but not in methicillin-susceptible S. aureus strains. One DAP-NS MRSA strain belonged to sequence type 72 (ST72) and four were ST5 MRSA strains, three of which were heteroresistant vancomycin (VAN)-intermediate S. aureus. All these five DAP-NS MRSA strains were from healthcare-associated infections without prior exposure to VAN within 30 days. While the ST72 MRSA strain exhibited DAP-NS phenotype via charge repulsion mechanism, four ST5 DAP-NS S. aureus strains had charge-independent DAP-NS mechanism. None of the five DAP-NS strains displayed significant increase in cell wall thickness, indicating that altered cell wall thickness was not associated with the observed DAP-NS phenotype.

Septic Thrombophlebitis with Persistent Methicillin-Resistant Staphylococcus Aureus Bacteremia and de Novo Resistance to Vancomycin and Daptomycin

Persistent methicillin-resistant Staphylococcus aureus (MRSA) bacteremia is associated with significant risk of mortality, especially when it occurs while on appropriate antimicrobial therapy. We herein describe an unusual case of a patient with prosthetic aortic tissue valve, who suffered from central venous catheter related MRSA bacteremia with septic thrombus formation in the superior vena cava. MRSA bacteremia persisted despite removal of the catheter and appropriate antimicrobial therapy including vancomycin, rifampin, and daptomycin. Subsequently, the MRSA strain exhibited de novo resistance to vancomycin, rifampin and daptomycin. Eventually, salvage combination therapy with high dose daptomycin and trimethoprim-sulfamethoxazole was successful and achieved clearance of MRSA bacteremia. The case illustrates the growing complexity of treating MRSA infections.

Ventilator-associated pneumonia by methicillin-susceptible Staphylococcus aureus: do minimum inhibitory concentrations to vancomycin and daptomycin matter?

The use of vancomycin minimum inhibitory concentration (MIC) as an outcome predictor in patients with methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia has become an important topic for debate in the last few years. Given these previous results, we decided to investigate whether MICs to vancomycin or daptomycin had any effect on the evolution of patients with ventilator-associated pneumonia (VAP) due to MSSA. An observational, retrospective, multicenter study was conducted among patients with MSSA VAP. We analyzed the relationship between vancomycin and daptomycin MICs and early clinical response (72 h), 30-day mortality, intensive care unit (ICU) length of stay (LOS), and duration on mechanical ventilation. Univariate and multivariate analyses were performed. Sixty-six patients from 12 centers were included. Twenty-six patients (39%) had an infection due to MSSA strains with a vancomycin MIC ≥1.5 μg/mL. Daptomycin MIC was determined in 58 patients, of whom 17 (29%) had an MIC ≥1.0 μg/mL. Ten patients (15%) did not respond to first-line treatment. Only daptomycin MIC ≥1.0 μg/mL had a significant association [odds ratio (OR): 30.00; 95% confidence interval (CI): 2.91-60.41] with early treatment failure. The 30-day mortality was 12% (n = 8). Any variable was associated with mortality in the multivariate analysis. None of the variables studied were associated with ICU LOS or duration on mechanical ventilation. In patients with MSSA VAP, vancomycin MIC does not influence the response to antibiotic treatment or the 30-day mortality. Daptomycin MIC was directly related to early treatment failure.

Comparative Genome Analysis of the Daptomycin-Resistant Streptococcus anginosus Strain J4206 Associated with Breakthrough Bacteremia

Streptococcus anginosus is a member of the normal oral flora that can become a pathogen causing pyogenic infections in humans. The genome of daptomycin-resistant strain J4206, originally isolated from a patient suffering from breakthrough bacteremia and septic shock at the University of Texas Health Science Center at San Antonio, was determined. The circular genome is 2,001,352 bp long with a GC content of 38.62% and contains multiple mobile genetic elements, including the phage-like chromosomal island SanCI that mediates a mutator phenotype, transposons, and integrative conjugative elements. Daptomycin resistance involves multiple alterations in the cell membrane and cell wall, and unique features were identified in J4206 that may contribute to resistance. A cluster of capsular polysaccharide (CPS) genes for choline metabolism and transport are present that may help neutralize cell surface charges, destabilizing daptomycin binding. Further, unique J4206 genes encoding sortases and LPXTG-target proteins that are involved in cell wall modification were present. The J4206 genome is phylogenetically closely related to the recently reported vancomycin-resistant SA1 strain; however, these genomes differ with SNPs in cardiolipin synthetase, histidine kinase yycG, teichoic acid modification genes, and other genes involved in cell surface modification. Transmission electron microscopy showed that the cell walls of both strains J4206 and SA1 were significantly thicker and more electron dense than daptomycin- and vancomycin-sensitive strain J4211. This comparative genomic study has identified unique genes as well as allelic variants in the J4206 genome that are involved in cell surface modification and thus might contribute to the acquisition of daptomycin resistance.

Evolving resistance among Gram-positive pathogens

Antimicrobial therapy is a key component of modern medical practice and a cornerstone for the development of complex clinical interventions in critically ill patients. Unfortunately, the increasing problem of antimicrobial resistance is now recognized as a major public health threat jeopardizing the care of thousands of patients worldwide. Gram-positive pathogens exhibit an immense genetic repertoire to adapt and develop resistance to virtually all antimicrobials clinically available. As more molecules become available to treat resistant gram-positive infections, resistance emerges as an evolutionary response. Thus, antimicrobial resistance has to be envisaged as an evolving phenomenon that demands constant surveillance and continuous efforts to identify emerging mechanisms of resistance to optimize the use of antibiotics and create strategies to circumvent this problem. Here, we will provide a broad perspective on the clinical aspects of antibiotic resistance in relevant gram-positive pathogens with emphasis on the mechanistic strategies used by these organisms to avoid being killed by commonly used antimicrobial agents.

Association between Accessory Gene Regulator Polymorphism and Mortality among Critically Ill Patients Receiving Vancomycin for Nosocomial MRSA Bacteremia: A Cohort Study

Background. Polymorphism of the accessory gene regulator group II (agr) in methicillin-resistant Staphylococcus aureus (MRSA) is predictive of vancomycin failure therapy. Nevertheless, the impact of group II agr expression on mortality of patients with severe MRSA infections is not well established. Objective. The goal of our study was to evaluate the association between agr polymorphism and all-cause in-hospital mortality among critically ill patients receiving vancomycin for nosocomial MRSA bacteremia. Methods. All patients with documented bacteremia by MRSA requiring treatment in the ICU between May 2009 and November 2011 were included in the study. Cox proportional hazards regression was performed to evaluate whether agr polymorphism was associated with all-cause in-hospital mortality. Covariates included age, APACHE II score, initial C-reactive protein plasma levels, initial serum creatinine levels, vancomycin minimum inhibitory concentration, vancomycin serum levels, and time to effective antibiotic administration. Results. The prevalence of group I and group II agr expression was 52.4% and 47.6%, respectively. Bacteremia by MRSA group III or group IV agr was not documented in our patients. The mean APACHE II of the study population was 24.3 (standard deviation 8.5). The overall cohort mortality was 66.6% (14 patients). After multivariate analysis, initial plasma C-reactive protein levels (P = 0.01), initial serum creatinine levels (P = 0.008), and expression of group II agr (P = 0.006) were positively associated with all-cause in-hospital mortality. Patients with bacteremia by MRSA with group II agr expression had their risk of death increased by 12.6 times when compared with those with bacteremia by MRSA with group I agr expression. Conclusion. Group II agr polymorphism is associated with an increase in mortality in critically ill patients with bacteremia by MRSA treated with vancomycin.

Empirical therapy in Methicillin-resistant Staphylococcus Aureus infections: An Up-To-Date approach

Methicillin-resistant Staphylococcus aureus (MRSA) continues to be an important pathogen worldwide, with high prevalence of infection in both community and hospital settings. Timely and appropriate choice of empirical therapy in the setting of MRSA infection is imperative due to the high rate of associated morbidity and mortality with MRSA infections. Initial choices should be made based on the site and severity of the infection, most notably moderate skin and soft tissue infections which may be treated with oral antibiotics (trimethoprim-sulfamethoxazole, clindamycin, doxycycline/minocycline, linezolid) in the outpatient setting, versus choice of parenteral therapy in the inpatient setting of more invasive or severe disease. Though the current recommendations continue to strongly rely on vancomycin as a standard empiric choice in the setting of severe/invasive infections, alternative therapies exist with studies supporting their non-inferiority. This includes the use of linezolid in pneumonia and severe skin and skin structure infections (SSSI) and daptomycin for MRSA bacteremia, endocarditis, SSSIs and bone/joint infections. Additionally, concerns continue to arise in regards to vancomycin, such as increasing isolate MICs, and relatively high rates of clinical failures with vancomycin. Thus, the growing interest in vanomycin alternatives, such as ceftaroline, ceftobribole, dalbavancin, oritavancin, and tedizolid, and their potential role in treating MRSA infections.

Worldwide Epidemiology and Antibiotic Resistance of Staphylococcus aureus

Staphylococcus aureus is an important human pathogen, responsible for infections in the community and the healthcare setting. Although much of the attention is focused on the methicillin-resistant "variant" MRSA, the methicillin-susceptible counterpart (MSSA) remains a prime species in infections. The epidemiology of S. aureus, especially of MRSA, showed a rapid evolution in the last years. After representing a typical nosocomial multidrug-resistant pathogen, MRSA has recently emerged in the community and among farmed animals thanks to its ability to evolve and adapt to different settings. Global surveillance has shown that MRSA represents a problem in all continents and countries where studies have been carried out, determining an increase in mortality and the need to use last-resource expensive antibiotics. S. aureus can easily acquire resistance to antibiotics and MRSA is characteristically multidrug resistant. Resistance to vancomycin, the principal anti-MRSA antibiotic is rare, although isolates with decreased susceptibility are recovered in many areas. Resistance to the more recently introduced antibiotics, linezolid and daptomycin, has emerged; however, they remain substantially active against the large majority of MSSA and MRSA. Newer antistaphylococcal drugs have been developed, but since their clinical use has been very limited so far, little is known about the emergence of resistance. Molecular typing techniques have allowed to identify the major successful clones and lineages of MSSA and MRSA, including high-risk clones, and to trace their diffusion. In the face of a continuously evolving scenario, this review depicts the most common clones circulating in different geographical areas and in different settings at present. Since the evolution of S. aureus will continue, it is important to maintain the attention on the epidemiology of S. aureus in the future with a global view.

The Possible Role of Anti-Methicillin-Resistant Staphylococcus Aureus Antimicrobial Agents in Spontaneous Bacterial Peritonitis

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In vitro and in vivo activity of a novel sorafenib derivative SC5005 against MRSA

OBJECTIVES

The emergence of MRSA strains resistant to most antibiotics is a serious threat to public health. Based on our discovery that the tyrosine kinase inhibitor sorafenib exhibits inhibitory activity against Staphylococcus species, the objective of this study is to exploit this unique antibacterial activity of sorafenib to develop novel antibacterial agents against MRSA.

METHODS

A sorafenib-based focused compound library was synthesized by substituting the pyridinyl and phenyl groups with different functional groups. The resulting sorafenib derivatives were screened for growth-suppressive activities against Staphylococcus aureus and Staphylococcus epidermidis following CLSI guidelines and for cytotoxicity towards human cells using MTT cell viability assays. Compounds with high selectivity for bacterial inhibition over cytotoxicity were further evaluated by time-kill assay and Caenorhabditis elegans and mice survival assays to evaluate their efficacy in vitro and in vivo.

RESULTS

The screening of sorafenib derivatives led to the identification of compound SC5005 as a lead compound with high potency in killing different clinical strains of MRSA with an MIC90 of 0.5 mg/L and with low cytotoxicity, as demonstrated by IC50-to-MIC ratios of up to 40. In addition, SC5005 showed a significant protective effect in MSSA- or MRSA-infected C. elegans. Intraperitoneal administration of SC5005 at 10 mg/kg significantly improved the survival of MRSA-infected C57BL/6 mice.

CONCLUSIONS

In light of its high potency in suppressing MRSA in both in vitro and in vivo models, SC5005 represents a potential lead agent for continued preclinical development as a therapeutic intervention against MRSA.

Mechanisms of drug resistance: daptomycin resistance

Daptomycin (DAP) is a cyclic lipopeptide with in vitro activity against a variety of Gram-positive pathogens, including multidrug-resistant organisms. Since its introduction into clinical practice in 2003, DAP has become an important key frontline antibiotic for severe or deep-seated infections caused by Gram-positive organisms. Unfortunately, DAP resistance (DAP-R) has been extensively documented in clinically important organisms such as Staphylococcus aureus, Enterococcus spp., and Streptococcus spp. Studies on the mechanisms of DAP-R in Bacillus subtilis and other Gram-positive bacteria indicate that the genetic pathways of DAP-R are diverse and complex. However, a common phenomenon emerging from these mechanistic studies is that DAP-R is associated with important adaptive changes in cell wall and cell membrane homeostasis with critical changes in cell physiology. Findings related to these adaptive changes have provided novel insights into the genetics and molecular mechanisms of bacterial cell envelope stress response and the manner in which Gram-positive bacteria cope with the antimicrobial peptide attack and protect vital structures of the cell envelope, such as the cell membrane. In this review, we will examine the most recent findings related to the molecular mechanisms of resistance to DAP in relevant Gram-positive pathogens and discuss the clinical implications for therapy against these important bacteria.

Medical treatment of prosthetic vascular graft infections: Review of the literature and proposals of a Working Group

More than 400000 vascular grafts are inserted annually in the USA. Graft insertion is complicated by infection in 0.5-4% of cases. Vascular graft infections (VGIs) are becoming one of the most frequent prosthesis-related infections and are associated with considerable mortality, ranging from 10 to 25% within 30 days following the diagnosis. Treatment of VGI is based on urgent surgical removal of the infected graft followed by prolonged antibiotherapy. Data regarding the best antibiotherapy to use are lacking since no well designed trial to study antimicrobial treatment of VGI exists. Moreover, since VGIs demonstrate very specific pathophysiology, guidelines on other material-related infections or infective endocarditis treatment cannot be entirely applied to VGI. A French multidisciplinary group gathering infectious diseases specialists, anaesthesiologists, intensivists, microbiologists, radiologists and vascular surgeons was created to review the literature dealing with VGI and to make some proposals regarding empirical and documented antibiotic therapy for these infections. This article reveals these proposals.

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.

Staphylococcus aureus metabolic adaptations during the transition from a daptomycin susceptibility phenotype to a daptomycin nonsusceptibility phenotype

Staphylococcus aureus is a major cause of nosocomial and community-acquired infections. The success of S. aureus as a pathogen is due in part to its many virulence determinants and resistance to antimicrobials. In particular, methicillin-resistant S. aureus has emerged as a major cause of infections and led to increased use of the antibiotics vancomycin and daptomycin, which has increased the isolation of vancomycin-intermediate S. aureus and daptomycin-nonsusceptible S. aureus strains. The most common mechanism by which S. aureus acquires intermediate resistance to antibiotics is by adapting its physiology and metabolism to permit growth in the presence of these antibiotics, a process known as adaptive resistance. To better understand the physiological and metabolic changes associated with adaptive resistance, six daptomycin-susceptible and -nonsusceptible isogenic strain pairs were examined for changes in growth, competitive fitness, and metabolic alterations. Interestingly, daptomycin nonsusceptibility coincides with a slightly delayed transition to the postexponential growth phase and alterations in metabolism. Specifically, daptomycin-nonsusceptible strains have decreased tricarboxylic acid cycle activity, which correlates with increased synthesis of pyrimidines and purines and increased carbon flow to pathways associated with wall teichoic acid and peptidoglycan biosynthesis. Importantly, these data provided an opportunity to alter the daptomycin nonsusceptibility phenotype by manipulating bacterial metabolism, a first step in developing compounds that target metabolic pathways that can be used in combination with daptomycin to reduce treatment failures.

Clinical implications of vancomycin heteroresistant and intermediately susceptible Staphylococcus aureus

Staphylococcus aureus (S. aureus) has proven to be a major pathogen with the emergence of methicillin-resistant S. aureus (MRSA) infections and recently with heteroresistant vancomycin-intermediate S. aureus (hVISA) and vancomycin-intermediate S. aureus (VISA) infections. Although vancomycin is traditionally a first-line and relatively effective antibiotic, its continued use is under question because reports of heteroresistance in S. aureus isolates are increasing. Both hVISA and VISA infections are associated with complicated clinical courses and treatment failures. The prevalence, mechanism of resistance, clinical significance, and laboratory detection of hVISA and VISA infections are not conclusive, making it difficult to apply research findings to clinical situations. We provide an evidence-based review of S. aureus isolates expressing heterogenic and reduced susceptibility to vancomycin.

Fatal persistent methicillin-resistant Staphylococcus aureus bacteremia and vascular graft infections complicated with the formation of multiple abscesses despite aggressive medical therapy

A 40-year-old man underwent ascending aorta replacement for an acute type A aortic dissection. After the operations, methicillin-resistant Staphylococcus aureus was identified in sputum and blood cultures. Although anti-methicillin-resistant Staphylococcus aureus drugs were administered, most of the intermittent blood cultures remained positive. The focus of methicillin-resistant Staphylococcus aureus infection was not evident in the early stages, and no specific symptoms such as abscess or endocarditis were observed. However, abscesses in the brain, mediastinum and spleen were found 3 years after the operation. The minimum inhibitory concentration of vancomycin gradually increased from 1 to 4 µg/mL during the course of treatment. This case provides evidence for a potential role of combination therapy.

Fusion with a cell wall binding domain renders autolysin LytM a potent anti-Staphylococcus aureus agent

Despite intense efforts by the medical and pharmaceutical communities, Staphylococcus aureus continues to be a pervasive pathogen that causes a myriad of diseases and a high level of morbidity and mortality among infected patients. Thus, discovering or designing novel therapeutics able to kill both drug-resistant and drug-sensitive S. aureus remains a top priority. Bacteriolytic enzymes, mostly from phage, have shown great promise in preclinical studies, but little consideration has been given to cis-acting autolytic enzymes derived from the pathogen itself. Here, we use the S. aureus autolysin LytM as a proof of principal to demonstrate the antibacterial potential of endogenous peptidoglycan-degrading enzymes. While native LytM is only marginally bactericidal, fusion of LytM to the lysostaphin cell wall binding domain enhances its anti-staphylococcal activity approximately 540-fold, placing it on par with many phage lysins currently in preclinical development. The potential to therapeutically co-opt a pathogen's endogenous peptidoglycan recycling machinery opens the door to a previously untapped reservoir of antibacterial drug candidates.

Daptomycin and methicillin-resistant Staphylococcus aureus isolated from a catheter-related bloodstream infection: a case report

Background

Daptomycin is an alternative option for the treatment of catheter-related bloodstream-infections caused by methicillin-resistant Staphylococcus aureus. This study reports a case of a daptomycin and methicillin-resistant Staphylococcus aureus isolate recovered from the blood of a Brazilian patient undergoing hemodialysis.

Case presentation

A 64-year-old white male patient suffering from diabetes mellitus, systolic hypertension, heart disease with a coronary stent, obesity and chronic renal failure and on use of permcath catheter developed a catheter-related bloodstream-infection by a daptomycin-methicillin-resistant Staphylococcus aureus isolate after one month of daptomycin therapy. The isolate was identified as the SCCmec II/USA100/sequence type 5 lineage by molecular techniques.

Conclusions

In this work we described a Brazilian patient with bloodstream infection caused by a daptomycin and methicillin-resistant Staphylococcus aureus belonging to the lineage USA100/sequence type 5. Our case highlights the careful management of bloodstream infections and the importance of the judicious use of antimicrobials due the possibility of daptomycin-resistance developing among S. aureus isolates, especially in patients under hemodialysis, which are frequently exposed to vancomycin and daptomycin therapy.

Novel formulations for antimicrobial peptides

Peptides in general hold much promise as a major ingredient in novel supramolecular assemblies. They may become essential in vaccine design, antimicrobial chemotherapy, cancer immunotherapy, food preservation, organs transplants, design of novel materials for dentistry, formulations against diabetes and other important strategical applications. This review discusses how novel formulations may improve the therapeutic index of antimicrobial peptides by protecting their activity and improving their bioavailability. The diversity of novel formulations using lipids, liposomes, nanoparticles, polymers, micelles, etc., within the limits of nanotechnology may also provide novel applications going beyond antimicrobial chemotherapy.

Methicillin-resistant Staphylococcus aureus: an evolving pathogen

The horizontal transmission of methicillin resistance to Staphylococcus aureus (MRSA) in hospital and community settings, and growing prevalence of these strains, presents a significant clinical challenge to the management of serious infections worldwide. While infection control initiatives have stemmed the rising prevalence, MRSA remains a significant pathogen. More recently, evidence that MRSA is becoming resistant to glycopeptides and newer therapies raises concern about the use of these therapies in clinical practice. Vancomycin resistance has become evident in select clinical settings through rising MICs, growing awareness of heteroresistance, and emergence of intermediate-resistant and fully resistant strains. While resistance to linezolid and daptomycin remains low overall, point mutations leading to resistance have been described for linezolid, and horizontal transmission of cfr-mediated resistance to linezolid has been reported in clinical isolates. These resistance trends for newer therapies highlight the ongoing need for new and more potent antimicrobial therapies.

A current perspective on daptomycin for the clinical microbiologist

Daptomycin is a lipopeptide antimicrobial with in vitro bactericidal activity against Gram-positive bacteria that was first approved for clinical use in 2004 in the United States. Since this time, significant data have emerged regarding the use of daptomycin for the treatment of serious infections, such as bacteremia and endocarditis, caused by Gram-positive pathogens. However, there are also increasing reports of daptomycin nonsusceptibility, in Staphylococcus aureus and, in particular, Enterococcus faecium and Enterococcus faecalis. Such nonsusceptibility is largely in the context of prolonged treatment courses and infections with high bacterial burdens, but it may occur in the absence of prior daptomycin exposure. Nonsusceptibility in both S. aureus and Enterococcus is mediated by adaptations to cell wall homeostasis and membrane phospholipid metabolism. This review summarizes the data on daptomycin, including daptomycin's unique mode of action and spectrum of activity and mechanisms for nonsusceptibility in key pathogens, including S. aureus, E. faecium, and E. faecalis. The challenges faced by the clinical laboratory in obtaining accurate susceptibility results and reporting daptomycin MICs are also discussed.

Genotypically different clones of Staphylococcus aureus are diverse in the antimicrobial susceptibility patterns and biofilm formations

This study evaluated whether genotypically different clinical isolates of S. aureus have similar susceptibilities to individual antibiotics. It further aims to check the impact of biofilm on the in vitro activity of vancomycin, daptomycin, linezolid, and tigecycline against S. aureus clones. The study used a total of 60 different clinical MSSA and MRSA isolates. Susceptibilities were performed in planktonic cultures by macrobroth dilution and epsilon-test (E test) system. Biofilm production was determined using an adherent plate assay. The efficacy of antimicrobial activities against biofilms formation was checked using confocal laser scanning microscopy (CLSM). The study found that similar and different spa, MLST, and SCCmec types displayed high variation in their susceptibilities to antibiotics with tigecycline and daptomycin being the most effective. The biofilms were found resistant to high concentrations of most antibiotics tested with daptomycin being the most effective drug used in adhesive biofilms. A considerable difference exists among similar and various clone types against antibiotics tested. This variation could have contributed to the degree of virulence even within the same clonal genotype and enhanced heterogeneity in the infection potential. Thus, the development of a rapid and precise identification profile for each clone in human infections is important.