Nosocomial methicillin-resistant Staphylococcus aureus (MRSA) bacteremia in Taiwan: mortality analyses and the impact of vancomycin, MIC = 2 mg/L, by the broth microdilution method

Clinical Practice Guidelines for Therapeutic Drug Monitoring of Vancomycin in the Framework of Model-Informed Precision Dosing: A Consensus Review by the Japanese Society of Chemotherapy and the Japanese Society of Therapeutic Drug Monitoring

Background: To promote model-informed precision dosing (MIPD) for vancomycin (VCM), we developed statements for therapeutic drug monitoring (TDM). Methods: Ten clinical questions were selected. The committee conducted a systematic review and meta-analysis as well as clinical studies to establish recommendations for area under the concentration-time curve (AUC)-guided dosing. Results: AUC-guided dosing tended to more strongly decrease the risk of acute kidney injury (AKI) than trough-guided dosing, and a lower risk of treatment failure was demonstrated for higher AUC/minimum inhibitory concentration (MIC) ratios (cut-off of 400). Higher AUCs (cut-off of 600 μg·h/mL) significantly increased the risk of AKI. Although Bayesian estimation with two-point measurement was recommended, the trough concentration alone may be used in patients with mild infections in whom VCM was administered with q12h. To increase the concentration on days 1–2, the routine use of a loading dose is required. TDM on day 2 before steady state is reached should be considered to optimize the dose in patients with serious infections and a high risk of AKI. Conclusions: These VCM TDM guidelines provide recommendations based on MIPD to increase treatment response while preventing adverse effects.

Association between high vancomycin minimum inhibitory concentration and clinical outcomes in patients with methicillin-resistant Staphylococcus aureus bacteremia: a meta-analysis

PURPOSE

To assess the relationship between high vancomycin minimum inhibitory concentrations (MIC), in patients with methicillin-resistant Staphylococcus aureus bacteremia (MRSAB), and both mortality and complicated bacteremia.

METHODS

Embase, Medline, EBM, Scopus and Web of Science were searched for studies published from January 1st 2014 to February 29th 2020. "High" vancomycin MIC cut off was defined as ≥ 1.5 mg/L. Three referees independently reviewed studies that compared outcomes in patients with MRSAB stratified by vancomycin MIC. Subgroup analyses were performed for rates of mortality and complicated bacteremia.

RESULTS

A total of 13 studies with 2089 patients were included. Overall, mortality was 27.7% and 23.3% in the high and low vancomycin MIC group, respectively. No significant difference was found between vancomycin MIC groups for overall mortality, in-hospital mortality, late mortality, persistent bacteremia, severe sepsis or septic shock, acute renal failure, septic emboli or endocarditis, and osteomyelitis or septic arthritis. Early mortality was significantly associated with low vancomycin MIC. Mortality in studies using broth microdilution method (BMD) and need for mechanical ventilation were significantly associated with high vancomycin MIC.

CONCLUSION

Overall mortality and complicated bacteremia were not significantly associated with high vancomycin MICs in a patient with MRSAB. Randomized controlled trials to assess the utility of vancomycin MIC values in predicting mortality and other adverse clinical outcomes are warranted.

Synthesis, Characterization, and Pharmacodynamics Study of Enrofloxacin Mesylate

Introduction

Enrofloxacin is used in the treatment of a wide variety of bacterial infections in mammals. However, its poor solubility limits the clinical use.

Methods

In order to improve the solubility of enrofloxacin, the enrofloxacin mesylate (EM) were obtained by a chemical synthesis method. The characterization of EM was carried out using ultraviolet scan (UV), synchronous thermal analysis (SDT), fourier transform infrared spectrometer (FTIR) and mass spectrometry (MS), nuclear magnetic resonance (NMR) and X-ray powder diffraction analysis (XRPD). Acute toxicity of EM in Kunming mice was studied. Besides, pharmacokinetic studies were performed in New Zealand rabbits at a single oral dose of 10 mg/kg, and the antibacterial activity of EM was also evaluated.

Results

EM was successfully synthesized and purified. The stoichiometric ratio of mesylate to enrofloxacin was 1:1 and the aqueous solubility of EM was 483.01±4.06 mg/mL, the solubility of EM was about 2000 times higher than enrofloxacin. The oral lethal dose (LD₅₀) of EM was 1168.364 mg/kg, and the pharmacokinetics indicated that the oral relative bioavailability of EM was about 1.79 times and 1.48 times higher than that of enrofloxacin and enrofloxacin hydrochloride, respectively. In addition, the in vitro antibacterial activity of EM was not significantly changed compared with enrofloxacin and enrofloxacin hydrochloride.

Conclusion

EM has higher solubility, low toxicity for oral use, and increases the oral bioavailability in rabbit. This study may be of benefit for the development of new enrofloxacin drugs.

Application of a MALDI-TOF analysis platform (ClinProTools) for rapid and preliminary report of MRSA sequence types in Taiwan

Background

The accurate and rapid preliminarily identification of the types of methicillin-resistant Staphylococcus aureus (MRSA) is crucial for infection control. Currently, however, expensive, time-consuming, and labor-intensive methods are used for MRSA typing. By contrast, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a potential tool for preliminary lineage typing. The approach has not been standardized, and its performance has not been analyzed in some regions with geographic barriers (e.g., Taiwan Island).

Methods

The mass spectra of 306 MRSA isolates were obtained from multiple reference hospitals in Taiwan. The multilocus sequence types (MLST) of the isolates were determined. The spectra were analyzed for the selection of characteristic peaks by using the ClinProTools software. Furthermore, various machine learning (ML) algorithms were used to generate binary and multiclass models for classifying the major MLST types (ST5, ST59, and ST239) of MRSA.

Results

A total of 10 peaks with the highest discriminatory power (m/z range: 2,082–6,594) were identified and evaluated. All the single peaks revealed significant discriminatory power during MLST typing. Moreover, the binary and multiclass ML models achieved sufficient accuracy (82.80–94.40% for binary models and >81.00% for multiclass models) in classifying the major MLST types.

Conclusions

A combination of MALDI-TOF MS analysis and ML models is a potentially accurate, objective, and efficient tool for infection control and outbreak investigation.

Impact of teicoplanin maintenance dose and MIC values on the clinical outcomes of patients treated for methicillin-resistant Staphylococcus aureus bacteremia

Objectives

Teicoplanin, a glycopeptide, is regarded as among the drug choices for methicillin-resistant Staphylococcus aureus (MRSA) infections. Few studies have evaluated the relationship between teicoplanin minimal inhibitory concentrations (MICs) and outcomes among patients with serious MRSA infections.

Subjects and methods

We investigated the relationship between teicoplanin maintenance dose and clinical outcomes, on the completion of teicoplanin therapy, in bacteremia patients with MRSA infection, with different teicoplanin MICs. A total of 146 adult patients with MRSA bacteremia were enrolled at Kaohsiung Chang Gung Memorial Hospital between September 2012 and September 2015.

Results

A higher number of patients in the high-dose regimen group (6 mg/kg/12 h) had favorable outcomes than those in the standard-dose regimen group (6 mg/kg/24 h) (84.1% vs 41.2%; p<0.01), regardless of the teicoplanin MICs. In the multivariate analysis, a Pittsburgh bacteremia score ≥4 (OR, 0.07, 95% CI, 0.03–0.19) was a risk factor for an unfavorable final clinical response, whereas high-dose teicoplanin maintenance therapy for MRSA bacteremia was significantly associated with a favorable final response (OR, 25.3 [95% CI, 4.43–144.03] for isolates with a teicoplanin MIC ≥1.5 mg/L and OR, 5.6 [95% CI, 1.57–19.91] for isolates with a teicoplanin MIC <1.5 mg/L). Survival at 30 days was significantly better for patients receiving high-dose teicoplanin maintenance treatment, regardless of the teicoplanin MICs of the MRSA isolates. Patients were selected using propensity score matching, based on the independent predictors of a favorable final outcome. After appropriate propensity score matching, patients in the high-dose regimen group still had a statistically significant favorable outcome at the end of treatment (84.1% vs 40.9%; p<0.01).

Conclusion

The results suggested that high-dose teicoplanin maintenance treatment is associated with more favorable outcomes than standard-dose teicoplanin maintenance treatment, for patients with MRSA bacteremia, regardless of the teicoplanin MIC.

Risk factors of treatment failure and 30-day mortality in patients with bacteremia due to MRSA with reduced vancomycin susceptibility

Bacteremia caused by MRSA with reduced vancomycin susceptibility (MRSA-RVS) frequently resulted in treatment failure and mortality. The relation of bacterial factors and unfavorable outcomes remains controversial. We retrospectively reviewed clinical data of patients with bacteremia caused by MRSA with vancomycin MIC = 2 mg/L from 2009 to 2012. The significance of bacterial genotypes, agr function and heterogeneous vancomycin-intermediate S. aureus (hIVSA) phenotype in predicting outcomes were determined after clinical covariates adjustment with multivariate analysis. A total of 147 patients with mean age of 63.5 (±18.1) years were included. Seventy-nine (53.7%) patients failed treatment. Forty-seven (31.9%) patients died within 30 days of onset of MRSA bacteremia. The Charlson index, Pitt bacteremia score and definitive antibiotic regimen were independent factors significantly associated with either treatment failure or mortality. The hVISA phenotype was a potential risk factor predicting treatment failure (adjusted odds ratio 2.420, 95% confidence interval 0.946–6.191, P = 0.0652). No bacterial factors were significantly associated with 30-day mortality. In conclusion, the comorbidities, disease severity and antibiotic regimen remained the most relevant factors predicting treatment failure and 30-day mortality in patients with MRSA-RVS bacteremia. hIVSA phenotype was the only bacterial factor potentially associated with unfavorable outcome in this cohort.

Methicillin-resistant Staphylococcus aureus with reduced vancomycin susceptibility in Taiwan

Staphylococcus aureus is a versatile pathogen which can cause various mild to life-threatening infectious diseases. The evolution of S. aureus resistance is notorious, from penicillin and oxacillin to vancomycin. Vancomycin, introduced in 1956, was once considered a most reliable antibiotic for methicillin-resistant S. aureus (MRSA); unfortunately, the first strain of S. aureus with decreased susceptibility to vancomycin emerged in 1996. Vancomycin has been approved in Taiwan since 1983, and the prevalence rates of heteroresistant vancomycin-intermediate S. aureus (hVISA) and vancomycin-intermediate S. aureus (VISA) in 2003 were 0.7% and 0.2%, respectively. However, a ten-fold increase of hVISA and VISA to 10% and 2.7%, respectively, in 2012-2013 could indicate a challenging clinical situation in Taiwan. The most commonly reported staphylococcal cassette chromosome mec (SCCmec) types of hVISA and VISA are usually SCCmec type III or II, typical nosocomial MRSA strains. Preventing the spread of resistant pathogens through infection control interventions and judicious antibiotic stewardship is a serious medical issue.

Predictors of Adverse Outcomes in Children With Staphylococcus aureus Bacteremia

OBJECTIVES

Staphylococcus aureus bacteremia is a common infection, associated with significant morbidity and mortality in children. Factors associated with adverse treatment outcomes are poorly understood in the pediatric population.

METHODS

Our study compared clinical and microbiologic characteristics of children admitted during a 5-year period (2007-2012) to a large university-based hospital and found to have S aureus bacteremia with outcome measures, in order to identify risk factors associated with treatment failure (defined as 30-day mortality, delayed microbiologic resolution, or recurrence of S aureus bacteremia within 60 days of completing effective antibiotic therapy).

RESULTS

In all, 71 patients were found to have S aureus bacteremia, and of these, 17 patients (24%) experienced treatment failure. Based on the logistic regression model, only high vancomycin minimum inhibitory concentration in combination with a high-risk source of infection (i.e., infected graft or device, intra-abdominal infection, or respiratory tract infection) was significantly associated with risk of treatment failure.

CONCLUSIONS

Infection associated with a high-risk source may increase the chance of treatment failure in pediatric patients with S aureus bacteremia. Vancomycin minimum inhibitory concentration alone was not found to be a predictor of treatment outcomes.

Ceftaroline-Resistant, Daptomycin-Tolerant, and Heterogeneous Vancomycin-Intermediate Methicillin-Resistant Staphylococcus aureus Causing Infective Endocarditis

We report a case of infective endocarditis (IE) caused by ceftaroline-resistant, daptomycin-tolerant, and heterogeneous vancomycin-intermediate methicillin-resistant S. aureus (MRSA). Resistance to ceftaroline emerged in the absence of drug exposure, and the E447K substitution in the active site of PBP2a previously associated with ceftaroline resistance was identified. Additionally, we present evidence of patient-to-patient transmission of the strain within the same unit. This case illustrates the difficulties in treating MRSA IE in the setting of a multidrug-resistant phenotype.

Vancomycin MIC Does Not Predict 90-Day Mortality, Readmission, or Recurrence in a Prospective Cohort of Adults with Staphylococcus aureus Bacteremia

Staphylococcus aureus bacteremia (SAB) is a tremendous health burden. Previous studies examining the association of vancomycin MIC and outcomes in patients with SAB have been inconclusive. This study evaluated the association between vancomycin MICs and 30- or 90-day mortality in individuals with SAB. This was a prospective cohort study of adults presenting from 2008 to 2013 with a first episode of SAB. Subjects were identified by an infection surveillance system. The main predictor was vancomycin MIC by MicroScan. The primary outcomes were death at 30 and 90 days, and secondary outcomes included recurrence, readmission, or a composite of death, recurrence, and readmission at 30 and 90 days. Covariates included methicillin susceptibility, demographics, illness severity, comorbidities, infectious source, and antibiotic use. Cox proportional-hazards models with propensity score adjustment were used to estimate 30- and 90-day outcomes. Of 429 unique first episodes of SAB, 11 were excluded, leaving 418 individuals for analysis. Eighty-three (19.9%) participants had a vancomycin MIC of 2 μg/ml. In the propensity-adjusted Cox model, a vancomycin MIC of 2 μg/ml compared to <2 μg/ml was not associated with a greater hazard of mortality or composite outcome of mortality, readmission, and recurrence at either 30 days (hazard ratios [HRs] of 0.86 [95% confidence interval {CI}, 0.41, 1.80] [P = 0.70] and 0.94 [95% CI, 0.55, 1.58] [P = 0.80], respectively) or 90 days (HRs of 0.91 [95% CI, 0.49, 1.69] [P = 0.77] and 0.69 [95% CI, 0.46, 1.04] [P = 0.08], respectively) after SAB diagnosis. In a prospective cohort of patients with SAB, vancomycin MIC was not associated with 30- or 90-day mortality or a composite of mortality, disease recurrence, or hospital readmission.

Effects of inappropriate empirical antibiotic therapy on mortality in patients with healthcare-associated methicillin-resistant Staphylococcus aureus bacteremia: a propensity-matched analysis

Background

The purported value of empirical therapy to cover methicillin-resistant Staphylococcus aureus (MRSA) has been debated for decades. The purpose of this study was to evaluate the effects of inappropriate empirical antibiotic therapy on clinical outcomes in patients with healthcare-associated MRSA bacteremia (HA-MRSAB).

Methods

A prospective, multicenter, observational study was conducted in 15 teaching hospitals in the Republic of Korea from February 2010 to July 2011. The study subjects included adult patients with HA-MRSAB. Covariate adjustment using the propensity score was performed to control for bias in treatment assignment. The predictors of in-hospital mortality were determined by multivariate logistic regression analyses.

Results

In total, 345 patients with HA-MRSAB were analyzed. The overall in-hospital mortality rate was 33.0 %. Appropriate empirical antibiotic therapy was given to 154 (44.6 %) patients. The vancomycin minimum inhibitory concentrations of the MRSA isolates ranged from 0.5 to 2 mg/L by E-test. There was no significant difference in mortality between propensity-matched patient pairs receiving inappropriate or appropriate empirical antibiotics (odds ratio [OR] = 1.20; 95 % confidence interval [CI] = 0.71–2.03). Among patients with severe sepsis or septic shock, there was no significant difference in mortality between the treatment groups. In multivariate analyses, severe sepsis or septic shock (OR = 5.45; 95 % CI = 2.14–13.87), Charlson’s comorbidity index (per 1-point increment; OR = 1.52; 95 % CI = 1.27–1.83), and prior receipt of glycopeptides (OR = 3.24; 95 % CI = 1.08–9.67) were independent risk factors for mortality.

Conclusion

Inappropriate empirical antibiotic therapy was not associated with clinical outcome in patients with HA-MRSAB. Prudent use of empirical glycopeptide therapy should be justified even in hospitals with high MRSA prevalence.

Population structure of colonizing and invasive Staphylococcus aureus strains in northern Vietnam

Staphylococcus aureus is an important global health problem worldwide. There is still scarce information on the population structure of S. aureus strains in Asia, where the majority of the world population lives. This study characterized the diversity of S. aureus strains in northern Vietnam through multilocus sequence typing (MLST). Eighty-five carriage isolates from the community and 77 invasive isolates from the clinical setting were selected and tested for meticillin resistance and the presence of Panton-Valentine leukocidin (PVL). MLST was performed on these isolates, of which CC59 (25.4 %), CC188 (17.3 %) and CC45 (16.7 %) were the predominant clonal complexes (CCs). CC59 carriage isolates had significantly lower rates of meticillin-resistant S. aureus (MRSA) than their corresponding clinical group isolates (32 vs 83 %). There were no significant differences in rates of MRSA between carriage isolates and clinical isolates of CC45 and CC188. CC59 carriage isolates were significantly lower in rates of PVL⁺ than CC59 clinical isolates (32 vs 83 %), but the converse was shown in CC45 isolates (14 vs 0 %, respectively). This study revealed vast differences in the molecular epidemiology and population structure of S. aureus in community and clinical settings in Vietnam. Nevertheless, the data underline the spread of virulent and/or resistant strains (MRSA and/or PVL⁺) in the community, suggesting the necessity for further surveillance to determine the mechanism of transmission of these strains (i.e. MRSA/PVL⁺) outside clinical settings.

Comparison of Outcomes among Adult Patients with Nosocomial Bacteremia Caused by Methicillin-Susceptible and Methicillin-Resistant Staphylococcus aureus: A Retrospective Cohort Study

Several studies have shown that patients with bacteremia caused by methicillin-resistant Staphylococcus aureus (MRSA) have worse outcomes than those with bacteremia caused by methicillin-susceptible S. aureus (MSSA). However, only a limited number of studies have stratified the MRSA isolates into healthcare-associated (HA-) and community-associated (CA-) MRSA strains in such a comparison. This three-year retrospective cohort study, enrolling adult patients with nosocomial S. aureus bacteremia (SAB), was designed to investigate whether CA-MRSA and/or HA-MRSA strains were associated with different outcomes in comparison to MSSA in such a setting. The drug susceptibilities and staphylococcal cassette chromosome mec (SCCmec) types were determined for all of the causative isolates available. The MRSA bacteremia was further categorized into those caused by CA-MRSA strains (CA-MRSA-S bacteremia) when the causative isolates carried the type IV or V SCCmec element, those caused by HA-MRSA strains (HA-MRSA-S bacteremia) when the isolates carried the type I, II, or III SCCmec element, or unclassified MRSA bacteremia when the isolates were not available. The relevant demographic, clinical, and laboratory data were collected by reviewing the patients’ charts. The primary outcome was all-cause in-hospital mortality. A total of 353 patients were studied. The overall in-hospital mortality rate was 32.6%, with 23.3% in MSSA, 30.5% in CA-MRSA-S, 47.5% in HA-MRSA-S, and 35.3% in unclassified MRSA bacteremia, respectively. The multivariate analysis showed that HA-MRSA-S, but not CA-MRSA-S, bacteremia was associated with a significantly worse outcome compared with MSSA. The other risk factors independently associated with all-cause in-hospital mortality included the Charlson co-morbidity index, septic shock, thrombocytopenia, and persistent bacteremia. Resistance to linezolid and daptomycin was found among the MRSA isolates. The present study showed that bacteremia caused by HA-MRSA-S, but not CA-MRSA-S, was an independent risk factor for all-cause in-hospital mortality in patients with nosocomial SAB. Continuous monitoring regarding the susceptibilities of MRSA to linezolid and daptomycin is necessary.

The association of molecular typing, vancomycin MIC, and clinical outcome for patients with methicillin-resistant Staphylococcus aureus infections

BACKGROUND/PURPOSE

There are reports of an increase in vancomycin minimum inhibitory concentration (MIC) against methicillin-resistant Staphylococcus aureus (MRSA) over time, a phenomenon referred to as "MIC creep", but some studies have conflicting results. The aim of this study is to evaluate the association of molecular typing, vancomycin MIC, and clinical outcome for patients with MRSA infections.

METHODS

Thirty-two MRSA isolates from Taichung Veterans General Hospital (TCVGH), Taichung, Taiwan during the period of 2003 to 2008 were analyzed for the association of sequence typing, vancomycin MIC, and the correlated clinical outcome for patients with MRSA infections. The vancomycin MICs of 28 additional isolates from 2014 were used for the detection of MIC creep.

RESULTS

Among the genotypes of 32 isolates, there were 17 (53.1%) isolates with ST239-SCCmecIII, seven (21.9%) isolates with ST5-SCCmecII, six (18.8%) isolates with ST59-SCCmecIV, and two (6.2%) isolates with ST59-SCCmecV_T. Two isolates had an MIC of 2 μg/mL and were identified as ST239-SCCmecIII. No statistically significant change in the distribution of MICs of all isolates was observed between 2003 and 2014 (p = 0.263). There was no significant difference in the mortality rates between two groups of patients with vancomycin MICs < 2 μg/mL and ≥ 2 μg/mL (p = > 0.99).

CONCLUSION

There was no vancomycin MIC creep in the period from 2003 to 2014 in this study. Appropriate prognostic models for assessment of the association among sequence types, vancomycin MICs, and clinical outcome warrant further investigation.

Rates of susceptibility of carbapenems, ceftobiprole, and colistin against clinically important bacteria collected from intensive care units in 2007: Results from the Surveillance of Multicenter Antimicrobial Resistance in Taiwan (SMART)

BACKGROUND

Data on susceptibility to ceftobiprole and colistin, and the complete evolutionary trends of minimum inhibitory concentrations (MICs) of important carbapenem agents among important pathogens collected in intensive care units (ICUs) in Taiwan are lacking.

METHODS

We surveyed the MIC distribution patterns of ceftobiprole and colistin and susceptibility profiles of some important pathogens collected from patients hospitalized in intensive care units (ICUs) of major teaching hospitals throughout Taiwan in 2007. We also investigated the rates of nonsusceptibility to powerful carbapenems (imipenem, meropenem) among four important species of Enterobacteriaceae (Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, and Proteus mirabilis) collected during the same period. MIC breakpoints recommended by the Clinical and Laboratory Standards Institute in 2014 were applied.

RESULTS

Colistin showed excellent in vitro activity (susceptibility rate, 96%) against Acinetobacter baumannii isolates but moderate (73-77% susceptibility rate) activity against isolates of Pseudomonas aeruginosa and E. cloacae. The ceftobiprole MIC₉₀ value was 4 μg/mL for methicillin-resistant Staphylococcus aureus and 16 μg/mL for P. aeruginosa. The phenotype of methicillin resistance did not markedly increase the MIC value of ceftobiprole among S. aureus isolates. Interestingly, the proportion of isolates that displayed nonsusceptibility to imipenem was significantly higher among P. mirabilis isolates than among isolates of the other three Enterobacteriaceae species, regardless of the production of extended-spectrum β-lactamase.

CONCLUSION

Continuous monitoring of susceptibility profiles of ICU pathogens to important antibiotics is warranted to provide appropriate antimicrobial regimens against infections in the ICU.

Clinical, microbiological, and genetic characteristics of heteroresistant vancomycin-intermediate Staphylococcus aureus bacteremia in a teaching hospital

The emergence of vancomycin intermediate Staphylococcus aureus (VISA) and heterogeneous VISA (hVISA) is of major concern worldwide. Our objective was to investigate the prevalence, phenotypic and molecular features of hVISA strains isolated from bacteremic patients and to determine the clinical significance of the hVISA phenotype in patients with bacteremia. A total of 104 S. aureus blood isolates were collected from a teaching hospital of Argentina between August 2009 and November 2010. No VISA isolate was recovered, and 3 out of 92 patients (3.3%) were infected with hVISA, 2 of them methicillin-resistant S. aureus (MRSA) (4.5% of MRSA). Macro Etest and prediffusion method detected 3/3 and 2/3 hVISA respectively. Considering the type of bacteremia, the three cases were distributed as follows: two patients had suffered multiple episodes of bacteremia (both hVISA strains recovered in the second episode), while only one patient had suffered a single episode of bacteremia with hVISA infection. MRSA bloodstream isolates exhibiting the hVISA phenotype were related to HA-MRSA Cordobes clone (ST5-SCCmec I-spa t149) and MRSA Argentinean pediatric clone (ST100-SCCmec IV_NV-spa t002), but not to CA-MRSA-ST30-SCCmec IV-spa t019 clone that was one of the most frequent in our country. Although still relatively infrequent in our hospital, hVISA strains were significantly associated with multiple episodes of bacteremia (p=0.037) and genetically unrelated.

The Japanese guidelines for the management of sepsis

This is a guideline for the management of sepsis, developed by the Sepsis Registry Committee of The Japanese Society of Intensive Care Medicine (JSICM) launched in March 2007. This guideline was developed on the basis of evidence-based medicine and focuses on unique treatments in Japan that have not been included in the Surviving Sepsis Campaign guidelines (SSCG), as well as treatments that are viewed differently in Japan and in Western countries. Although the methods in this guideline conform to the 2008 SSCG, the Japanese literature and the results of the Sepsis Registry Survey, which was performed twice by the Sepsis Registry Committee in intensive care units (ICUs) registered with JSICM, are also referred. This is the first and original guideline for sepsis in Japan and is expected to be properly used in daily clinical practice.

This article is translated from Japanese, originally published as “The Japanese Guidelines for the Management of Sepsis” in the Journal of the Japanese Society of Intensive Care Medicine (J Jpn Soc Intensive Care Med), 2013; 20:124–73. The original work is at http://dx.doi.org/10.3918/jsicm.20.124.

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.

A correlation between reduced susceptibilities to vancomycin and daptomycin among the MRSA isolates selected in mutant selection window of both vancomycin and daptomycin

Guidelines for the treatment of MRSA infection, recently published by the IDSA and JSC, recommend daptomycin for sepsis and skin and soft tissue infections comparably to or more strongly than vancomycin. Meanwhile MIC creeping with an increased isolation frequency of MRSA isolates with vancomycin MIC of 2 μg/mL has become a problem. In the present study, the MIC creeping rate of MRSA strains in the Tohoku district, Japan in 2012 was 13%, a significantly higher value than 3.3% in 2008 (P < 0.01). Of these isolates, the MIC and mutant prevention concentration (MPC) values of daptomycin and vancomycin were determined for 30 clinical isolates of MRSA in 2012. The MIC50/MIC80 values of daptomycin and vancomycin were 0.125/0.5 μg/mL and 0.125/1 μg/mL, respectively. The MPC50/MPC80 values of daptomycin and vancomycin were both 32/64 μg/mL. In the present study, the mutant selection window (MSW) of daptomycin and vancomycin was ≥64 MIC. Of strains that selected in the MSW, daptomycin non-susceptible isolates accounted for 70.0%, while MRSA with vancomycin MIC of 2 μg/mL accounted for 26.7%. On the other hand, 50% of the strains that selected in the vancomycin MSW were daptomycin non-susceptible strain. The detection rate of MRSA with vancomycin MIC of 2 μg/mL that selected in the daptomycin MSW was 36.7%. These results showed that MRSA with vancomycin MIC of 2 μg/mL and daptomycin non-susceptible isolates were selected by exposure to both antibiotics. Therefore, though vancomycin is frequently used for treatment of MRSA infection, both antibiotics should be selected as a first-line drug appropriately.

Trend in vancomycin susceptibility and correlation with molecular characteristics of methicillin-resistant Staphylococcus aureus causing invasive infections in Taiwan: results from the Tigecycline in vitro Surveillance in Taiwan (TIST) study, 2006-2010

This study was intended to investigate the trend in vancomycin susceptibility and correlation with molecular characteristics of methicillin-resistant Staphylococcus aureus (MRSA) causing invasive infections. A total of 670 MRSA isolates were collected from patients with invasive infections as part of bacterial collection in the Tigecycline in vitro Surveillance in Taiwan (TIST) from 2006 to 2010. MICs of the isolates to vancomycin were determined using the agar dilution method. Characteristics of staphylococcal cassette chromosome mec (SCCmec), mec-associated hypervariable region (dru), and accessory gene regulator (agr) of the isolates were identified by polymerase chain reaction methods. MRSA isolates with SCCmec types I, II, and III were molecularly defined as hospital-associated MRSA (HA-MRSA), and those with SCCmec types IV, V, and VT were assigned as community-associated MRSA (CA-MRSA). All but 1 MRSA isolates exhibited vancomycin MICs ≤1 mg/L. A declining trend in vancomycin MICs among MRSA isolates was noted, which was associated with the decline in proportion of HA-MRSA. The percentage of CA-MRSA increased from 25.6% in 2006 to 46.0% in 2010. An increase in the geometric mean of vancomycin MICs was found in MRSA with particular molecular types such as SCCmec types II and III, agr groups I and II, and dru10-14. A significant correlation among particular molecular types was found, including SCCmecII-agr group II-dru4, SCCmecIII-agr group I-dru11-14, SCCmecIV-agr group II-dru9, and SCCmecVT-agr group I-dru9 and dru11. There was no vancomycin creep among MRSA isolates, and the declining trend of vancomycin MIC against MRSA was attributed to the increasing prevalence of CA-MRSA over time.

Observation of "seesaw effect" with vancomycin, teicoplanin, daptomycin and ceftaroline in 150 unique MRSA strains

Introduction

Vancomycin (VAN) failures associated with the treatment of complicated methicillin-resistant Staphylococcus aureus (MRSA) infections have been well described. The reported “seesaw effect” demonstrates improved β-lactam activity when VAN and/or daptomycin (DAP) susceptibility decreases. However, there are minimal data comparing ceftaroline (CPT) susceptibility with these agents or teicoplanin (TEI). Therefore, to further explore the seesaw effect, we evaluated the relationship between CPT and VAN, TEI, and DAP susceptibilities.

Methods

One hundred and fifty clinical MRSA isolates from the Anti-Infective Research Laboratory (Detroit, MI, USA) from 2008 to 2012 were analyzed. VAN, TEI, DAP and CPT minimum inhibitory concentrations (MIC) were determined via Etest methodology. MIC₅₀ and MIC₉₀ were calculated for each antibiotic. Additionally, four isogenic strain pairs were randomly selected for evaluation by time–kill methodology for the potential of enhanced killing by CPT as MICs increased to VAN, TEI, and DAP.

Results

CPT MICs were inversely correlated with VAN, DAP, and TEI MICs with correlation coefficients of −0.535, −0.483, and −0.386, respectively (P ≤ 0.05). Comparison of the MIC relationship for glycopeptides and lipopeptides resulted in a positive correlation for all agent combinations. In time–kill evaluations, CPT demonstrated greater reductions in log₁₀ colony-forming unit (CFU)/mL against mutant strains (3.73 ± 0.67) versus parents (2.79 ± 0.75) despite no change in CPT MIC (P = 0.112).

Conclusion

This study demonstrated a marked “seesaw effect” whereby CPT displayed increased susceptibility as the VAN, DAP, and TEI MICs increased. Additionally, we observed a positive linear correlation between VAN, DAP, and TEI MICs for all agent combinations. Enhanced activity was noted with CPT in mutant strains versus the parent strains despite no change in MIC. Based upon the enhanced CPT activity observed against strains with decreased susceptibility to VAN, DAP and TEI, CPT may provide an option for infections with reduced susceptibility to glycopeptides or lipopeptides. Further evaluation is warranted to investigate the clinical implications of the seesaw effect.

Electronic supplementary material

The online version of this article (doi:10.1007/s40121-014-0023-0) contains supplementary material, which is available to authorized users.

Predictive factors for mortality in patients with methicillin-resistant Staphylococcus aureus bloodstream infection: impact on outcome of host, microorganism and therapy

Mortality related to methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infection (BSI) remains high, despite changes in the epidemiology. To analyze the current predictive factors for mortality we conducted a prospective study in a large cohort of patients with MRSA-BSI from 21 Spanish hospitals. Epidemiology, clinical data, therapy and outcome were recorded. All MRSA strains were analysed, including susceptibility to antibiotics and molecular characterization. Vancomycin MICs (V-MIC) were tested by the E-test and microdilution methods. Time until death was the dependent variable in a Cox regression analysis. Overall, 579 episodes were included. Acquisition was nosocomial in 59% and vascular catheter was the most frequent source (38%). A dominant PFGE genotype was found in 368 (67%) isolates, which belonged to Clonal Complex (CC)5 and carried SCCmecIV and agr2. Microdilution V-MIC50 and V-MIC90 were 0.7 and 1.0 mg/L, respectively. Initial therapy was appropriate in 66% of episodes. Overall mortality was observed in 179 (32%) episodes. The Cox-regression analysis identified age >70 years (HR 1.88), previous fatal disease (HR 2.16), Pitt score >1 (HR 3.45), high-risk source (HR 1.85) and inappropriate initial treatment (HR 1.39) as independent predictive factors for mortality. CC5 and CC22 (HR 0.52 and 0.45) were associated with significantly lower mortality rates than CC8. V-MIC ≥1.5 did not have a significant impact on mortality, regardless of the method used to assess it.

Multicenter prospective observational study of the comparative efficacy and safety of vancomycin versus teicoplanin in patients with health care-associated methicillin-resistant Staphylococcus aureus bacteremia

The purpose of this study was to compare the clinical efficacy and safety of vancomycin to those of teicoplanin for the treatment of adult patients with health care-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) bacteremia. A multicenter observational study was prospectively conducted in 15 teaching hospitals in Korea between February 2010 and July 2011. Adult patients (≥18 years old) with HA-MRSA bacteremia who were initially treated with vancomycin (VAN) (n = 134) or teicoplanin (TEC) (n = 56) were enrolled. Clinical and microbiological responses and drug-related adverse events were compared between the two treatment groups using univariate and multivariate logistic regression analyses. The vancomycin and teicoplanin MICs were determined by Etest. The MRSA-related mortality, duration of fever, and duration of MRSA bacteremia in the treatment groups were not significantly different. There was no significant difference in the occurrence of drug-related adverse events. Among the 190 MRSA isolates, the VAN MICs ranged from 0.5 to 2 μg/ml (MIC50 and MIC90, 1.5 μg/ml), and the TEC MIC ranged from 0.5 to 8 μg/ml (MIC50, 3 μg/ml; MIC90, 6 μg/ml). In multivariate analyses, the antibiotic type (vancomycin or teicoplanin) was not associated with treatment outcomes. This study indicates that teicoplanin is an effective and safe alternative to vancomycin for the treatment of HA-MRSA bacteremia.

Acute MRSA sinusitis with intracranial extension and marginal vancomycin susceptibility

Methicillin resistant Staphylococcus aureus (MRSA) is increasingly being described as a cause of acute sinusitis. We present a patient with acute MRSA sinusitis complicated by rapid intracranial extension, marginal vancomycin susceptibility (MIC = 2 mg/L), delayed drainage of intracranial abscess, and subsequent development of rifampin resistance. Given the relatively high risk of intracranial extension of severe acute bacterial sinusitis and high mortality associated with invasive MRSA infections, we suggest early surgical drainage of intracranial abscesses in these circumstances. We believe this is important given the limited intracranial penetration of currently available treatment options for MRSA, especially those with a vancomycin minimal inhibitory concentration (MIC) of ≥2 mg/L.

High vancomycin minimum inhibitory concentration and clinical outcomes in adults with methicillin-resistant Staphylococcus aureus infections: a meta-analysis

BACKGROUND

Patients with methicillin-resistant Staphylococcus aureus (MRSA) infections caused by isolates with a high but 'susceptible' minimum inhibitory concentration (MIC) to vancomycin may suffer poor outcomes. The aim of this study was to determine the association of high compared to low vancomycin MICs and clinical outcomes (treatment failure and mortality) in patients with MRSA infections.

METHODS

PubMed, the Cochrane Library, and electronic abstracts from meetings were queried from January 2000 to July 2010. Two reviewers independently screened titles and abstracts of studies evaluating outcomes of patients with MRSA infections, using broth microdilution (BMD) or the Etest to determine MIC, for full-text review. Patients participating in included studies were classified into two mutually exclusive groups: high MIC or low MIC. High MIC was defined as MIC ≥1mg/l by BMD or ≥1.5mg/l by Etest. Study-defined failure and mortality were assessed in each group.

RESULTS

Fourteen publications and six electronic abstracts met the inclusion criteria, with 2439 patients (1492 high MIC and 947 low MIC). There was no evidence of publication bias or heterogeneity. An increased risk of failure was observed in the high MIC group compared to the low MIC group (summary risk ratio (RR) 1.40, 95% confidence interval (CI) 1.15-1.71). The overall mortality risk was greater in the high MIC group than in the low MIC group (summary RR 1.42, 95% CI 1.08-1.87). Sensitivity analyses showed similar findings for failure (summary RR 1.37, 95% CI 1.09-1.73) and mortality (summary RR 1.46, 95% CI 1.06-2.01) for patients with bacteremia. The study quality was poor-to-moderate, and study-defined endpoints were variable.

CONCLUSIONS

A susceptible but high MIC to vancomycin is associated with increased mortality and treatment failure among patients with MRSA infections.

Mechanisms of daptomycin resistance in Staphylococcus aureus: role of the cell membrane and cell wall

The bactericidal, cell membrane-targeting lipopeptide antibiotic daptomycin (DAP) is an important agent in treating invasive Staphylococcus aureus infections. However, there have been numerous recent reports of development of daptomycin resistance (DAP-R) during therapy with this agent. The mechanisms of DAP-R in S. aureus appear to be quite diverse. DAP-R strains often exhibit progressive accumulation of single nucleotide polymorphisms in the multipeptide resistance factor gene (mprF) and the yycFG components of the yycFGHI operon. Both loci are involved in key cell membrane (CM) events, with mprF being responsible for the synthesis and outer CM translocation of the positively charged phospholipid, lysyl-phosphotidylglycerol (L-PG), while the yyc operon is involved in the generalized response to stressors such as antimicrobials. In addition, other perturbations of the CM have been identified in DAP-R strains, including extremes in CM order, resistance to CM depolarization and permeabilization, and reduced surface binding of DAP. Moreover, modifications of the cell wall (CW) appear to also contribute to DAP-R, including enhanced expression of the dlt operon (involved in d-alanylation of CW teichoic acids) and progressive CW thickening.

Impact of vancomycin minimum inhibitory concentration on clinical outcomes of patients with vancomycin-susceptible Staphylococcus aureus infections: a meta-analysis and meta-regression

Although the vancomycin minimum inhibitory concentration (VMIC) susceptibility breakpoint for Staphylococcus aureus was recently lowered to ≤2 mg/L, it is argued that isolates in the higher levels of the susceptible range may bear adverse clinical outcomes. Clinical outcomes (all-cause mortality and treatment failure) of patients with S. aureus infections by 'high-VMIC' (conventionally defined as VMIC >1 mg/L but ≤2 mg/L) and 'low-VMIC' (VMIC≤1 mg/L) isolates were compared by performing a systematic review and meta-analysis. The effect of potential confounders was assessed by univariate meta-regression analyses. In total, 33 studies (6210 patients) were included. Most studies were retrospective (28/33), used the Etest (22/33) and referred to meticillin-resistant S. aureus (MRSA) infections (26/33) and bacteraemia (23/33). Irrespective of VMIC testing method, meticillin resistance and site of infection, the high-VMIC group had higher mortality [relative risk (RR)=1.21 (95% confidence interval 1.03-1.43); 4612 patients] and more treatment failures [RR=1.67 (1.26-2.21); 2049 patients] than the low-VMIC group. The results were not affected by the potential confounders and were reproduced in the subset of patients with MRSA infections [mortality, RR=1.19 (1.02-1.40), 2956 patients; treatment failure, RR=1.69 (1.26-2.25), 1793 patients]. In conclusion, infection by vancomycin-susceptible S. aureus with VMIC>1mg/L appears to be associated with higher mortality than VMIC≤1mg/L. Further research is warranted to verify these results and to assess the impact of VMIC on meticillin-susceptible S. aureus infections. Evaluation of alternative antimicrobial agents also appears justified.

Methicillin-resistant Staphylococcus aureus bacteremia in hemodialysis and nondialysis patients

BACKGROUND/PURPOSE

Increased mortality has been reported in patients treated with vancomycin for methicillin-resistant Staphylococcus aureus (MRSA) bacteremia with high minimum inhibitory concentration (MIC) values within the susceptibility range. However, this finding has not been verified in hemodialysis patients, who have much higher invasive MRSA infection rates than nondialysis patients. We aimed at comparing vancomycin MICs between hemodialysis and nondialysis patients, and identifying predictors of high vancomycin MICs and infection-related mortality in hemodialysis patients with MRSA bacteremia.

METHODS

Patients with MRSA bacteremia from January 2008 through December 2009 were enrolled. Vancomycin MIC was determined for each first isolate using the Etest method. Clinical characteristics and vancomycin MICs were compared between hemodialysis and nondialysis patients. Factors associated with high vancomycin MIC (2 μg/mL) and infection-related mortality in hemodialysis patients were analyzed.

RESULTS

A total of 162 MRSA bacteremia episodes were identified. Forty-four (27.0%) isolates were obtained from hemodialysis patients and 118 (73.0%) from nondialysis patients. Diabetes (63.3% vs. 39.8%, p = 0.007) and prior vancomycin exposure in 30 days (31.8% vs. 12.7%, p = 0.005) were more prevalent in hemodialysis group than in nondialysis group. A higher prevalence of vancomycin MIC of 2 μg/mL was observed in hemodialysis group in comparison with nondialysis group (11.4% vs. 1.7%, p = 0.016). In following analyses of hemodialysis group, patients with initial presentation of septic shock had a higher risk of vancomycin MIC of 2 μg/mL than nonseptic shock patients (100.0% vs. 38.5% p = 0.014). Infection-related mortality was associated with age, Acute Physiology and Chronic Health Evaluation II (APACHE-II) score >15, presence of septic shock, receipt of mechanical ventilation, and failure to remove source of bacteremia in univariate analysis.

CONCLUSION

Hemodialysis patients with MRSA bacteremia are more likely to have a high vancomycin MIC (2 μg/mL) compared with nondialysis patients. Infection-related mortality is associated with the patient's clinical manifestations, including age, APACHE-II score >15, presence of septic shock, receipt of mechanical ventilation, and failure to remove source of bacteremia. Treatment selection should be tailored according to the patient's clinical condition.

Relationship of teicoplanin MICs to treatment failure in teicoplanin-treated patients with methicillin-resistant Staphylococcus aureus pneumonia

BACKGROUND/PURPOSE

The objective of this study was to determine the predictive value of teicoplanin minimal inhibitory concentrations (MICs) for treatment failure among patients with methicillin-resistant Staphylococcus aureus (MRSA) pneumonia.

METHODS

In this study, all patients with ≥1 tracheal aspirates or sputum cultures positive for MRSA admitted to the hospital between April 2011 and September 2011 were reviewed. We enrolled patients who are ≥18 years of age, with a diagnosis of pneumonia, and with a receipt of teicoplanin therapy throughout the course. The relationship between teicoplanin Etest MICs and treatment outcomes of MRSA pneumonia was analyzed to identify the breakpoint of teicoplanin MICs influencing treatment outcomes.

RESULTS

Of the 80 patients enrolled, 31 had a lower teicoplanin MIC level (<2.0 mg/L) and 49 had a higher MIC level (≥2.0 mg/L) for MRSA. The lower MIC group had a higher clinical resolution rate in 14 days [24 (77.4%) vs. 23 (46.9%), p = 0.007] and a lower treatment failure rate at the end of teicoplanin treatment [4 (12.9%) vs. 18 (36.7%), p = 0.020]. A comparison between the treatment success and failure groups showed that the former had a longer duration of teicoplanin use (18.76 ± 10.34vs.12.41 ± 5.65 days; p = 0.014). Results of a multivariate analysis showed that teicoplanin MICs ≥ 2.0 mg/Land shorter duration of teicoplanin therapy were independent risk factors for treatment failure.

CONCLUSION

A higher teicoplanin MIC value (≥2.0 mg/L) may predict the treatment failure among patients with teicoplanin-treated MRSA pneumonia.

Effect of reduced vancomycin susceptibility on clinical and economic outcomes in Staphylococcus aureus bacteremia

Reduced vancomycin susceptibility (RVS) may lead to poor clinical outcomes in Staphylococcus aureus bacteremia. The objective of this study was to evaluate the clinical and economic impact of RVS in patients with bacteremia due to S. aureus. A cohort study of patients who were hospitalized from December 2007 to May 2009 with S. aureus bacteremia was conducted within a university health system. Multivariable logistic regression and zero-truncated negative binomial regression models were developed to evaluate the association of RVS with 30-day in-hospital mortality, length of stay, and hospital charges. One hundred thirty-four (34.2%) of a total of 392 patients had bacteremia due to S. aureus with RVS as defined by a vancomycin Etest MIC of >1.0 μg/ml. Adjusted risk factors for 30-day in-hospital mortality included the all patient refined-diagnosis related group (APRDRG) risk-of-mortality score (odds ratio [OR], 7.11; 95% confidence interval [CI], 3.04 to 16.6), neutropenia (OR, 13.4; 95% CI, 2.46 to 73.1), white blood cell count (OR, 1.05; 95% CI, 1.01 to 1.09), immunosuppression (OR, 6.31; 95% CI, 1.74 to 22.9), and intensive care unit location (OR, 3.51; 95% CI, 1.65 to 7.49). In multivariable analyses, RVS was significantly associated with increased mortality in patients with S. aureus bacteremia as a result of methicillin-susceptible (OR, 3.90; 95% CI, 1.07 to 14.2) but not methicillin-resistant (OR, 0.53; 95% CI, 0.19 to 1.46) isolates. RVS was associated with greater 30-day in-hospital mortality in patients with bacteremia due to methicillin-susceptible S. aureus but not methicillin-resistant S. aureus. Further research is needed to identify optimal treatment strategies to reduce mortality associated with RVS in S. aureus bacteremia.

Reduced vancomycin susceptibility and staphylococcal cassette chromosome mec (SCCmec) type distribution in methicillin-resistant Staphylococcus aureus bacteraemia

OBJECTIVES

Recent epidemiological evidence suggests that genotypic and phenotypic characteristics that have typically distinguished community-associated methicillin-resistant Staphylococcus aureus (MRSA) and healthcare-associated MRSA strains may be evolving. The objective of this study was to examine the association between reduced vancomycin susceptibility (RVS) and staphylococcal cassette chromosome mec (SCCmec) type in MRSA bloodstream isolates.

METHODS

A cohort study of patients who were hospitalized from 2007 to 2009 with S. aureus bacteraemia was conducted within a university health system. Bivariable analyses were conducted to determine the association between RVS and SCCmec type, as well as other microbiological characteristics including Panton-Valentine leucocidin, accessory gene regulator (agr) dysfunction and vancomycin heteroresistance.

RESULTS

A total of 188 patients with MRSA bacteraemia were identified: 116 (61.7%) and 72 (38.3%) patients had infections due to healthcare-associated MRSA and community-associated MRSA, respectively. As defined by a vancomycin Etest MIC > 1.0 mg/L, the prevalence of RVS was 40.4%. Isolates with RVS were significantly more likely to be associated with SCCmec II compared with isolates without RVS (74.7% and 47.3%, respectively, P < 0.001), but not with Panton-Valentine leucocidin (P = 0.10), agr dysfunction (P = 0.19) or healthcare-associated infection (P = 0.36).

CONCLUSIONS

The results of our study demonstrate important microbiological characteristics among MRSA isolates characterized by RVS, including a significant association between SCCmec II and elevated vancomycin MIC. It is clear that the clinical and molecular epidemiology of MRSA is evolving, and further understanding of factors determining virulence will be important for the elucidation of optimal treatment approaches for associated infections.

Impact of vancomycin MIC creep on patients with methicillin-resistant Staphylococcus aureus bacteremia

BACKGROUND/PURPOSE

To date, vancomycin is still the standard treatment for methicillin-resistant Staphylococcus aureus (MRSA) infections, but minimum inhibitory concentration (MIC) creep is becoming a major concern. The aims of this study were to investigate trends in vancomycin use and MIC values over the last decade at our institute and to evaluate the outcomes of bacteremic patients infected with MRSA isolates with reduced vancomycin susceptibility.

METHODS

Vancomycin use and density were evaluated using the defined daily doses (DDD) method. Patients with MRSA bacteremia were enrolled retrospectively. Patient demographic data and clinical outcomes were analyzed. The first isolate from each patient was collected for E-testing in order to determine vancomycin MIC. MIC trends were assessed as MIC(50), MIC(90), and the geometric mean.

RESULTS

Vancomycin use has increased over the last decade. One hundred and forty patients were enrolled and their respective isolates were retrieved, including isolates from 45 patients in 2001, 46 patients in 2005, and 49 patients in 2009. The geometric mean (± standard deviation) of the vancomycin MIC for MRSA isolates obtained in 2009 was 1.39 ± 0.30 μg/mL, which is significantly higher than the mean vancomycin MIC obtained in 2001 (1.19 ± 0.34 μg/mL, p < 0.01) and 2005 (1.99 ± 0.25 μg/mL, p < 0.001). There were no significant differences in terms of the in-hospital mortality rate between patients with MRSA isolates with MICs ≥ 1.5 μg/mL or < 1.5 μg/mL.

CONCLUSION

We identified a significant upward trend in the use of vancomycin and its MIC over the last decade. This study shows that patients infected with MRSA isolates with high MICs (≥1.5 μg/mL) do not have a significantly higher mortality rate compared with isolates with low MICs (<1.5 μg/mL).

Derivation and validation of clinical prediction rules for reduced vancomycin susceptibility in Staphylococcus aureus bacteraemia

Reduced vancomycin susceptibility (RVS) may lead to poor clinical outcomes in Staphylococcus aureus bacteraemia. We conducted a cohort study of 392 patients with S. aureus bacteraemia within a university health system. The association between RVS, as defined by both Etest [vancomycin minimum inhibitory concentration (MIC) >1·0 μg/ml] and broth microdilution (vancomycin MIC ≥1·0 μg/ml), and patient and clinical variables were evaluated to create separate predictive models for RVS. In total, 134 (34·2%) and 73 (18·6%) patients had S. aureus isolates with RVS by Etest and broth microdilution, respectively. The final model for RVS by Etest included methicillin resistance [odds ratio (OR) 1·51, 95% confidence interval (CI) 0·97-2·34], non-white race (OR 0·67, 95% CI 0·42-1·07), healthcare-associated infection (OR 0·56, 95% CI 0·32-0·96), and receipt of any antimicrobial therapy ≤30 days prior to the culture date (OR 3·06, 95% CI 1·72-5·44). The final model for RVS by broth microdilution included methicillin resistance (OR 2·45, 95% CI 1·42-4·24), admission through the emergency department (OR 0·54, 95% CI 0·32-0·92), presence of an intravascular device (OR 2·24, 95% CI 1·30-3·86), and malignancy (OR 0·51, 95% CI 0·26-1·00). The availability of an easy and rapid clinical prediction rule for early identification of RVS can be used to help guide the timely and individualized management of these serious infections.

Predictors of mortality in Staphylococcus aureus Bacteremia

Staphylococcus aureus bacteremia (SAB) is an important infection with an incidence rate ranging from 20 to 50 cases/100,000 population per year. Between 10% and 30% of these patients will die from SAB. Comparatively, this accounts for a greater number of deaths than for AIDS, tuberculosis, and viral hepatitis combined. Multiple factors influence outcomes for SAB patients. The most consistent predictor of mortality is age, with older patients being twice as likely to die. Except for the presence of comorbidities, the impacts of other host factors, including gender, ethnicity, socioeconomic status, and immune status, are unclear. Pathogen-host interactions, especially the presence of shock and the source of SAB, are strong predictors of outcomes. Although antibiotic resistance may be associated with increased mortality, questions remain as to whether this reflects pathogen-specific factors or poorer responses to antibiotic therapy, namely, vancomycin. Optimal management relies on starting appropriate antibiotics in a timely fashion, resulting in improved outcomes for certain patient subgroups. The roles of surgery and infectious disease consultations require further study. Although the rate of mortality from SAB is declining, it remains high. Future international collaborative studies are required to tease out the relative contributions of various factors to mortality, which would enable the optimization of SAB management and patient outcomes.

The clinical significance of vancomycin minimum inhibitory concentration in Staphylococcus aureus infections: a systematic review and meta-analysis

BACKGROUND

Emerging data suggest that vancomycin may be less effective against serious methicillin-resistant Staphylococcus aureus (MRSA) infections with minimum inhibitory concentration (MIC) values at the higher end of the susceptibility range. The purpose of this review is to examine the strength of these associations.

METHODS

All relevant studies pertaining to treatment outcomes or mortality associated with vancomycin MIC were retrieved from the medical literature from January 1996 through August 2011 and analyzed according to Cochrane guidelines.

RESULTS

Of the 270 studies identified, 48 studies were reviewed, with 22 studies included in the final meta-analysis. Vancomycin MIC was significantly associated with mortality for MRSA infection irrespective of the source of infection or MIC methodology (odds ratio [OR], 1.64; 95% confidence interval [CI], 1.14-2.37; P < .01). This mortality association was predominantly driven by bloodstream infections (BSIs; OR, 1.58; 95% CI, 1.06-2.37; P = .03) and isolates with a vancomycin MIC of 2 μg/mL by Etest (OR, 1.72; 95% CI, 1.34-2.21; P < .01). Vancomycin MIC was significantly associated with treatment failure irrespective of source of infection or MIC methodology (OR, 2.69; 95% CI, 1.60-4.51; P < .01).

CONCLUSION

High vancomycin MIC was associated with a higher mortality rate in MRSA BSI. Thus, institutions should consider conducting Etest MICs on all MRSA BSI isolates. Although these data highlight concerns about vancomycin, currently, there are no data to support better survival rates with alternative antibiotics. Data are sorely needed to determine whether other agents can remedy these outcomes observed with vancomycin for MRSA infections with elevated vancomycin MIC values.

Reduced vancomycin susceptibility among clinical Staphylococcus aureus isolates ('the MIC Creep'): implications for therapy

Methicillin-resistant S. aureus (MRSA) has emerged as the most common hospital-acquired pathogen and is associated with increased morbidity and mortality compared with other strains. Vancomycin has been the cornerstone of treatment of patients with serious MRSA infections for some decades and while more than 99% of clinical S. aureus isolates remain susceptible to vancomycin, we are beginning to see strains of MRSA with reduced susceptibility. This review discusses this phenomenon, the predictors of infection with such forms of MRSA, and current and future management options.

Molecular typing and phenotype characterization of methicillin-resistant Staphylococcus aureus isolates from blood in Taiwan

Background

Staphylococcus aureus causes a variety of severe infections such as bacteremia and sepsis. At present, 60–80% of S. aureus isolates from Taiwan are methicillin resistant (MRSA). It has been shown that certain MRSA clones circulate worldwide. The goals of this study were to identify MRSA clones in Taiwan and to correlate the molecular types of isolates with their phenotypes.

Methods

A total of 157 MRSA isolates from bacteremic patients were collected from nine medical centers. They were typed based on polymorphisms in agr, SCCmec, MLST, spa, and dru. Phenotypes characterized included Panton-Valentine leucocidin (pvl), inducible macrolide-lincosamide-streptogramin B resistance (MLSBi), vancomycin (VA) and daptomycin (DAP) minimal inhibitory concentrations (MIC), and superantigenic toxin gene profiles. Difference between two consecutive samples was determined by Mann-Whitney-U test, and difference between two categorical variables was determined by Fisher's exact test.

Results

Four major MRSA clone complexes CC1, CC5, CC8, and CC59 were found, including 4 CC1, 9 CC5, 111 CC8, and 28 CC59 isolates. These clones had the following molecular types: CC1: SCCmecIV and ST573; CC5: SCCmecII and ST5; CC8: SCCmecIII, ST239, and ST241, and CC59: SCCmecIV, SCCmecV_T, ST59, and ST338. The toxin gene profiles of these clones were CC1: sec-seg-(sei)-sell-selm-(seln)-selo; CC5: sec-seg-sei-sell-selm-(seln)-selp-tst1; CC8: sea-selk-selq, and CC59: seb-selk-selq. Most isolates with SCCmecV_T, ST59, spat437, and dru11 types were pvl⁺ (13 isolates), while multidrug resistance (≥4 antimicrobials) were associated with SCCmecIII, ST239, spa t037, agrI, and dru14 (119 isolates) (p<0.001). One hundred and twenty four isolates with the following molecular types had higher VA MIC: SCCmecII and SCCmecIII; ST5, ST239, and ST241; spa t002, t037, and t421; dru4, dru10, dru12, dru13, and dru14 (p<0.05). No particular molecular types were found to be associated with MLSBi phenotype.

Conclusions

Four major MRSA clone complexes were found in Taiwan. Further studies are needed to delineate the evolution of MRSA isolates.

Prior vancomycin use is a risk factor for reduced vancomycin susceptibility in methicillin-susceptible but not methicillin-resistant Staphylococcus aureus bacteremia

OBJECTIVE

Staphylococcus aureus is a cause of community- and healthcare-acquired infections and is associated with substantial morbidity, mortality, and costs. Vancomycin minimum inhibitory concentrations (MICs) among S. aureus have increased, and reduced vancomycin susceptibility (RVS) may be associated with treatment failure. We aimed to identify clinical risk factors for RVS in S. aureus bacteremia.

DESIGN

Case-control.

SETTING

Academic tertiary care medical center and affiliated urban community hospital.

PATIENTS

Cases were patients with RVS S. aureus isolates (defined as vancomycin E-test MIC >1.0 μg/mL). Controls were patients with non-RVS S. aureus isolates.

RESULTS

Of 392 subjects, 134 (34.2%) had RVS. Fifty-eight of 202 patients (28.7%) with methicillin-susceptible S. aureus (MSSA) isolates had RVS, and 76 of 190 patients (40.0%) with methicillin-resistant S. aureus (MRSA) isolates had RVS (P = .02). In unadjusted analyses, prior vancomycin use was associated with RVS (odds ratio [OR], 2.08; 95% confidence interval [CI], 1.00-4.32; P = .046). In stratified analyses, there was significant effect modification by methicillin susceptibility on the association between vancomycin use and RVS (P =.04). In multivariable analyses, after hospital of admission and prior levofloxacin use were controlled for, the association between vancomycin use and RVS was significant for patients with MSSA infection (adjusted OR, 4.02; 95% CI, 1.11-14.50) but not MRSA infection (adjusted OR, 0.87; 95% CI, 0.36-2.13).

CONCLUSIONS

A substantial proportion of patients with S. aureus bacteremia had RVS. The association between prior vancomycin use and RVS was significant for patients with MSSA infection but not MRSA infection, suggesting a complex relationship between the clinical and molecular epidemiology of RVS in S. aureus.

Influence of teicoplanin MICs on treatment outcomes among patients with teicoplanin-treated methicillin-resistant Staphylococcus aureus bacteraemia: a hospital-based retrospective study

OBJECTIVES

Higher vancomycin MIC values (≥1.5 mg/L via Etest) may be associated with vancomycin treatment failure among patients with serious methicillin-resistant Staphylococcus aureus (MRSA) infections. As there were limited similar data for teicoplanin, this retrospective cohort study intended to determine the predictive value of teicoplanin MICs for treatment failure among patients with MRSA bacteraemia.

PATIENTS AND METHODS

All patients with at least one blood culture positive for MRSA admitted to the hospital between January 2010 and January 2011 were reviewed. Patients with an age ≥18 years and receipt of teicoplanin therapy throughout the course or receipt of <72 h of vancomycin therapy and then teicoplanin for >3 days were enrolled. Teicoplanin Etest(®) MICs and treatment outcomes for MRSA bacteraemia were reviewed to identify the breakpoint of teicoplanin MICs influencing treatment outcomes.

RESULTS

Of the 101 patients enrolled, 56 had a lower teicoplanin MIC (≤1.5 mg/L) for MRSA and 45 had a higher MIC (>1.5 mg/L) for MRSA. A lower teicoplanin MIC was associated with a favourable outcome [37 (66.1%) versus 13 (28.9%); P<0.001] and a lower rate of bloodstream infection-related mortality [15 (26.8%) versus 22 (48.9%); P=0.022]. Patients with chronic obstructive pulmonary disease, bacteraemic pneumonia or higher Pittsburgh bacteraemia score had an unfavourable outcome (P=0.028, 0.022 and <0.001, respectively). Multivariate analysis showed that teicoplanin MIC >1.5 mg/L, higher Pittsburgh bacteraemia score and bacteraemic pneumonia were independent risk factors for unfavourable outcome.

CONCLUSIONS

A higher teicoplanin MIC value (>1.5 mg/L) may predict an unfavourable outcome and higher mortality rate among teicoplanin-treated MRSA bacteraemic patients.

Antibiotic choice may not explain poorer outcomes in patients with Staphylococcus aureus bacteremia and high vancomycin minimum inhibitory concentrations

BACKGROUND

There are concerns about reduced efficacy of vancomycin in patients with Staphylococcus aureus bacteremia (SAB), especially when the minimum inhibitory concentration (MIC) nears the upper limit of the susceptible range.

METHODS

We examined the relationship between antibiotic treatment, 30-day mortality, and microbiologic parameters in a large Australasian cohort of patients with SAB.

RESULTS

We assessed 532 patients with SAB from 8 hospitals. All patients with methicillin-resistant S. aureus (MRSA) bacteremia were treated with vancomycin, and patients with methicillin-susceptible S. aureus (MSSA) bacteremia received either flucloxacillin or vancomycin. Increasing vancomycin MIC was associated with increased mortality in vancomycin-treated patients. However, even in patients with MSSA bacteremia treated with flucloxacillin, mortality was also higher if the vancomycin Etest MIC of their isolate was >1.5 μg/mL, compared with those with lower MIC isolates (26.8% vs 12.2%; P < .001). After adjustment in a multivariate model, age, hospital-onset SAB and vancomycin MIC were independently associated with mortality, but methicillin resistance and antibiotic choice were not.

CONCLUSIONS

We have confirmed an association between higher vancomycin MIC and increased mortality in patients with SAB, but surprisingly this relationship was not related to the antibiotic treatment received, suggesting that the use of vancomycin per se is not responsible for the poorer outcome.