Predictors of mortality in Staphylococcus aureus Bacteremia

Vancomycin 24-Hour Area under the Curve/Minimum Bactericidal Concentration Ratio as a Novel Predictor of Mortality in Methicillin-Resistant Staphylococcus aureus Bacteremia

While previous studies have examined the association between vancomycin (VAN) exposure and MIC with regard to outcomes in methicillin-resistant Staphylococcus aureus bacteremia (MRSA-B), none have explored if a relationship exists with the VAN minimum bactericidal concentration (MBC). The objective of this study was to evaluate the VAN 24-h area under the curve (AUC24)/MBC ratio as a pharmacodynamic predictor of mortality. This retrospective cohort study included patients treated with VAN for MRSA-B with the primary outcome of 30-day all-cause mortality. Data collected included patient demographics, comorbidities, antimicrobial treatment data, therapeutic drug levels, and laboratory and microbiological data. Vancomycin MICs and MBCs were determined by Etest (MIC only) and broth microdilution (BMD). The vancomycin AUC24 was determined by pharmacokinetic maximum a posteriori probability Bayesian (MAP-Bayesian) analysis. The most significant breakpoint for 30-day mortality was determined by classification and regression tree (CART) analysis. The association between pharmacodynamic parameters (VAN AUC24/MICBMD, VAN AUC24/MICEtest, and AUC24/MBCBMD) and mortality were determined by χ(2) and multivariable Poisson regression. Overall mortality in this cohort (n = 53) was 20.8% (n = 11/53), and all corresponding MRSA blood isolates were VAN susceptible (MIC range, 0.5 to 2 μg/ml; MIC50, 1 μg/ml; MIC90, 1 μg/ml). The CART-derived breakpoints for mortality were 176 (VAN AUC24/MBC) and 334 (VAN AUC24/MICBMD). In multivariable analysis, the association between a VAN AUC24/MBC of ≥176 and survival persisted, but VAN AUC24/MICBMD values (≥334 or ≥400) were not associated with improved mortality. In conclusion, VAN AUC24/MBC was a more important predictor of 30-day mortality than VAN AUC24/MIC for MRSA-B.

General Practitioner Antimicrobial Stewardship Programme Study (GAPS): protocol for a cluster randomised controlled trial

Background

There is a strong link between antibiotic consumption and the rate of antibiotic resistance. In Australia, the vast majority of antibiotics are prescribed by general practitioners, and the most common indication is for acute respiratory infections. The aim of this study is to assess if implementing a package of integrated, multifaceted interventions reduces antibiotic prescribing for acute respiratory infections in general practice.

Methods/design

This is a cluster randomised trial comparing two parallel groups of general practitioners in 28 urban general practices in Queensland, Australia: 14 intervention and 14 control practices. The protocol was peer-reviewed by content experts who were nominated by the funding organization.

This study evaluates an integrated, multifaceted evidence-based package of interventions implemented over a six month period. The included interventions, which have previously been demonstrated to be effective at reducing antibiotic prescribing for acute respiratory infections, are: delayed prescribing; patient decision aids; communication training; commitment to a practice prescribing policy for antibiotics; patient information leaflet; and near patient testing with C-reactive protein.

In addition, two sub-studies are nested in the main study: (1) point prevalence estimation carriage of bacterial upper respiratory pathogens in practice staff and asymptomatic patients; (2) feasibility of direct measures of antibiotic resistance by nose/throat swabbing.

The main outcome data are from Australia’s national health insurance scheme, Medicare, which will be accessed after the completion of the intervention phase. They include the number of antibiotic prescriptions and the number of patient visits per general practitioner for periods before and during the intervention. The incidence of antibiotic prescriptions will be modelled using the numbers of patients as the denominator and seasonal and other factors as explanatory variables. Results will compare the change in prescription rates before and during the intervention in the two groups of practices.

Semi-structured interviews will be conducted with the general practitioners and practice staff (practice nurse and/or practice manager) from the intervention practices on conclusion of the intervention phase to assess the feasibility and uptake of the interventions.

An economic evaluation will be conducted to estimate the costs of implementing the package, and its cost-effectiveness in terms of cost per unit reduction in prescribing.

Discussion

The results on the effectiveness, cost-effectiveness, acceptability and feasibility of this package of interventions will inform the policy for any national implementation.

Trial registration

The GAPS trial is registered under the Australian New Zealand Clinical Trials Register, reference number: ACTRN12615001128583 (registered 26/10/2015).

Outcome of Community-Acquired Staphylococcus aureus Bacteraemia in Patients with Diabetes: A Historical Population-Based Cohort Study

Background

Patients with diabetes (DM) experience increased risk of Staphylococcus aureus bacteraemia (SAB), but the prognostic impact of diabetes in patients with SAB remain unclear. Therefore, we investigated 30-day all-cause mortality in patients with and without DM.

Methods

Population-based medical databases were used to conduct a cohort study of all adult patients with community-acquired SAB in Northern Denmark, 2000–2011. Using Cox proportional hazards regression, we computed hazard ratios as estimates of 30-day mortality rate ratios (MRRs) among patients with and without DM. We further investigated whether the prognostic impact of DM differed among patients with and without recent preadmission healthcare contacts (within 30 days of the current hospitalization) and by age, sex, marital status, level of comorbidity, and DM-related characteristics (e.g., duration of DM and presence of DM complications).

Results

Among 2638 SAB patients, 713 (27.0%) had DM. Thirty-day cumulative mortality was 25.8% in patients with DM and 24.3% in patients without DM, for an adjusted MRR (aMRR) of 1.01 (95% confidence interval (CI), 0.84–1.20). In analyses with and without recent healthcare contacts, the corresponding aMRRs were 0.84 (95% CI, 0.62–1.14) and 1.13 (95% CI, 0.91–1.41), respectively. Compared to patients without DM, the aMRR was 0.94 (95% CI, 0.74–1.20) for male patients with DM and 1.13 (95% CI, 0.87–1.47) for female patients with DM. The prognostic influence of DM on mortality did not differ notably with age, level of comorbidity, or characteristics of patients with DM.

Conclusion

Patients with DM and community-acquired SAB did not experience higher 30-day mortality than patients without DM.

Epidemiology of antimicrobial resistance in bloodstream infections

Antimicrobial resistance in bacterial pathogens is a worldwide challenge leading high morbidity and mortality in clinical settings. Multidrug resistant patterns in gram-positive and -negative bacteria have resulted in difficult-to-treat or even untreatable infections with conventional antimicrobials. Since the early identification of causative microorganisms and their antimicrobial susceptibility patterns in patients with bacteremia and other serious infections is lacking in many healthcare institutions, broad spectrum antibiotics are liberally and mostly unnecessarily used. Such practice has, in turn, caused dramatic increases in emerging resistance and when coupled with poor practice of infection control, resistant bacteria can easily be disseminated to the other patients and the environment. Thus, availability of updated epidemiological data on antimicrobial resistance in frequently encountered bacterial pathogens will be useful not only for deciding on empirical treatment strategies, but also devising an effective antimicrobial stewardship program in hospitals.

The Impact of Infectious Disease Specialist Consultation for Staphylococcus aureus Bloodstream Infections: A Systematic Review

Staphylococcus aureus is a common cause of severe bloodstream infection. We performed a systematic review to assess whether consultation with infectious disease specialists decreased all-cause mortality or rate of complications of S aureus bloodstream infections. The review also assessed parameters associated with the quality of management of the infection. We searched for eligible studies in PubMed, Embase, Scopus, and clinical trials.gov as well as the references of included studies. We identified 22 observational studies and 1 study protocol for a randomized trial. A meta-analysis was not performed because of the high risk of bias in the included studies. The outcomes are reported in a narrative review. Most included studies reported survival benefit, in the adjusted analysis. Recommended management strategies were carried out significantly more often among patients seen by an infectious disease specialist. Trials, such as cluster-randomized controlled trials, can more validly assess the studies at low risk of bias.

Risk factors for long-term mortality of Staphylococcus aureus bacteremia

Staphylococcus aureus bacteremia (SAB) is a fatal disease. We aimed to describe risk factors for long-term mortality with SAB. We analyzed data from a retrospectively collected database including 1,692 patients with SAB. We considered variables of infection and background conditions for the analysis of long-term survival. The Kaplan-Meier procedure was used for analysis of long-term survival. Variables significantly associated with mortality were analyzed using a Cox regression model. We included 1,692 patients in the analysis. Patients were followed for up to 22 years. Within one year, 62% of patients died and within 5 years 72% died. A total of 82% of patients aged 65 years and older died within 5 years. Independent predictors of long-term mortality were older age (Hazard ratio 1.029, 95% confidence interval 1.022-1.036), female gender (HR 1.302, 95% CI 1.118-1.517), pneumonia or primary/ unknown source of infection (HR 1.441, 95% CI 1.230-1.689), dementia (HR 1.234, 95% CI 1.004-1.516), higher Charlson score (HR 1.155, 95% CI 1.115-1.196), shock at onset (HR 1.776, 95% CI 1.430-2.207) and arrival to hospitalization from an institution (HR 1.319, 95% CI 1.095-1.563). Long-term survival of patients older than 65 years and of women with SAB is severely curtailed.

Population-based epidemiology of Staphylococcus aureus bloodstream infection: clonal complex 30 genotype is associated with mortality

Staphylococcus aureus bloodstream infections (SABSI) are associated with a high burden of morbidity and mortality. The impact of specific S. aureus genotypes on outcome is unclear. The aim of this study was to evaluate the epidemiology and outcome of SABSI, with a special emphasis on the impact of bacterial clonal lineage on mortality. We conducted a 3-year population-based prospective study between 2011 and 2014, including 303 consecutive adult patients. Clinical data were obtained from interviews and medical records. S. aureus isolates were genotyped using DNA microarrays. The incidence rate of SABSI was 27.6 per 100,000 inhabitants [95 % confidence interval (CI) 24.6-31.0]. The median age of the patients was 71 years (interquartile range 56-81 years) and 61.4 % were male. Most SABSI (70.6 %) occurred in hospitals or associated to healthcare, and 34.1 % of these were associated with intravascular catheters. Only five (1.6 %) SABSI were caused by methicillin-resistant S. aureus (MRSA). The 30-day case fatality rate was 20.8 % (95 % CI 16.6-25.7). S. aureus clonal complex 30 [hazard ratio (HR) 3.9; 95 % CI 1.8-8.5, p = 0.001], unknown focus of infection (HR 4.5; 95 % CI 1.9-10.8, p = 0.001) and respiratory tract infection (HR 12.7; 95 % CI 4.6-34.6, p < 0.001) were independent predictors of mortality in a Cox regression analysis after adjusting for age, sex and underlying conditions. A high proportion of potential preventable SABSI calls for effective infection control measures. S. aureus clonal complex 30 genotype was associated with mortality in patients with bloodstream infections. The genetic basis underlying this association remains to be demonstrated.

Mortality predictors of Staphylococcus aureus bacteremia: a prospective multicenter study

Background

Staphylococcus aureus is one of the causes of both community and healthcare-associated bacteremia. The attributable mortality of S. aureus bacteremia (SAB) is still higher and predictors for mortality and clinical outcomes of this condition are need to be clarified. In this prospective observational study, we aimed to examine the predictive factors for mortality in patients with SAB in eight Turkish tertiary care hospitals.

Methods

Adult patients with signs and symptoms of bacteremia with positive blood cultures for S. aureus were included. All data for episodes of SAB including demographics, clinical and laboratory findings, antibiotics, and outcome were recorded for a 3-year (2010–2012) period. Cox proportional hazard model with forward selection was used to assess the independent effect of risk factors on mortality. A 28-day mortality was the dependent variable in the Cox regression analysis.

Results

A total of 255 episodes of SAB were enrolled. The median age of the patients was 59 years. Fifty-five percent of the episodes were considered as primary SAB and vascular catheter was the source of 42.1 %. Healthcare associated SAB was defined in 55.7 %. Blood cultures yielded methicillin-resistant S. aureus (MRSA) as a cause of SAB in 39.2 %. Initial empirical therapy was inappropriate in 28.2 %. Although overall mortality was observed in 52 (20.4 %), 28-day mortality rate was 15.3 %. Both the numbers of initial inappropriate empirical antibiotic treatment and the median hours to start an appropriate antibiotic between the cases of fatal outcome and survivors after fever onset were found to be similar (12/39 vs 60/216 and 6 vs 12 h, respectively; p > 0.05). High Charlson comorbidity index (CCI) score (p = 0.002), MRSA (p = 0.017), intensive care unit (ICU) admission (p < 0.001) and prior exposure to antibiotics (p = 0.002) all were significantly associated with mortality. The Cox analysis defined age [Hazard Ratio (HR) 1.03; p = 0.023], ICU admission (HR 6.9; p = 0.002), and high CCI score (HR 1.32; p = 0.002) as the independent predictive factors mortality.

Conclusions

The results of this prospective study showed that age, ICU stay and high CCI score of a patient were the independent predictors of mortality and MRSA was also significantly associated with mortality in SAB.

Cost-Effectiveness of a National Initiative to Improve Hand Hygiene Compliance Using the Outcome of Healthcare Associated Staphylococcus aureus Bacteraemia

BACKGROUND

The objective is to estimate the incremental cost-effectiveness of the Australian National Hand Hygiene Inititiave implemented between 2009 and 2012 using healthcare associated Staphylococcus aureus bacteraemia as the outcome. Baseline comparators are the eight existing state and territory hand hygiene programmes. The setting is the Australian public healthcare system and 1,294,656 admissions from the 50 largest Australian hospitals are included.

METHODS

The design is a cost-effectiveness modelling study using a before and after quasi-experimental design. The primary outcome is cost per life year saved from reduced cases of healthcare associated Staphylococcus aureus bacteraemia, with cost estimated by the annual on-going maintenance costs less the costs saved from fewer infections. Data were harvested from existing sources or were collected prospectively and the time horizon for the model was 12 months, 2011-2012.

FINDINGS

No useable pre-implementation Staphylococcus aureus bacteraemia data were made available from the 11 study hospitals in Victoria or the single hospital in Northern Territory leaving 38 hospitals among six states and territories available for cost-effectiveness analyses. Total annual costs increased by $2,851,475 for a return of 96 years of life giving an incremental cost-effectiveness ratio (ICER) of $29,700 per life year gained. Probabilistic sensitivity analysis revealed a 100% chance the initiative was cost effective in the Australian Capital Territory and Queensland, with ICERs of $1,030 and $8,988 respectively. There was an 81% chance it was cost effective in New South Wales with an ICER of $33,353, a 26% chance for South Australia with an ICER of $64,729 and a 1% chance for Tasmania and Western Australia. The 12 hospitals in Victoria and the Northern Territory incur annual on-going maintenance costs of $1.51M; no information was available to describe cost savings or health benefits.

CONCLUSIONS

The Australian National Hand Hygiene Initiative was cost-effective against an Australian threshold of $42,000 per life year gained. The return on investment varied among the states and territories of Australia.

One Dose of Staphylococcus aureus 4C-Staph Vaccine Formulated with a Novel TLR7-Dependent Adjuvant Rapidly Protects Mice through Antibodies, Effector CD4+ T Cells, and IL-17A

A rapidly acting, single dose vaccine against Staphylococcus aureus would be highly beneficial for patients scheduled for major surgeries or in intensive care units. Here we show that one immunization with a multicomponent S. aureus candidate vaccine, 4C-Staph, formulated with a novel TLR7-dependent adjuvant, T7-alum, readily protected mice from death and from bacterial dissemination, both in kidney abscess and peritonitis models, outperforming alum-formulated vaccine. This increased efficacy was paralleled by higher vaccine-specific and α-hemolysin-neutralizing antibody titers and Th1/Th17 cell responses. Antibodies played a crucial protective role, as shown by the lack of protection of 4C-Staph/T7-alum vaccine in B-cell-deficient mice and by serum transfer experiments. Depletion of effector CD4⁺ T cells not only reduced survival but also increased S. aureus load in kidneys of mice immunized with 4C-Staph/T7-alum. The role of IL-17A in the control of bacterial dissemination in 4C-Staph/T7-alum vaccinated mice was indicated by in vivo neutralization experiments. We conclude that single dose 4C-Staph/T7-alum vaccine promptly and efficiently protected mice against S. aureus through the combined actions of antibodies, CD4⁺ effector T cells, and IL-17A. These data suggest that inclusion of an adjuvant that induces not only fast antibody responses but also IL-17-producing cell-mediated effector responses could efficaciously protect patients scheduled for major surgeries or in intensive care units.

Antimicrobial activity of Melaleuca sp. oil against clinical isolates of antibiotics resistant Staphylococcus aureus

PURPOSE

To extract the Melaleuca sp. oil and to assess its in vitro inhibitory effect against Staphylococcus aureus isolates obtained from lower limb wounds and resistant to several antibiotics.

METHODS

A total of 14 test-tubes containing Mueller-Hinton broth were used to determine the Minimum Inhibitory Concentration (MIC). The following concentrations of the Melaleuca sp. oil were added to the first 11 tubes: 8; 4; 2; 1; 0.5; 0.2; 0.1; 0.05; 0.025; 0.0125 and 0.00625%. The 12th and 13th tubes, with and without oil, were used as the positive and negative controls, respectively. The experimental study was carried out in triplicate at 37ºC for 18 hours. The Minimum Bactericidal Concentration (MBC), able of killing all the microorganisms, was also determined. Two S. aureus isolates were obtained from lower limb wounds of female patients and the identification of the microorganisms (Staphylococcus aureus) and the test for susceptibility to the antimicrobial agents were carried out by automation using the apparatus MicroScan(r). After identification, the isolates were preserved in liquid Trypticase Soy medium, and inoculated for determination of the MIC and MBC.

RESULTS

The MIC was 0.2% and the MBC was 0.4%.

CONCLUSION

The Melaleuca sp. oil showed antimicrobial properties in vitro against strains isolated from lower limb wounds which were resistant to multiple antibiotics.

Emergence of Daptomycin-Resistant Staphylococcus aureus during Treatment

A 68-year-old man with persistent bacteremia accompanying a large iliopsoas abscess, vertebral osteomyelitis, discitis and central venous port infection caused by methicillin-resistant Staphylococcus aureus (MRSA) was admitted to our hospital. During the course of treatment, the emergence of a daptomycin (DAP)-resistant MRSA strain was confirmed; the minimum inhibitory concentration was 1 to 2 μg/mL for vancomycin and more than 1 μg/mL for DAP. Although the bacterial cell wall was not significantly thickened, an increased positive surface charge and single-nucleotide polymorphism within mprF have been confirmed in DAP-resistant strains. Still rare, but clinicians need to be cautious of the emergence of DAP-resistant MRSA during treatment.

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.

Contemporary genomic approaches in the diagnosis and typing of Staphylococcus aureus

Staphylococcus aureus is a major human pathogen, causing disease in both community and healthcare settings. Over the past two decades, the epidemiology of S. aureus disease has changed dramatically, with the emergence and spread of community-associated methicillin-resistant S. aureus clones. This epidemiological shift, coupled with the association between delayed antimicrobial therapy and increased mortality in S. aureus bacteraemia, has greatly facilitated advances in the rapid molecular diagnosis of S. aureus. Rapid molecular testing for S. aureus can greatly reduce laboratory turnaround time, and in some circumstances, may lead to improved clinical outcomes. In addition, advances in DNA sequencing technology and bioinformatic analysis have shed new lights on the molecular epidemiology and transmission dynamics of S. aureus. In this context, we provide an overview of the key advances in the molecular diagnosis and typing of S. aureus, with a particular focus on the clinical impact and utility of genomic technologies.

Rapid Detection of Methicillin-Resistant Staphylococcus aureus and Methicillin-Susceptible S. aureus Directly from Positive Blood Cultures by Use of the BD Max StaphSR Assay

The BD Max StaphSR assay is an automated qualitative in vitro diagnostic test for the direct detection and differentiation of methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA). A total of 460 specimens were tested, and the results were compared with standard culture-based identification. MRSA was detected in 48 samples (sensitivity of 100%; positive predictive value [PPV] of 100%). MSSA was detected in 112 samples (sensitivity of 99.1%; PPV of 100%), and 299 samples containing coagulase-negative staphylococcus and nonstaphylococcal species were negative by the BD Max StaphSR assay (specificity of 100%; negative predictive value [NPV] of 99.7 to 100%).

Staphylococcus aureus Bacteremia in Children: Changes During Eighteen Years

BACKGROUND

Staphylococcus aureus is a major cause of bacteremia in children and is associated with high morbidity. Complete data are lacking on the incidence, related risk factors and mortality associated with this infection.

METHODS

Descriptive study including patients younger than 16 years admitted to a tertiary reference hospital, with blood cultures exclusively positive for S. aureus. Four study periods were established: period 1, 1995-1999; period 2, 2000-2002; period 3, 2006-2008 and period 4, 2010-2012.

RESULTS

In total, 269 episodes of S. aureus bacteremia (SAB) occurred in 242 patients. Over the total time studied, the incidence increased from 1.3 to 3.3 cases per 1000 patients hospitalized (relative risk: 2.71; 95% confidence interval: 1.85-3.95) and mortality decreased from 18% to 6% (P = 0.008). There were no differences in the resistance patterns of S. aureus strains. The prevalence of methicillin-resistant S. aureus (MRSA) increased from 3% to 13% between periods 1 and 2 and decreased from 14% to 3% between periods 3 and 4 (P = 0.011). The 30-day cumulative mortality was 3.3%, and the SAB-related mortality was 1.5%. Nosocomial acquisition and age 12-16 years were factors independently related with death on multivariate analysis.

CONCLUSIONS

The incidence of SAB tripled during the years studied but remained stable in the last period. Antimicrobial resistances did not increase. Although a decrease in mortality was documented, approximately half the 30-day cumulative mortality was caused by SAB.

Antimicrobial Mechanisms of Macrophages and the Immune Evasion Strategies of Staphylococcus aureus

Habitually professional phagocytes, including macrophages, eradicate microbial invaders from the human body without overt signs of infection. Despite this, there exist select bacteria that are professional pathogens, causing significant morbidity and mortality across the globe and Staphylococcus aureus is no exception. S. aureus is a highly successful pathogen that can infect virtually every tissue that comprises the human body causing a broad spectrum of diseases. The profound pathogenic capacity of S. aureus can be attributed, in part, to its ability to elaborate a profusion of bacterial effectors that circumvent host immunity. Macrophages are important professional phagocytes that contribute to both the innate and adaptive immune response, however from in vitro and in vivo studies, it is evident that they fail to eradicate S. aureus. This review provides an overview of the antimicrobial mechanisms employed by macrophages to combat bacteria and describes the immune evasion strategies and some representative effectors that enable S. aureus to evade macrophage-mediated killing.

When sepsis persists: a review of MRSA bacteraemia salvage therapy

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

Staphylococcus aureus bacteraemia associated with injected new psychoactive substances

Injecting drug use is often associated with deep-seated infection. In Lothian in Scotland there has been a recent increase in the use of injected new psychoactive substances (NPS). Patients who have injected NPS have presented with Staphylococcus aureus bacteraemia (SAB) with life-threatening complications. We describe a unique case-series of 14 episodes of SAB in ten patients. Users of injected NPS had a significantly higher incidence of endocarditis and cavitating pulmonary lesions (P < 0·05) compared to those who inject only opiates. Cases of SAB in people who inject NPS have contributed to a significant rise in the overall incidence of SAB in people who inject drugs (P < 0·05) which has in turn impacted on the ability of Lothian to meet national targets for reducing the incidence of SAB.

Memory Th1 Cells Are Protective in Invasive Staphylococcus aureus Infection

Mechanisms of protective immunity to Staphylococcus aureus infection in humans remain elusive. While the importance of cellular immunity has been shown in mice, T cell responses in humans have not been characterised. Using a murine model of recurrent S. aureus peritonitis, we demonstrated that prior exposure to S. aureus enhanced IFNγ responses upon subsequent infection, while adoptive transfer of S. aureus antigen-specific Th1 cells was protective in naïve mice. Translating these findings, we found that S. aureus antigen-specific Th1 cells were also significantly expanded during human S. aureus bloodstream infection (BSI). These Th1 cells were CD45RO⁺, indicative of a memory phenotype. Thus, exposure to S. aureus induces memory Th1 cells in mice and humans, identifying Th1 cells as potential S. aureus vaccine targets. Consequently, we developed a model vaccine comprising staphylococcal clumping factor A, which we demonstrate to be an effective human T cell antigen, combined with the Th1-driving adjuvant CpG. This novel Th1-inducing vaccine conferred significant protection during S. aureus infection in mice. This study notably advances our understanding of S. aureus cellular immunity, and demonstrates for the first time that a correlate of S. aureus protective immunity identified in mice may be relevant in humans.

Staphylococcus aureus is a leading cause of skin, soft tissue and bone infections and, most seriously, bloodstream infection. When S. aureus does get into the bloodstream, it is more likely to kill than any other bacterial infection, despite all the treatments modern medicine has to offer. It has thus far developed resistance to all antibiotics licensed to treat it. Thus, there is an urgent need to develop a vaccine against S. aureus. However, such a vaccine remains elusive. This is largely due to the fact that we have a very limited understanding of how our immune system fights this infection. Here, we examine how certain T cells of the mouse immune system effectively recognise and respond to S. aureus, and show that transferring these cells to other mice improves their ability to clear infection. We then demonstrate that a vaccine which drives these specific T cells also improves clearance of infection. Until recently, it was not known if human T cells could recognise and respond to S. aureus. Here we show, for the first time, that these cells are expanded in patients with S. aureus bloodstream infection, and suggest that they should be targeted in anti-S. aureus vaccines.

Nonredundant Roles of Interleukin-17A (IL-17A) and IL-22 in Murine Host Defense against Cutaneous and Hematogenous Infection Due to Methicillin-Resistant Staphylococcus aureus

Staphylococcus aureus is the leading cause of skin and skin structure infections (SSSI) in humans. Moreover, the high frequency of recurring SSSI due to S. aureus, particularly methicillin-resistant S. aureus (MRSA) strains, suggests that infection induces suboptimal anamnestic defenses. The present study addresses the hypothesis that interleukin-17A (IL-17A) and IL-22 play distinct roles in immunity to cutaneous and invasive MRSA infection in a mouse model of SSSI. Mice were treated with specific neutralizing antibodies against IL-17A and/or IL-22 and infected with MRSA, after which the severity of infection and host immune response were determined. Neutralization of either IL-17A or IL-22 reduced T cell and neutrophil infiltration and host defense peptide elaboration in lesions. These events corresponded with increased abscess severity, MRSA viability, and CFU density in skin. Interestingly, combined inhibition of IL-17A and IL-22 did not worsen abscesses but did increase gamma interferon (IFN-γ) expression at these sites. The inhibition of IL-22 led to a reduction in IL-17A expression, but not vice versa. These results suggest that the expression of IL-17A is at least partially dependent on IL-22 in this model. Inhibition of IL-17A but not IL-22 led to hematogenous dissemination to kidneys, which correlated with decreased T cell infiltration in renal tissue. Collectively, these findings indicate that IL-17A and IL-22 have complementary but nonredundant roles in host defense against cutaneous versus hematogenous infection. These insights may support targeted immune enhancement or other novel approaches to address the challenge of MRSA infection.

Intracellular replication of Staphylococcus aureus in mature phagolysosomes in macrophages precedes host cell death, and bacterial escape and dissemination

The success of Staphylococcus aureus as a pathogen is partly attributable to its ability to thwart host innate immune responses, which includes resisting the antimicrobial functions of phagocytes. Here, we have studied the interaction of methicillin-resistant S. aureus (MRSA) strain USA300 with murine RAW 264.7 and primary human macrophages using molecular imaging and single cell analysis to obtain an unprecedented understanding of the interaction between the macrophage and MRSA. Herein we demonstrate that macrophages fail to control intracellular infection by MRSA USA300 despite trafficking the bacteria into mature phagolysosomes. Using fluorescence-based proliferation assays we also show that intracellular staphylococci proliferate and that replication commences while the bacteria are residing in mature phagolysosomes hours after initial phagocytosis. Finally, live-cell fluorescence video microscopy allowed for unprecedented visual insight into the escape of MRSA from macrophages, demonstrating that the macrophages die through a pathway characterized by membrane blebbing and activation of caspase-3 followed by acquisition of the vital dye propidium iodide. Moreover, cell death precedes the emergence of MRSA from infected macrophages, and these events can be ablated by prolonged exposure of infected phagocytes to gentamicin.

Impact of efflux in the development of multidrug resistance phenotypes in Staphylococcus aureus

Background

Efflux has been recognized as a resistance mechanism to antimicrobials in Staphylococcus aureus; however its role on the development of clinically relevant resistance is still poorly characterized. This study aimed to examine the impact of efflux on development of resistance to fluoroquinolones and other antimicrobials in S. aureus strains representing relevant phenotypes in terms of antibiotic susceptibility and efflux activity.

Methods

Two closely related methicillin- and ciprofloxacin-resistant Staphylococcus aureus clinical strains, with different efflux capacity and the pan-susceptible strain ATCC25923 were exposed to constant concentrations of the efflux pump (EP) substrates ciprofloxacin, ethidium bromide and cetrimide. Parental and exposed strains were tested regarding their susceptibility towards antibiotics, biocides and ethidium bromide, efflux capacity and levels of EP gene expression. Occurrence of resistance-associated mutations was screened by sequencing.

Results

Multidrug resistance phenotypes emerged upon exposure, independently of the substrate or its concentration, which were correlated with increased efflux capacity of the exposed strains. The temporal pattern of EP gene expression disclosed an early-response with high expression of several genes, followed by a late-response, characterized by overexpression of specific genes. The overall cell response was more pronounced for strains with an initial basal efflux activity. Remarkably, detection of the IS256 element in the promoter regions of mgrA and norA, in some cases associated with increased gene expression, suggests that these genes may be hot spots for IS256 insertion events.

The results obtained with exposure of ATCC25923 to ciprofloxacin were particularly striking, revealing a step-wise development of fluoroquinolone resistance, with a first efflux-mediated response, followed by the occurrence of a mutation in grlA that resulted in phenotypic resistance. Additionally, challenge by non-fluoroquinolone agents, particularly cetrimide, promoted cross resistance to fluoroquinolones, revealing the potential role of biocides as selective pressure for the emergence of resistance to these antibiotics.

Conclusions

This study reveals efflux as a significant component of S. aureus resistance to fluoroquinolones and biocides and as a primary mechanism to withstand stress imposed by antimicrobials. This efflux-mediated response can result in the emergence of multidrug resistance in healthcare environments and should be taken into account in the management of this major pathogen.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-015-0572-8) contains supplementary material, which is available to authorized users.

Impact of area under the concentration-time curve to minimum inhibitory concentration ratio on vancomycin treatment outcomes in methicillin-resistant Staphylococcus aureus bacteraemia

There have been few clinical studies on the association between the vancomycin 24-h area under the concentration-time curve (AUC24) to minimum inhibitory concentration (MIC) ratio and vancomycin treatment outcomes in methicillin-resistant Staphylococcus aureus (MRSA) infections. To examine this association and to establish a suitable cut-off value for AUC24/MIC, a multicentre prospective observational study was conducted in patients with MRSA bacteraemia. Data were collected on all patients aged ≥18 years with MRSA bacteraemia treated with vancomycin for ≥72 h without dialysis. The MIC was determined by broth microdilution (BMD) and Etest. Treatment failure was defined as (i) 30-day mortality, (ii) persistent bacteraemia (≥7 days) and (iii) recurrence (≤30 days after completion of therapy). AUC24 was estimated by a Bayesian approach based on individual vancomycin concentrations. The AUC24/MIC cut-off value for differentiating treatment success and failure was calculated by Classification and Regression Tree (CART) analysis. In total, 117 patients were enrolled, among which vancomycin treatment failure occurred in 38 (32.5%). In univariate analysis, high vancomycin MIC and low trough levels were unrelated to treatment outcomes. In the CART analysis, low vancomycin AUC24/MIC [<392.7 (BMD) and <397.2 (Etest)] was associated with treatment failure. In multivariate analysis, low AUC24/MIC was a risk factor for treatment failure [adjusted odds ratio (aOR)=3.50, 95% confidence interval (CI) 1.39-8.82 by BMD; aOR=5.61, 95% CI 2.07-15.24 by Etest]. AUC24/MIC is associated with vancomycin treatment outcomes in MRSA bacteraemia, and seeking individualised AUC24/MIC ratios above target (>400) may improve treatment outcomes.

[Impact of an infectious diseases consultation service on the quality of care and the survival of patients with infectious diseases]

While trained infectious diseases (ID) specialists are regularly involved in inpatient and outpatient care in the United States and Canada, these specialized services are only rarely established in Germany. This article aims to summarize the findings of numerous studies that investigated the impact of ID consultation services on patient care and outcome in patients suffering from infectious diseases. The strongest evidence for a clinical benefit is found in the context of Staphylococcus aureus bacteremia (SAB), where in-hospital- and day-30 mortality was significantly and consistently reduced by about 40% in patients that were evaluated and treated in cooperation with an ID physician. Furthermore, studies revealed that this effect was associated with an improved adherence to standards of care. Newer studies show a reduced length of hospital stay due to ID consultations, especially if patients are evaluated early in the course of their hospital stay. Of note, informal or curbside consultations do not seem to be equivalent to a formal ID consultation with bedside patient evaluation. Studies in other patient groups (solid organ transplant recipients or intensive care unit patients) or in the context of other infections (infective endocarditis, pneumonia, other bloodstream infections) also revealed positive effects of ID consultations. Higher rates of appropriate empirical and targeted antimicrobial treatments and de-escalation strategies due to successful pathogen identification were documented. These modifications resulted in lower treatment costs and decreased antimicrobial resistance development. Although there are methodological limitations in single studies, we consider the consistent and reproducible positive effects of ID consultations shown in studies in different countries and health care systems as convincing evidence for the improved quality of care and treatment outcomes in patients with infectious diseases. Thus, strong consideration should be given to establish ID consultation services in small and medium sized hospitals as well.

Biodegradable Antimicrobial Polycarbonates with In Vivo Efficacy against Multidrug-Resistant MRSA Systemic Infection

The threat of multidrug resistance requires development of new medicines to treat methicillin-resistant Staphylococcus aureus (MRSA) infection. The biodegradable polycarbonates that have broad-spectrum antibacterial activity and show the highest selectivity toward S. aureus are studied for their antibacterial properties against clinically isolated MRSA and toxicity both in vitro and in vivo. Minimum inhibitory concentrations of the polymers are demonstrated to be much lower than those of cefoxitin (a commonly used antibiotic) against all 31 isolates but slightly higher than those of vancomycin, a last resort medication for treating severe Gram-positive drug-resistant bacterial infections. Both polymers show low hemolytic activity toward human red blood cells, making them highly selective toward MRSA in vitro. A time-kill study reveals that these polymers have high bactericidal efficiency and eradicate MRSA more rapidly than vancomycin. Results from a resistance development study also attests to the polymers low tendency toward resistance. Furthermore, the in vivo study shows that one of the polymers is highly efficacious in a mouse systemic infection model, and reduced MRSA counts in the blood more promptly than vancomycin. The administration of the polymer to mice further indicates that it did not cause any dysfunctions of liver and kidney as well as blood electrolytes. This is the first example of a polymeric therapeutics for treating systemic MRSA infection. Taken together, the biodegradable antimicrobial polycarbonate may be a better candidate for treating MRSA infection.

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.

Treatment of methicillin-sensitive Staphylococcus aureus bacteremia secondary to septic phlebitis using dalbavancin

WHAT IS KNOWN AND OBJECTIVE

Treatment of bacteremia due to Staphylococcus aureus often requires prolonged therapy leading to increased hospital lengths of stay and associated costs. For certain patients, referral to an outpatient parenteral antimicrobial therapy (OPAT) programme serves as an alternative to increased inpatient length of stay. We report an alternative to OPAT using dalbavancin for the treatment of methicillin-sensitive Staphylococcus aureus (MSSA).

CASE SUMMARY

A 54-year-old Caucasian man was brought to the emergency department from a rehabilitation centre with altered mental status and possible seizure. A peripheral intravenous catheter was placed in the left forearm, and the patient was transferred to the intensive care unit (ICU) for management of his acute psychosis, possible seizure and hyponatremia. Seven days into admission, the patient became febrile thought to be secondary to septic phlebitis of the forearm. Blood cultures were taken and organism identification using Nanosphere Verigene^® BC-GP rapid diagnostic testing resulted in MSSA. The patient received treatment with cefazolin with a planned treatment duration of 14 days but because of the patient's history of alcohol abuse, psychosis requiring hospitalization via the Baker Act, and history of non-compliance to follow-up appointments, the patient was deemed ineligible for OPAT. Due to the limited treatment options, therapy for MSSA bacteremia was changed on day 6 of cefazolin therapy to dalbavancin to complete the 14-day treatment duration. Blood cultures were negative at the end of treatment and no relapse of infection occurred.

WHAT IS NEW AND CONCLUSION

To our knowledge, this is the first case report using dalbavancin in clinical practice for the treatment of MSSA bacteremia secondary to septic phlebitis. This report highlights the potential role of the newer lipoglycopeptides, such as dalbavancin, in treating patients who require long-term parenteral antimicrobial therapy and are ineligible for treatment via OPAT.

Protection of mice against Staphylococcus aureus infection by a recombinant protein ClfA-IsdB-Hlg as a vaccine candidate

Staphylococcus aureus is one of the most important causes of nosocomial infections. An effective vaccine to prevent S. aureus infections is urgently required due to the dramatic increase in the number of antibiotic-resistant strains. In this report, we evaluated a newly recombinant protein composed of selected antigenic regions of clumping factor A (ClfA), iron surface determinant B (IsdB) and gamma hemolysin B (HlgB) of S. aureus and sequence coding for hydrophobic linkers between three domains. The recombinant gene was constructed in pET-28a (+) and expressed in Escherichia coli BL21. In addition, sequence coding for a His(6)-tag was added followed by a hybrid procedure of nickel chelate protein purification. Immunization of BALB/c mice with the recombinant protein ClfA-IsdB-Hlg evoked antigen-specific antibodies that could opsonize S. aureus cells, enhancing in vitro phagocytosis by macrophages. Vaccination with the recombinant protein also reduced the bacterial load recovered from mice spleen samples and increased survival following the intraperitoneal challenge with pathogenic S. aureus compared to the control mice. Our results showed that the recombinant protein ClfA-IsdB-Hlg is a promising vaccine candidate for the prevention of S. aureus bacteremia infections.

The use of molecular methods for the detection and identification of methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen in many hospitals and long-term care facilities as well as in the community. To limit the spread of MRSA, early detection and proper treatment are essential. Because conventional culture as gold standard is time consuming, new techniques such as PCR-based and hybridization assays have emerged for the rapid detection of MRSA. This review will focus on the currently available molecular-based assays and on their utility and performance for detection of S. aureus, of its virulence factors and of the markers for acquired resistance.

Staphylococcus aureus infections: epidemiology, pathophysiology, clinical manifestations, and management

Staphylococcus aureus is a major human pathogen that causes a wide range of clinical infections. It is a leading cause of bacteremia and infective endocarditis as well as osteoarticular, skin and soft tissue, pleuropulmonary, and device-related infections. This review comprehensively covers the epidemiology, pathophysiology, clinical manifestations, and management of each of these clinical entities. The past 2 decades have witnessed two clear shifts in the epidemiology of S. aureus infections: first, a growing number of health care-associated infections, particularly seen in infective endocarditis and prosthetic device infections, and second, an epidemic of community-associated skin and soft tissue infections driven by strains with certain virulence factors and resistance to β-lactam antibiotics. In reviewing the literature to support management strategies for these clinical manifestations, we also highlight the paucity of high-quality evidence for many key clinical questions.

Population-based epidemiology and microbiology of community-onset bloodstream infections

Bloodstream infection (BSI) is a major cause of infectious disease morbidity and mortality worldwide. While a positive blood culture is mandatory for establishment of the presence of a BSI, there are a number of determinants that must be considered for establishment of this entity. Community-onset BSIs are those that occur in outpatients or are first identified <48 h after admission to hospital, and they may be subclassified further as health care associated, when they occur in patients with significant prior health care exposure, or community associated, in other cases. The most common causes of community-onset BSI include Escherichia coli, Staphylococcus aureus, and Streptococcus pneumoniae. Antimicrobial-resistant organisms, including methicillin-resistant Staphylococcus aureus and extended-spectrum β-lactamase/metallo-β-lactamase/carbapenemase-producing Enterobacteriaceae, have emerged as important etiologies of community-onset BSI.

Staphylococcus aureus Bloodstream Infection and Endocarditis--A Prospective Cohort Study

OBJECTIVES

To update the epidemiology of S. aureus bloodstream infection (SAB) in a high-income country and its link with infective endocarditis (IE).

METHODS

All consecutive adult patients with incident SAB (n = 2008) were prospectively enrolled between 2009 and 2011 in 8 university hospitals in France.

RESULTS

SAB was nosocomial in 54%, non-nosocomial healthcare related in 18% and community-acquired in 26%. Methicillin resistance was present in 19% of isolates. SAB Incidence of nosocomial SAB was 0.159/1000 patients-days of hospitalization (95% confidence interval [CI] 0.111-0.219). A deep focus of infection was detected in 37%, the two most frequent were IE (11%) and pneumonia (8%). The higher rates of IE were observed in injecting drug users (IE: 38%) and patients with prosthetic (IE: 33%) or native valve disease (IE: 20%) but 40% of IE occurred in patients without heart disease nor injecting drug use. IE was more frequent in case of community-acquired (IE: 21%, adjusted odds-ratio (aOR) = 2.9, CI = 2.0-4.3) or non-nosocomial healthcare-related SAB (IE: 12%, aOR = 2.3, CI = 1.4-3.5). S. aureus meningitis (IE: 59%), persistent bacteremia at 48 hours (IE: 25%) and C-reactive protein > 190 mg/L (IE: 15%) were also independently associated with IE. Criteria for severe sepsis or septic shock were met in 30% of SAB without IE (overall in hospital mortality rate 24%) and in 51% of IE (overall in hospital mortality rate 35%).

CONCLUSION

SAB is still a severe disease, mostly related to healthcare in a high-income country. IE is the most frequent complication and occurs frequently in patients without known predisposing conditions.

Improving Clinical Outcomes in Patients With Methicillin-Sensitive Staphylococcus aureus Bacteremia and Reported Penicillin Allergy

BACKGROUND

Methicillin-sensitive Staphylococcus aureus (MSSA) bacteremia is a morbid infection. First-line MSSA therapies (nafcillin, oxacillin, cefazolin) are generally avoided in the 10% of patients reporting penicillin (PCN) allergy, but most of these patients are not truly allergic. We used a decision tree with sensitivity analyses to determine the optimal evaluation and treatment for patients with MSSA bacteremia and reported PCN allergy.

METHODS

Our model simulates 3 strategies: (1) no allergy evaluation, give vancomycin (Vanc); (2) allergy history-guided treatment: if history excludes anaphylactic features, give cefazolin (Hx-Cefaz); and (3) complete allergy evaluation with history-appropriate PCN skin testing: if skin test negative, give cefazolin (ST-Cefaz). Model outcomes included 12-week MSSA cure, recurrence, and death; allergic reactions including major, minor, and potentially iatrogenic; and adverse drug reactions.

RESULTS

Vanc results in the fewest patients achieving MSSA cure and the highest rate of recurrence (67.3%/14.8% vs 83.4%/9.3% for Hx-Cefaz and 84.5%/8.9% for ST-Cefaz) as well as the greatest frequency of allergic reactions (3.0% vs 2.4% for Hx-Cefaz and 1.7% for ST-Cefaz) and highest rates of adverse drug reactions (5.2% vs 4.6% for Hx-Cefaz and 4.7% for ST-Cefaz). Even in a "best case for Vanc" scenario, Vanc yields the poorest outcomes. ST-Cefaz is preferred to Hx-Cefaz although sensitive to input variations.

CONCLUSIONS

Patients with MSSA bacteremia and a reported PCN allergy should have the allergy addressed for optimal treatment. Full allergy evaluation with skin testing seems to be preferred, although more data are needed.

The search for endocarditis in patients with candidemia: a systematic recommendation for echocardiography? A prospective cohort

Most current guidelines do not recommend systematic screening with echocardiography in patients with candidemia, as Candida infective endocarditis (CIE) is considered an uncommon disease. During the study period, we recommended echocardiography systematically to all candidemic patients that did not have contraindications and accepted to participate in the study. We intended to assess the incidence of unrecognized CIE in adult patients with candidemia. Our institution is a tertiary teaching hospital in which we follow all patients with candidemia. From January 2007 to October 2012, echocardiography was systematically recommended to suitable candidates. We recorded 263 cases of candidemia in adult patients. Echocardiography was not performed in 76 of these patients for the following reasons: patients had died when blood cultures became positive (17), patients were critically or terminally ill (38), or the patient or physician refused the procedure (21). The remaining 187 patients constitute the basis of this report. CIE was diagnosed in 11 cases (4.2 % of the whole candidemic population and 5.9 % of the population with echocardiographic study). The results of transthoracic echocardiography (TTE) suggested infective endocarditis (IE) in 5/172 patients (2.9 %), and the result of transesophageal echocardiography (TEE) was positive in 10/87 (11.5 %). Among 11 confirmed cases of CIE, the disease was clinically unsuspected in three patients. At least 4.2 % of all candidemic patients have CIE. CIE is frequently clinically unsuspected and echocardiography is required to demonstrate a high proportion of cases.

Incidence and outcome of Staphylococcus aureus endocarditis--a 10-year single-centre northern European experience

Staphylococcus aureus is a leading cause of infective endocarditis. Little has been published on the outcome and epidemiology of S. aureus endocarditis (SAE) in the twenty-first century. Our aim was to evaluate the short-term and long-term outcome of SAE in Stockholm, Sweden, and assess its incidence over time. Patients treated for SAE from January 2004 through December 2013 were retrospectively identified at the Karolinska University Hospital. Clinical data were obtained from medical records and the diagnosis was verified according to the modified Duke criteria. Of 245 SAE cases, 152 (62%) were left-sided and 120 (49%) occurred in intravenous drug users. The calculated incidence in Stockholm County was 1.56/100 000 person-years, increasing from 1.28 in 2004-08 to 1.82/100 000 person-years in 2009-13 (p 0.002). In-hospital and 1-year mortality rates were 9.0% (22/245) and 19.5% (46/236), respectively. Age (OR 1.06 per year) and female sex (OR 3.0) were independently associated with in-hospital mortality in multivariate analysis. Involvement of the central nervous system (CNS) was observed in 30 (12%) patients, and valvular surgery was performed during hospitalization in 37 (15%). In left-sided endocarditis the strongest predictors for surgery were severe valvular insufficiency (OR 8.9), lower age (OR 1.07 per year) and no intravenous drug use (OR 10.7), and for CNS involvement lower age (OR 1.04 per year). In conclusion we noted low mortality, low CNS complication rate, and low valvular surgery frequency associated with SAE in our setting. The incidence was high and increased over time. The study provides an update on the outcome and epidemiology of SAE in the twenty-first century.

Strain Specific Phage Treatment for Staphylococcus aureus Infection Is Influenced by Host Immunity and Site of Infection

The response to multi-drug resistant bacterial infections must be a global priority. While mounting resistance threatens to create what the World Health Organization has termed a “post-antibiotic era”, the recent discovery that antibiotic use may adversely impact the microbiome adds further urgency to the need for new developmental approaches for anti-pathogen treatments. Methicillin-resistant Staphylococcus aureus (MRSA), in particular, has declared itself a serious threat within the United States and abroad. A potential solution to the problem of antibiotic resistance may not entail looking to the future for completely novel treatments, but instead looking into our history of bacteriophage therapy. This study aimed to test the efficacy, safety, and commercial viability of the use of phages to treat Staphylococcus aureus infections using the commercially available phage SATA-8505. We found that SATA-8505 effectively controls S. aureus growth and reduces bacterial viability both in vitro and in a skin infection mouse model. However, this killing effect was not observed when phage was cultured in the presence of human whole blood. SATA-8505 did not induce inflammatory responses in peripheral blood mononuclear cultures. However, phage did induce IFN gamma production in primary human keratinocyte cultures and induced inflammatory responses in our mouse models, particularly in a mouse model of chronic granulomatous disease. Our findings support the potential efficacy of phage therapy, although regulatory and market factors may limit its wider investigation and use.

Clinical and microbiologic analysis of the risk factors for mortality in patients with heterogeneous vancomycin-intermediate Staphylococcus aureus bacteremia

The prevalence of the heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) phenotype among methicillin-resistant S. aureus (MRSA) blood isolates can reach 38%. hVISA bacteremia is known to be associated with vancomycin treatment failure, including persistent bacteremia. We conducted this study to evaluate risk factors for 12-week mortality in patients with hVISA bacteremia through a detailed clinical and microbiological analysis of a prospective cohort of patients with S. aureus bacteremia. All isolates were collected on the first day of bacteremia and subjected to population analysis profiling for hVISA detection, genotyping, and PCR analysis for 39 virulence factors. Of 382 patient with MRSA bacteremia, 121 (32%) had hVISA bacteremia. Deceased patients were more likely to have hematologic malignancy (P = 0.033), ultimately or rapidly fatal disease (P = 0.007), and a higher Pitt bacteremia score (P = 0.010) than surviving patients. The sequence type 239 (ST239) clonal type and definitive linezolid treatment were associated with a trend toward reduced mortality (P = 0.061 and 0.072, respectively), but a high vancomycin MIC (≥2 mg/liter) was not associated with increased mortality (P = 0.368). In a multivariate analysis, ultimately or rapidly fatal disease (adjusted odds ratio [aOR], 2.80; 95% confidence interval [CI], 1.14 to 6.85) and a high Pitt bacteremia score (aOR, 1.26; 95% CI, 1.07 to 1.48) were independent risk factors for mortality. Hematologic malignancy was associated with a trend toward increased mortality (P = 0.094), and ST239 was associated with a trend toward reduced mortality (P = 0.095). Our study suggests that ST239 hVISA is a possible predictor of survival in hVISA bacteremia.

Inducible Expression of a Resistance-Nodulation-Division-Type Efflux Pump in Staphylococcus aureus Provides Resistance to Linoleic and Arachidonic Acids

Although Staphylococcus aureus is exposed to antimicrobial fatty acids on the skin, in nasal secretions, and in abscesses, a specific mechanism of inducible resistance to this important facet of innate immunity has not been identified. Here, we have sequenced the genome of S. aureus USA300 variants selected for their ability to grow at an elevated concentration of linoleic acid. The fatty acid-resistant clone FAR7 had a single nucleotide polymorphism resulting in an H₁₂₁Y substitution in an uncharacterized transcriptional regulator belonging to the AcrR family, which was divergently transcribed from a gene encoding a member of the resistance-nodulation-division superfamily of multidrug efflux pumps. We named these genes farR and farE, for regulator and effector of fatty acid resistance, respectively. Several lines of evidence indicated that FarE promotes efflux of antimicrobial fatty acids and is regulated by FarR. First, expression of farE was strongly induced by arachidonic and linoleic acids in an farR-dependent manner. Second, an H₁₂₁Y substitution in FarR resulted in increased expression of farE and was alone sufficient to promote increased resistance of S. aureus to linoleic acid. Third, inactivation of farE resulted in a significant reduction in the inducible resistance of S. aureus to the bactericidal activity of 100 μM linoleic acid, increased accumulation of [(14)C]linoleic acid by growing cells, and severely impaired growth in the presence of nonbactericidal concentrations of linoleic acid. Cumulatively, these findings represent the first description of a specific mechanism of inducible resistance to antimicrobial fatty acids in a Gram-positive pathogen.

IMPORTANCE

Staphylococcus aureus colonizes approximately 25% of humans and is a leading cause of human infectious morbidity and mortality. To persist on human hosts, S. aureus must have intrinsic defense mechanisms to cope with antimicrobial fatty acids, which comprise an important component of human innate defense mechanisms. We have identified a novel pair of genes, farR and farE, that constitute a dedicated regulator and effector of S. aureus resistance to linoleic and arachidonic acids, which are major fatty acids in human membrane phospholipid. Expression of farE, which encodes an efflux pump, is induced in an farR-dependent mechanism, in response to these antimicrobial fatty acids that would be encountered in a tissue abscess.

Epidemiology and outcome of Staphylococcus aureus bloodstream infection and sepsis in a Norwegian county 1996-2011: an observational study

Background

Staphylococcus aureus is one of the most common and lethal causes of bloodstream infection and the incidence is increasing. We carried out a prospective observational study of patients with Staphylococcus aureus bloodstream infection and sepsis in Nord-Trøndelag county in Norway from 1996–2011. The main outcome of interest was all-cause mortality within 30 and 90 days.

Methods

Positive blood cultures were registered prospectively by the microbiology laboratory and clinical variables were retrospectively registered from patients’ hospital records. The severity of sepsis was assigned according to the 2001 International Sepsis Definition Conference criteria. The association between clinical characteristics and mortality was studied using logistic regression analysis, and adjusted 30- and 90-day mortality risks were estimated.

Results

Among 373 patients, the median age was 74 years and 60.3% were male. 0.8% of the patients were diagnosed with MRSA. 29.8% of the patients developed severe sepsis and 12.9% developed septic shock. The all-cause mortality was 14.5%, 27.3% and 36.2% at 7, 30 and 90 days, respectively. Compared to patients with sepsis without organ failure (Mortality risk 13.3%, 95% CI 7.5-16.3%), the 30-day mortality risk was 3-fold higher among those with severe sepsis (39.9%, 95% CI 29.5-48.5%) and more than 4-fold higher for those with septic shock (57.3%, 95% CI 42.5-72.2%). The 30-day all-cause mortality varied by focus of infection, with the highest 30-day mortality risk among those with a pulmonary focus (42.4%, 95% CI 26.0-58.5%) and unknown focus of infection (38.7%, 95% CI 27.5-48.2%). The mortality risk did not differ between the first and second halves of the study period with a 30-day mortality risk of 27.3%, (95% CI 18.1-33.1%) for 1996–2003 versus 27.4% (95% CI 19.4-31.4%) for 2004–2011. The same pattern was seen for 90-day mortality risk.

Conclusion

Staphylococcus aureus bloodstream infection carries a high case fatality rate, especially among those with severe sepsis and septic shock and among those with a pulmonary or unknown focus of infection. There was no decrease in 30- or 90-day mortality risk during the study period. This underscores the importance of continuing surveillance and efforts to improve the outcome of this serious disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-015-0849-4) contains supplementary material, which is available to authorized users.

Ceftaroline fosamil salvage therapy: an option for reduced-vancomycin-susceptible MRSA bacteraemia

OBJECTIVES

To examine the activity of ceftaroline against reduced-vancomycin-susceptible MRSA isolates.

METHODS

One-hundred and three MRSA blood culture isolates (predominantly ST239-MRSA-III), with varying vancomycin phenotypes, had their ceftaroline MICs determined by broth microdilution and MIC Evaluator strip (Oxoid-Thermo Fisher). Statistical analyses were performed that examined relationships with vancomycin and daptomycin MICs. Mutations in mecA were also examined.

RESULTS

All 103 isolates (including 60 heteroresistant vancomycin-intermediate Staphylococcus aureus/vancomycin-intermediate S. aureus) were susceptible to ceftaroline, with one isolate displaying heteroresistance that may be related to a mecA mutation. Higher ceftaroline MICs were associated with vancomycin-susceptible S. aureus isolates.

CONCLUSIONS

This study highlights that ceftaroline fosamil is an option for salvage therapy based on in vitro activity.

Comparative effectiveness of cefazolin versus cloxacillin as definitive antibiotic therapy for MSSA bacteraemia: results from a large multicentre cohort study

OBJECTIVES

We compared the effectiveness of cefazolin versus cloxacillin in the treatment of MSSA bacteraemia in terms of mortality and relapse.

METHODS

A retrospective cohort study examined consecutive patients with Staphylococcus aureus bacteraemia from six academic and community hospitals between 2007 and 2010. Patients with MSSA bacteraemia who received cefazolin or cloxacillin as the predominant definitive antibiotic therapy were included in the study. Ninety-day mortality was compared between the two groups matched by propensity scores.

RESULTS

Of 354 patients included in the study, 105 (30%) received cefazolin and 249 (70%) received cloxacillin as the definitive antibiotic therapy. In 90 days, 96 (27%) patients died: 21/105 (20%) in the cefazolin group and 75/249 (30%) in the cloxacillin group. Within 90 days, 10 patients (3%) had a relapse of S. aureus infection: 6/105 (6%) in the cefazolin group and 4/249 (2%) in the cloxacillin group. All relapses in the cefazolin group were related to a deep-seated infection. Based on the estimated propensity score, 90 patients in the cefazolin group were matched with 90 patients in the cloxacillin group. In the propensity score-matched groups, cefazolin had an HR of 0.58 (95% CI 0.31-1.08, P = 0.0846) for 90 day mortality.

CONCLUSIONS

There was no significant clinical difference between cefazolin and cloxacillin in the treatment of MSSA bacteraemia with respect to mortality. Cefazolin was associated with non-significantly more relapses compared with cloxacillin, especially in deep-seated S. aureus infections.

Bacteremia, Sepsis, and Infective Endocarditis Associated with Staphylococcus aureus

Bacteremia and infective endocarditis (IE) are important causes of morbidity and mortality associated with Staphylococcus aureus infections. Increasing exposure to healthcare, invasive procedures, and prosthetic implants has been associated with a rising incidence of S. aureus bacteremia (SAB) and IE since the late twentieth century. S. aureus is now the most common cause of bacteremia and IE in industrialized nations worldwide and is associated with excess mortality when compared to other pathogens. Central tenets of management include identification of complicated bacteremia, eradicating foci of infection, and, for many, prolonged antimicrobial therapy. Evolving multidrug resistance and limited therapeutic options highlight the many unanswered clinical questions and urgent need for further high-quality clinical research.

Mechanisms of NDV-3 vaccine efficacy in MRSA skin versus invasive infection

Increasing rates of life-threatening infections and decreasing susceptibility to antibiotics urge development of an effective vaccine targeting Staphylococcus aureus. This study evaluated the efficacy and immunologic mechanisms of a vaccine containing a recombinant glycoprotein antigen (NDV-3) in mouse skin and skin structure infection (SSSI) due to methicillin-resistant S. aureus (MRSA). Compared with adjuvant alone, NDV-3 reduced abscess progression, severity, and MRSA density in skin, as well as hematogenous dissemination to kidney. NDV-3 induced increases in CD3+ T-cell and neutrophil infiltration and IL-17A, IL-22, and host defense peptide expression in local settings of SSSI abscesses. Vaccine induction of IL-22 was necessary for protective mitigation of cutaneous infection. By comparison, protection against hematogenous dissemination required the induction of IL-17A and IL-22 by NDV-3. These findings demonstrate that NDV-3 protective efficacy against MRSA in SSSI involves a robust and complementary response integrating innate and adaptive immune mechanisms. These results support further evaluation of the NDV-3 vaccine to address disease due to S. aureus in humans.