Clinical management of Staphylococcus aureus bacteraemia

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.

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.

Epicatechin gallate, a naturally occurring polyphenol, alters the course of infection with β-lactam-resistant Staphylococcus aureus in the zebrafish embryo

(-)-epicatechin gallate (ECg) substantially modifies the properties of Staphylococcus aureus and reversibly abrogates β-lactam resistance in methicillin/oxacillin resistant (MRSA) isolates. We have determined the capacity of ECg to alter the course of infection in zebrafish embryos challenged with epidemic clinical isolate EMRSA-16. At 30 h post fertilization (hpf), embryos were infected by injection of 1–5 × 10³ colony forming units (CFU) of EMRSA-16 into the circulation valley or yolk sac. Infection by yolk sac injection was lethal with a challenge dose above 3 × 10³ CFU, with no survivors at 70 hpf. In contrast, survival at 70 hpf after injection into the circulation was 83 and 44% following challenge with 3 × 10³ and 1–5 × 10³ CFU, respectively. No significant increases in survival were noted when infected embryos were maintained in medium containing 12.5–100 μg/mL ECg with or without 4 or 16 μg/mL oxacillin. However, when EMRSA-16 was grown in medium containing 12.5 μg/mL ECg and the bacteria used to infect embryos by either the circulation valley or yolk sac, there were significant increases in embryo survival in both the presence and absence of oxacillin. ECg-modified and unmodified, GFP-transformed EMRSA-16 bacteria were visualized within phagocytic cells in the circulation and yolk sac; pre-treatment with ECg also significantly increased induction of the respiratory burst and suppressed increases in IL-1β expression typical of infection with untreated EMRSA-16. We conclude that exposure to ECg prior to infection reduces the lethality of EMRSA-16, renders cells more susceptible to elimination by immune processes and compromises their capacity to establish an inflammatory response in comparison to non-exposed bacteria.

Inability to sustain intraphagolysosomal killing of Staphylococcus aureus predisposes to bacterial persistence in macrophages

Macrophages are critical effectors of the early innate response to bacteria in tissues. Phagocytosis and killing of bacteria are interrelated functions essential for bacterial clearance but the rate-limiting step when macrophages are challenged with large numbers of the major medical pathogen Staphylococcus aureus is unknown. We show that macrophages have a finite capacity for intracellular killing and fail to match sustained phagocytosis with sustained microbial killing when exposed to large inocula of S. aureus (Newman, SH1000 and USA300 strains). S. aureus ingestion by macrophages is associated with a rapid decline in bacterial viability immediately after phagocytosis. However, not all bacteria are killed in the phagolysosome, and we demonstrate reduced acidification of the phagolysosome, associated with failure of phagolysosomal maturation and reduced activation of cathepsin D. This results in accumulation of viable intracellular bacteria in macrophages. We show macrophages fail to engage apoptosis-associated bacterial killing. Ultittop mately macrophages with viable bacteria undergo cell lysis, and viable bacteria are released and can be internalized by other macrophages. We show that cycles of lysis and reuptake maintain a pool of viable intracellular bacteria over time when killing is overwhelmed and demonstrate intracellular persistence in alveolar macrophages in the lungs in a murine model.

A bacterial regulatory RNA attenuates virulence, spread and human host cell phagocytosis

Staphylococcus aureus pathogenesis is directed by regulatory proteins and RNAs. We report the case of an RNA attenuating virulence and host uptake, possibly to sustain commensalism. A S. aureus sRNA, SprC (srn_3610), reduced virulence and bacterial loads in a mouse infection model. S. aureus deleted for sprC became more virulent and increased bacterial dissemination in colonized animals. Conversely, inducing SprC expression lowered virulence and the bacterial load. Without sprC, S. aureus phagocytosis by monocytes and macrophages was higher, whereas bacteria were internalized at lower yields when SprC expression was stimulated. Without sprC, higher internalization led to a greater number of extracellular bacteria, facilitating colonization. SprC expression decreased after phagocytosis, concurring with the facilitated growth of bacteria lacking the sRNA in the presence of an oxidant. The major staphylococcal autolysin facilitates S. aureus uptake by human phagocytes. ATL proved to be negatively regulated by SprC. The SprC domains involved in pairing with atl mRNA were analyzed. The addition of ATL reduced phagocytosis of bacteria lacking sprC with no effects on wild-type bacterial uptake, implying that SprC influences phagocytosis, at least in part, by controlling ATL. Since the control of SprC on ATL was modest, other factors must contribute to atl regulation.

Impact of the β-Lactam Resistance Modifier (-)-Epicatechin Gallate on the Non-Random Distribution of Phospholipids across the Cytoplasmic Membrane of Staphylococcus aureus

The polyphenol (−)-epicatechin gallate (ECg) inserts into the cytoplasmic membrane (CM) of methicillin-resistant Staphylococcus aureus (MRSA) and reversibly abrogates resistance to β-lactam antibiotics. ECg elicits an increase in MRSA cell size and induces thickened cell walls. As ECg partially delocalizes penicillin-binding protein PBP2 from the septal division site, reduces PBP2 and PBP2a complexation and induces CM remodelling, we examined the impact of ECg membrane intercalation on phospholipid distribution across the CM and determined if ECg affects the equatorial, orthogonal mode of division. The major phospholipids of the staphylococcal CM, lysylphosphatidylglycerol (LPG), phosphatidylglycerol (PG), and cardiolipin (CL), were distributed in highly asymmetric fashion; 95%–97% of LPG was associated with the inner leaflet whereas PG (~90%) and CL (~80%) were found predominantly in the outer leaflet. ECg elicited small, significant changes in LPG distribution. Atomic force microscopy established that ECg-exposed cells divided in similar fashion to control bacteria, with a thickened band of encircling peptidoglycan representing the most recent plane of cell division, less distinct ribs indicative of previous sites of orthogonal division and concentric rings and “knobbles” representing stages of peptidoglycan remodelling during the cell cycle. Preservation of staphylococcal membrane lipid asymmetry and mode of division in sequential orthogonal planes appear key features of ECg-induced stress.

Bacteremia in children: epidemiology, clinical diagnosis and antibiotic treatment

The diagnosis of bacteremia in children is important and it can be clinically challenging to recognize the signs and symptoms. The reported rates of bacteremia are higher in young children but with the increasing vaccine coverage, there has been a decrease in bacteremia due to the three vaccine preventable bacteria (Streptococcus pneumoniae, Haemophilus influenzae group b and Neisseria meningitidis). Notably, there have been increases in healthcare-associated bacteremias with a rise in Staphylococcus aureus and Gram negative bacteremias. This review provides a brief overview of the clinical diagnosis of bacteremia in children, focusing on the epidemiology, clinical characteristics, risk factors, antibiotic treatment, outcomes and preventative measures to reduce the incidence of bacteremia and improve morbidity and mortality.

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.

New Insight on Epidemiology and Management of Bacterial Bloodstream Infection in Patients with Hematological Malignancies

Bloodstream infections (BSI) are a significant cause of morbidity and mortality in onco-hematologic patients. The Gram-negative bacteria were the main responsible for the febrile neutropenia in the sixties; their impact declined due to the use of fluoroquinolone prophylaxis. This situation was followed by the gradual emergence of Gram-positive bacteria also following the increased use of intravascular devices and the introduction of new chemotherapeutic strategies. In the last decade, the Gram-negative etiology is raising again because of the emergence of resistant strains that make questionable the usefulness of current strategies for prophylaxis and empirical treatment. Gram-negative BSI attributable mortality is relevant, and the appropriate empirical treatment significantly improves the prognosis; on the other hand the adequate delayed treatment of Gram-positive BSI does not seem to have a high impact on survival. The clinician has to be aware of the epidemiology of his institution and colonizations of his patients to choose the most appropriate empiric therapy. In a setting of high endemicity of multidrug-resistant infections also the choice of targeted therapy can be a challenge, often requiring strategies based on off-label prescriptions and low grade evidence.

In this review, we summarize the current evidence for the best targeted therapies for difficult to treat bacteria BSIs and future perspectives in this topic. We also provide a flow chart for a rational approach to the empirical treatment of febrile neutropenia in a multidrug resistant, high prevalence setting.

Rapid Progressive Seeding of a Community Acquired Pathogen in an Immune-Competent Host: End Organ Damage from Head to Bone

Methicillin-sensitive Staphylococcus aureus (MSSA) meningitis is a rare disease when not related to neurosurgery: there are only few reported cases in the literature to date. We describe a case that highlights not only meningeal but also diffuse and rapidly progressive systemic involvement with multi-organ failure. A 64-year-old male presented to our hospital with a chief complaint of acute worsening of his usual chronic lower back pain, progressive weakness in lower extremities and subjective fevers at home. Hospital course demonstrated MSSA bacteremia, of questionable source, that resulted in endocarditis affecting right and left heart in a patient with no history of intravenous drug use. The case was complicated by septic emboli to systemic circulation involving the kidneys, vertebral spine, lungs and brain with consequent meningitis and stroke, even when treated empirically with vancomycin and then switched to nafcillin as indicated. Even though MSSA infections are well known, there are very few case reports describing such an acute-simultaneous-manifestation of multi-end-organ failure, including meningitis and stroke. Our case, also presented with an uncommon manifestation of persistent infection dissemination despite adequate antibiotic treatment.

Strategies to reduce curative antibiotic therapy in intensive care units (adult and paediatric)

Emerging resistance to antibiotics shows no signs of decline. At the same time, few new antibacterials are being discovered. There is a worldwide recognition regarding the danger of this situation. The urgency of the situation and the conviction that practices should change led the Société de Réanimation de Langue Française (SRLF) and the Société Française d'Anesthésie et de Réanimation (SFAR) to set up a panel of experts from various disciplines. These experts met for the first time at the end of 2012 and have since met regularly to issue the following 67 recommendations, according to the rigorous GRADE methodology. Five fields were explored: i) the link between the resistance of bacteria and the use of antibiotics in intensive care; ii) which microbiological data and how to use them to reduce antibiotic consumption; iii) how should antibiotic therapy be chosen to limit consumption of antibiotics; iv) how can antibiotic administration be optimized; v) review and duration of antibiotic treatments. In each institution, the appropriation of these recommendations should arouse multidisciplinary discussions resulting in better knowledge of local epidemiology, rate of antibiotic use, and finally protocols for improving the stewardship of antibiotics. These efforts should contribute to limit the emergence of resistant bacteria.

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.

Diagnosis and treatment of bacteremia and endocarditis due to Staphylococcus aureus. A clinical guideline from the Spanish Society of Clinical Microbiology and Infectious Diseases (SEIMC)

Both bacteremia and infective endocarditis caused by Staphylococcus aureus are common and severe diseases. The prognosis may darken not infrequently, especially in the presence of intracardiac devices or methicillin-resistance. Indeed, the optimization of the antimicrobial therapy is a key step in the outcome of these infections. The high rates of treatment failure and the increasing interest in the influence of vancomycin susceptibility in the outcome of infections caused by both methicillin-susceptible and -resistant isolates has led to the research of novel therapeutic schemes. Specifically, the interest raised in recent years on the new antimicrobials with activity against methicillin-resistant staphylococci has been also extended to infections caused by susceptible strains, which still carry the most important burden of infection. Recent clinical and experimental research has focused in the activity of new combinations of antimicrobials, their indication and role still being debatable. Also, the impact of an appropriate empirical antimicrobial treatment has acquired relevance in recent years. Finally, it is noteworthy the impact of the implementation of a systematic bundle of measures for improving the outcome. The aim of this clinical guideline is to provide an ensemble of recommendations in order to improve the treatment and prognosis of bacteremia and infective endocarditis caused by S. aureus, in accordance to the latest evidence published.

Bacteremia Antibiotic Length Actually Needed for Clinical Effectiveness (BALANCE): study protocol for a pilot randomized controlled trial

Background

Bacteremia is a leading cause of mortality and morbidity in critically ill adults. No previous randomized controlled trials have directly compared shorter versus longer durations of antimicrobial treatment in these patients.

Methods/Design

This is a multicenter pilot randomized controlled trial in critically ill patients with bacteremia. Eligible patients will be adults with a positive blood culture with pathogenic bacteria identified while in the intensive care unit. Eligible, consented patients will be randomized to either 7 days or 14 days of adequate antimicrobial treatment for the causative pathogen(s) detected on blood cultures. The diversity of pathogens and treatment regimens precludes blinding of patient and clinicians, but allocation concealment will be extended to day 7 and outcome adjudicators will be blinded. The primary outcome for the main trial will be 90-day mortality. The primary outcome for the pilot trial is feasibility defined by (i) rate of recruitment exceeding 1 patient per site per month and (ii) adherence to treatment duration protocol ≥ 90%. Secondary outcomes include intensive care unit, hospital and 90-day mortality rates, relapse rates of bacteremia, antibiotic-related side effects and adverse events, rates of Clostridium difficile infection, rates of secondary infection or colonization with antimicrobial resistant organisms, ICU and hospital lengths of stay, mechanical ventilation and vasopressor duration in intensive care unit, and procalcitonin levels on the day of randomization, and day 7, 10 and 14 after the index blood culture.

Discussion

The BALANCE pilot trial will inform the design and execution of the subsequent BALANCE main trial, which will evaluate shorter versus longer duration treatment for bacteremia in critically ill patients, and thereby provide an evidence basis for treatment duration decisions for these infections.

Trial registration

The Pilot Trial was registered on 26 September 2014. Trial registration number: NCT02261506.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-015-0688-z) contains supplementary material, which is available to authorized users.

Improved outcome with early rifampicin combination treatment in methicillin-sensitive Staphylococcus aureus bacteraemia with a deep infection focus - a retrospective cohort study

INTRODUCTION

Rifampicin has been used as adjunctive therapy in Staphylococcus aureus bacteraemia (SAB) with a deep infection focus. However, data for prognostic impact of rifampicin therapy is unestablished including the optimal initiation time point. We studied the impact of rifampicin therapy and the optimal initiation time for rifampicin treatment on prognosis in methicillin-sensitive S. aureus bacteraemia with a deep infection.

METHODS

Retrospective, multicentre study in Finland including 357 SAB patients with a deep infection focus. Patients with alcoholism, liver disease or patients who died within 3 days were excluded. Patients were categorised according to duration of rifampicin therapy and according to whether rifampicin was initiated early (within 7 days) or late (7 days after) after the positive blood cultures. Primary end point was 90 days mortality.

RESULTS

Twenty-seven percent of patients received no rifampicin therapy, 14% received rifampicin for 1-13 days whereas 59% received rifampicin ≥14 days. The 90 day mortality was; 26% for patients treated without rifampicin, 16% for rifampicin therapy of any length and 10% for early onset rifampicin therapy ≥14 days. Lack of rifampicin therapy increased (OR 1.89, p=0.026), rifampicin of any duration decreased (OR 0.53, p=0.026) and rifampicin therapy ≥14 days with early onset lowered the risk for a fatal outcome (OR 0.33, p<0.01) during 90 days follow-up.

CONCLUSION

Rifampicin adjunctive therapy for at least 14 days and initiated within 7 days of positive blood culture associated with improved outcome among SAB patients with a deep infection.

Molecular mechanisms of NET formation and degradation revealed by intravital imaging in the liver vasculature

Neutrophil extracellular traps (NETs) composed of DNA decorated with histones and proteases trap and kill bacteria but also injure host tissue. Here we show that during a bloodstream infection with methicillin-resistant Staphylococcus aureus, the majority of bacteria are sequestered immediately by hepatic Kupffer cells, resulting in transient increases in liver enzymes, focal ischaemic areas and a robust neutrophil infiltration into the liver. The neutrophils release NETs into the liver vasculature, which remain anchored to the vascular wall via von Willebrand factor and reveal significant neutrophil elastase (NE) proteolytic activity. Importantly, DNase although very effective at DNA removal, and somewhat effective at inhibiting NE proteolytic activity, fails to remove the majority of histones from the vessel wall and only partly reduces injury. By contrast, inhibition of NET production as modelled by PAD4-deficiency, or prevention of NET formation and proteolytic activity as modelled in NE^−/− mice prevent collateral host tissue damage.

Neutrophil extracellular traps (NETs) released by neutrophils trap pathogens but may also cause tissue damage. Here the authors show that during systemic Staphylococcus aureus infection NETs anchoring to the vasculature are only partially DNase-sensitive, advocating for better anti-NET therapies.

Flucloxacillin and fusidic acid-associated neutropenia in a patient with periaortic abscess: rare side effects of commonly used antibiotics

The use of long-term antibiotics for deep-seated infections is very common, and is associated with many clinically significant side effects. In this report we describe the history of a 48-year-old man who attended West Suffolk Hospital with nausea and vomiting, and was subsequently found to have a deep-seated infection following his repeat aortic valve replacement. He completed a 7-week course of intravenous flucloxacillin and oral fusidic acid, however, prior to finishing this course a random blood test revealed a neutrophil count of zero. He was re-admitted to hospital with fever, and was treated accordingly as per the trust's neutropenic sepsis protocol with the addition of growth colony stimulating factor (GCSF). His neutrophil count recovered after 3 days and has remained within the normal range ever since.

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.

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.

Innate immunity. A Spaetzle-like role for nerve growth factor β in vertebrate immunity to Staphylococcus aureus

Many key components of innate immunity to infection are shared between Drosophila and humans. However, the fly Toll ligand Spaetzle is not thought to have a vertebrate equivalent. We have found that the structurally related cystine-knot protein, nerve growth factor β (NGFβ), plays an unexpected Spaetzle-like role in immunity to Staphylococcus aureus infection in chordates. Deleterious mutations of either human NGFβ or its high-affinity receptor tropomyosin-related kinase receptor A (TRKA) were associated with severe S. aureus infections. NGFβ was released by macrophages in response to S. aureus exoproteins through activation of the NOD-like receptors NLRP3 and NLRP4 and enhanced phagocytosis and superoxide-dependent killing, stimulated proinflammatory cytokine production, and promoted calcium-dependent neutrophil recruitment. TrkA knockdown in zebrafish increased susceptibility to S. aureus infection, confirming an evolutionarily conserved role for NGFβ-TRKA signaling in pathogen-specific host immunity.

Staphylococcus aureus bacteraemia in Gauteng academic hospitals, South Africa

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) infections are responsible for longer hospital stays, increased hospital costs, and poorer outcomes compared to methicillin-sensitive S. aureus (MSSA) infections. We aimed to describe the epidemiology of S. aureus bacteraemia (SAB) and to determine factors associated with MRSA infection in South Africa.

METHODS

Cases of SAB were reported from September 2012 to September 2013 from three sentinel sites. A case was defined as the isolation of S. aureus from a blood culture during a 21-day period. Detailed clinical information was collected. Multivariable logistic regression was done to determine factors associated with MRSA infection and mortality.

RESULTS

There were 442 cases of SAB reported; antimicrobial susceptibility testing was performed on 240 isolates (54%). Thirty-six percent (86/240) of cases had an MRSA infection. A longer hospital stay before positive specimen collection (odds ratio (OR) 1.08, 95% confidence interval (CI) 1.02-1.13, p=0.004), hospitalization in the last year (OR 15.7, 95% CI 2.5-99.5, p=0.003), HIV infection (OR 4.9, 95% CI 1.05-22.90, p=0.044), and antibiotic use in the previous 2 months (OR 0.1, 95% CI 0.01-0.68, p=0.022) were independent predictors of MRSA. Older age, and in particular age 25-44 years (OR 22.2, 95% CI 2.7-185.5, p=0.004, compared to those aged<5 years), was the only independent predictor of mortality amongst cases with SAB. MRSA isolates were non-susceptible to more antimicrobial agents compared to MSSA isolates.

CONCLUSIONS

HIV infection was an independent risk factor for MRSA infection. The selection of appropriate empirical antimicrobial treatment is essential in patients with MRSA infections because of non-susceptibility to many other antimicrobial classes.

A refined technique for extraction of extracellular matrices from bacterial biofilms and its applicability

Biofilm-forming bacteria embedded in polymeric extracellular matrices (ECMs) that consist of polysaccharides, proteins and/or extracellular DNAs (eDNAs) acquire high resistance to antimicrobial agents and host immune systems. To understand molecular mechanisms of biofilm formation and maintenance and to develop therapeutic countermeasures against chronic biofilm-associated infections, reliable methods to isolate ECMs are inevitable. In this study, we refined the ECM extraction method recently reported and evaluated its applicability. Using three Staphylococcus aureus biofilms in which proteins, polysaccharides or eDNAs are major contributors to their integrity, ECMs were extracted using salts and detergents. We found that extraction with 1.5 M sodium chloride (NaCl) could be optimum for not only ECM proteins but also polysaccharides and eDNAs. In addition, long-time incubation was not necessary for efficient ECM isolation. Lithium chloride (LiCl) was comparative to NaCl but is more expensive. In contrast to SDS, NaCl hardly caused leakage of intracellular proteins and did not affect viability of bacterial cells within biofilms. Furthermore, this method is applicable to other bacteria such as Gram-positive Staphylococcus epidermidis and Gram-negative Escherichia coli and Pseudomonas aeruginosa. Thus, this refined method is very simple, rapid, low cost and non-invasive and could be used for a broad range of applications.

BDCA1-positive dendritic cells (DCs) represent a unique human myeloid DC subset that induces innate and adaptive immune responses to Staphylococcus aureus Infection

Staphylococcus aureus bloodstream infection (bacteremia) is a major cause of morbidity and mortality and places substantial cost burdens on health care systems. The role of peripheral blood dendritic cells (PBDCs) in the immune responses against S. aureus infection has not been well characterized. In this study, we demonstrated that BDCA1(+) myeloid DCs (mDCs) represent a unique PBDC subset that can induce immune responses against S. aureus infection. BDCA1(+) mDCs could engulf S. aureus and strongly upregulated the expression of costimulatory molecules and production of proinflammatory cytokines. Furthermore, BDCA1(+) mDCs expressed high levels of major histocompatibility complex (MHC) class I and II molecules in response to S. aureus and greatly promoted proliferation and gamma interferon (IFN-γ) production in CD4 and CD8 T cells. Moreover, BDCA1(+) mDCs expressed higher levels of Toll-like receptor 2 (TLR-2) and scavenger receptor A (SR-A) than those on CD16(+) and BDCA3(+) mDCs, and these two receptors were both required for the recognition of S. aureus and the subsequent activation of BDCA1(+) mDCs. Finally, BDCA1(+) mDC-mediated immune responses against S. aureus were dependent on MyD88 signaling pathways. These results demonstrate that human BDCA1(+) mDCs represent a unique subset of mDCs that can respond to S. aureus to undergo maturation and activation and to induce Th1 and Tc1 immune responses.

Impact of infectious diseases consultation on the management of Staphylococcus aureus bacteraemia in children

OBJECTIVES

Infectious diseases consultation (IDC) in adults with Staphylococcus aureus bacteraemia (SAB) has been shown to improve management and outcome. The aim of this study was to evaluate the impact of IDC on the management of SAB in children.

STUDY DESIGN

Observational cohort study of children with SAB.

SETTING

Cambridge University Hospitals National Health Service (NHS) Foundation Trust, a large acute NHS Trust in the UK.

PARTICIPANTS

All children with SAB admitted to the Cambridge University Hospitals NHS Foundation Trust between 16 July 2006 and 31 December 2012.

METHODS

Children with SAB between 2006 and 31 October 2009 were managed by routine clinical care (pre-IDC group) and data were collected retrospectively by case notes review. An IDC service for SAB was introduced in November 2009. All children with SAB were reviewed regularly and data were collected prospectively (IDC group) until 31 December 2012. Baseline characteristics, quality metrics and outcome were compared between the pre-IDC group and IDC group.

RESULTS

There were 66 episodes of SAB in 63 children-28 patients (30 episodes) in the pre-IDC group, and 35 patients (36 episodes) in the IDC group. The median age was 3.4 years (IQR 0.2-10.7 years). Patients in the IDC group were more likely to have echocardiography performed, a removable focus of infection identified and to receive a longer course of intravenous antimicrobial therapy. There were no differences in total duration of antibiotic therapy, duration of hospital admission or outcome at 30 or 90 days following onset of SAB.

CONCLUSIONS

IDC resulted in improvements in the investigation and management of SAB in children.

Comparative evaluation of the tolerability of cefazolin and nafcillin for treatment of methicillin-susceptible Staphylococcus aureus infections in the outpatient setting

BACKGROUND

Nafcillin and cefazolin are considered first-line therapy for most infections with methicillin-susceptible Staphylococcus aureus (MSSA), and recent studies have suggested similar clinical efficacy. Limited data are available on the comparative tolerability of these agents.

METHODS

In this retrospective cohort analysis of patients treated with either nafcillin or cefazolin for MSSA infection in the outpatient parenteral antimicrobial therapy clinic at Massachusetts General Hospital from 2007 to 2011, the frequency of premature antimicrobial discontinuation (PAD) and drug-emergent events (DEEs) was calculated.

RESULTS

Three hundred sixty-six and 119 patients were treated with nafcillin or cefazolin, respectively. The median anticipated duration of therapy was comparable at 28 (interquartile range [IQR], 16-37) and 29 (IQR, 24-39) days, respectively, for those treated with nafcillin and cefazolin. Fewer patients completed the prespecified treatment course with nafcillin than with cefazolin (PAD rate, 33.8% vs 6.7%; P < .0001). The hazard ratio for PAD in the nafcillin vs cefazolin groups was 2.81 (95% confidence interval [CI], 1.26-3.68). More patients in the nafcillin group developed rash (13.9% vs 4.2%; P = .002), renal dysfunction (11.4% vs 3.3%; P = .006), and liver function abnormalities (8.1% vs 1.6%; P = .01). Overall rates of DEEs per 1000 patient-days were 16.9 (95% CI, 10.4-27.3) and 4.8 (95% CI, 1.1-10.2), respectively. In 9 cases of nafcillin discontinuation, treatment was changed to cefazolin; all 9 completed treatment with no further observed DEEs.

CONCLUSIONS

Nafcillin treatment was associated with higher rates of both PAD as well as DEEs compared with cefazolin treatment. This difference in tolerability, in addition to efficacy and cost, should be considered when decisions for outpatient parenteral MSSA treatment are made.

Liposome-encapsulated ISMN: a novel nitric oxide-based therapeutic agent against Staphylococcus aureus biofilms

Background

Staphylococcus aureus in its biofilm form has been associated with recalcitrant chronic rhinosinusitis with significant resistance to conventional therapies. This study aims to determine if liposomal-encapsulation of a precursor of the naturally occurring antimicrobial nitric oxide (NO) enhances its desired anti-biofilm effects against S. aureus, in the hope that improving its efficacy can provide an effective topical agent for future clinical use.

Methodology

S. aureus ATCC 25923 biofilms were grown in-vitro using the Minimum Biofilm Eradication Concentration (MBEC) device and exposed to 3 and 60 mg/mL of the NO donor isosorbide mononitrate (ISMN) encapsulated into different anionic liposomal formulations based on particle size (unilamellar ULV, multilamellar MLV) and lipid content (5 and 25 mM) at 24 h and 5 min exposure times. Biofilms were viewed using Live-Dead Baclight stain and confocal scanning laser microscopy and quantified using the software COMSTAT2.

Results

At 3 and 60 mg/mL, ISMN-ULV liposomes had comparable and significant anti-biofilm effects compared to untreated control at 24 h exposure (p = 0.012 and 0.02 respectively). ULV blanks also had significant anti-biofilm effects at both 24 h and 5 min exposure (p = 0.02 and 0.047 respectively). At 5 min exposure, 60 mg/mL ISMN-MLV liposomes appeared to have greater anti-biofilm effects compared to pure ISMN or ULV particles. Increasing liposomal lipid content improved the anti-biofilm efficacy of both MLV and ULVs at 5 min exposure.

Conclusion

Liposome-encapsulated “nitric oxide” is highly effective in eradicating S. aureus biofilms in-vitro, giving great promise for use in the clinical setting to treat this burdensome infection. Further studies however are needed to assess its safety and efficacy in-vivo before clinical translation is attempted.

Tolerability of cefazolin after immune-mediated hypersensitivity reactions to nafcillin in the outpatient setting

The objective of the present study was to assess the safety and tolerability of cefazolin therapy among patients with methicillin-sensitive Gram-positive bacterial infections who develop non-IgE-mediated hypersensitivity reactions (HSRs) to nafcillin. In this retrospective cohort analysis of the Outpatient Parenteral Antimicrobial Therapy program at the Massachusetts General Hospital from 2007 through 2013, we identified patients switched from nafcillin to cefazolin after an immune-mediated HSR. We reviewed patient demographics, details about the original HSR, and outcomes after the switch to cefazolin therapy. HSRs were classified by reaction type and likely mechanism. There were 467 patients treated with nafcillin, of which 60 (12.8%) were switched to cefazolin during their prescribed course. Of the 60 patients who transitioned to cefazolin, 17 (28.3%) were switched because of non-IgE-mediated HSRs. HSRs included maculopapular rash (n = 10), immune-mediated nephritis (n = 3), isolated eosinophilia (n = 2), immune-mediated hepatitis (n = 1), and a serum sickness-like reaction (n = 1). All but one patient (94.1%) who switched to cefazolin tolerated the drug with resolution of the HSR and completed their therapy with cefazolin. No patient experienced worsening of their rash or progressive organ dysfunction. With appropriate monitoring, therapy with cefazolin after non-IgE-mediated HSRs to nafcillin appears to be safe.

Clonal expansion during Staphylococcus aureus infection dynamics reveals the effect of antibiotic intervention

To slow the inexorable rise of antibiotic resistance we must understand how drugs impact on pathogenesis and influence the selection of resistant clones. Staphylococcus aureus is an important human pathogen with populations of antibiotic-resistant bacteria in hospitals and the community. Host phagocytes play a crucial role in controlling S. aureus infection, which can lead to a population "bottleneck" whereby clonal expansion of a small fraction of the initial inoculum founds a systemic infection. Such population dynamics may have important consequences on the effect of antibiotic intervention. Low doses of antibiotics have been shown to affect in vitro growth and the generation of resistant mutants over the long term, however whether this has any in vivo relevance is unknown. In this work, the population dynamics of S. aureus pathogenesis were studied in vivo using antibiotic-resistant strains constructed in an isogenic background, coupled with systemic models of infection in both the mouse and zebrafish embryo. Murine experiments revealed unexpected and complex bacterial population kinetics arising from clonal expansion during infection in particular organs. We subsequently elucidated the effect of antibiotic intervention within the host using mixed inocula of resistant and sensitive bacteria. Sub-curative tetracycline doses support the preferential expansion of resistant microorganisms, importantly unrelated to effects on growth rate or de novo resistance acquisition. This novel phenomenon is generic, occurring with methicillin-resistant S. aureus (MRSA) in the presence of β-lactams and with the unrelated human pathogen Pseudomonas aeruginosa. The selection of resistant clones at low antibiotic levels can result in a rapid increase in their prevalence under conditions that would previously not be thought to favor them. Our results have key implications for the design of effective treatment regimes to limit the spread of antimicrobial resistance, where inappropriate usage leading to resistance may reduce the efficacy of life-saving drugs.

Evaluation of MRSASelect (™) chromogenic medium for the early detection of methicillin-resistant Staphylococcus aureus from blood cultures

INTRODUCTION

Staphylococcus aureus bacteremia is associated with considerable morbidity and mortality. In theory, reducing the turnaround time in reporting of methicillin-resistant S aureus (MRSA) among patients with bactermia could assist with the rapid optimization of antimicrobial therapy.

OBJECTIVE

To evaluate the sensitivity and specificity of MRSASelect (Bio-Rad Laboratories, USA), a chromogenic medium, in the early detection of MRSA from blood cultures growing Gram-positive cocci in clusters, and to confirm that routine use of this medium would, in fact, reduce turnaround time for MRSA identification.

METHODS

The present study was conducted at three microbiology laboratories in Manitoba. Between April 2010 and May 2011, positive blood cultures with Gram-positive cocci in clusters visualized on Gram stain were subcultured to both MRSASelect and routine media. MRSA isolates were identified using conventional microbiological methods from routine media and using growth with the typical colony morphology (pink colony) on MRSASelect medium.

RESULTS

A total of 490 blood cultures demonstrating Gram-positive cocci in clusters on Gram stain were evaluated. S aureus was recovered from 274 blood cultures, with 51 S aureus isolates (51 of 274 [18.6%]) identified as MRSA. MRSASelect medium had a sensitivity of 98%, a specificity of 100%, a positive predictive value of 100% and a negative predictive value of 99.8% for the recovery and identification of MRSA directly from positive blood culture bottles. In addition, use of MRSASelect medium was found to improve turnaround time in the detection of MRSA by almost 24 h relative to conventional methods.

DISCUSSION

These data support the utility of MRSASelect medium for the rapid identification of MRSA from positive blood cultures. Further clinical studies are warranted to determine whether the improvement in turnaround time will result in a measurable reduction in suboptimal antimicrobial therapy and/or improvement in patient outcome.

Staphylococcus aureus bloodstream infection: a pooled analysis of five prospective, observational studies

OBJECTIVES

Staphylococcus aureus bacteraemia is a common, often fatal infection. Our aim was to describe how its clinical presentation varies between populations and to identify common determinants of outcome.

METHODS

We conducted a pooled analysis on 3395 consecutive adult patients with S. aureus bacteraemia. Patients were enrolled between 2006 and 2011 in five prospective studies in 20 tertiary care centres in Germany, Spain, United Kingdom, and United States.

RESULTS

The median age of participants was 64 years (interquartile range 50-75 years) and 63.8% were male. 25.4% of infections were associated with diabetes mellitus, 40.7% were nosocomial, 20.6% were caused by methicillin-resistant S. aureus (MRSA), although these proportions varied significantly across studies. Intravenous catheters were the commonest identified infective focus (27.7%); 8.3% had endocarditis. Crude 14 and 90-day mortality was 14.6% and 29.2%, respectively. Age, MRSA bacteraemia, nosocomial acquisition, endocarditis, and pneumonia were independently associated with death, but a strong association was with an unidentified infective focus (adjusted hazard ratio for 90-day mortality 2.92; 95% confidence interval 2.33 to 3.67, p < 0.0001).

CONCLUSION

The baseline demographic and clinical features of S. aureus bacteraemia vary significantly between populations. Mortality could be reduced by assiduous MRSA control and early identification of the infective focus.

Improving the management of Staphylococcus aureus bacteraemia, including MRSA

Staphylococcus aureus bacteraemia is a serious infection associated with significant complications, including recurrence of bacteraemia, endocarditis and metastatic foci of infection. The management of these patients is often complex, involving appropriate source control, a thorough review and investigations to exclude metastatic foci and infective endocarditis. Additionally, a prolonged course of intravenous antibiotics is often required. As part of our quality improvement project, the following five aspects were evaluated in 56 patients with S. aureus bacteraemia at two District General Hospitals: 1) adequate and timely removal of the source of bacteraemia, 2) echocardiography to exclude endocarditis, 3) repeat blood culture to prove clearance of bacteraemia, 4) adequate duration and choice of antibiotics and 5) documentation of bacteraemia in the discharge summary. After an initial review revealed several areas for improvement, we instituted five Plan-Do-Study-Act learning cycles which involved: teaching microbiology trainees and junior doctors, improving clinical liaison and communication between the microbiology team and clinicians, as well as a clinical review of patients by the microbiology team where appropriate. The post-intervention review evaluated 24 patients with S. aureus bacteraemia between November 2012 and May 2013. The proportion of patients undergoing an echocardiogram improved from 49% to 88%. Another marked improvement was seen in the timely obtaining of clearance blood cultures, with 88% of patients having clearance blood cultures within the 2-4 day window, compared to 56% pre-intervention. 70% of patients with uncomplicated S. aureus bacteraemia received an appropriate antibiotic course post-intervention, compared with 59% pre-intervention. Documentation of the S. aureus bacteraemia in the discharge summary improved from 65% to 75%. The support of the entire microbiology team was pivotal in the successful outcome of the quality improvement project.

Improved understanding of factors driving methicillin-resistant Staphylococcus aureus epidemic waves

Methicillin-resistant Staphylococcus aureus (MRSA) remains one of the most important causes of nosocomial infections worldwide. Since the global spread of MRSA in the 1960s, MRSA strains have evolved with increased pathogenic potential. Notably, some strains are now capable of causing persistent infections not only in hospitalized patients but also in healthy individuals in the community. Furthermore, MRSA is increasingly associated with infections among livestock-associated workers, primarily because of transmission from animals to humans. Moreover, many MRSA strains have gained resistance to most available antibiotics. In this review, we will present current knowledge on MRSA epidemiology and discuss new endeavors being undertaken to understand better the molecular and epidemiological underpinnings of MRSA outbreaks.

A nationwide study of comorbidity and risk of reinfection after Staphylococcus aureus bacteraemia

BACKGROUND

Data on risk factors and rates of reinfection associated with Staphylococcus aureus bacteraemia (SAB) are sparse.

METHODS

We conducted a nationwide cohort study of cases of SAB diagnosed between 1995 and 2008. Reinfection was defined as an episode of SAB more than 90 days after the initial episode of SAB. Comorbidity was evaluated by the Charlson Comorbidity Index (CCI). Cox proportional hazards modelling was used to estimate hazard rates (HR).

RESULTS

Of 10,891 eligible patients, 774 (7.1%) experienced reinfection a median of 458 days (range 90-5021 days) after their primary SAB episode corresponding to a reinfection rate of 1459 (95% confidence interval (CI): 1357-1562) per 100,000 personyears. In multivariate analysis, sex, origin, a vascular or peritoneal device, endocarditis and comorbidity were associated with reinfection. The association was more than two-fold higher among patients in dialysis and for patients with severe comorbidity (CCI ≥ 2). HIV infection (Hazard ratio (HR) 6.18, 95% CI: 4.17-9.16), renal disease (HR 3.92, 95% CI: 3.22-4.78), diabetes with complications (HR 2.11, 95% CI: 1.69-2.62), diabetes without complications (HR 1.61, 95% CI: 1.34-1.93), mild (HR: 1.94, 95% CI: 1.36-2.76) and severe liver disease (HR 2.08, 95% CI: 1.08-4.03), peptic ulcer (HR 1.33, 95% CI: 1.03-1.72), and paraplegia (HR 2.15, 95% CI: 1.02-4.54) were each associated with an increased risk of reinfection.

CONCLUSIONS

Patients with previous SAB have a 60-fold higher risk of SAB compared to the general population. Patients with HIV infection, renal disease, diabetes, liver disease, peptic ulcer and paraplegia had the highest rates of reinfection.

Echocardiography is dispensable in uncomplicated Staphylococcus aureus bacteremia

Current Staphylococcus aureus bacteremia (SAB) practice guidelines stratify treatment duration according to the likelihood of complications and recommend transesophageal echocardiography (TEE) in all cases. The benefit of TEE in uncomplicated SAB has not been validated. We performed a retrospective analysis of TEE and transthoracic echocardiography (TTE) among hospitalized adults with SAB in 3 prior observational studies (2002-2003, 2005-2006, and 2008-2009). Echocardiograms were ordered at the attending physician's discretion. SAB cases were stratified into the following types: complicated (persistent bacteremia [duration ≥3 d], relapse, and/or secondary foci); device-associated (intracardiac prosthetic devices); suspected endocarditis (the presence of murmurs or emboli); and uncomplicated (bacteremia duration ≤2 d, no device and/or secondary foci). We encountered 960 SAB cases; 83 were excluded (57 death/transfer/discharge within 48 h; 19 contaminants/no treatment; 7 care withdrawn). TEE and TTE were performed within 0-28 days of SAB onset in 177 (20.2%) and 321 (36.6%) instances, respectively. TEE was positive (with signs of endocarditis) in 42/177 (23.7%) cases: 7/39 (17.9%) community associated and 35/138 (25.4%) health care associated. It was positive in 29/120 (24.2%) complicated, 3/11 (27.3%) device-associated, 9/15 (60.0%) suspected endocarditis, and 1/31 (3.2%) uncomplicated cases of SAB. TTE was positive in 25/321 (7.8%) cases of SAB, 1 was uncomplicated; it was negative in 20/30 (66.7%) TEE-positive cases. Follow-up of ≥100 days was possible in 282/361 (78.1%) uncomplicated SAB; many (46.8%) received ≤15 days of therapy. None of them had relapses or secondary foci.These findings suggest that echocardiography is dispensable in cases of uncomplicated community-associated and health care-associated SAB. It should be limited to subsets with clinical findings of endocarditis, persistence, intracardiac devices, secondary foci, and relapse. The cost effectiveness of TTE prior to TEE among these patients is unknown.

Infection mechanism of biofilm-forming Staphylococcus aureus on indwelling foreign materials in mice

Indwelling foreign-body infections are a critical medical problem, especially in immunocompromised patients. To examine the pathogenicity of biofilm-forming bacteria settling on foreign materials, mice implanted with plastic discs were infected with Staphylococcus aureus. After opening a wide subcutaneous pocket on the dorsal side of mice with or without temporal leukocytopenia, a plastic sheet was placed in the left subcutaneous space; subsequently, bacteria in a planktonic state were dispersed over the subcutaneous space. Bacterial numbers were examined 7 days after inoculation. In subcutaneous tissue on the right, S. aureus was found only in leukocytopenic mice. Meanwhile, bacteria were detected on the plastic and neighbouring tissue in both leukocytopenic and normal mice; however, colony-forming analysis indicated that leukocytopenic mice possessed significantly more bacteria. Tissue reaction against bacteria was pathologically examined. Invading S. aureus induced severe inflammation. In transient leukocytopenic mice, bacterial microcolonies formed on the plastic as well as in the developed necrotic tissue - both of which were shielded from inflammatory cell infiltration - result in bacteraemia. These results indicate that biofilm-forming S. aureus settling on indwelling foreign material are tolerant against host immunity and assault neighbouring tissue, which may lead to chronic wound infection.

Clinical and microbiologic features guiding treatment recommendations for brain abscesses in children

BACKGROUND

There are no guidelines for the management of brain abscesses in children, and there is a paucity of recent data describing clinical and microbiologic features. We aimed to identify factors affecting outcome to inform antibiotic recommendations.

METHODS

From 1999 to 2009, 118 children presented with brain abscesses to 4 neurosurgical centers in the United Kingdom. Clinical, microbiologic and treatment data were collected.

RESULTS

The commonest preceding infection was sinusitis, with 59% of all children receiving antibiotics before diagnosis. Nonspecific symptoms were common, with only 13% having the triad of fever, headache and focal neurological deficit. Time between symptom onset and diagnosis varied widely (median, 10 days; range, 0-44). Magnetic resonance imaging was more frequently diagnostic than computed tomography. The most frequent organisms were Streptococcus milleri (38%), except after penetrating head injury or neurosurgery, for which Staphylococcus aureus was most common. The commonest empiric antibiotics were ceftriaxone/cefotaxime and metronidazole, which offered effective antimicrobial therapy in up to 83% of cases. Metronidazole added benefit in a maximum of 7% of cases, with ceftriaxone/cefotaxime alone sufficient in at least 76% and in all cases with cyanotic congenital heart disease or meningitis. A carbapenem would have been effective in 90%. The case fatality rate was 6% (33% in the immunocompromised). Long-term neurological sequelae affected 35%. Age younger than 5 years and a Glasgow Coma Scale score ≤8 were associated with poor outcome at 6 months.

CONCLUSIONS

We recommend ceftriaxone/cefotaxime and metronidazole as empiric treatment, although metronidazole may be unnecessary in many cases, with antistaphylococcal cover in cases of head trauma. Meropenem potentially would be a better choice in the immunocompromised. A prospective study of intravenous and oral treatment guided by clinical improvement is required beause 1-2 weeks of intravenous antibiotics during a total of 6 weeks may be sufficient in children.

Three cases of severely disseminated Staphylococcus aureus infection in patients treated with tocilizumab

We report three cases of severe disseminated Staphylococcus aureus infection in patients with rheumatoid arthritis (RA) treated with tocilizumab. Tocilizumab is a new drug, unknown to most internists, and injections given weeks before admission may not be considered by the patient as part of their 'current medical treatment', and the physician may not be aware that the patient is severely immunosuppressed. Severe infections in RA patients treated with tocilizumab may present with mild symptoms despite severe and disseminated infection and, as these patients are severely immunodeficient-intensive diagnostic work-up and early treatment should be performed. Systematic postmarketing studies are needed to clarify if there is a true increased risk of disseminated S aureus infections. We suggest caution when prescribing tocilizumab to patients with prosthetic joints and/or prior invasive S aureus infections and that patients are taught to inform health staff about their medication history and their increased risk of infection.

Adjunctive rifampicin to reduce early mortality from Staphylococcus aureus bacteraemia (ARREST): study protocol for a randomised controlled trial

Background

Staphylococcus aureus bacteraemia is a common and serious infection, with an associated mortality of ~25%. Once in the blood, S. aureus can disseminate to infect almost any organ, but bones, joints and heart valves are most frequently affected. Despite the infection’s severity, the evidence guiding optimal antibiotic therapy is weak: fewer than 1,500 patients have been included in 16 randomised controlled trials investigating S. aureus bacteraemia treatment. It is uncertain which antibiotics are most effective, their route of administration and duration, and whether antibiotic combinations are better than single agents. We hypothesise that adjunctive rifampicin, given in combination with a standard first-line antibiotic, will enhance killing of S. aureus early in the treatment course, sterilise infected foci and blood faster, and thereby reduce the risk of dissemination, metastatic infection and death. Our aim is to determine whether adjunctive rifampicin reduces all-cause mortality within 14 days and bacteriological failure or death within 12 weeks from randomisation.

Methods

We will perform a parallel group, randomised (1:1), blinded, placebo-controlled trial in NHS hospitals across the UK. Adults (≥18 years) with S. aureus (meticillin-susceptible or resistant) grown from at least one blood culture who have received ≤96 h of active antibiotic therapy for the current infection and do not have contraindications to the use of rifampicin will be eligible for inclusion. Participants will be randomised to adjunctive rifampicin (600-900mg/day; orally or intravenously) or placebo for the first 14 days of therapy in combination with standard single-agent antibiotic therapy. The co-primary outcome measures will be all-cause mortality up to 14 days from randomisation and bacteriological failure/death (all-cause) up to 12 weeks from randomisation. 940 patients will be recruited, providing >80% power to detect 45% and 30% reductions in the two co-primary endpoints of death by 14 days and bacteriological failure/death by 12 weeks respectively.

Discussion

This pragmatic trial addresses the long-standing hypothesis that adjunctive rifampicin improves outcome from S. aureus bacteraemia through enhanced early bacterial killing. If proven correct, it will provide a paradigm through which further improvements in outcome from S. aureus bacteraemia can be explored.

Trial registration

Current Controlled Trial ISRCTN 37666216

Treatment duration for uncomplicated Staphylococcus aureus bacteremia to prevent relapse: analysis of a prospective observational cohort study

Practice guidelines recommend at least 14 days of antibiotic therapy for uncomplicated Staphylococcus aureus bacteremia (SAB). However, these recommendations have not been formally evaluated in clinical studies. To evaluate the duration of therapy for uncomplicated SAB, we analyzed data from our prospective cohort of patients with SAB. A prospective observational cohort study was performed in patients with SAB at a tertiary-care hospital in Korea between August 2008 and September 2010. All adult patients with SAB were prospectively enrolled and observed over a 12-week period. Uncomplicated SAB was defined as follows: negative results of follow-up blood cultures at 2 to 4 days, defervescence within 72 h of therapy, no evidence of metastatic infection, and catheter-related bloodstream infection or primary bacteremia without evidence of endocarditis on echocardiography. Of 483 patients with SAB, 111 met the study criteria for uncomplicated SAB. Fifty-three (47.7%) had methicillin-resistant SAB. When short-course therapy (<14 days) and intermediate-course therapy (≥14 days) were compared, the treatment failure rates (10/38 [26.3%] versus 16/73 [21.9%]) and crude mortality (7/38 [18.4%] versus 16/73 [21.9%]) did not differ significantly between the two groups. However, short-course therapy was significantly associated with relapse (3/38 [7.9%] versus 0/73; P = 0.036). In multivariate analysis, primary bacteremia was associated with a trend toward increased treatment failure (P = 0.06). Therefore, in the treatment of uncomplicated SAB, it seems reasonable to consider at least 14 days of antibiotic therapy to prevent relapse, as practice guidelines recommend. Because of its poor prognosis, primary bacteremia, even with a low risk of complication, should not be treated with short-course therapy.

A privileged intraphagocyte niche is responsible for disseminated infection of Staphylococcus aureus in a zebrafish model

The innate immune system is the primary defence against the versatile pathogen, Staphylococcus aureus. How this organism is able to avoid immune killing and cause infections is poorly understood. Using an established larval zebrafish infection model, we have shown that overwhelming infection is due to subversion of phagocytes by staphylococci, allowing bacteria to evade killing and found foci of disease. Larval zebrafish coinfected with two S. aureus strains carrying different fluorescent reporter gene fusions (but otherwise isogenic) had bacterial lesions, at the time of host death, containing predominantly one strain. Quantitative data using two marked strains revealed that the strain ratios, during overwhelming infection, were often skewed towards the extremes, with one strain predominating. Infection with passaged bacterial clones revealed the phenomenon not to bedue to adventitious mutations acquired by the pathogen. After infection of the host, all bacteria are internalized by phagocytes and the skewing of population ratios is absolutely dependent on the presence of phagocytes. Mathematical modelling of pathogen population dynamics revealed the data patterns are consistent with the hypothesis that a small number of infected phagocytes serve as an intracellular reservoir for S. aureus, which upon release leads to disseminated infection. Strategies to specifically alter neutrophil/macrophage numbers were used to map the potential subpopulation of phagocytes acting as a pathogen reservoir, revealing neutrophils as the likely ‘niche’. Subsequently in a murine sepsis model, S. aureus abscesses in kidneys were also found to be predominantly clonal, therefore likely founded by an individual cell, suggesting a potential mechanism analogous to the zebrafish model with few protected niches. These findings add credence to the argument that S. aureus control regimes should recognize both the intracellular as well as extracellular facets of the S. aureus life cycle.

Characterization of the mechanism of protection mediated by CS-D7, a monoclonal antibody to Staphylococcus aureus iron regulated surface determinant B (IsdB)

We previously reported the development of a human monoclonal antibody (CS-D7, IgG₁) with specificity and affinity for the iron regulated surface determinant B (IsdB) of Staphylococcus aureus. CS-D7 mediates opsonophagocytic killing in vitro and protection in a murine sepsis model. In light of recent data indicating that IsdB specific T cells (CD4+, Th17), not Ab, mediate protection after vaccination with IsdB, it is important to investigate the mechanism of protection mediated by CS-D7. The mAb was examined to determine if it blocked heme binding to IsdB in vitro. The mAb was not found to have heme blocking activity, nor did it prevent bacterial growth under in vivo conditions, in an implanted growth chamber. To assess the role of the mAb Fc a point mutation was introduced at aa 297 (CS-D7·N297A). This point mutation removes Fc effector functions. In vitro analysis of the mutein confirmed that it lacked measurable binding to FcγR, and that it did not fix complement. The mutein had dramatically reduced in vitro opsonic OP activity compared to CS-D7. Nonetheless, the mutein conferred protection equivalent to the wild type mAb in the murine sepsis model. Both wild type and mutein mAbs were efficacious in FcγR deletion mice (including both FcγRII^−/− mice and FcγRIII^−/− mice), indicating that these receptors were not essential for mAb mediated protection in vivo. Protection mediated by CS-D7 was lost in Balb/c mice depleted of C3 with cobra venom factor (CFV), was lost in mice depleted of superoxide dismutase (SOD) in P47phox deletion mice, and as previously reported, was absent in SCID mice (Joshi et al., 2012). Enhanced clearance of S. aureus in the liver of CS-D7 treated mice and enhanced production of IFN-γ, but not of IL17, may play a role in the mechanism of protection mediated by the mAb. CS-D7 apparently mediates survival in challenged mice through a mechanism involving complement, phagocytes, and lymphocytes, but which does not depend on interaction with FcγR, or on blocking heme uptake.