Staphylococcus aureus clonal complex 75 (herein referred to as S. argenteus) lacks the carotenoid pigment operon, crtOPQMN, responsible for production of the putative virulence factor, staphyloxanthin. Although a common cause of community-onset skin infections among Indigenous populations in northern Australia, this clone is infrequently isolated from hospital-based patients with either bacteremic or nonbacteremic infections. We hypothesized that S. argenteus would have attenuated virulence compared to other S. aureus strains due to its staphyloxanthin “deficiency.” Compared to prototypical S. aureus strains, S. argenteus was more susceptible to oxidative stress and neutrophil killing in vitro and had reduced virulence in murine sepsis and skin infection models. Transformation with pTX-crtOPQMN resulted in staphyloxanthin expression and increased resistance to oxidative stress in vitro. However, neither resistance to neutrophil killing nor in vivo virulence was increased. Thus, reduced virulence of S. argenteus in these models is due to mechanisms unrelated to lack of staphyloxanthin production.
Staphylococcus aureus; staphyloxanthin; virulence; Australia; carotenoid pigment
The lungs are a major target for infection and a key battleground in the fight against the development of antimicrobial drug–resistant pathogens. Ventilator-associated pneumonia (VAP) is associated with mortality rates of 24–50%. The optimal duration of antibiotic therapy against VAP is unknown, but prolonged courses are associated with the emergence of bacterial resistance. De-escalation strategies in which treatment is discontinued based on signs of clinical resolution, fixed durations of therapy (generally 7–8 d), or serum procalcitonin responses have been shown to decrease antibiotic consumption. Outcomes are comparable to longer treatment courses, with the possible exception of VAP due to nonfermenting, gram-negative bacilli such as Pseudomonas aeruginosa. Staphylococcus aureus is a leading cause of VAP and other infections. Outcomes after S. aureus infection are shaped by the interplay between environmental, bacterial, and host genetic factors. It is increasingly clear that mechanisms of pathogenesis vary in different types of S. aureus infections. Genome-scale studies of S. aureus strains, host responses, and host genetics are redefining our understanding of the pathogenic mechanisms underlying VAP. Genome-sequencing technologies are also revolutionizing our understanding of the molecular epidemiology, evolution, and transmission of influenza. Deep sequencing using next-generation technology platforms is defining the remarkable genetic diversity of influenza strains within infected hosts. Investigators have demonstrated that antiviral drug-resistant influenza may be present prior to the initiation of treatment. Moreover, drug-resistant minor variant influenza strains can be transmitted from person to person in the absence of selection pressure. Studies of lung infections and the causative pathogens will remain at the cutting edge of clinical and basic medical research.
pneumonia; ventilator-associated pneumonia; Staphylococcus aureus; influenza
Gram-negative bacterial bloodstream infection (BSI) is a serious condition with estimated 30% mortality. Clinical outcomes for patients with severe infections improve when antibiotics are appropriately chosen and given early. The objective of this study was to estimate the association of prior healthcare exposure on time to appropriate antibiotic therapy in patients with gram-negative BSI.
We performed a multicenter cohort study of adult, hospitalized patients with gram-negative BSI using time to event analysis in nine community hospitals from 2003-2006. Event time was defined as the first administration of an antibiotic with in
vitro activity against the infecting organism. Healthcare exposure status was categorized as community-acquired, healthcare-associated, or hospital-acquired. Time to appropriate therapy among groups of patients with differing healthcare exposure status was assessed using Kaplan-Meier analyses and multivariate Cox proportional hazards models.
The cohort included 578 patients with gram-negative BSI, including 320 (55%) healthcare-associated, 217 (38%) community-acquired, and 41 (7%) hospital-acquired infections. 529 (92%) patients received an appropriate antibiotic during their hospitalization. Time to appropriate therapy was significantly different among the groups of healthcare exposure status (log-rank p=0.02). Time to first antibiotic administration regardless of drug appropriateness was not different between groups (p=0.3). The unadjusted hazard ratios (HR) (95% confidence interval) were 0.80 (0.65-0.98) for healthcare-associated and 0.72 (0.63-0.82) for hospital-acquired, relative to patients with community-acquired BSI. In multivariable analysis, interaction was found between the main effect and baseline Charlson comorbidity index. When Charlson index was 3, adjusted HRs were 0.66 (0.48-0.92) for healthcare-associated and 0.57 (0.44-0.75) for hospital-acquired, relative to patients with community-acquired infections.
Patients with healthcare-associated or hospital-acquired BSI experienced delays in receipt of appropriate antibiotics for gram-negative BSI compared to patients with community-acquired BSI. This difference was not due to delayed initiation of antibiotic therapy, but due to the inappropriate choice of antibiotic.
Aggressive diagnosis and treatment of patients presenting to the emergency department (ED) with septic shock has been shown to reduce mortality. To enhance the ability to intervene in patients with lesser illness severity, a better understanding of the natural history of the early progression from simple infection to more severe illness is needed.
The objectives were to 1) describe the clinical presentation of ED sepsis, including types of infection and causative microorganisms, and 2) determine the incidence, patient characteristics, and mortality associated with early progression to septic shock among ED patients with infection.
This was a multicenter study of adult ED patients with sepsis but no evidence of shock. Multivariable logistic regression was used to identify patient factors for early progression to shock and its association with 30-day mortality.
Of 472 patients not in shock at ED presentation (systolic blood pressure > 90 mm Hg and lactate < 4 mmol / L), 84 (17.8%) progressed to shock within 72 hours. Independent factors associated with early progression to shock included older age, female sex, hyperthermia, anemia, comorbid lung disease, and vascular access device infection. Early progression to shock (vs. no progression) was associated with higher 30-day mortality (13.1% vs. 3.1%, odds ratio [OR] = 4.72, 95% confidence interval [CI] = 2.01 to 11.1; p ≤ 0.001). Among 379 patients with uncomplicated sepsis (i.e., no evidence of shock or any end-organ dysfunction), 86 (22.7%) progressed to severe sepsis or shock within 72 hours of hospital admission.
A significant portion of ED patients with less severe sepsis progress to severe sepsis or shock within 72 hours. Additional diagnostic approaches are needed to risk stratify and more effectively treat ED patients with sepsis.
sepsis; outcomes; septic shock; progression; biomarkers
Carbapenem resistance in Gram-negative bacteria is on the rise in the United States. A regional network was established to study microbiological and genetic determinants of clinical outcomes in hospitalized patients with carbapenem-resistant (CR) Klebsiella pneumoniae in a prospective, multicenter, observational study. To this end, predefined clinical characteristics and outcomes were recorded and K. pneumoniae isolates were analyzed for strain typing and resistance mechanism determination. In a 14-month period, 251 patients were included. While most of the patients were admitted from long-term care settings, 28% of them were admitted from home. Hospitalizations were prolonged and complicated. Nonsusceptibility to colistin and tigecycline occurred in isolates from 7 and 45% of the patients, respectively. Most of the CR K. pneumoniae isolates belonged to repetitive extragenic palindromic PCR (rep-PCR) types A and B (both sequence type 258) and carried either blaKPC-2 (48%) or blaKPC-3 (51%). One isolate tested positive for blaNDM-1, a sentinel discovery in this region. Important differences between strain types were noted; rep-PCR type B strains were associated with blaKPC-3 (odds ratio [OR], 294; 95% confidence interval [CI], 58 to 2,552; P < 0.001), gentamicin nonsusceptibility (OR, 24; 95% CI, 8.39 to 79.38; P < 0.001), amikacin susceptibility (OR, 11.0; 95% CI, 3.21 to 42.42; P < 0.001), tigecycline nonsusceptibility (OR, 5.34; 95% CI, 1.30 to 36.41; P = 0.018), a shorter length of stay (OR, 0.98; 95% CI, 0.95 to 1.00; P = 0.043), and admission from a skilled-nursing facility (OR, 3.09; 95% CI, 1.26 to 8.08; P = 0.013). Our analysis shows that (i) CR K. pneumoniae is seen primarily in the elderly long-term care population and that (ii) regional monitoring of CR K. pneumoniae reveals insights into molecular characteristics. This work highlights the crucial role of ongoing surveillance of carbapenem resistance determinants.
The significance of heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) is unknown. Using a multinational collection of isolates from methicillin-resistant S. aureus (MRSA) infective endocarditis (IE), we characterized IE patients with and without hVISA, and genotyped the infecting strains.
MRSA bloodstream isolates from 65 patients with definite IE from 8 countries underwent PCR for 31 virulence genes, pulsed-field gel electrophoresis, and multilocus sequence typing. hVISA was defined using population analysis profiling (PAP).
Nineteen (29.2%) of 65 MRSA IE isolates exhibited hVISA by PAP. Isolates from Oceania and Europe were more likely to exhibit hVISA than isolates from the United States (77.8% vs. 35.0% vs. 13.9%; P < .001). The prevalence of hVISA was higher among isolates with a vancomycin minimum inhibitory concentration of 2 mg/L (P = .026). hVISA-infected patients were more likely to have persistent bacteremia (68.4% vs. 37.0%; P = .029) and heart failure (47.4% vs. 19.6%; P = .033). Mortality of hVISA- and non-hVISA-infected patients did not differ (42.1% vs. 34.8%, P = .586). hVISA and non-hVISA isolates were genotypically similar.
In these analyses, hVISA occurred in over one-quarter of MRSA IE isolates, was associated with certain IE complications, and varied in frequency by geographic region.
hVISA; Methicillin-resistant Staphylococcus aureus; endocarditis; genotype
Background. Using multinational collections of methicillin-susceptible Staphylococcus aureus (MSSA) isolates from infective endocarditis (IE) and soft tissue infections (STIs), we sought to (1) validate the finding that S. aureus in clonal complex (CC) 30 is associated with hematogenous complications and (2) test the hypothesis that specific genetic characteristics in S. aureus are associated with infection severity.
Methods. IE and STI isolates from 2 cohorts were frequency matched by geographic origin. Isolates underwent spa typing to infer CC and multiplex polymerase chain reaction for presence of virulence genes.
Results. 114 isolate pairs were genotyped. IE isolates were more likely to be CC30 (19.5% vs 6.2%; P = .005) and to contain 3 adhesins (clfB, cna, map/eap; P < .0001 for all) and 5 enterotoxins (tst, sea, sed, see, and sei; P ≤ .005 for all). CC30 isolates were more likely to contain cna, tst, sea, see, seg, and chp (P < .05 for all).
Conclusions. MSSA IE isolates were significantly more likely to be CC30 and to possess a distinct repertoire of virulence genes than MSSA STI isolates from the same region. The genetic basis of this association requires further study.
The impact of Panton-Valentine leukocidin (PVL) on the outcome in Staphylococcus aureus pneumonia is controversial. We genotyped S. aureus isolates from patients with hospital-acquired pneumonia (HAP) enrolled in two registrational multinational clinical trials for the genetic elements carrying pvl and 30 other virulence genes. A total of 287 isolates (173 methicillin-resistant S. aureus [MRSA] and 114 methicillin-susceptible S. aureus [MSSA] isolates) from patients from 127 centers in 34 countries for whom clinical outcomes of cure or failure were available underwent genotyping. Of these, pvl was detected by PCR and its product confirmed in 23 isolates (8.0%) (MRSA, 18/173 isolates [10.4%]; MSSA, 5/114 isolates [4.4%]). The presence of pvl was not associated with a higher risk for clinical failure (4/23 [17.4%] versus 48/264 [18.2%]; P = 1.00) or mortality. These findings persisted after adjustment for multiple potential confounding variables. No significant associations between clinical outcome and (i) presence of any of the 30 other virulence genes tested, (ii) presence of specific bacterial clone, (iii) levels of alpha-hemolysin, or (iv) delta-hemolysin production were identified. This study suggests that neither pvl presence nor in vitro level of alpha-hemolysin production is the primary determinant of outcome among patients with HAP caused by S. aureus.
We describe the development and application of a pooled Suppression Subtractive Hybridization (PSSH) method to describe differences between the genomic content of a pool of clinical Staphylococcus aureus isolates and a sequenced reference strain. In comparative bacterial genomics, Suppression Subtractive Hybridization (SSH) is normally utilized to compare genomic features or expression profiles of one strain versus another, which limits its ability to analyze communities of isolates. However, a PSSH approach theoretically enables the user to characterize the entirety of gene content unique to a related group of isolates in a single reaction. These unique fragments may then be linked to individual isolates through standard PCR. This method was applied to examine the genomic diversity found in pools of Staphylococcus aureus isolates associated with complicated bacteremia infections leading to endocarditis and osteomyelitis. Across four pools of 10 isolates each, four hundred and twenty nine fragments not found in or significantly divergent from the S. aureus NCTC 8325 reference genome were detected. These fragments could be linked to individual strains within its pool by PCR. This is the first use of PSSH to examine the S. aureus pangenome. We propose that PSSH is a powerful tool for researchers interested in rapidly comparing the genomic content of multiple unstudied isolates.
Staphylococcus aureus; pangenome; subtractive hybridization
The role of vancomycin has been challenged by the availability of alternative antibiotics, increased reports of vancomycin failure, and uncertainties in dosing. This manuscript considers the optimal treatment of methicillin-resistant Staphylococcus aureus infections.
For more than 4 decades, vancomycin has been the antibiotic of choice for methicillin-resistant Staphylococcus aureus (MRSA) infections. Recently, infections due to isolates with high but susceptible vancomycin minimum inhibitory concentrations have been associated with additional treatment failures and patient mortality. These poorer outcomes may in part be explained by the inability of attaining appropriate vancomycin levels in these patients. However, assumptions that these poor outcomes are solely due to failure to achieve optimal serum levels of vancomycin are premature. The availability of effective alternatives further erodes the position of vancomycin as first-line therapy. The emergence of resistance and cost considerations, however, favor a more measured approach when using alternative antimicrobials. Collectively, the current available data suggest that the optimal therapy for MRSA infections remains unclear. In the absence of further data, the Infectious Diseases Society of America guidelines remain relevant and inform clinicians of best practice for treating patients with MRSA infections.
Staphylococcus aureus; MRSA, hVISA, VISA; vancomycin; AUC/MIC targets; minimum inhibitory concentration (MIC)
Using A/J mice, which are susceptible to Staphylococcus aureus, we sought to identify genetic determinants of susceptibility to S. aureus, and evaluate their function with regard to S. aureus infection. One QTL region on chromosome 11 containing 422 genes was found to be significantly associated with susceptibility to S. aureus infection. Of these 422 genes, whole genome transcription profiling identified five genes (Dcaf7, Dusp3, Fam134c, Psme3, and Slc4a1) that were significantly differentially expressed in a) S. aureus –infected susceptible (A/J) vs. resistant (C57BL/6J) mice and b) humans with S. aureus blood stream infection vs. healthy subjects. Three of these genes (Dcaf7, Dusp3, and Psme3) were down-regulated in susceptible vs. resistant mice at both pre- and post-infection time points by qPCR. siRNA-mediated knockdown of Dusp3 and Psme3 induced significant increases of cytokine production in S. aureus-challenged RAW264.7 macrophages and bone marrow derived macrophages (BMDMs) through enhancing NF-κB signaling activity. Similar increases in cytokine production and NF-κB activity were also seen in BMDMs from CSS11 (C57BL/6J background with chromosome 11 from A/J), but not C57BL/6J. These findings suggest that Dusp3 and Psme3 contribute to S. aureus infection susceptibility in A/J mice and play a role in human S. aureus infection.
Staphylococcus aureus causes life-threatening infections in humans. Host genetic determinants influence the outcome of S. aureus infection, yet are poorly understood. Susceptible A/J and resistant C57BL/6J mice provide a unique platform to study the genetic difference responsible for variable host response to S. aureus infection. We showed that chromosome 11 in A/J was responsible for susceptibility to S. aureus. We further identified a QTL locus on Chromosome 11 significantly associated with S. aureus susceptibility. Five genes in the QTL (Dcaf7, Dusp3, Fam134c, Psme3, and Slc4a1) were significantly differently expressed in a) susceptible vs. resistant mice, and b) humans with S. aureus blood stream infection vs. healthy human subjects. Three genes (Dusp3, Psme3, and Dcaf7) were down-regulated in susceptible A/J mice. siRNA-mediated knockdown of Dusp3 and Psme3 in bone marrow derived macrophage (BMDMs) significantly enhanced cytokine responses through NF-κB activity upon S. aureus challenge in a pattern that was also present in S. aureus-challenged BMDMs from susceptible CSS11 (chr. 11 from A/J but otherwise C57BL/6J) mice, but not resistant C57BL/6J mice. These findings suggest that Dusp3 and Psme3 contribute to S. aureus infection susceptibility in A/J mice and play a role in human S. aureus infection.
The use of daptomycin in Gram-positive left-sided infective endocarditis (IE) has significantly increased. The purpose of this study was to assess the influence of high-dose daptomycin on the outcome of left-sided IE due to Gram-positive pathogens. This was a prospective cohort study based on 1,112 cases from the International Collaboration on Endocarditis (ICE)-Plus database and the ICE-Daptomycin Substudy database from 2008 to 2010. Among patients with left-sided IE due to Staphylococcus aureus, coagulase-negative staphylococci, and Enterococcus faecalis, we compared those treated with daptomycin (cohort A) to those treated with standard-of-care (SOC) antibiotics (cohort B). The primary outcome was in-hospital mortality. Time to clearance of bacteremia, 6-month mortality, and adverse events (AEs) ascribable to daptomycin were also assessed. There were 29 and 149 patients included in cohort A and cohort B, respectively. Baseline comorbidities did not differ between the two cohorts, except for a significantly higher prevalence of diabetes and previous episodes of IE among patients treated with daptomycin. The median daptomycin dose was 9.2 mg/kg of body weight/day. Two-thirds of the patients treated with daptomycin had failed a previous antibiotic regimen. In-hospital and 6-month mortalities were similar in the two cohorts. In cohort A, median time to clearance of methicillin-resistant S. aureus (MRSA) bacteremia was 1.0 day, irrespective of daptomycin dose, representing a significantly faster bacteremia clearance compared to SOC (1.0 versus 5.0 days; P < 0.01). Regimens with higher daptomycin doses were not associated with increased incidence of AEs. In conclusion, higher-dose daptomycin may be an effective and safe alternative to SOC in the treatment of left-sided IE due to common Gram-positive pathogens.
While the majority of healthcare in the US is provided in community hospitals, the epidemiology and treatment of bloodstream infections in this setting is unknown.
Methods and Findings
We undertook this multicenter, retrospective cohort study to 1) describe the epidemiology of bloodstream infections (BSI) in a network of community hospitals and 2) determine risk factors for inappropriate therapy for bloodstream infections in community hospitals. 1,470 patients were identified as having a BSI in 9 community hospitals in the southeastern US from 2003 through 2006. The majority of BSIs were community-onset, healthcare associated (n = 823, 56%); 432 (29%) patients had community-acquired BSI, and 215 (15%) had hospital-onset, healthcare-associated BSI. BSIs due to multidrug-resistant pathogens occurred in 340 patients (23%). Overall, the three most common pathogens were S. aureus (n = 428, 28%), E. coli (n = 359, 24%), coagulase-negative Staphylococci (n = 148, 10%), though type of infecting organism varied by location of acquisition (e.g., community-acquired). Inappropriate empiric antimicrobial therapy was given to 542 (38%) patients. Proportions of inappropriate therapy varied by hospital (median = 33%, range 21–71%). Multivariate logistic regression identified the following factors independently associated with failure to receive appropriate empiric antimicrobial therapy: hospital where the patient received care (p<0.001), assistance with ≥3 ADLs (p = 0.005), Charlson score (p = 0.05), community-onset, healthcare-associated infection (p = 0.01), and hospital-onset, healthcare-associated infection (p = 0.02). Important interaction was observed between Charlson score and location of acquisition.
Our large, multicenter study provides the most complete picture of BSIs in community hospitals in the US to date. The epidemiology of BSIs in community hospitals has changed: community-onset, healthcare-associated BSI is most common, S. aureus is the most common cause, and 1 of 3 patients with a BSI receives inappropriate empiric antimicrobial therapy. Our data suggest that appropriateness of empiric antimicrobial therapy is an important and needed performance metric for physicians and hospital stewardship programs in community hospitals.
Sepsis is a common cause of death, but outcomes in individual patients are difficult to predict. Elucidating the molecular processes that differ between sepsis patients who survive and those who die may permit more appropriate treatments to be deployed. We examined the clinical features, and the plasma metabolome and proteome of patients with and without community-acquired sepsis, upon their arrival at hospital emergency departments and 24 hours later. The metabolomes and proteomes of patients at hospital admittance who would die differed markedly from those who would survive. The different profiles of proteins and metabolites clustered into fatty acid transport and β-oxidation, gluconeogenesis and the citric acid cycle. They differed consistently among several sets of patients, and diverged more as death approached. In contrast, the metabolomes and proteomes of surviving patients with mild sepsis did not differ from survivors with severe sepsis or septic shock. An algorithm derived from clinical features together with measurements of seven metabolites predicted patient survival. This algorithm may help to guide the treatment of individual patients with sepsis.
To identify metabolomic biomarkers predictive of Intensive Care Unit (ICU) mortality in adults.
Comprehensive metabolomic profiling of plasma at ICU admission to identify biomarkers associated with mortality has recently become feasible.
We performed metabolomic profiling of plasma from 90 ICU subjects enrolled in the BWH Registry of Critical Illness (RoCI). We tested individual metabolites and a Bayesian Network of metabolites for association with 28-day mortality, using logistic regression in R, and the CGBayesNets Package in MATLAB. Both individual metabolites and the network were tested for replication in an independent cohort of 149 adults enrolled in the Community Acquired Pneumonia and Sepsis Outcome Diagnostics (CAPSOD) study.
We tested variable metabolites for association with 28-day mortality. In RoCI, nearly one third of metabolites differed among ICU survivors versus those who died by day 28 (N = 57 metabolites, p<.05). Associations with 28-day mortality replicated for 31 of these metabolites (with p<.05) in the CAPSOD population. Replicating metabolites included lipids (N = 14), amino acids or amino acid breakdown products (N = 12), carbohydrates (N = 1), nucleotides (N = 3), and 1 peptide. Among 31 replicated metabolites, 25 were higher in subjects who progressed to die; all 6 metabolites that are lower in those who die are lipids. We used Bayesian modeling to form a metabolomic network of 7 metabolites associated with death (gamma-glutamylphenylalanine, gamma-glutamyltyrosine, 1-arachidonoylGPC(20:4), taurochenodeoxycholate, 3-(4-hydroxyphenyl) lactate, sucrose, kynurenine). This network achieved a 91% AUC predicting 28-day mortality in RoCI, and 74% of the AUC in CAPSOD (p<.001 in both populations).
Both individual metabolites and a metabolomic network were associated with 28-day mortality in two independent cohorts. Metabolomic profiling represents a valuable new approach for identifying novel biomarkers in critically ill patients.
Major postoperative infections (MPIs) are poorly understood complications of cardiac surgery. We examined the epidemiology, microbiology, and outcome of MPIs occurring after cardiac surgery.
The study cohort was drawn from the Society of Thoracic Surgeon National Cardiac Database and comprised adults who underwent cardiac surgery at 5 tertiary hospitals between 2000 and 2004. We studied the incidence, microbiology, and risk factors of MPI (bloodstream or chest wound infections within 30 days after surgery), as well as 30-day mortality. We used multivariate regression analyses to evaluate the risk of MPI and mortality.
MPI was identified in 341 of 10,522 patients (3.2%). Staphylococci were found in 52.5% of these patients, gram-negative bacilli (GNB) in 24.3%, and other pathogens in 23.2%. High body mass index, previous coronary bypass surgery, emergency surgery, renal impairment, immunosuppression, cardiac failure, and peripheral/cerebrovascular disease were associated with the development of MPI. Median postoperative duration of hospitalization (15 days vs 6 days) and mortality (8.5% vs 2.2%) were higher in patients with MPIs. Compared with uninfected individuals, odds of mortality were higher in patients with S aureus MPIs (adjusted odds ratio, 3.7) and GNB MPIs (adjusted odds ratio, 3.0).
Staphylococci accounted for the majority of MPIs after cardiac surgery. Mortality was higher in patients with Staphylococcus aureus- and GNB-related MPIs than in patients with MPIs caused by other pathogens and uninfected patients. Preventive strategies should target likely pathogens and high-risk patients undergoing cardiac surgery.
Wound infection; Sepsis; Cardiac surgical procedures; Morbidity; Mortality
Circulating biomarkers can facilitate sepsis diagnosis enabling early management and improved outcomes. Procalcitonin (PCT) has been suggested to have superior diagnostic utility compared to other biomarkers.
Adults with suspected sepsis in the Emergency Department were enrolled. PCT, CRP, and IL-6 were correlated with infection likelihood, sepsis severity, and septicemia. Multivariable models were constructed for length-of-stay and discharge to a higher level of care.
Of 336 enrolled subjects, 60% had definite infection, 13% possible infection and 27% no infection. Of those with infection, 202 presented with sepsis, 28 with severe sepsis, and 17 with septic shock. Overall, 21% of subjects were septicemic. PCT, IL6, and CRP levels were significantly higher in septicemia (median PCT 2.3 vs. 0.2ng/mL; IL-6 178 vs. 72pg/mL; CRP 106 vs. 62mg/dL, p<0.001). Biomarker concentrations increased with greater likelihood of infection and sepsis severity. Using ROC analysis, PCT best predicted septicemia (0.78 vs. IL-6 0.70 and CRP 0.67) but CRP better identified clinical infection (0.75 vs. PCT 0.71 and IL-6 0.69). A PCT cut-off of 0.5ng/mL had 72.6% sensitivity and 69.5% specificity for bacteremia as well as 40.7% sensitivity and 87.2% specificity for diagnosing infection. A combined clinical-biomarker model revealed that CRP was marginally associated with length-of-stay (p=0.015), but no biomarker independently predicted discharge to a higher level of care.
In adult Emergency Department patients with suspected sepsis, PCT, IL-6, and CRP highly correlate with several infection parameters, but do not meaningfully predict length-of-stay or need for discharge to a higher level of care.
Sepsis; Procalcitonin; Interleukin-6; C-Reactive Protein; Sensitivity and Specificity
Staphylococcus aureus is a leading cause of catheter infections, and biofilm formation plays a key role in the pathogenesis. Metal ion chelators inhibit bacterial biofilm formation and viability, making them attractive candidates as components in catheter lock solutions. The goal of this study was to characterize further the effect of chelators on biofilm formation. The effect of the calcium chelators ethylene glycol tetraacetic acid (EGTA) and trisodium citrate (TSC) on biofilm formation by 30 S. aureus strains was tested. The response to subinhibitory doses of EGTA and TSC varied dramatically depending on strain variation. In some strains, the chelators prevented biofilm formation, in others they had no effect, and they actually enhanced biofilm formation in others. The molecular basis for this phenotypic variability was investigated using two related strains: Newman, in which biofilm formation was inhibited by chelators, and 10833, which formed strong biofilms in the presence of chelators. It was found that deletion of the gene encoding the surface adhesin clumping factor B (clfB) completely eliminated chelator-induced biofilm formation in strain 10833. The role of ClfB in biofilm formation activity in chelators was confirmed in additional strains. It was concluded that biofilm-forming ability varies strikingly depending on strain background, and that ClfB is involved in biofilm formation in the presence EGTA and citrate. These results suggest that subinhibitory doses of chelating agents in catheter lock solutions may actually augment biofilm formation in certain strains of S. aureus, and emphasize the importance of using these agents appropriately so that inhibitory doses are achieved consistently.
The clinical profile and outcome of nosocomial and non-nosocomial health care–associated native valve endocarditis are not well defined.
To describe the prevalence, clinical characteristics, and outcomes of nosocomial and non-nosocomial health care–associated native valve endocarditis.
Prospective observational study.
61 hospitals in 28 countries.
Patients with definite native valve endocarditis and no history of injection drug use who were enrolled in the International Collaboration on Endocarditis–Prospective Cohort Study from June 2000 to August 2005.
Characteristics of nosocomial and non-nosocomial health care–associated native valve endocarditis cases were described and compared with those cases acquired in the community.
Health care–associated native valve endocarditis was present in 557 (34%) of 1622 patients with native valve endocarditis and no history of injection drug use (nosocomial native valve endocarditis 303 patients [54%]; non-nosocomial health care–associated native valve endocarditis 254 patients [46%]). Staphylococcus aureus was the most common cause of health care-associated native valve endocarditis (nosocomial native valve endocarditis, 47%; non-nosocomial health care–associated native valve endocarditis, 42%; p=0.3), with a notable proportion of methicillin-resistant S. aureus (nosocomial native valve endocarditis, 57%; non-nosocomial health care–associated native valve endocarditis, 41%; p=0.014). Patients with health care–associated native valve endocarditis had lower rates of cardiac surgery (41% health care–associated native valve endocarditis vs 51% community-acquired native valve endocarditis, p<0.001) and higher in-hospital mortality rates than patients with community-acquired native valve endocarditis (25% health care–associated native valve endocarditis vs. 13% community-acquired native valve endocarditis vs., p<0.001). Multivariable analysis confirmed a higher mortality associated with health care–associated native valve endocarditis (incidence risk ratio=1.20 (CI 95%, 1.03–1.61).
This study involves tertiary hospitals with cardiac surgery programs. The results may not be generalized to patient populations receiving care in other types of facility.
More than one-third of all cases of native valve endocarditis in non-drug users involve contact with health care. S. aureus is the leading cause of health care–associated native valve endocarditis. Non-nosocomial health care–associated native valve endocarditis is common, especially in the US. Patients with health care-associated and community-acquired native valve endocarditis differ in their presentation, microbiology, and outcome. By contrast, patients with nosocomial and non-nosocomial healthcare-associated endocarditis are similar.
infective endocarditis; healthcare-associated endocarditis; nosocomial endocarditis; non-nosocomial healthcare-associated endocarditis; community-acquired endocarditis; Staphylococcal aureus endocarditis; MRSA endocarditis; Coagulase-negative staphylococcal endocarditis; Surgery; Outcome
The aim of this study was to provide a contemporary picture of the presentation, etiology and outcome of infective endocarditis (IE) in a large patient cohort from multiple locations worldwide.
Prospective cohort study of 2781 adults with definite IE admitted to 58 hospitals in 25 countries between June 2000 and September 2005.
The median age of the cohort was 57.9 (IQR 43.2–71.8) years and 72% had native valve IE. Most (77%) patients presented early in the disease (<30 days) with few of the classic clinical hallmarks of IE. Recent health-care exposure was found in one quarter of patients. Staphylococcus aureus was the most common pathogen (31%). Mitral (41%) and aortic (38%) valves were infected most commonly. Complications were common: stroke (17%); embolization other than stroke (23%); heart failure (32%) and intracardiac abscess (14%). Surgical therapy was common (48%) and in-hospital mortality remained high (18%). Prosthetic valve involvement (OR 1.47, 95%CI 1.13–1.90), increasing age (OR 1.30, 95%CI 1.17–1.46 per 10-year interval), pulmonary edema (OR 1.79, 95%CI 1.39–2.30), S. aureus infection (OR 1.54, 95%CI 1.14–2.08), coagulase-negative staphylococcal infection (OR 1.50, 95%CI 1.07–2.10), mitral valve vegetation (OR 1.34, 95%CI 1.06–1.68), and paravalvular complications (OR 2.25, 95%CI 1.64–3.09) were associated with increased risk of in-hospital death, while viridans streptococcal infection (OR 0.52, 95%CI 0.33–0.81) and surgery (OR 0.61, 95%CI 0.44–0.83) were associated with decreased risk.
In the early 21st century, IE is more often an acute disease, characterized by a high rate of S. aureus infection. Mortality remains relatively high.
Linezolid (L), a potent antibiotic for Methicillin Resistant Staphylococcus aureus (MRSA), inhibits bacterial protein synthesis. By contrast, vancomycin (V) is a cell wall active agent. Here, we used a murine sepsis model to test the hypothesis that L treatment is associated with differences in bacterial and host characteristics as compared to V. Mice were injected with S. aureus USA300, and then intravenously treated with 25 mg/kg of either L or V at 2 hours post infection (hpi). In vivo alpha-hemolysin production was reduced in both L and V-treated mice compared to untreated mice but the reduction did not reach the statistical significance [P = 0.12 for L; P = 0.70 for V). PVL was significantly reduced in L-treated mice compared to untreated mice (P = 0.02). However the reduction of in vivo PVL did not reach the statistical significance in V- treated mice compared to untreated mice (P = 0.27). Both antibiotics significantly reduced IL-1β production [P = 0.001 for L; P = 0.006 for V]. IL-6 was significantly reduced with L but not V antibiotic treatment [P<0.001 for L; P = 0.11 for V]. Neither treatment significantly reduced production of TNF-α. Whole-blood gene expression profiling showed no significant effect of L and V on uninfected mice. In S. aureus-infected mice, L altered the expression of a greater number of genes than V (95 vs. 42; P = 0.001). Pathway analysis for the differentially expressed genes identified toll-like receptor signaling pathway to be common to each S. aureus-infected comparison. Expression of immunomodulatory genes like Cxcl9, Cxcl10, Il1r2, Cd14 and Nfkbia was different among the treatment groups. Glycerolipid metabolism pathway was uniquely associated with L treatment in S. aureus infection. This study demonstrates that, as compared to V, treatment with L is associated with reduced levels of toxin production, differences in host inflammatory response, and distinct host gene expression characteristics in MRSA sepsis.
The impact of early surgery on mortality in patients with native valve endocarditis (NVE) is unresolved. This study seeks to evaluate valve surgery compared to medical therapy for NVE, and to identify characteristics of patients who are most likely to benefit from early surgery.
Methods and Results
Using a prospective, multinational cohort of patients with definite NVE, the effect of early surgery on in-hospital mortality was assessed using propensity-based matching adjusting for survivor bias, and instrumental variable analysis. Patients were stratified by propensity quintile, paravalvular complications, valve perforation, systemic embolization, stroke, Staphylococcus aureus infection and congestive heart failure.
Of the 1552 patients with NVE, 720 (46%) underwent early surgery and 832 (54%) were treated with medical therapy. Compared to medical therapy, early surgery was associated with a significant reduction in mortality in the overall cohort (12.1% [87/720] vs. 20.7% [172/832]) and after propensity-based matching and adjustment for survivor bias (absolute risk reduction (ARR) = -5.9 %; p<0.001). Using a combined instrument, the instrumental variable adjusted ARR in mortality associated with early surgery was -11.2% (p<0.001). In sub-group analysis, surgery was found to confer a survival benefit compared to medical therapy among patients with a higher propensity for surgery (ARR= -10.9% for quintiles 4 and 5; p=0.002); those with paravalvular complications (ARR= -17.3 %; p<0.001), systemic embolization (ARR= -12.9%; p=0.002), S aureus NVE (ARR= -20.1%; p<0.001) and stroke (ARR= -13%; p=0.02) but not with valve perforation or congestive heart failure.
Early surgery for NVE is associated with an in-hospital mortality benefit compared to medical therapy alone.
early surgery; infective endocarditis; medical therapy; in hospital mortality
Staphylococcus aureus is a human commensal that can also cause a broad spectrum of clinical disease. Factors associated with clinical disease are myriad and dynamic and include pathogen virulence, antimicrobial resistance and host susceptibility. Additionally, infection control measures aimed at the environmental niches of S. aureus and therapeutic advances continue to impact upon the incidence and outcomes of staphylococcal infections. This review article focuses on the clinical relevance of advances in our understanding of staphylococcal colonization, virulence, host susceptibility and therapeutics.
Over the past decade key developments have arisen. First, rates of nosocomial methicillin-resistant S. aureus (MRSA) infections have significantly declined in many countries. Second, we have made great strides in our understanding of the molecular pathogenesis of S. aureus in general and community-associated MRSA in particular. Third, host risk factors for invasive staphylococcal infections, such as advancing age, increasing numbers of invasive medical interventions, and a growing proportion of patients with healthcare contact, remain dynamic. Finally, several new antimicrobial agents active against MRSA have become available for clinical use.
Humans and S. aureus co-exist and the dynamic interface between host, pathogen and our attempts to influence these interactions will continue to rapidly change. Although progress has been made in the past decade, we are likely to face further surprises such as the recent waves of community-associated MRSA.
Staphylococcus aureus; methicillin-resistant; MRSA; epidemiology; pathogenesis; treatment
Staphylococcus aureus causes a spectrum of human infection. Diagnostic delays and uncertainty lead to treatment delays and inappropriate antibiotic use. A growing literature suggests the host’s inflammatory response to the pathogen represents a potential tool to improve upon current diagnostics. The hypothesis of this study is that the host responds differently to S. aureus than to E. coli infection in a quantifiable way, providing a new diagnostic avenue. This study uses Bayesian sparse factor modeling and penalized binary regression to define peripheral blood gene-expression classifiers of murine and human S. aureus infection. The murine-derived classifier distinguished S. aureus infection from healthy controls and Escherichia coli-infected mice across a range of conditions (mouse and bacterial strain, time post infection) and was validated in outbred mice (AUC>0.97). A S. aureus classifier derived from a cohort of 94 human subjects distinguished S. aureus blood stream infection (BSI) from healthy subjects (AUC 0.99) and E. coli BSI (AUC 0.84). Murine and human responses to S. aureus infection share common biological pathways, allowing the murine model to classify S. aureus BSI in humans (AUC 0.84). Both murine and human S. aureus classifiers were validated in an independent human cohort (AUC 0.95 and 0.92, respectively). The approach described here lends insight into the conserved and disparate pathways utilized by mice and humans in response to these infections. Furthermore, this study advances our understanding of S. aureus infection; the host response to it; and identifies new diagnostic and therapeutic avenues.