Mortality Risk Profiling of Staphylococcus aureus Bacteremia by Multi-omic Serum Analysis Reveals Early Predictive and Pathogenic Signatures.

Staphylococcus aureus bacteremia (SaB) causes significant disease in humans, carrying mortality rates of ∼25%. The ability to rapidly predict SaB patient responses and guide personalized treatment regimens could reduce mortality. Here, we present a resource of SaB prognostic biomarkers. Integrating proteomic and metabolomic techniques enabled the identification of >10,000 features from >200 serum samples collected upon clinical presentation. We interrogated the complexity of serum using multiple computational strategies, which provided a comprehensive view of the early host response to infection. Our biomarkers exceed the predictive capabilities of those previously reported, particularly when used in combination. Last, we validated the biological contribution of mortality-associated pathways using a murine model of SaB. Our findings represent a starting point for the development of a prognostic test for identifying high-risk patients at a time early enough to trigger intensive monitoring and interventions.

Predicting community acquired bloodstream infection in infants using full blood count parameters and C-reactive protein; a machine learning study.

Early recognition of bloodstream infection (BSI) in infants can be difficult, as symptoms may be non-specific, and culture can take up to 48 h. As a result, many infants receive unneeded antibiotic treatment while awaiting the culture results. In this study, we aimed to develop a model that can reliably identify infants who do not have positive blood cultures (and, by extension, BSI) based on the full blood count (FBC) and C-reactive protein (CRP) values. Several models (i.e. multivariable logistic regression, linear discriminant analysis, K nearest neighbors, support vector machine, random forest model and decision tree) were trained using FBC and CRP values of 2693 infants aged 7 to 60 days with suspected BSI between 2005 and 2022 in a tertiary paediatric hospital in Dublin, Ireland. All models tested showed similar sensitivities (range 47% - 62%) and specificities (range 85%-95%). A trained decision tree and random forest model were applied to the full dataset and to a dataset containing infants with suspected BSI in 2023 and showed good segregation of a low-risk and high-risk group. Negative predictive values for these two models were high for the full dataset (> 99%) and for the 2023 dataset (> 97%), while positive predictive values were low in both dataset (4%-20%).   Conclusion: We identified several models that can predict positive blood cultures in infants with suspected BSI aged 7 to 60 days. Application of these models could prevent administration of antimicrobial treatment and burdensome diagnostics in infants who do not need them. What is Known: • Bloodstream infection (BSI) in infants cause non-specific symptoms and may be difficult to diagnose. • Results of blood cultures can take up to 48 hours. What is New: • Machine learning models can contribute to clinical decision making on BSI in infants while blood culture results are not yet known.

Time-dependent changes in cell population data obtained using Sysmex XN-series hematology analyzer in bacterial infections.

BACKGROUND: Time-dependent changes in cell populations during acute bacterial infections remain unclear. We assessed time-dependent changes in fluorescent light intensity of the neutrophil area (NE-SFL) and fluorescent light distribution width index of the neutrophil area (NE-WY) and their association with sepsis and bacteremia. METHODS: Patients with acute bacterial infections were enrolled in this prospective, observational cohort study. Blood samples were collected from all patients at the onset of bacterial infections (day 0) and on days 1 and 3. Microbiological evaluation included the examination of blood bacterial load using PCR. Cell population data were assessed using an automated hematology analyzer (Sysmex series XN-2000). RESULTS: Forty-three participants with acute bacterial infections were enrolled in the study. Twenty-five participants developed definite sepsis. All the participants improved after the onset of infection. NE-WY levels showed significant time-dependent changes in participants with sepsis, peaking on day 0 and significantly decreasing until day 3, whereas these changes were not statistically significant for NE-SFL. A significant correlation with the Sequential Organ Failure Assessment score was observed with NE-WY and NE-SFL in the entire cohort on days 0 and 1. However, only NE-WY showed a significant correlation with blood bacterial load on days 0 and 1. CONCLUSION: This study demonstrated that NE-WY elevation in sepsis peaked earlier than NE-SFL, which may partly reflect the early bacterial invasion into circulation. These findings advocate caution in interpreting cell population data values as sepsis biomarkers and propose the potential of NE-WY as a therapeutic indicator.

PCT, IL-6, and IL-10 facilitate early diagnosis and pathogen classifications in bloodstream infection.

BACKGROUND: In the diagnosis of bloodstream infection (BSI), various inflammatory markers such as C-reactive protein (CRP), procalcitonin (PCT), interleukins (IL), white blood cell count (WBC), neutrophil percentage (NE%), platelet count (PLT), and erythrocyte sedimentation rate (ESR) have been extensively utilized. However, their specific roles in distinguishing BSI from local bacterial infection (LBI) and in classifying BSI pathogens remain uncertain. METHODS: A historical cohort study was conducted, involving the enrollment of 505 patients with BSI and 102 patients with LBI. To validate the reliability of the clinical data obtained from this cohort, mouse models of BSI were utilized. RESULTS: Our findings revealed that patients with BSI had significantly higher levels of inflammatory markers, including CRP, PCT, IL-6, IL-10, WBC, NE%, and ESR, compared to those with LBI (p < 0.05). The receiver operating characteristic (ROC) curve analysis demonstrated that CRP, PCT, IL-6, IL-10, ESR and NE% exhibited excellent diagnostic efficacy for BSI. Additionally, we observed significant differences in CRP, PCT, IL-6, and IL-10 levels between patients with BSI caused by Gram-positive bacteria (GP-BSI) and Gram-negative bacteria (GN-BSI), but no significant variations were found among specific bacterial species. Furthermore, our study also found that CRP, PCT, and IL-10 have good discriminatory ability for vancomycin-resistant Enterococcus (VRE), but they show no significant diagnostic efficacy for other multidrug-resistant organisms (MDROs) such as carbapenem-resistant Enterobacteriaceae (CRE), carbapenem-resistant Pseudomonas aeruginosa (CRPA), and methicillin-resistant Staphylococcus aureus (MRSA). In our mouse model experiments, we observed a remarkable increase in PCT, IL-6, and IL-10 levels in mice with GN-BSI compared to those with GP-BSI. CONCLUSION: Our study has confirmed that PCT, IL-6, and IL-10 are efficient biomarkers for distinguishing between BSI and LBI. Furthermore, they can be utilized to classify BSI pathogens and differentiate between VRE and vancomycin-susceptible Enterococcus. These findings are extremely valuable for clinicians as they enable timely initiation of empiric antibiotic therapies and ultimately lead to improved clinical outcomes for patients with BSI.

Bacterial behavior in human blood reveals complement evaders with some persister-like features.

Bacterial bloodstream infections (BSI) are a major health concern and can cause up to 40% mortality. Pseudomonas aeruginosa BSI is often of nosocomial origin and is associated with a particularly poor prognosis. The mechanism of bacterial persistence in blood is still largely unknown. Here, we analyzed the behavior of a cohort of clinical and laboratory Pseudomonas aeruginosa strains in human blood. In this specific environment, complement was the main defensive mechanism, acting either by direct bacterial lysis or by opsonophagocytosis, which required recognition by immune cells. We found highly variable survival rates for different strains in blood, whatever their origin, serotype, or the nature of their secreted toxins (ExoS, ExoU or ExlA) and despite their detection by immune cells. We identified and characterized a complement-tolerant subpopulation of bacterial cells that we named "evaders". Evaders shared some features with bacterial persisters, which tolerate antibiotic treatment. Notably, in bi-phasic killing curves, the evaders represented 0.1-0.001% of the initial bacterial load and displayed transient tolerance. However, the evaders are not dormant and require active metabolism to persist in blood. We detected the evaders for five other major human pathogens: Acinetobacter baumannii, Burkholderia multivorans, enteroaggregative Escherichia coli, Klebsiella pneumoniae, and Yersinia enterocolitica. Thus, the evaders could allow the pathogen to persist within the bloodstream, and may be the cause of fatal bacteremia or dissemination, in particular in the absence of effective antibiotic treatments.

Bacteremia in Febrile, Non-neutropenic, and Well-appearing Children With Cancer.

Fever in a neutropenic pediatric oncology patient requires prompt assessment due to the risk of infectious complications. The appropriate management of fever in non-neutropenic patients, however, is not well-established. We describe the rate of bacteremia in a cohort of non-neutropenic pediatric oncology patients with fever at a large institution. Patients were included if they presented to the emergency department or outpatient clinic between 2009 and 2014 with fever, had a central venous catheter (CVC), and were not neutropenic. Three hundred eighty-six episodes of fever occurring in 159 patients were included in the data analysis. Fifty-nine percent of patients were male, 41% had a diagnosis of acute lymphoblastic leukemia, and 90% had a port-a-cath as CVC. The rate of bacteremia was 3.4%; presence of a port-a-cath was protective against bacteremia whereas a white blood cell count >20,000/mm3 was associated with a higher likelihood of bacteremia. Gram-positive microorganisms were most commonly isolated (64.3%) and frequently resistant to cephalosporins. In summary, in our study, the rate of bacteremia was low among non-neutropenic, well-appearing pediatric cancer patients with a CVC and was not associated with any serious medical complications. Prospective research is needed to determine the most appropriate management of these patients.

The use of serum endothelial adhesion molecules in pediatric patients with leukemia with febrile neutropenia to predict bacteremia.

OBJECTIVE: Febrile neutropenia (FN) represents a life-threatening complication in hematological malignancies. We aimed to analyze the utility of soluble vascular cell adhesion molecule 1 (sVCAM-1), intercellular adhesion molecule 1 (sICAM-1), vascular endothelial growth factor (VEGF) levels compared with C-reactive protein (CRP) and procalcitonin (PCT) during febrile neutropenia episodes of pediatric patients with leukemia. METHODS: Two plasma samples, on day 0 (initial of episode) and day 3 (48-72 h after episode), for VCAM-1, ICAM-1 and VEGF, CRP and PCT were prospectively collected concomitantly during each febrile neutropenic episode between December 2016 and December 2017. The primary outcome was bacteremia and the secondary outcome was intensive care unit (ICU) admission. RESULTS: Twenty-two (28.6%) acute lymphoblastic lymphoma (ALL), seventeen (22.1%) acute myeloblastic lymphoma (AML) patients and thirty-eight (49.3%) control patients with no known underlying disease or fever were included in this study. Of the 39 patients; 16 (41%) had bacteremia. Mean serum sVCAM1 and sICAM1 levels were significantly higher in control group, compared to FN patients (p < 0.001). Mean serum sVCAM2 level was significantly higher in FN patients with bacteremia compared to FN patients without bacteremia (144.97 ± 70.35 pg/mL vs 85.45 ± 53.76 pg/mL, p = 0.022). Mean sVCAM1 and 2 levels were higher in FN patients with ICU admission. In this study, we found that sVCAM-1 and VEGF, when combined to CRP and PCT, could predict gram-negative bacteremia in FN episodes of pediatric hematological malignancy. CONCLUSION: Serum endothelial adhesion molecules, excluding sVCAM-1, cannot predict bacteremia and ICU admission alone in FN patients; but may be associated with clinical outcome when used with PCT and CRP.

Seasonal variations in blood culture numbers and time to positivity and potential impact of reducing incubation periods.

Patients with viral respiratory infections often present symptoms compatible with bloodstream infections. Consequently, the winter period commonly associated with epidemic respiratory illnesses shows an increase in the number of blood cultures (BC) and to occasional saturation of automated BC systems. Here, we explored the seasonal variations in BC samples and the potential impact of shortening the incubation time of BC when automated BC systems are close to saturation. A retrospective study was conducted during a 3-year period in 4 hospitals located in the Paris region, France. All aerobic and anaerobic bottles were included, except pediatric bottles and those sampled for suspicion of endocarditis. The number of BC bottles collected during the winter period was compared to the annual baseline. All bottles positive after a 4-day incubation were analyzed regarding clinical and microbiological findings. The number of BC bottles was significantly higher during the winter periods, compared to the annual baseline (up to 14%). A total of 292,349 BC bottles were analyzed with 23,363 (8.0%) positive, including 236 (1%) after a 4-day incubation. Of these 236 bottles, 76 (64.8%) were positive with a contaminant, 78 (33.1%) with a clinically significant microorganism identified for the same patient in the previous 4 days, and only 5 (2.1%) with a clinically significant microorganism not previously identified. Winter periods were associated with a significant increase in BC samples. Shortening the incubation time of BC bottles from 5 to 4 days seems a relevant option when automated BC systems are close to saturation.

C-reactive protein predicts persistent bacteremia caused by community-acquired methicillin-resistant Staphylococcus aureus strain.

There is limited data on persistent bacteremia (PB) caused by community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). Here, we aimed to investigate the clinical and microbiological characteristics of PB caused by the major CA-MRSA strain in Korea (ST72-SCCmecIV). All adult patients with S. aureus bacteremia were prospectively investigated from August 2008 to December 2018. Patients with ST72 MRSA bacteremia were included in the study. Patients were stratified into the PB group (defined as positive blood cultures for ≥ 3 days) and short bacteremia (SB) group. A total of 291 patients were included, comprising 115 (39.5%) with PB and 176 (60.5%) with SB. Although the 30-day mortality did not differ between PB and SB, recurrent bacteremia within 12 weeks was significantly more common in PB (8.7% vs 1.7%; P = 0.01). Multivariate analysis showed risk factors of PB were liver cirrhosis (adjusted odds ratio [aOR], 3.27; 95% confidence interval [CI], 1.50-7.12), infective endocarditis (aOR, 7.13; 95% CI, 1.37-37.12), bone and joint infections (aOR, 3.76; 95% CI, 1.62-8.77), C-reactive protein ≥ 10 mg/dL (aOR, 2.20; 95% CI, 1.22-3.95), metastatic infection (aOR, 7.35; 95% CI, 3.53-15.29), and agr dysfunction (aOR, 2.47; 95% CI, 1.05-5.81). PB occurred in approximately 40% of bacteremia caused by ST72 MRSA with a significantly higher recurrence rate. Patients with risk factors of PB, including liver cirrhosis, high initial CRP, infective endocarditis, or bone and joint infections, might require early aggressive treatment.

Citrulline as a biomarker of bacteraemia during induction treatment for childhood acute lymphoblastic leukaemia.

BACKGROUND: Systemic infections are a major cause of morbidity in children with acute lymphoblastic leukaemia (ALL). However, identification of patients at increased risk is still a challenge. Knowing that both neutropaenia and gastrointestinal toxicity are risk factors for bacteraemia, we aimed at comparing absolute neutrophil counts (ANC) and plasma citrulline levels (indicating enterocyte loss) in children with ALL with and without bacteraemia during induction treatment. PROCEDURE: We prospectively included 61 children with ALL treated according to the Nordic Society of Paediatric Haematology and Oncology (NOPHO) ALL-2008 protocol. ANC and plasma C-reactive protein (CRP) were measured on treatment days 1, 8, 15, 22 and 29. Plasma citrulline was measured on days 1, 8, 15 and 29. Bacteraemia episodes during induction treatment were recorded retrospectively. RESULTS: Nineteen of sixty-one (31%) patients experienced bacteraemia occurring on median day 13 (range 5-20). Patients with bacteraemia during induction treatment had lower citrulline level on day 15 (P < .01) compared to patients without bacteraemia, indicating more severe enterocyte loss. Nevertheless, ANC was similar in the two patient groups on days 8 and 15. CRP was negatively correlated with same-day citrulline (P < .03 for all) and ANC (P < .04 for all). CONCLUSIONS: During chemotherapy-induced neutropaenia, plasma citrulline may help identify patients at increased risk of bacteraemia.

Outcomes and Disposition of Oncology Patients With Non-neutropenic Fever and Positive Blood Cultures.

Children with cancer and non-neutropenic fever (NNF) episodes are often treated as outpatients if they appear well. However, a small subset have bloodstream infections (BSIs) and must return for further evaluation. These patients may be directly admitted to inpatient units, whereas others are first evaluated in outpatient settings before admission. The best practice for securing care for patients discovered to have outpatient bacteremia are unclear. To determine outcomes and compare time to antibiotics between the 2 disposition, we retrospectively reviewed all NNF initially treated as outpatients and later had positive blood cultures from 2012 to 2016. Of 845 NNF cases initially treated in outpatient settings, 48 episodes (n=43 patients) had BSIs. Of those, 77.1% (n=37) were re-evaluated as outpatients and admitted; 14.6% (n=7) were direct admissions. The median time to antibiotic did not significantly differ between outpatient re-evaluations (119 min) and direct admissions (191 min), P=0.11. One patient met sepsis criteria upon return and required intensive care unit admission for vasopressor support. No patient died within 1 week of the febrile episode. Most patients with NNF and BSIs initially discharged are stable upon return. Institutions should evaluate their patient flows to ensure that patients receive timely care.

Immature platelet indices alongside procalcitonin for sensitive and specific identification of bacteremia in the intensive care unit.

Hematological markers that can be rapidly analyzed and regularly monitored during a patient's stay on ICU, and that can identify bacterial causes of sepsis are being extensively sought. The significance of platelets in early immunological responses provides justification for assessing their usefulness in the identification of bacteremia amongst sepsis patients. In this preliminary study, the full blood count, including the platelet count by impedance (PLT-I), Immature Platelet Fraction (IPF%) and absolute immature platelet count (AIPC), were analyzed in eighty-two sepsis patients daily over the first 5 days stay on ICU. C-Reactive Protein (CRP), procalcitonin (PCT), and lactate were also analyzed daily. Blood cultures confirmed or excluded the presence of bacteremia. PCT provided the earliest indicator of bacteremia, with significant differences between the two cohorts on day 1. The change in IPF% and AIPC from day 1 to day 2 (Δ IPF% and Δ AIPC) provided the most accurate indication; A combination of Δ IPF% and day 2 PCT, provided a positive predictive value and negative predictive value of 100% and 96.10%, respectively. These data provide strong justification for larger multi-center validation studies to confirm the usefulness of these platelet indices during the assessment of sepsis on the ICU.

G-CSF as a potential early biomarker for diagnosis of bloodstream infection.

BACKGROUND: Cytokines play an important role in bacterial infection, and thus, we aim to find out cytokines that may be diagnostically significant in early stage of bacterial bloodstream infection. METHODS: Mice models infected with Staphylococcus aureus and Klebsiella pneumoniae were established. Then dynamic changes of nine serum cytokines were monitored within 48 hours after the infection. Cytokines with significant differences between the infected groups and control group were further analyzed. Clinical samples of patients who were suspected of bloodstream infection were collected. Then the diagnostic efficiency of screened cytokines was determined with receiver operating characteristic curve analysis. RESULTS: As for mice models infected by Staphylococcus aureus and Klebsiella pneumoniae, six cytokines including IL-1ß, IL-6, IL-12p70, G-CSF, IFN-γ, and TNF-α were significantly different (P < .05) between two bacterial infected groups. As for clinical samples, three cytokines including IL-6, IL-12p70, and G-CSF showed significant differences between infection group (Staphylococcus aureus and Klebsiella pneumonia group) and negative control group. With the area under curve of 0.7350 and 0.6431 for G-CSF and IL-6, respectively, these two cytokines were significantly different between Staphylococcus aureus and Klebsiella pneumoniae infection groups. Combination of G-CSF and IL-6 could improve the AUC to 0.8136. CONCLUSIONS: G-CSF cannot only identify bacterial bloodstream infection, but can also distinguish the infection of Staphylococcus aureus from Klebsiella pneumoniae. Further investigation should be performed concerning the diagnostic efficiency of G-CSF in diagnosing different types of bacterial bloodstream infection.

Catabacter hongkongensis bacteremia identified by direct metagenomic sequencing of positive blood culture fluid, first case report in the US.

Catabacter hongkongensis, an increasingly recognized bacteria in clinical samples, was identified by direct metagenomic sequencing of positive blood culture fluid from a 55-year-old patient with colonic perforation. The bacteremia was cleared by both antibiotic treatment and surgical intervention. This is the first case report of C. hongkongensis infection in the US.

The Serratia marcescens Siderophore Serratiochelin Is Necessary for Full Virulence during Bloodstream Infection.

Serratia marcescens is a bacterium frequently found in the environment, but over the last several decades it has evolved into a concerning clinical pathogen, causing fatal bacteremia. To establish such infections, pathogens require specific nutrients; one very limited but essential nutrient is iron. We sought to characterize the iron acquisition systems in S. marcescens isolate UMH9, which was recovered from a clinical bloodstream infection. Using RNA sequencing (RNA-seq), we identified two predicted siderophore gene clusters (cbs and sch) that were regulated by iron. Mutants were constructed to delete each iron acquisition locus individually and in conjunction, generating both single and double mutants for the putative siderophore systems. Mutants lacking the sch gene cluster lost their iron-chelating ability as quantified by the chrome azurol S (CAS) assay, whereas the cbs mutant retained wild-type activity. Mass spectrometry-based analysis identified the chelating siderophore to be serratiochelin, a siderophore previously identified in Serratia plymuthica Serratiochelin-producing mutants also displayed a decreased growth rate under iron-limited conditions created by dipyridyl added to LB medium. Additionally, mutants lacking serratiochelin were significantly outcompeted during cochallenge with wild-type UMH9 in the kidneys and spleen after inoculation via the tail vein in a bacteremia mouse model. This result was further confirmed by an independent challenge, suggesting that serratiochelin is required for full S. marcescens pathogenesis in the bloodstream. Nine other clinical isolates have at least 90% protein identity to the UMH9 serratiochelin system; therefore, our results are broadly applicable to emerging clinical isolates of S. marcescens causing bacteremia.

The Development and Validation of a Machine Learning Model to Predict Bacteremia and Fungemia in Hospitalized Patients Using Electronic Health Record Data.

OBJECTIVES: Bacteremia and fungemia can cause life-threatening illness with high mortality rates, which increase with delays in antimicrobial therapy. The objective of this study is to develop machine learning models to predict blood culture results at the time of the blood culture order using routine data in the electronic health record. DESIGN: Retrospective analysis of a large, multicenter inpatient data. SETTING: Two academic tertiary medical centers between the years 2007 and 2018. SUBJECTS: All hospitalized patients who received a blood culture during hospitalization. INTERVENTIONS: The dataset was partitioned temporally into development and validation cohorts: the logistic regression and gradient boosting machine models were trained on the earliest 80% of hospital admissions and validated on the most recent 20%. MEASUREMENTS AND MAIN RESULTS: There were 252,569 blood culture days-defined as nonoverlapping 24-hour periods in which one or more blood cultures were ordered. In the validation cohort, there were 50,514 blood culture days, with 3,762 cases of bacteremia (7.5%) and 370 cases of fungemia (0.7%). The gradient boosting machine model for bacteremia had significantly higher area under the receiver operating characteristic curve (0.78 [95% CI 0.77-0.78]) than the logistic regression model (0.73 [0.72-0.74]) (p < 0.001). The model identified a high-risk group with over 30 times the occurrence rate of bacteremia in the low-risk group (27.4% vs 0.9%; p < 0.001). Using the low-risk cut-off, the model identifies bacteremia with 98.7% sensitivity. The gradient boosting machine model for fungemia had high discrimination (area under the receiver operating characteristic curve 0.88 [95% CI 0.86-0.90]). The high-risk fungemia group had 252 fungemic cultures compared with one fungemic culture in the low-risk group (5.0% vs 0.02%; p < 0.001). Further, the high-risk group had a mortality rate 60 times higher than the low-risk group (28.2% vs 0.4%; p < 0.001). CONCLUSIONS: Our novel models identified patients at low and high-risk for bacteremia and fungemia using routinely collected electronic health record data. Further research is needed to evaluate the cost-effectiveness and impact of model implementation in clinical practice.

Development and utility assessment of a machine learning bloodstream infection classifier in pediatric patients receiving cancer treatments.

BACKGROUND: Objectives were to build a machine learning algorithm to identify bloodstream infection (BSI) among pediatric patients with cancer and hematopoietic stem cell transplantation (HSCT) recipients, and to compare this approach with presence of neutropenia to identify BSI. METHODS: We included patients 0-18 years of age at cancer diagnosis or HSCT between January 2009 and November 2018. Eligible blood cultures were those with no previous blood culture (regardless of result) within 7 days. The primary outcome was BSI. Four machine learning algorithms were used: elastic net, support vector machine and two implementations of gradient boosting machine (GBM and XGBoost). Model training and evaluation were performed using temporally disjoint training (60%), validation (20%) and test (20%) sets. The best model was compared to neutropenia alone in the test set. RESULTS: Of 11,183 eligible blood cultures, 624 (5.6%) were positive. The best model in the validation set was GBM, which achieved an area-under-the-receiver-operator-curve (AUROC) of 0.74 in the test set. Among the 2236 in the test set, the number of false positives and specificity of GBM vs. neutropenia were 508 vs. 592 and 0.76 vs. 0.72 respectively. Among 139 test set BSIs, six (4.3%) non-neutropenic patients were identified by GBM. All received antibiotics prior to culture result availability. CONCLUSIONS: We developed a machine learning algorithm to classify BSI. GBM achieved an AUROC of 0.74 and identified 4.3% additional true cases in the test set. The machine learning algorithm did not perform substantially better than using presence of neutropenia alone to predict BSI.

α-Haemolysin production, as a single factor, causes fulminant sepsis in a model of Escherichia coli-induced bacteraemia.

α-Haemolysin (HlyA) from uropathogenic Escherichia coli has been demonstrated to be a significant virulence factor for ascending urinary tract infections. Once the E. coli reach the well-vascularised kidneys, there is a high risk of bacteraemia and a subsequent septic host response. Despite this, HlyA has the potential to accelerate the host response both directly and via its ability to facilitate adenosine triphosphate release from cells. It has not been settled whether HlyA aggravates bacteraemia into a septic state. To address this, we used an E. coli strain in a model of acute urosepsis that was either transfected with a plasmid containing the full HlyA operon or one with deletion in the HlyA gene. Here, we show that HlyA accelerates the host response to E. coli in the circulation. Mice exposed to HlyA-producing E. coli showed massively increased proinflammatory cytokines, a substantial fall in circulating thrombocytes, extensive haematuria, and intravascular haemolysis. This was not seen in mice exposed to either E. coli that do not secrete HlyA or vehicle controls. Consistent with the massive host response to the bacteria, the mice exposed to HlyA-producing E. coli died exceedingly early, whereas mice exposed to E. coli without HlyA production and vehicle controls survived the entire observation period. These data allow us to conclude that HlyA is a virulence factor that accelerates a state of bacteraemia into fulminant sepsis in a mouse model.

Bacteriophage-receptor binding proteins for multiplex detection of Staphylococcus and Enterococcus in blood.

Healthcare-associated infections (HCAIs) affect hundreds of millions of patients, representing a significant burden for public health. They are usually associated to multidrug resistant bacteria, which increases their incidence and severity. Bloodstream infections are among the most frequent and life-threatening HCAIs, with Enterococcus and Staphylococcus among the most common isolated pathogens. The correct and fast identification of the etiological agents is crucial for clinical decision-making, allowing to rapidly select the appropriate antimicrobial and to prevent from overuse and misuse of antibiotics and the consequent increase in antimicrobial resistance. Conventional culture methods are still the gold standard to identify these pathogens, however, are time-consuming and may lead to erroneous diagnosis, which compromises an efficient treatment. (Bacterio)phage receptor binding proteins (RBPs) are the structures responsible for the high specificity conferred to phages against bacteria and thus are very attractive biorecognition elements with high potential for specific detection and identification of pathogens. Taking into account all these facts, we have designed and developed a new, fast, accurate, reliable and unskilled diagnostic method based on newly identified phage RBPs and spectrofluorometric techniques that allows the multiplex detection of Enterococcus and Staphylococcus in blood samples in less than 1.5 hr after an enrichment step.

Complement levels in patients with bloodstream infection due to Staphylococcus aureus or Gram-negative bacteria.

The complement system is a vital component of the innate immune system, though its role in bacteremia is poorly understood. We present complement levels in Staphylococcus aureus bacteremia (SAB) and Gram-negative bacteremia (GNB) and describe observed associations of complement levels with clinical outcomes. Complement and cytokine levels were measured in serum samples from 20 hospitalized patients with SAB, 20 hospitalized patients with GNB, 10 non-infected hospitalized patients, and 10 community controls. C5a levels were significantly higher in patients with SAB as compared to patients with GNB. Low C4 and C3 levels were associated with septic shock and 30-day mortality in patients with GNB, and elevated C3 was associated with a desirable outcome defined as absence of (1) septic shock, (2) acute renal failure, and (3) death within 30 days of bacteremia. Low levels of C9 were associated with septic shock in patients with GNB but not SAB. Elevated IL-10 was associated with increased 30-day mortality in patients with SAB. Complement profiles differ in patients with SAB and those with GNB. Measurement of IL-10 in patients with SAB and of C4, C3, and C9 in patients with GNB may help to identify those at higher risk for poor outcomes.