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Summary: Staphylococcus aureus is a leading human pathogen that frequently causes relapsing infections. The failure of antibiotics to eradicate infection contributes to infection relapse. Host-pathogen interactions have a substantial impact on antibiotic susceptibility and the formation of antibiotic tolerant cells. In this study, we interrogate how a major S. aureus virulence factor, α-toxin, interacts with macrophages to alter the microenvironment of the pathogen, thereby influencing its susceptibility to antibiotics. We find α-toxin-mediated activation of the NLRP3 inflammasome induces antibiotic tolerance. Induction of tolerance is driven by increased glycolysis in the host cells, resulting in glucose limitation and ATP depletion in S. aureus. Additionally, inhibition of NLRP3 activation improves antibiotic efficacy in vitro and in vivo, suggesting that this strategy has potential as a host-directed therapeutic to improve outcomes. Our findings identify interactions between S. aureus and the host that result in metabolic crosstalk that can determine the outcome of antimicrobial therapy.

IntroductionStaphylococcus aureus bacteremia (SAB) is a life-threatening infection particularly involving methicillin-resistant S. aureus (MRSA). In contrast to resolving MRSA bacteremia (RB), persistent MRSA bacteremia (PB) blood cultures remain positive despite appropriate antibiotic treatment. Host immune responses distinguishing PB vs. RB outcomes are poorly understood. Here, integrated transcriptomic, IL-10 cytokine levels, and genomic analyses sought to identify signatures differentiating PB vs. RB outcomes.MethodsWhole-blood transcriptomes of propensity-matched PB (n=28) versus RB (n=30) patients treated with vancomycin were compared in one independent training patient cohort. Gene expression (GE) modules were analyzed and prioritized relative to host IL-10 cytokine levels and DNA methyltransferase-3A (DNMT3A) genotype.ResultsDifferential expression of T and B lymphocyte gene expression early in MRSA bacteremia discriminated RB from PB outcomes. Significant increases in effector T and B cell signaling pathways correlated with RB, lower IL-10 cytokine levels and DNMT3A heterozygous A/C genotype. Importantly, a second PB and RB patient cohort analyzed in a masked manner demonstrated high predictive accuracy of differential signatures.DiscussionCollectively, the present findings indicate that human PB involves dysregulated immunity characterized by impaired T and B cell responses associated with excessive IL-10 expression in context of the DNMT3A A/A genotype. These findings reveal distinct immunologic programs in PB vs. RB outcomes, enable future studies to define mechanisms by which host and/or pathogen drive differential signatures and may accelerate prediction of PB outcomes. Such prognostic assessment of host risk could significantly enhance early anti-infective interventions to avert PB and improve patient outcomes.

Abstract Objectives To identify risk stratification biomarkers to enrich for the subset of Staphylococcus aureus bacteraemia patients who develop deep‐seated tissue infections with high morbidity and mortality to guide clinical trial enrolment and clinical management. Methods We evaluated the prognostic value of eight biomarkers for persistent bacteraemia, mortality and endovascular infection foci in a validation cohort of 160 patients with S. aureus bacteraemia enrolled consecutively over 3 years. Results High levels of IL‐17A, IL‐10 or soluble E‐selectin at bacteraemia diagnosis correlated with the duration of positive blood cultures. When thresholds defined in an independent cohort were applied, these biomarkers were robust predictors of persistent bacteraemia or endovascular infection. High serum levels of IL‐17A and IL‐10 often preceded the radiographic diagnosis of infective endocarditis, suggesting potential utility for prioritising diagnostic radiographic imaging. High IL‐8 was prognostic for all‐cause mortality, while IL‐17A and IL‐10 were superior to clinical metrics in discriminating between attributable mortality and non‐attributable mortality. High IL‐17A and IL‐10 identified more patients who developed microbiological failure or mortality than were identified by infective endocarditis diagnosis. Conclusion These biomarkers offer potential utility to identify patients at risk of persistent bacteraemia to guide diagnostic imaging and clinical management. Low biomarker levels could be used to rule out the need for more invasive TEE imaging in patients at lower risk of infective endocarditis. These biomarkers could enable clinical trials by enriching for patients with the greatest need for novel therapies.

Abstract Objective To understand the relationships of Staphylococcus aureus (SA) bacteremic pneumonia (SABP) outcome with patient‐specific and SA‐specific variables. Methods We analysed SA bloodstream isolates and matching sera in SABP patients by sequencing SA isolates (n = 50) and measuring in vitro AT production, haemolytic activity and expression of ClfA and ClfB. Controls were sera from gram‐negative bacteremia patients with or without pneumonia and uninfected subjects. Levels of IgGs, IgMs and neutralizing antibodies (NAbs) against SA antigens were quantified and analysed by one‐way ANOVA. Associations of patient outcomes with patient variables, antibody levels and isolate characteristics were evaluated by univariate and multivariate logistic regression analyses. Results SABP patients had higher levels of IgGs against eight virulence factors and anti‐alpha toxin (AT) NAbs than uninfected controls. Levels of IgG against AT and IgMs against ClfA, FnbpA and SdrC were higher in clinically cured SABP patients than in clinical failures. Anti‐LukAB NAb levels were elevated in all cohorts. Increased odds of cure correlated with higher haemolytic activity of SA strains, longer time between surgery and bacteremia (> 30 days), longer duration of antibiotic therapy, lower acute physiology and total APACHE II scores, lack of persistent fever for > 72 h and higher levels of antibodies against AT (IgG), ClfA (IgM), FnbpA (IgM) and SdrC (IgM). Discussion Limitations included the cross‐sectional observational nature of the study, small sample size and inability to measure antibody levels against all SA virulence factors. Conclusion Our results suggest that SABP patients may benefit from immunotherapy targeting multiple SA antigens.

Atomic force microscopy was used to “fish” for binding reactions between a fibronectin-coated probe (i.e., substrate simulating an implant device) and each of 15 different isolates of Staphylococcus aureusobtained from either patients with an infected cardiac prosthesis (invasive group) or healthy human subjects (control group). There is a strong distinction (p0.01) in the binding-force signature observed for the invasive versus control populations. This observation suggests that a microorganism's “force taxonomy” may provide a fundamental and practical indicator of the pathogen-related risk that infections pose to patients with implanted medical devices. [ABSTRACT FROM AUTHOR]

We report here the first case of endocarditis due to CA-MRSA not associated with healthcare contact in Brazil in Brazil. A previously healthy patient presented with history of endocarditis following a traumatic wound infection. Patient had multiple positive blood cultures within 72 h of admission and met modified Duke's criterion for infective endocarditis. The isolate was typed as Staphylococcal cassette chromosome (SCC) mec type IV and was positive for presence of Panton-Valentine leukocidin (PVL). Increased incidence of CA-MRSA endocarditis is a challenge for the internist to choose the best empirical therapy. Several authors have suggested an empirical therapy with both a beta-lactam and an anti-MRSA agent for serious S. aureus infections. Our patient was treated with Vancomycin and made complete recovery in 3 months.