Prognostic significance of early platelet dynamics in Staphylococcus aureus bacteremia.

BACKGROUND: Platelets are recognized as key immune effectors, but they are targets of bacterial virulence factors. In the present study, we aimed to examine the relationship between early platelet dynamics and the outcome of Staphylococcus aureus bacteremia (SAB). METHOD: Electronic medical records of adult patients hospitalized for SAB between July 2012 and November 2020 were retrospectively reviewed for relevant demographic, laboratory, and clinical data. The outcome endpoints were mortality and microbial persistence. RESULTS: Among the 811 patients evaluated, 29% experienced thrombocytopenia on Day 1. Platelet count nadir occurred on Days 2-3 following SAB onset, and Day 4 was a determining point of platelet count trajectory and mortality. Mortality risk was 6% or less for those with normal platelet count by Day 4 regardless of whether they experienced thrombocytopenia on Day 1, but the risk increased to 16-21% for those who experienced thrombocytopenia on Day 4 regardless of whether they had normal platelet count on Day 1 or sustained thrombocytopenia. The duration of bacteremia was prolonged by one day (median 3 d vs. 2 d) for those with sustained thrombocytopenia compared to those without. CONCLUSION: Early platelet dynamics during SAB have prognostic significance and represent an early window for potential platelet-directed therapeutic interventions to improve outcome.

Derivation, Validation, and Clinical Relevance of a Pediatric Sepsis Phenotype With Persistent Hypoxemia, Encephalopathy, and Shock.

OBJECTIVES: Untangling the heterogeneity of sepsis in children and identifying clinically relevant phenotypes could lead to the development of targeted therapies. Our aim was to analyze the organ dysfunction trajectories of children with sepsis-associated multiple organ dysfunction syndrome (MODS) to identify reproducible and clinically relevant sepsis phenotypes and determine if they are associated with heterogeneity of treatment effect (HTE) to common therapies. DESIGN: Multicenter observational cohort study. SETTING: Thirteen PICUs in the United States. PATIENTS: Patients admitted with suspected infections to the PICU between 2012 and 2018. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: We used subgraph-augmented nonnegative matrix factorization to identify candidate trajectory-based phenotypes based on the type, severity, and progression of organ dysfunction in the first 72 hours. We analyzed the candidate phenotypes to determine reproducibility as well as prognostic, therapeutic, and biological relevance. Overall, 38,732 children had suspected infection, of which 15,246 (39.4%) had sepsis-associated MODS with an in-hospital mortality of 10.1%. We identified an organ dysfunction trajectory-based phenotype (which we termed persistent hypoxemia, encephalopathy, and shock) that was highly reproducible, had features of systemic inflammation and coagulopathy, and was independently associated with higher mortality. In a propensity score-matched analysis, patients with persistent hypoxemia, encephalopathy, and shock phenotype appeared to have HTE and benefit from adjuvant therapy with hydrocortisone and albumin. When compared with other high-risk clinical syndromes, the persistent hypoxemia, encephalopathy, and shock phenotype only overlapped with 50%-60% of patients with septic shock, moderate-to-severe pediatric acute respiratory distress syndrome, or those in the top tier of organ dysfunction burden, suggesting that it represents a nonsynonymous clinical phenotype of sepsis-associated MODS. CONCLUSIONS: We derived and validated the persistent hypoxemia, encephalopathy, and shock phenotype, which is highly reproducible, clinically relevant, and associated with HTE to common adjuvant therapies in children with sepsis.

HOME2 Study: Household Versus Personalized Decolonization in Households of Children With Methicillin-Resistant Staphylococcus aureus Skin and Soft Tissue Infection-A Randomized Clinical Trial.

BACKGROUND: A household approach to decolonization decreases skin and soft tissue infection (SSTI) incidence, though this is burdensome and costly. As prior SSTI increases risk for SSTI, we hypothesized that the effectiveness of decolonization measures to prevent SSTI when targeted to household members with prior year SSTI would be noninferior to decolonizing all household members. METHODS: Upon completion of our 12-month observational Household Observation of Methicillin-resistant Staphylococcus aureus in the Environment (HOME) study, 102 households were enrolled in HOME2, a 12-month, randomized noninferiority trial. Pediatric index patients with community-associated methicillin-resistant Staphylococcus aureus (MRSA) SSTI, their household contacts, and pets were enrolled. Households were randomized 1:1 to the personalized (decolonization performed only by household members who experienced SSTI during the HOME study) or household (decolonization performed by all household members) approaches. The 5-day regimen included hygiene education, twice-daily intranasal mupirocin, and daily bleach-water baths. At 5 follow-up visits in participants' homes, swabs to detect S. aureus were collected from participants, environmental surfaces, and pets; incident SSTIs were ascertained. RESULTS: Noninferiority of the personalized approach was established for the primary outcome 3-month cumulative SSTI: 23 of 212 (10.8%) participants reported SSTI in household approach households, while 23 of 236 (9.7%) participants reported SSTI in personalized approach households (difference in proportions, -1.1% [95% confidence interval, -6.7% to 4.5%]). In multivariable analyses, prior year SSTI and baseline MRSA colonization were associated with cumulative SSTI. CONCLUSIONS: The personalized approach was noninferior to the household approach in preventing SSTI. Future studies should interrogate longer durations of decolonization and/or decontamination of the household environment to reduce household MRSA burden. CLINICAL TRIALS REGISTRATION: NCT01814371.

Staphylococcus aureus pore-forming toxins: The interface of pathogen and host complexity.

Staphylococcus aureus is a prominent human pathogen capable of infecting a variety of host species and tissue sites. This versatility stems from the pathogen's ability to secrete diverse host-damaging virulence factors. Among these factors, the S. aureus pore-forming toxins (PFTs) α-toxin and the bicomponent leukocidins, have garnered much attention for their ability to lyse cells at low concentrations and modulate disease severity. Although many of these toxins were discovered nearly a century ago, their host cell specificities have only been elucidated over the past five to six years, starting with the discovery of the eukaryotic receptor for α-toxin and rapidly followed by identification of the leukocidin receptors. The identification of these receptors has revealed the species- and cell type-specificity of toxin binding, and provided insight into non-lytic effects of PFT intoxication that contribute to disease pathogenesis.

Vancomycin Monotherapy May Be Insufficient to Treat Methicillin-resistant Staphylococcus aureus Coinfection in Children With Influenza-related Critical Illness.

Background: Coinfection with influenza virus and methicillin-resistant Staphylococcus aureus (MRSA) causes life-threatening necrotizing pneumonia in children. Sporadic incidence precludes evaluation of antimicrobial efficacy. We assessed the clinical characteristics and outcomes of critically ill children with influenza-MRSA pneumonia and evaluated antibiotic use. Methods: We enrolled children (<18 years) with influenza infection and respiratory failure across 34 pediatric intensive care units 11/2008-5/2016. We compared baseline characteristics, clinical courses, and therapies in children with MRSA coinfection, non-MRSA bacterial coinfection, and no bacterial coinfection. Results: We enrolled 170 children (127 influenza A, 43 influenza B). Children with influenza-MRSA pneumonia (N = 30, 87% previously healthy) were older than those with non-MRSA (N = 61) or no (N = 79) bacterial coinfections. Influenza-MRSA was associated with increased leukopenia, acute lung injury, vasopressor use, extracorporeal life support, and mortality than either group (P ≤ .0001). Influenza-related mortality was 40% with MRSA compared to 4.3% without (relative risk [RR], 9.3; 95% confidence interval [CI], 3.8-22.9). Of 29/30 children with MRSA who received vancomycin within the first 24 hours of hospitalization, mortality was 12.5% (N = 2/16) if treatment also included a second anti-MRSA antibiotic compared to 69.2% (N = 9/13) with vancomycin monotherapy (RR, 5.5; 95% CI, 1.4, 21.3; P = .003). Vancomycin dosing did not influence initial trough levels; 78% were <10 µg/mL. Conclusions: Influenza-MRSA coinfection is associated with high fatality in critically ill children. These data support early addition of a second anti-MRSA antibiotic to vancomycin in suspected severe cases.

Staphylococcus aureus alpha toxin activates Notch in vascular cells.

Staphylococcus aureus infection is one of the leading causes of morbidity in hospitalized patients in the United States, an effect compounded by increasing antibiotic resistance. The secreted agent hemolysin alpha toxin (Hla) requires the receptor A Disintegrin And Metalloproteinase domain-containing protein 10 (ADAM10) to mediate its toxic effects. We hypothesized that these effects are in part regulated by Notch signaling, for which ADAM10 activation is essential. Notch proteins function in developmental and pathological angiogenesis via the modulation of key pathways in endothelial and perivascular cells. Thus, we hypothesized that Hla would activate Notch in vascular cells. Human umbilical vein endothelial cells were treated with recombinant Hla (rHla), Hla-H35L (genetically inactivated Hla), or Hank's solution (HBSS), and probed by different methods. Luciferase assays showed that Hla (0.01 µg/mL) increased Notch activation by 1.75 ± 0.5-fold as compared to HBSS controls (p < 0.05), whereas Hla-H35L had no effect. Immunocytochemistry and Western blotting confirmed these findings and revealed that ADAM10 and γ-secretase are required for Notch activation after inhibitor and siRNA assays. Retinal EC in mice engineered to express yellow fluorescent protein (YFP) upon Notch activation demonstrated significantly greater YFP intensity after Hla injection than controls. Aortic rings from Notch reporter mice embedded in matrix and incubated with rHla or Hla-H35L demonstrate increased Notch activation occurs at tip cells during sprouting. These mice also had higher skin YFP intensity and area of expression after subcutaneous inoculation of S. aureus expressing Hla than a strain lacking Hla in both EC and pericytes assessed by microscopy. Human liver displayed strikingly higher Notch expression in EC and pericytes during S. aureus infection by immunohistochemistry than tissues from uninfected patients. In sum, our results demonstrate that the S. aureus toxin Hla can potently activate Notch in vascular cells, an effect which may contribute to the pathobiology of infection with this microorganism.

Bacteria activate sensory neurons that modulate pain and inflammation.

Nociceptor sensory neurons are specialized to detect potentially damaging stimuli, protecting the organism by initiating the sensation of pain and eliciting defensive behaviours. Bacterial infections produce pain by unknown molecular mechanisms, although they are presumed to be secondary to immune activation. Here we demonstrate that bacteria directly activate nociceptors, and that the immune response mediated through TLR2, MyD88, T cells, B cells, and neutrophils and monocytes is not necessary for Staphylococcus aureus-induced pain in mice. Mechanical and thermal hyperalgesia in mice is correlated with live bacterial load rather than tissue swelling or immune activation. Bacteria induce calcium flux and action potentials in nociceptor neurons, in part via bacterial N-formylated peptides and the pore-forming toxin α-haemolysin, through distinct mechanisms. Specific ablation of Nav1.8-lineage neurons, which include nociceptors, abrogated pain during bacterial infection, but concurrently increased local immune infiltration and lymphadenopathy of the draining lymph node. Thus, bacterial pathogens produce pain by directly activating sensory neurons that modulate inflammation, an unsuspected role for the nervous system in host-pathogen interactions.

Comprehensive modeling reveals proximity, seasonality, and hygiene practices as key determinants of MRSA colonization in exposed households.

BACKGROUND: Staphylococcus aureus is the leading cause of skin and soft tissue infections (SSTIs). To develop interventions to prevent recurrent infections, household attributes and individual practices influencing S. aureus colonization must be discerned. METHODS: Households of healthy children with methicillin-resistant S. aureus (MRSA) SSTI (n = 150; 671 participants) were interviewed regarding health history, activities, and hygiene practices. S. aureus colonization was assessed in household members, and recovered isolates were typed by repetitive sequence-based PCR. RESULTS: The number of unique strain types in a household (median 1, range 0-7) correlated with the number of colonized individuals (p < 0.001). The MRSA infecting strain type colonized a household member in 57% of 91 households with an available infecting strain, and was the most common strain type recovered in 45% of these households. In multivariable models, household MRSA colonization burden (p < 0.001), sharing a bedroom with MRSA-colonized individuals (p = 0.03), renting dwelling (p = 0.048), and warmer seasons (p = 0.02) were associated with increased MRSA colonization. Increasing age (p = 0.02), bathing at least daily (p = 0.01), and antibacterial soap use (p = 0.03) correlated with reduced MRSA colonization. CONCLUSIONS: This study identified practices that correlate with MRSA colonization, which will inform physician counseling and multifaceted interventions among MRSA-affected households to mitigate MRSA in the community.

Strain competition restricts colonization of an enteric pathogen and prevents colitis.

The microbiota is a major source of protection against intestinal pathogens; however, the specific bacteria and underlying mechanisms involved are not well understood. As a model of this interaction, we sought to determine whether colonization of the murine host with symbiotic non-toxigenic Bacteroides fragilis could limit acquisition of pathogenic enterotoxigenic B. fragilis We observed strain-specific competition with toxigenic B. fragilis, dependent upon type VI secretion, identifying an effector-immunity pair that confers pathogen exclusion. Resistance against host acquisition of a second non-toxigenic strain was also uncovered, revealing a broader function of type VI secretion systems in determining microbiota composition. The competitive exclusion of enterotoxigenic B. fragilis by a non-toxigenic strain limited toxin exposure and protected the host against intestinal inflammatory disease. Our studies demonstrate a novel role of type VI secretion systems in colonization resistance against a pathogen. This understanding of bacterial competition may be utilized to define a molecularly targeted probiotic strategy.

Vaccine composition formulated with a novel TLR7-dependent adjuvant induces high and broad protection against Staphylococcus aureus.

Both active and passive immunization strategies against Staphylococcus aureus have thus far failed to show efficacy in humans. With the attempt to develop an effective S. aureus vaccine, we selected five conserved antigens known to have different roles in S. aureus pathogenesis. They include the secreted factors α-hemolysin (Hla), ess extracellular A (EsxA), and ess extracellular B (EsxB) and the two surface proteins ferric hydroxamate uptake D2 and conserved staphylococcal antigen 1A. The combined vaccine antigens formulated with aluminum hydroxide induced antibodies with opsonophagocytic and functional activities and provided consistent protection in four mouse models when challenged with a panel of epidemiologically relevant S. aureus strains. The importance of antibodies in protection was demonstrated by passive transfer experiments. Furthermore, when formulated with a toll-like receptor 7-dependent (TLR7) agonist recently designed and developed in our laboratories (SMIP.7-10) adsorbed to alum, the five antigens provided close to 100% protection against four different staphylococcal strains. The new formulation induced not only high antibody titers but also a Th1 skewed immune response as judged by antibody isotype and cytokine profiles. In addition, low frequencies of IL-17-secreting T cells were also observed. Altogether, our data demonstrate that the rational selection of mixtures of conserved antigens combined with Th1/Th17 adjuvants can lead to promising vaccine formulations against S. aureus.

Staphylococcus aureus in the Intensive Care Unit: Are These Golden Grapes Ripe for a New Approach?

Staphylococcus aureus is the leading cause of infection in the setting of critical illness and injury. This pathogen causes life-threatening infection in otherwise healthy individuals and also complicates the clinical course of patients requiring intensive care as a result of their primary medical or surgical disease processes. S. aureus infection in the intensive care unit (ICU) most commonly manifests as sepsis, ventilator-associated pneumonia, and infection of surgical sites and indwelling medical devices. With the epidemic spread of methicillin-resistant S. aureus, many cases of staphylococcal infection in the ICU are now classified as drug resistant, prompting hospital-based screening for methicillin-resistant S. aureus and implementation of both isolation practices and decolonization strategies in ICU patients. The genetic adaptability of S. aureus, heterogeneity of disease presentation, clinical course, and outcome between individual S. aureus-infected ICU patients remains enigmatic, suggesting a need to define disease classification subtypes that inform disease progression and therapy. We propose that S. aureus infection in the ICU now presents a unique opportunity for individualized risk stratification coupled with the investigation of novel approaches to mitigate disease. Given our increasing knowledge of the molecular pathogenesis of S. aureus disease, we suggest that the application of molecular pathological epidemiology to S. aureus infection can usher in a new era of highly focused personalized therapy that may be particularly beneficial in the setting of critical illness and injury.

Pediatric Multiple Organ Dysfunction Syndrome: Promising Therapies.

OBJECTIVE: To describe the state of the science, identify knowledge gaps, and offer potential future research questions regarding promising therapies for children with multiple organ dysfunction syndrome presented during the Eunice Kennedy Shriver National Institute of Child Health and Human Development Workshop on Pediatric Multiple Organ Dysfunction Syndrome (March 26-27, 2015). DATA SOURCES: Literature review, research data, and expert opinion. STUDY SELECTION: Not applicable. DATA EXTRACTION: Moderated by an expert from the field, issues relevant to the association of multiple organ dysfunction syndrome with a variety of conditions were presented, discussed, and debated with a focus on identifying knowledge gaps and research priorities. DATA SYNTHESIS: Summary of presentations and discussion supported and supplemented by relevant literature. CONCLUSIONS: Among critically ill children, multiple organ dysfunction syndrome is relatively common and associated with significant morbidity and mortality. For outcomes to improve, effective therapies aimed at preventing and treating this condition must be discovered and rigorously evaluated. In this article, a number of potential opportunities to enhance current care are highlighted including the need for a better understanding of the pharmacokinetics and pharmacodynamics of medications, the effect of early and optimized nutrition, and the impact of effective glucose control in the setting of multiple organ dysfunction syndrome. Additionally, a handful of the promising therapies either currently being implemented or developed are described. These include extracorporeal therapies, anticytokine therapies, antitoxin treatments, antioxidant approaches, and multiple forms of exogenous steroids. For the field to advance, promising therapies and other therapies must be assessed in rigorous manner and implemented accordingly.

Staphylococcus aureus α-Toxin Response Distinguishes Respiratory Virus-Methicillin-Resistant S. aureus Coinfection in Children.

BACKGROUND: Development of methicillin-resistant Staphylococcus aureus (MRSA) pneumonia after a respiratory viral infection is frequently fatal in children. In mice, S. aureus α-toxin directly injures pneumocytes and increases mortality, whereas α-toxin blockade mitigates disease. The role of α-toxin in pediatric staphylococcal-viral coinfection is unclear. METHODS: We enrolled children across 34 North American pediatric intensive care units with acute respiratory failure and suspected influenza virus infection. Serial serum anti-α-toxin antibody titers and functional α-toxin neutralization capacity were compared across children coinfected with MRSA or methicillin-susceptible S. aureus (MSSA) and control children infected with influenza virus only. MRSA isolates were tested for α-toxin production and lethality in a murine pneumonia model. RESULTS: Influenza virus was identified in 22 of 25 children with MRSA coinfection (9 died) and 22 patients with MSSA coinfection (all survived). Initial α-toxin-specific antibody titers were similar, compared with those in the 13 controls. In patients with serial samples, only MRSA-coinfected patients showed time-dependent increases in anti-α-toxin titer and functional neutralization capacity. MRSA α-toxin production from patient isolates correlated with initial serologic titers and with mortality in murine pneumonia. CONCLUSIONS: These data implicate α-toxin as a relevant antigen in severe pediatric MRSA pneumonia associated with respiratory viral infection, supporting a potential role for toxin-neutralizing therapy.

Activation Mechanism of the Bacteroides fragilis Cysteine Peptidase, Fragipain.

Enterotoxigenic Bacteroides fragilis produces a secreted metalloprotease known as B. fragilis toxin (BFT), which contributes to anaerobic sepsis, colitis, and colonic malignancy in mouse models of disease. A C11 family cysteine protease, fragipain (Fpn), directly activates BFT in the B. fragilis cell by removing the BFT prodomain. Fpn is itself a proenzyme and is autoactivated upon cleavage at an arginine residue in its activation loop. We have defined the proteolytic active site of Fpn, demonstrated that Fpn autoactivation can occur by an in trans loop cleavage mechanism, and characterized structural features of the Fpn activation loop that control peptidase activity against several substrates, including BFT. An arginine residue at the autocleavage site determines the fast activation kinetics of Fpn relative to the homologous C11 protease, PmC11, which is cleaved at lysine. Arginine to alanine substitution at the cleavage site ablated peptidase activity, as did partial truncation of the Fpn activation loop. However, complete truncation of the activation loop yielded an uncleaved, pro form of Fpn that was active as a peptidase against both Fpn and BFT substrates. Thus, Fpn can be transformed into an active peptidase in the absence of activation loop cleavage. This study provides insight into the mechanism of fragipain activation and, more generally, defines the role of the C11 activation loop in the control of peptidase activity and substrate specificity.

Staphylococcus aureus and the skin: a longstanding and complex interaction.

Staphylococcus aureus is a leading cause of human bacterial infection, most notable for its ability to infect any tissue in the human host. Among the most common sites of S aureus infection is the skin, predicated by the existence of this organism as a part of the commensal flora in up to half of the population. While the molecular mechanisms by which S aureus adapts to the ecologic niche of the skin and transitions to cause both skin infection and more severe invasive disease are incompletely defined, these represent an exciting and rapidly moving area of research. The ultimate goal of these investigations is to understand human disease pathogenesis, define host susceptibility factors that predispose to colonization and infection, and utilize this knowledge to inform the strategic development of novel preventive and therapeutic strategies.

Targeting Staphylococcus aureus α-toxin as a novel approach to reduce severity of recurrent skin and soft-tissue infections.

Staphyococcus aureus frequently causes recurrent skin and soft-tissue infection (SSTI). In the pediatric population, elevated serum antibody targeting S. aureus α-toxin is correlated with a reduced incidence of recurrent SSTI. Using a novel model of recurrent SSTI, we demonstrated that expression of α-toxin during primary infection increases the severity of recurrent disease. Antagonism of α-toxin by either a dominant-negative toxin mutant or a small molecule inhibitor of the toxin receptor ADAM10 during primary infection reduces reinfection abscess severity. Early neutralization of α-toxin activity during S. aureus SSTI therefore offers a new therapeutic strategy to mitigate primary and recurrent disease.

The psmα locus regulates production of Staphylococcus aureus alpha-toxin during infection.

Staphylococcus aureus is a leading cause of human bacterial infection, causing a wide spectrum of disease ranging from skin and soft tissue infections to life-threatening pneumonia and sepsis. S. aureus toxins play an essential role in disease pathogenesis, contributing to both immunomodulation and host tissue injury. Prominent among these toxins are the membrane-active pore-forming cytolysin alpha-toxin (Hla) and the amphipathic α-helical phenol-soluble modulin (PSM) peptides. As deletion of either the hla or psm locus leads to a phenotypically similar virulence defect in skin and soft tissue infection, we sought to determine the relative contribution of each locus to disease pathogenesis. Here we show that production of Hla can be modulated by PSM expression. An S. aureus mutant lacking PSM expression exhibits a transcriptional delay in hla mRNA production and therefore fails to secrete normal levels of Hla at early phases of growth. This leads to attenuation of virulence in vitro and in murine skin and lung models of infection, correlating with reduced recovery of Hla from host tissues. Production of Hla and restoration of staphylococcal virulence can be achieved in the psm mutant by plasmid-driven overexpression of hla. Our study suggests the coordinated action of Hla and PSMs in host tissue during early pathogenesis, confirming a major role for Hla in epithelial injury during S. aureus infection. These findings highlight the possibility that therapeutics targeting PSM production may simultaneously prevent Hla-mediated tissue injury.

Molecular differentiation of historic phage-type 80/81 and contemporary epidemic Staphylococcus aureus.

Staphylococcus aureus is a bacterial pathogen known to cause infections in epidemic waves. One such epidemic was caused by a clone known as phage-type 80/81, a penicillin-resistant strain that rose to world prominence in the late 1950s. The molecular underpinnings of the phage-type 80/81 outbreak have remained unknown for decades, nor is it understood why related S. aureus clones became epidemic in hospitals in the early 1990s. To better understand the molecular basis of these epidemics, we sequenced the genomes of eight S. aureus clinical isolates representative of the phage-type 80/81 clone, the Southwest Pacific clone [a community-associated methicillin-resistant S. aureus (MRSA) clone], and contemporary S. aureus clones, all of which are genetically related and belong to the same clonal complex (CC30). Genome sequence analysis revealed that there was coincident divergence of these clones from a recent common ancestor, a finding that resolves controversy about the evolutionary history of the lineage. Notably, we identified nonsynonymous SNPs in genes encoding accessory gene regulator C (agrC) and α-hemolysin (hla)--molecules important for S. aureus virulence--that were present in virtually all contemporary CC30 hospital isolates tested. Compared with the phage-type 80/81 and Southwest Pacific clones, contemporary CC30 hospital isolates had reduced virulence in mouse infection models, the result of SNPs in agrC and hla. We conclude that agr and hla (along with penicillin resistance) were essential for world dominance of phage-type 80/81 S. aureus, whereas key SNPs in contemporary CC30 clones restrict these pathogens to hospital settings in which the host is typically compromised.

Bacteroides fragilis toxin expression enables lamina propria niche acquisition in the developing mouse gut.

Bacterial toxins are well-studied virulence factors; however, recent studies have revealed their importance in bacterial niche adaptation. Enterotoxigenic Bacteroides fragilis (ETBF) expresses B. fragilis toxin (BFT) that we hypothesized may contribute to both colonic epithelial injury and niche acquisition. We developed a vertical transmission model for ETBF in mice that showed that BFT enabled ETBF to access a lamina propria (LP) niche during colonic microbiome development that was inaccessible to non-toxigenic B. fragilis. LP entry by ETBF required BFT metalloprotease activity, and showed temporal restriction to the pre-weaning period, dependent on goblet-cell-associated passages. In situ single-cell analysis showed bft expression at the apical epithelial surface and within the LP. BFT expression increased goblet cell number and goblet-cell-associated passage formation. These findings define a paradigm by which bacterial toxin expression specifies developmental niche acquisition, suggesting that a selective advantage conferred by a toxin may impact long-term host health.

A serologic correlate of protective immunity against community-onset Staphylococcus aureus infection.

BACKGROUND: Staphylococcus aureus is among the leading causes of human infection. Widespread drug resistance, emergence of highly virulent strains, and the ability of S. aureus to colonize >30% of the human population contribute to this organism's pathogenic success. Human serologic responses to S. aureus and their relationship to protective immunity remain incompletely defined, challenging the strategic development of efficacious vaccines. METHODS: We measured humoral responses to 2 staphylococcal exotoxins, α-hemolysin (Hla) and Panton-Valentine leukocidin (PVL; LukF-PV/LukS-PV subunits), both premier targets of current vaccine and immunotherapy development. We correlated acute and convalescent serum antibody levels with incidence of recurrent infection over 12 months follow-up in 235 children with S. aureus colonization, primary or recurrent skin and soft tissue infection, or invasive disease. RESULTS: Cutaneous infection elicited transient increases in anti-Hla and anti-PVL antibodies; however, subsequent infection risk was similar between primary and recurrent cutaneous infection cohorts. Patients with invasive infections had the lowest preexisting titers against Hla and LukF but displayed the highest convalescent titers. Across cohorts, convalescent anti-Hla titers correlated with protection against subsequent S. aureus infection. CONCLUSIONS: Cutaneous S. aureus infection does not reliably provoke durable, protective immune responses. This study provides the first link between protection from disease recurrence and the humoral response to Hla, a virulence factor already implicated in disease pathogenesis. These observations can be utilized to refine ongoing vaccine and immunotherapy efforts and inform the design of clinical trials.