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ABSTRACTStaphylococcus aureusis 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. aureustoxins 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 a-helical phenol-soluble modulin (PSM) peptides. As deletion of either the hlaor psmlocus 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. aureusmutant lacking PSM expression exhibits a transcriptional delay in hlamRNA production and therefore fails to secrete normal levels of Hla at early phases of growth. This leads to attenuation of virulence in vitroand 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 psmmutant 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. aureusinfection. These findings highlight the possibility that therapeutics targeting PSM production may simultaneously prevent Hla-mediated tissue injury.

ABSTRACTStaphylococcus aureusis a frequent cause of skin infection and sepsis in humans. Preclinical vaccine studies with S. aureushave used a mouse model with intraperitoneal challenge and survival determination as a measure for efficacy. To appreciate the selection of protective antigens in this model, we sought to characterize the pathological attributes of S. aureusinfection in the peritoneal cavity. Testing C57BL/6J and BALB/c mice, >109CFU of S. aureusNewman were needed to produce a lethal outcome in 90% of animals infected via intraperitoneal injection. Both necropsy and histopathology revealed the presence of intraperitoneal abscesses in the vicinity of inoculation sites. Abscesses were comprised of fibrin as well as collagen deposits and immune cells with staphylococci replicating at the center of these lesions. Animals that succumbed to challenge harbored staphylococci in abscess lesions and in blood. The establishment of lethal infections, but not the development of intraperitoneal abscesses, was dependent on S. aureusexpression of alpha-hemolysin (Hla). Active immunization with nontoxigenic HlaH35Lor passive immunization with neutralizing monoclonal antibodies protected mice against early lethal events associated with intraperitoneal S. aureusinfection but did not affect the establishment of abscess lesions. These results characterize a mouse model for the study of intraperitoneal abscess formation by S. aureus, a disease that occurs frequently in humans undergoing continuous ambulatory peritoneal dialysis for end-stage renal disease.

ABSTRACTStaphylococcus aureuspneumonia causes significant morbidity and mortality. Alpha-hemolysin (Hla), a pore-forming cytotoxin of S. aureus, has been identified through animal models of pneumonia as a critical virulence factor that induces lung injury. In spite of considerable molecular knowledge of how this cytotoxin injures the host, the precise host response to Hla in the context of infection remains poorly understood. We employed whole-genome expression profiling of infected lungs to define the host response to wild-type S. aureuscompared with the response to an Hla-deficient isogenic mutant in experimental pneumonia. These data provide a complete expression profile at 4 and at 24 h postinfection, revealing a unique response to the toxin-expressing strain. Gene ontogeny analysis revealed significant differences in the extracellular matrix and cardiomyopathy pathways, both of which govern cellular interactions in the tissue microenvironment. Evaluation of individual transcript responses to Hla-secreting staphylococci was notable for upregulation of host cytokine and chemokine genes, including the p19 subunit of interleukin-23. Consistent with this observation, the cellular immune response to infection was characterized by a prominent Th17 response to the wild-type pathogen. These findings define specific host mRNA responses to Hla-producing S. aureus, coupling the pulmonary Th17 response to the secretion of this cytotoxin. Expression profiling to define the host response to a single virulence factor proved to be a valuable tool in identifying pathways for further investigation in S. aureuspneumonia. This approach may be broadly applicable to the study of bacterial toxins, defining host pathways that can be targeted to mitigate toxin-induced disease.

ABSTRACTStaphylococcus aureuspneumonia is one of the most common invasive diseases caused by this human pathogen. S. aureusalpha-hemolysin, a pore-forming cytotoxin, is an essential virulence factor in the pathogenesis of pneumonia. Vaccine-based targeting of this toxin provides protection against lethal staphylococcal pneumonia in a murine model system, suggesting that a monoclonal antibody-based therapy may likewise prove to be efficacious for prevention and treatment of this disease. We report the generation of two distinct anti-alpha-hemolysin monoclonal antibodies that antagonize toxin activity, preventing human lung cell injury in vitro and protecting experimental animals against lethal S. aureuspneumonia. Each of these two monoclonal antibodies recognized an epitope within the first 50 amino acid residues of the mature toxin and blocked the formation of a stable alpha-hemolysin oligomer on the target cell surface. Active immunization with the first 50 amino acids of the toxin also conferred protection against S. aureuspneumonia. Together, these data reveal passive and active immunization strategies for prevention or therapy of staphylococcal pneumonia and highlight the potential role that a critical epitope may play in defining human susceptibility to this deadly disease.

Staphylococcus aureus pneumonia is one of the most common invasive diseases caused by this human pathogen. S. aureus alpha-hemolysin, a pore-forming cytotoxin, is an essential virulence factor in the pathogenesis of pneumonia. Vaccine-based targeting of this toxin provides protection against lethal staphylococcal pneumonia in a murine model system, suggesting that a monoclonal antibody-based therapy may likewise prove to be efficacious for prevention and treatment of this disease. We report the generation of two distinct anti-alpha-hemolysin monoclonal antibodies that antagonize toxin activity, preventing human lung cell injury in vitro and protecting experimental animals against lethal S. aureus pneumonia. Each of these two monoclonal antibodies recognized an epitope within the first 50 amino acid residues of the mature toxin and blocked the formation of a stable alpha-hemolysin oligomer on the target cell surface. Active immunization with the first 50 amino acids of the toxin also conferred protection against S. aureus pneumonia. Together, these data reveal passive and active immunization strategies for prevention or therapy of staphylococcal pneumonia and highlight the potential role that a critical epitope may play in defining human susceptibility to this deadly disease.

ABSTRACTA model of Staphylococcus aureus-induced pneumonia in adult, immunocompetent C57BL/6J mice is described. This model closely mimics the clinical and pathological features of pneumonia in human patients. Using this system, we defined a role for S. aureusstrain Newman surface proteins and secreted exotoxins in pneumonia-related mortality.

ABSTRACTYersinia pestisis the causative agent of plague, a disease that can manifest as either bubonic or pneumonic plague. An interesting feature of plague is that it is a rapidly progressive disease, suggesting that Y. pestiseither evades and/or suppresses the innate immune response to infection. Therefore, the early host response during the course of primary pneumonic plague was investigated in two mouse strains, the outbred strain CD1 and the inbred strain C57BL/6. A comparative analysis of the course of disease in these two strains of mice indicated that they are susceptible to intranasal Y. pestisCO92 infection and have similar 50% lethal doses and kinetics of infection with respect to colonization of the lung, liver, and spleen. Significantly, in both strains of mice, robust neutrophil recruitment to the lungs was not observed until 48 h after infection, suggesting that there was a delay in inflammatory cell recruitment to the site of infection. In addition, proinflammatory cytokines (interleukin-6 [IL-6], tumor necrosis factor alpha, gamma interferon, IL-12p70, monocyte chemoattractant protein 1) and chemokines (KC, MIP-2) in the bronchoalveolar lavage fluids were not readily detected until 48 h after infection, which coincided with the increase in polymorphonuclear leukocyte (PMN) recruitment to the lungs. In comparison, CD1 mice with gram-negative pneumonia caused by Klebsiella pneumoniaeexhibited strong inflammatory responses early in infection, with PMNs comprising the majority of the cells in the bronchoalveolar lavage fluid 24 h postinfection, indicating that PMN recruitment to the lungs could occur earlier in this infection than in Y. pestisinfection. Together, our results indicate that there is a delay in the recruitment of neutrophils to the lungs in the mouse model of primary plague pneumonia that correlates with delayed expression of proinflammatory cytokines and chemokines in both outbred and inbred mice.

Yersinia pestis is the causative agent of plague, a disease that can manifest as either bubonic or pneumonic plague. An interesting feature of plague is that it is a rapidly progressive disease, suggesting that Y. pestis either evades and/or suppresses the innate immune response to infection. Therefore, the early host response during the course of primary pneumonic plague was investigated in two mouse strains, the outbred strain CD1 and the inbred strain C57BL/6. A comparative analysis of the course of disease in these two strains of mice indicated that they are susceptible to intranasal Y. pestis CO92 infection and have similar 50% lethal doses and kinetics of infection with respect to colonization of the lung, liver, and spleen. Significantly, in both strains of mice, robust neutrophil recruitment to the lungs was not observed until 48 h after infection, suggesting that there was a delay in inflammatory cell recruitment to the site of infection. In addition, proinflammatory cytokines (interleukin-6 [IL-6], tumor necrosis factor alpha, gamma interferon, IL-12p70, monocyte chemoattractant protein 1) and chemokines (KC, MIP-2) in the bronchoalveolar lavage fluids were not readily detected until 48 h after infection, which coincided with the increase in polymorphonuclear leukocyte (PMN) recruitment to the lungs. In comparison, CD1 mice with gram-negative pneumonia caused by Klebsiella pneumoniae exhibited strong inflammatory responses early in infection, with PMNs comprising the majority of the cells in the bronchoalveolar lavage fluid 24 h postinfection, indicating that PMN recruitment to the lungs could occur earlier in this infection than in Y. pestis infection. Together, our results indicate that there is a delay in the recruitment of neutrophils to the lungs in the mouse model of primary plague pneumonia that correlates with delayed expression of proinflammatory cytokines and chemokines in both outbred and inbred mice.

A model of Staphylococcus aureus-induced pneumonia in adult, immunocompetent C57BL/6J mice is described. This model closely mimics the clinical and pathological features of pneumonia in human patients. Using this system, we defined a role for S. aureus strain Newman surface proteins and secreted exotoxins in pneumonia-related mortality.