Sandra Gonzalez

Pathogens have evolved to be highly adapted to their natural host. Community-associated methicillin-resistant Staphylococcus aureus USA300, for instance, is a lineage responsible for the epidemic of skin and soft tissue infections (SSTIs) in humans. Owing to its human tropism, mechanisms that enabled the rise of USA300 as a major skin pathogen remain incompletely defined. By leveraging a rodent-adapted strain of S. aureus , we developed a natural model of SSTIs. We found that LukMF′, a pore-forming leukocidin homolog to the human-specific LukSF-PV toxin, drives skin pathology in mice. LukMF′ lyses neutrophils via the chemokine receptor CCR1, which in turn fuels inflammatory pathology and microbial survival within the infectious nidus. Ablation of CCR1, depletion of neutrophils, or vaccination with LukMF′ all protected mice from skin pathology. Thus, these data support epidemiological studies linking leukocidins with human SSTIs and highlight the power of natural models to unearth potential targets to curtail infections.

Dehydration and malnutrition are common and often underdiagnosed in hospital settings. Multidrug-resistant bacterial infections result in more than 35,000 deaths a year in nosocomial patients. The effect of temporal dietary and water restriction (DWR) on susceptibility to multidrug-resistant pathogens is unknown. We report that DWR markedly increased susceptibility to systemic infection by ESKAPE pathogens. Using a murine bloodstream model of methicillin-resistant Staphylococcus aureus infection, we show that DWR leads to significantly increased mortality and morbidity. DWR causes increased bacterial burden, severe pathology, and increased numbers of phagocytes in the kidney. DWR appears to alter the functionality of these phagocytes and is therefore unable to control infection. Mechanistically, we show that DWR impairs the ability of macrophages to phagocytose multiple bacterial pathogens and efferocytose apoptotic neutrophils. Together, this work highlights the crucial impact that diet and hydration play in protecting against infection.

Extracellular DNase DNASE1L3 maintains tolerance to self-DNA in humans and mice, whereas the role of its homolog DNASE1 remains controversial, and the overall function of secreted DNases in immunity is unclear. We report that deletion of murine DNASE1 neither caused autoreactivity in isolation nor exacerbated lupus-like disease in DNASE1L3-deficient mice. However, combined deficiency of DNASE1 and DNASE1L3 rendered mice susceptible to bloodstream infection with Staphylococcus aureus. DNASE1/DNASE1L3 double-deficient mice mounted a normal innate response to S. aureus and did not accumulate neutrophil extracellular traps (NETs). However, their kidneys manifested severe pathology, increased bacterial burden, and biofilm-like bacterial lesions that contained bacterial DNA and excluded neutrophils. Furthermore, systemic administration of recombinant DNASE1 protein during S. aureus infection rescued the mortality of DNase-deficient mice and ameliorated the disease in wild-type mice. Thus, DNASE1 and DNASE1L3 jointly facilitate the control of bacterial infection by digesting extracellular microbial DNA in biofilms, suggesting the original evolutionary function of secreted DNases as antimicrobial agents.