Staphylococcus aureus Biofilms Induce Macrophage Dysfunction Through Leukocidin AB and Alpha-Toxin

Abstract

The macrophage response to planktonic Staphylococcus aureus involves the induction of proinflammatory microbicidal activity. However, S. aureus biofilms can interfere with these responses in part by polarizing macrophages toward an anti-inflammatory profibrotic phenotype. Here we demonstrate that conditioned medium from mature S. aureus biofilms inhibited macrophage phagocytosis and induced cytotoxicity, suggesting the involvement of a secreted factor(s). Iterative testing found the active factor(s) to be proteinaceous and partially agr-dependent. Quantitative mass spectrometry identified alpha-toxin (Hla) and leukocidin AB (LukAB) as critical molecules secreted by S. aureus biofilms that inhibit murine macrophage phagocytosis and promote cytotoxicity. A role for Hla and LukAB was confirmed by using hla and lukAB mutants, and synergy between the two toxins was demonstrated with a lukAB hla double mutant and verified by complementation. Independent confirmation of the effects of Hla and LukAB on macrophage dysfunction was demonstrated by using an isogenic strain in which Hla was constitutively expressed, an Hla antibody to block toxin activity, and purified LukAB peptide. The importance of Hla and LukAB during S. aureus biofilm formation in vivo was assessed by using a murine orthopedic implant biofilm infection model in which the lukAB hla double mutant displayed significantly lower bacterial burdens and more macrophage infiltrates than each single mutant. Collectively, these findings reveal a critical synergistic role for Hla and LukAB in promoting macrophage dysfunction and facilitating S. aureus biofilm development in vivo.

Infectious Dose Dictates the Host Response during Staphylococcus aureus Orthopedic-Implant Biofilm Infection

“…1 and 2, respectively) and thus was not considered biologically significant. UAMS-1 and LAC were utilized for all subsequent dose-response studies, since UAMS-1 originated from an orthopedic infection and we have a great deal of knowledge about the behavior of LAC in the orthopedic-implant model (25)(26)(27)40). This approach was further justified by the finding that MW2 behaved similarly to both UAMS-1 and LAC in terms of immune profiles and biofilm burdens.…”

Humanized Mice Exhibit Increased Susceptibility toStaphylococcus aureusPneumonia

“…This may be explained by either additional targets that are recognized by this toxin, cellular targets not reconstituted in this model, and/or multiple conflicting effects of the LukAB/CD11b interaction. In a murine model of joint infection, LukAB and α-toxin were expressed together in biofilms, facilitating S. aureus growth and suppression of macrophage function [41], suggesting activity toward murine macrophages. However, single lukAB mutants have been shown to have a phenotype in a mouse renal abscess model [42] but not in models of bacteremia or rabbit skin and abscess formation [43].…”

Impact of sarA and Phenol-Soluble Modulins on the Pathogenesis of Osteomyelitis in Diverse Clinical Isolates of Staphylococcus aureus

“…Indeed, it has been suggested that, as with cancer, "remission" is a more appropriate term than "cure" in the context of osteomyelitis (2). Several factors contribute to this therapeutic recalcitrance, including the inability to diagnose the infection before it has progressed to a chronic stage in which the local vasculature is compromised, the formation of a bacterial biofilm that limits the efficacy of both conventional antibiotics and host defenses, the emergence of phenotypic variants within the biofilm (persister cells and small-colony variants) that exhibit metabolic traits that limit their antibiotic susceptibility, and the ability of the pathogens involved, including S. aureus, to invade and replicate within host cells, including osteoblasts (3)(4)(5)(6)(7)(8)(9). Collectively, these factors dictate that the clinical problem of osteomyelitis extends far beyond acquired resistance and the increasingly limited availability of effective antibiotics.…”