The anti-inflammatory properties of granulocytic myeloid-derived suppressor cells (G-MDSCs) promote Staphylococcus aureus (S. aureus) biofilm persistence. Evidence suggests that G-MDSC activity is shaped not only by S. aureus products but also by intrinsic metabolic programs. This study explores whether G-MDSC activity can be modulated by increasing mitochondrial abundance using a co-culture paradigm with macrophages as a mitochondrial donor. Macrophages transfer mitochondria directly to G-MDSCs via tunneling nanotubes, enhancing G-MDSC respiration, as reflected by increased basal, maximal, and spare respiratory capacity. Augmenting mitochondrial abundance in G-MDSCs enhances T cell-suppressive activity and reduces tumor necrosis factor (TNF) and interleukin 6 (IL-6) production. In a mouse model of S. aureus prosthetic joint infection, adoptively transferred macrophages deliver mitochondria to G-MDSCs, enhancing their suppressive activity and increasing bacterial burden, which is reversed when macrophages with non-functional mitochondria are introduced. These findings support the theory that G-MDSCs exploit mitochondria to augment their anti-inflammatory properties in response to S. aureus biofilm.

Staphylococcus aureus (S. aureus) is a leading cause of prosthetic joint infection (PJI). These infections are often intractable due to biofilm formation, which are complex bacterial communities that adhere to biotic and abiotic surfaces. Within a biofilm, there is considerable heterogeneity in bacterial metabolism and gene expression that serves to create an anti-inflammatory milieu at the site of infection. This is due, in part, to the preferential recruitment of granulocytic myeloid-derived suppressor cells (G-MDSCs), a population of pathologically activated immature leukocytes with immunosuppressive features. Our prior work revealed that G-MDSCs are integral for promoting biofilm persistence via the production of interleukin-10 (IL-10) in response to biofilm-derived lactate. However, the mechanism responsible for G-MDSC anti-inflammatory activity in the context of biofilm infection is unknown. Using a mouse model of S. aureus PJI, time-course single-cell RNA sequencing (scRNA-seq) revealed a significant enrichment in glycolytic and hypoxic transcriptional signatures in infiltrating G-MDSCs. G-MDSCs significantly increased their glycolytic activity when co-cultured with S. aureus biofilm in vitro and inhibiting glycolysis during PJI in vivo with 2-DG nanoparticles significantly attenuated G-MDSC suppressive activity concomitant with a significant reduction in bacterial burden. This study demonstrates that glycolysis is required for G-MDSC-mediated immunosuppression and biofilm persistence during S. aureus PJI. Furthermore, our results demonstrate that G-MDSC metabolism can be targeted to improve infection outcomes. Supported by funding from NIH (2P01 AI083211) & UNMC (UNMC Graduate Fellowship)

Abstract Craniotomy is a neurosurgery performed to resolve severe neurological complications. Despite prophylaxis, nearly 1-3% of craniotomies are complicated by infection, with approximately half attributed to Staphylococcus aureus (S. aureus). Using our novel mouse model, we established a protective role for CD4+ T cells during S. aureus craniotomy infection. Rag1 knock out (KO) mice or animals treated with anti-CD4 Ab showed significantly elevated bacterial burden, suggesting an important role for adaptive immunity in controlling infection. These findings were corroborated in mice treated with VLA-4 and LFA-1 Abs, underscoring the importance of peripheral CD4+ T cell responses. scRNA-seq revealed phenotypic heterogeneity within brain CD3+ infiltrates with CD4+ cells being most predominant that were typified by robust inflammatory and glycolytic profiles. CD4+ T cells displayed attributes of both Th1 and Th17 phenotypes, whose functional importance was validated in vivo as adoptive transfer of either Th1 or Th17 cells prevented S. aureus outgrowth in Rag1 KO mice. Interestingly, milder phenotypes were observed in IL-17A/F or IFN-γ KO mice, suggesting a redundant and cooperative role of both Th1 and Th17 driven responses. This was confirmed by treatment of IFN-γ KO mice with IL-17A/F neutralizing Ab, which recapitulated phenotypes of Rag1 KO animals. Collectively, our results implicate a critical role for CD4+ T cells in S. aureus containment during craniotomy infection.

Staphylococcus aureus is a leading cause of biofilm-associated prosthetic joint infection (PJI). A primary contributor to infection chronicity is an expansion of granulocytic myeloid-derived suppressor cells (G-MDSCs), which are critical for orchestrating the antiinflammatory biofilm milieu. Single-cell sequencing and bioinformatic metabolic algorithms were used to explore the link between G-MDSC metabolism and S. aureus PJI outcome. Glycolysis and the hypoxia response through HIF1a were significantly enriched in G-MDSCs. Interfering with both pathways in vivo, using a 2-deoxyglucose nanopreparation and granulocyte-targeted Hif1a conditional KO mice, respectively, attenuated G-MDSC-mediated immunosuppression and reduced bacterial burden in a mouse model of S. aureus PJI. In addition, single-cell RNA-Seq (scRNA-Seq) analysis of granulocytes from PJI patients also showed an enrichment in glycolysis and hypoxia-response genes. These findings support the importance of a glycolysis/HIF1a axis in promoting G-MDSC antiinflammatory activity and biofilm persistence during PJI.

Neurosurgeries complicated by infection are associated with prolonged treatment and significant morbidity. Craniotomy is a common neurosurgical procedure; however, the cellular and molecular signatures associated with craniotomy infection in human subjects are unknown. A retrospective study of over 2,500 craniotomies reveals diverse patient demographics, pathogen identity, and surgical landscapes associated with infection. Leukocyte profiling in patient tissues from craniotomy infection characterizes a predominance of granulocytic myeloid-derived suppressor cells that may arise from transmigrated blood neutrophils, based on single-cell RNA sequencing (scRNA-seq) trajectory analysis. Single-cell transcriptomic analysis identifies metabolic shifts in tissue leukocytes, including a conserved hypoxia-inducible factor (HIF) signature. The importance of HIF signaling was validated using a mouse model of Staphylococcus aureus craniotomy infection, where HIF inhibition increases chemokine production and leukocyte recruitment, exacerbating tissue pathology. These findings establish conserved metabolic and transcriptional signatures that may represent promising future therapeutic targets for human craniotomy infection in the face of increasing antimicrobial resistance.

Abstract Prosthetic joint infection (PJI) is a severe complication following hip and knee arthroplasty and is reported to affect 1-2% of total arthroplasties. Staphylococcus aureus (S. aureus) contributes to most PJIs, with a higher treatment failure rate partly due to biofilm formation. Granulocytic myeloid-derived suppressor cell (G-MDSC) expansion and IL-10 secretion are critical for inducing an immunosuppressive environment that supports S. aureus persistence during PJI. Recently, S. aureus-derived lactate was shown to promote IL-10 production by G-MDSCs. However, the importance of G-MDSC metabolism in programming their anti-inflammatory activity is unknown. Single-cell RNA sequencing (scRNA-seq) of infected tissues from a mouse model of S. aureus PJI revealed enrichment of glycolysis and hypoxia pathway genes in G-MDSCs. Increased glycolytic activity in G-MDSCs was confirmed following S. aureus biofilm co-culture and attenuating glycolysis with either 2-deoxyglucose or granulocyte-specific HIF-1a deletion reduced bacterial growth during S. aureus PJI. These changes coincided with less G-MDSC suppressive activity and a transformation towards a proinflammatory phenotype. scRNA-seq of samples from PJI patients revealed heightened glycolysis and hypoxia signatures, supporting findings with the mouse PJI model. Together, these results suggest that glycolysis and HIF-1a pathways are critical for the anti-inflammatory activity of G-MDSCs during S. aureus biofilm infection.

Treatment of brain tumors, epilepsy, or hemodynamic abnormalities requires a craniotomy to access the brain. Despite prophylaxis, infectious complications after craniotomy range from 1–3% with approximately half caused by Staphylococcus aureus(S. aureus). Using our novel mouse model of craniotomy infection, a critical role of CD4 +T cells was established since bacterial burdens were significantly increased in the brain, galea, and bone flap of RAG1 −/−mice as well as following CD4 +T cell depletion. Bacterial burdens were also increased following anti-VLA-4 & LFA-1 treatment, further establishing a beneficial role for peripheral CD4 +infiltrates. Adoptive transfer of in vitroskewed Th1 or Th17 cells into RAG1 −/−mice returned infectious burdens back to wild type (WT) levels. Ex vivostaining of transferred CD4 +T cells recovered from the brains of RAG1 −/−mice revealed a dominant IFN-γ signature, even following Th17 adoptive transfer, suggesting that Th1 responses are critical for infection containment. Further evidence of Th1 and Th17 involvement was demonstrated by exacerbated infection in Tbet −/−and RORγt −/−mice, respectively. Interestingly, phenotypes were not evident in either IL-17A/F −/−KO or IFN-γ −/−mice, whereas adoptive transfer of CD4 +T cells from either IL-17 −/−or IFN-γ −/−animals mitigated bacterial outgrowth in RAG1 −/−mice, suggesting the combined action of Th1- and Th17-derived mediators. scRNA-seq identified an increased IFN-γ-regulated signature (gbp1/5, isg15, irf1, stat1) in select microglial and infiltrating granulocytic clusters. This suggests that T cell-innate immune cell crosstalk is necessary for bacterial containment during craniotomy infection. R01 AI169788

Most coagulase-negative staphylococcal species, including the opportunistic pathogen Staphylococcus epidermidis, struggle to maintain redox homeostasis and grow under nitrosative stress. Under these conditions, growth can only resume once nitric oxide (NO) is detoxified by the flavohemoglobin Hmp. Paradoxically, S. epidermidis produces endogenous NO through its genetically encoded nitric oxide synthase (seNOS) and heavily relies on its activity for growth. In this study, we investigate the basis of the growth advantage attributed to seNOS activity. Our findings reveal that seNOS supports growth by countering Hmp toxicity. S. epidermidis relies on Hmp activity for its survival in the host under NO stress. However, in the absence of nitrosative stress, Hmp generates significant amounts of the harmful superoxide radical (O2•-) from its heme prosthetic group which impedes growth. To limit Hmp toxicity, nitrite (NO2−) derived from seNOS promotes CymR-CysK regulatory complex activity, which typically regulates cysteine metabolism, but we now demonstrate to also repress hmp transcription. These findings reveal a critical mechanism through which the bacterial NOS-Hmp axis drives staphylococcal fitness.

Background Treatment of brain tumors, epilepsy, or hemodynamic abnormalities requires a craniotomy to access the brain. Nearly 1 million craniotomies are performed in the US annually, which increase to ~ 14 million worldwide and despite prophylaxis, infectious complications after craniotomy range from 1 to 3%. Approximately half are caused by Staphylococcus aureus ( S. aureus ), which forms a biofilm on the bone flap that is recalcitrant to antibiotics and immune-mediated clearance. However, the mechanisms responsible for the persistence of craniotomy infection remain largely unknown. The current study examined the role of IL-10 in promoting bacterial survival. Methods A mouse model of S. aureus craniotomy infection was used with wild type (WT), IL-10 knockout (KO), and IL-10 conditional KO mice where IL-10 was absent in microglia and monocytes/macrophages ( CX3CR1 Cre IL-10 fl/fl ) or neutrophils and granulocytic myeloid-derived suppressor cells (G-MDSCs; Mrp8 Cre IL-10 fl/fl ), the major immune cell populations in the infected brain vs. subcutaneous galea, respectively. Mice were examined at various intervals post-infection to quantify bacterial burden, leukocyte recruitment, and inflammatory mediator production in the brain and galea to assess the role of IL-10 in craniotomy persistence. In addition, the role of G-MDSC-derived IL-10 on neutrophil activity was examined. Results Granulocytes (neutrophils and G-MDSCs) were the major producers of IL-10 during craniotomy infection. Bacterial burden was significantly reduced in IL-10 KO mice in the brain and galea at day 14 post-infection compared to WT animals, concomitant with increased CD4 + and γδ T cell recruitment and cytokine/chemokine production, indicative of a heightened proinflammatory response. S. aureus burden was reduced in Mrp8 Cre IL-10 fl/fl but not CX3CR1 Cre IL-10 fl/fl mice that was reversed following treatment with exogenous IL-10, suggesting that granulocyte-derived IL-10 was important for promoting S. aureus craniotomy infection. This was likely due, in part, to IL-10 production by G-MDSCs that inhibited neutrophil bactericidal activity and TNF production. Conclusion Collectively, these findings reveal a novel role for granulocyte-derived IL-10 in suppressing S. aureus clearance during craniotomy infection, which is one mechanism to account for biofilm persistence.

Biofilms are bacterial communities characterized by antibiotic tolerance. Staphylococcus aureus is a leading cause of biofilm infections on medical devices, including prosthetic joints, which represent a significant health care burden. The major leukocyte infiltrate associated with S. aureus prosthetic joint infection (PJI) is granulocytic myeloid-derived suppressor cells (G-MDSCs), which produce IL-10 to promote biofilm persistence by inhibiting monocyte and macrophage proinflammatory activity. To determine how S. aureus biofilm responds to G-MDSCs and macrophages, biofilms were cocultured with either leukocyte population followed by RNA sequencing. Several genes involved in fermentative pathways were significantly upregulated in S. aureus biofilm following G-MDSC coculture, including formate acetyltransferase (pflB), which catalyzes the conversion of pyruvate and coenzyme-A into formate and acetyl-CoA. A S. aureus pflB mutant (ΔpflB) did not exhibit growth defects in vitro. However, ΔpflB formed taller and more diffuse biofilm compared to the wild-type strain as revealed by confocal microscopy. In a mouse model of PJI, the bacterial burden was significantly reduced with ΔpflB during later stages of infection, which coincided with decreased G-MDSC influx and increased neutrophil recruitment, and ΔpflB was more susceptible to macrophage killing. Although formate was significantly reduced in the soft tissue surrounding the joint of ΔpflB-infected mice levels were increased in the femur, suggesting that host-derived formate may also influence bacterial survival. This was supported by the finding that a ΔpflBΔfdh strain defective in formate production and catabolism displayed a similar phenotype to ΔpflB. These results revealed that S. aureus formate metabolism is important for promoting biofilm persistence.

Craniotomies are performed to treat a variety of intracranial pathology. Surgical site infection remains a complication of craniotomy despite the use of prophylactic antibiotics and universal sterile precautions. Infections occur in 1-3% of procedures, with approximately half caused by Staphylococcus aureus that forms a biofilm on the bone flap and is recalcitrant to systemic antibiotic therapy. We used an S. aureus-dsRed construct to compare the phagocytic capacity of leukocytes and microglia in vitro and in vivo using a mouse model of craniotomy infection. In addition, single-cell RNA sequencing (scRNA-seq) was applied to determine whether a transcriptional signature could be identified for phagocytic versus nonphagocytic cells in vivo. S. aureus was phagocytosed to equivalent extents in microglia, macrophages, neutrophils, and granulocytic myeloid-derived suppressor cells in vitro; however, microglial uptake of S. aureus was limited in vivo, whereas the other leukocyte populations exhibited phagocytic activity. scRNA-seq comparing the transcriptional signatures of phagocytic (S. aureus-dsRed+) versus nonphagocytic (S. aureus-dsRed-) leukocytes identified classical pathways enriched in phagocytic cells (i.e., reactive oxygen species [ROS]/reactive nitrogen species, lysosome, iron uptake, and transport), whereas nonphagocytic populations had increased ribosomal, IFN, and hypoxia signatures. scRNA-seq also revealed a robust ROS profile, which led to the exploration of craniotomy infection in NADPH oxidase 2 knockout mice. S. aureus burden, leukocyte recruitment, and intracellular bacterial load were significantly increased in NADPH oxidase 2 KO compared with wild-type animals. Collectively, these results highlight the importance of ROS generation in phagocytes for S. aureus biofilm containment, but not clearance, during craniotomy infection.

A craniotomy is performed to access the brain for tumor resection, localization and resection of epileptogenic foci, and aneurysm clipping. Despite prophylaxis, infectious complications after craniotomy range from 1–3%, with approximately half caused by Staphylococcus aureus (S. aureus), which forms a biofilm on the bone flap that is recalcitrant to antibiotics. Using our novel mouse model of S. aureus craniotomy infection, Th1 and Th17 infiltrates were found to preferentially home to the brain but not the subcutaneous galea; however, their functional importance is unknown. RAG1 knockout (KO) mice displayed significant increases in bacterial burden in the brain, galea, and bone flap at days 3, 7, and 14 post-infection, which was negated following the adoptive transfer of either in vitro skewed Th1 or Th17 cells. Interestingly, in vitro skewed Th17 cells acquired Th1 characteristics upon migrating into the brain in vivo as revealed by the production of Th1-associated cytokines such as IFN-γ and TNF-α with minimal IL-17A. We established that the window of T cell protection was during acute infection, since delaying Th1 or Th17 adoptive transfer until day 7 post-infection was no longer able to attenuate S. aureus burden in RAG1 KO mice compared to T cell transfers at day −1 or 3 after infection that were effective. In vitro studies established that both Th1 and Th17 cells augmented microglial, macrophage, and neutrophil S. aureus bactericidal activity and IL-12p70 and CXCL10 production. Collectively, these findings highlight the importance of an early adaptive immune response for bacterial containment during S. aureus craniotomy infection by promoting the antimicrobial activity of infiltrating leukocytes and resident microglia.

Neurosurgery for brain tumor resection or epilepsy treatment requires a craniotomy to gain access to the brain. Despite prophylactic measures, infectious complications occur at a frequency of 1-3%, with approximately half caused by Staphylococcus aureus (S. aureus) that forms a biofilm on the bone flap and is recalcitrant to antibiotics. Using single-cell RNA sequencing in a mouse model of S. aureus craniotomy infection, this study revealed the complex transcriptional heterogeneity of resident microglia and infiltrating monocytes in the brain, in addition to transcriptionally diverse granulocyte subsets in the s.c. galea and bone flap. In the brain, trajectory analysis identified the transition of microglia from a homeostatic/anti-inflammatory to proinflammatory and proliferative populations, whereas granulocytes in the brain demonstrated a trajectory from a granulocyte myeloid-derived suppressor cell (MDSC)-like phenotype to a small population of mature polymorphonuclear neutrophils (PMNs). In the galea, trajectory analysis identified the progression from two distinct granulocyte-MDSC-like populations to PMN clusters enriched for IFN signaling and cell cycle genes. Based on their abundance in the galea and bone flap, PMNs and MDSCs were depleted using anti-Ly6G, which resulted in increased bacterial burden. This revealed a critical role for PMNs in S. aureus containment because MDSCs were found to attenuate PMN antibacterial activity, which may explain, in part, why craniotomy infection persists in the presence of PMN infiltrates. These results demonstrate the existence of a transcriptionally diverse leukocyte response that likely influences the chronicity of S. aureus craniotomy infection.

Neurosurgery for brain tumor or epilepsy resection requires a craniotomy to access the brain. Infectious complications occur at a frequency of 1–3%, with approximately half caused by Staphylococcus aureus (S. aureus) that forms a biofilm on the bone flap. Our recent scRNA-seq study revealed the transcriptional heterogeneity of infiltrating leukocyte populations during S. aureus craniotomy infection, several of which were enriched for IFN-γ-regulated genes. In the current report, we examined the functional importance of IFN-γ signaling during S. aureus craniotomy infection in IFN-γR knockout (KO) mice. Bacterial burden was significantly increased in the subcutaneous galea of IFN-γR KO compared to WT mice throughout the 28 day time course, whereas titers in the brain and bone flap were similar, highlighting a compartmentalized immune response. Leukocyte infiltrates in the galea were equivalent in IFN-γR KO and WT animals, which led us to utilize scRNA-seq to interrogate alterations in leukocyte activation following IFN-γR loss. Bioinformatics revealed the predominance of granulocyte-myeloid-derived suppressor cell (G-MDSC)-like subsets in the galea of both IFN-γR KO and WT mice. Hallmark pathway analysis identified a significant reduction in not only the IFN-γ pathway in G-MDSC-like subsets, but also a decrease in IFN-α and inflammatory (IL-1β, IL-18, and PLAUR) pathways in IFN-γR KO mice. Collectively, these results demonstrate the importance of IFN-γR signaling in preventing S. aureus outgrowth in the galea and a likely synergism between Type I and Type II IFN pathways in controlling craniotomy infection.

Bone metastatic prostate cancer (BM-PCa) significantly reduces overall patient survival and is currently incurable. Current standard immunotherapy showed promising results for PCa patients with metastatic, but less advanced, disease (i.e., fewer than 20 bone lesions) suggesting that PCa growth in bone contributes to response to immunotherapy. We found that: (1) PCa stimulates recruitment of neutrophils, the most abundant immune cell in bone, and (2) that neutrophils heavily infiltrate regions of prostate tumor in bone of BM-PCa patients. Based on these findings, we examined the impact of direct neutrophil-prostate cancer interactions on prostate cancer growth. Bone marrow neutrophils directly induced apoptosis of PCa in vitro and in vivo, such that neutrophil depletion in bone metastasis models enhanced BM-PCa growth. Neutrophil-mediated PCa killing was found to be mediated by suppression of STAT5, a transcription factor shown to promote PCa progression. However, as the tumor progressed in bone over time, neutrophils from late-stage bone tumors failed to elicit cytotoxic effector responses to PCa. These findings are the first to demonstrate that bone-resident neutrophils inhibit PCa and that BM-PCa are able to progress via evasion of neutrophil-mediated killing. Enhancing neutrophil cytotoxicity in bone may present a novel therapeutic option for bone metastatic prostate cancer.

Medical device-associated biofilm infections are a therapeutic challenge based on their antibiotic tolerance and ability to evade immune-mediated clearance. The virulence determinants responsible for bacterial biofilm to induce a maladaptive immune response remain largely unknown. This study identified a critical role for S. aureus ATP synthase in influencing the host immune response to biofilm infection. An S. aureus ATP synthase alpha subunit mutant (Δ atpA ) elicited heightened proinflammatory cytokine production by leukocytes in vitro and in vivo , which coincided with improved biofilm clearance in a mouse model of prosthetic joint infection. The ability of S. aureus Δ atpA to augment host proinflammatory responses was cell lysis-dependent, as inhibition of bacterial lysis by polyanethole sodium sulfanate or a Δ atpA Δ atl biofilm did not elicit heightened cytokine production. These studies reveal a critical role for AtpA in shaping the host immune response to S. aureus biofilm.

Little information is available on the functional activity of leukocytes after arthroplasty or the expansion of populations with immune suppressive properties during the acute post-operative period. Synovial fluid and matched pre- and post-surgical blood samples were collected from total hip and knee arthroplasty patients (THA and TKA, respectively) to examine the impact of surgery on peripheral blood leukocyte frequency, bactericidal activity, and inflammatory mediator expression. For spinal surgeries, inflammatory mediator production by peripheral blood mononuclear cells (PBMCs) pre- and post-surgery was examined. An expansion of immune suppressive granulocytic myeloid-derived suppressor cells (G-MDSCs) was observed following arthroplasty, which correlated with significantly increased serum interleukin-10 (IL-10) levels. Analysis of synovial fluid from THA and TKAs revealed reduced granulocyte colony-stimulating factor (G-CSF) and soluble CD40 ligand (sCD40L) and increased interleukin-6 (IL-6), monocyte chemoattractant protein 2 (CCL2) and Fms-like tyrosine kinase 3 ligand (Flt-3L) compared to pre- and post-surgical serum. For the spinal surgery cohort, stimulation of PBMCs isolated post-surgery with bacterial antigens produced significantly less pro-inflammatory (IL-1α, IL-1β, interleukin-1 receptor antagonist (IL-1RA), IL-12p40, growth-related oncogene-α/GRO-α (CXCL1) and 6Ckine (CCL21)) and more anti-inflammatory/tissue repair mediators (IL-10, G-CSF and granulocyte-macrophage colony-stimulating factor (GM-CSF)) compared to PBMCs recovered before surgery. The observed bias towards systemic anti-inflammatory changes without concomitant increases in pro-inflammatory responses may influence susceptibility to infection following orthopaedic surgery in the context of underlying co-morbidities or risk factors.

Abstract Background A craniotomy is required to access the brain for tumor resection or epilepsy treatment, and despite precautionary measures, infectious complications occur at a frequency of 1–3%. Approximately half of craniotomy infections are caused by Staphylococcus aureus (S. aureus) that forms a biofilm on the bone flap, which is recalcitrant to antibiotics. Our prior work in a mouse model of S. aureus craniotomy infection revealed a critical role for myeloid differentiation factor 88 (MyD88) in bacterial containment and pro-inflammatory mediator production. Since numerous receptors utilize MyD88 as a signaling adaptor, the current study examined the importance of Toll-like receptor 2 (TLR2) and TLR9 based on their ability sense S. aureus ligands, namely lipoproteins and CpG DNA motifs, respectively. We also examined the role of caspase-1 based on its known association with TLR signaling to promote IL-1β release. Methods A mouse model of craniotomy-associated biofilm infection was used to investigate the role of TLR2, TLR9, and caspase-1 in disease progression. Wild type (WT), TLR2 knockout (KO), TLR9 KO, and caspase-1 KO mice were examined at various intervals post-infection to quantify bacterial burden, leukocyte recruitment, and inflammatory mediator production in the galea, brain, and bone flap. In addition, the role of TLR2-dependent signaling during microglial/macrophage crosstalk with myeloid-derived suppressor cells (MDSCs) was examined. Results TLR2, but not TLR9, was important for preventing S. aureus outgrowth during craniotomy infection, as revealed by the elevated bacterial burden in the brain, galea, and bone flap of TLR2 KO mice concomitant with global reductions in pro-inflammatory mediator production compared to WT animals. Co-culture of MDSCs with microglia or macrophages, to model interactions in the brain vs. galea, respectively, also revealed a critical role for TLR2 in triggering pro-inflammatory mediator production. Similar to TLR2, caspase-1 KO animals also displayed increased S. aureus titers coincident with reduced pro-inflammatory mediator release, suggestive of pathway cooperativity. Treatment of caspase-1 KO mice with IL-1β microparticles significantly reduced S. aureus burden in the brain and galea compared to empty microparticles, confirming the critical role of IL-1β in limiting S. aureus outgrowth during craniotomy infection. Conclusions These results demonstrate the existence of an initial anti-bacterial response that depends on both TLR2 and caspase-1 in controlling S. aureus growth; however, neither pathway is effective at clearing infection in the WT setting, since craniotomy infection persists when both molecules are present.