Superoxide anions produced by Streptococcus pyogenes group A-stimulated keratinocytes are responsible for cellular necrosis and bacterial growth inhibition

Impact of Phosphorylcholine Expression on the Adherence and Invasion of Streptococcus pyogenes to Epithelial Cells

Phosphorylcholine (PC) is a structural component of various pathogens and is involved in bacterial adhesion via the platelet-activating factor receptor (PAF-R). In this study, we investigated how PC expression affects cell adhesion and invasion of Streptococcus pyogenes (S. pyogenes). Eight clinical strains of S. pyogenes were cultured, and PC expression was measured using fluorescence-activated cell sorting. Bacterial adherence and invasion were examined using Detroit 562 cells. An anti-PC-specific monoclonal antibody (TEPC-15) was used to inhibit bacterial PC, and a PAF-R antagonist (ABT-491) was used to inhibit cellular PAF-R. The emm gene was amplified by the polymerase chain reaction with the standard primers. The level of PC expressed on the S. pyogenes surfaces differed in each strain and differed even in the same emm genotype. Adherence assay experiments showed a significant negative correlation between TEPC-15 and ABT-491 inhibitory effects and PC expression in S. pyogenes. Similarly, intracellular invasion assay experiments showed a significant negative correlation between TEPC-15 and ABT-491 inhibitory effects and PC expression in S. pyogenes. This study suggests that S. pyogenes is involved in cell adhesion and invasion by PC.

Evaluation of IL-17D in Host Immunity to Group A Streptococcus Infection

IL-17D is a cytokine that belongs to the IL-17 family and is conserved in vertebrates and invertebrates. In contrast to IL-17A and IL-17F, which are expressed in Th17 cells, IL-17D is expressed broadly in nonimmune cells. IL-17D can promote immune responses to cancer and viruses in part by inducing chemokines and recruiting innate immune cells such as NK cells. Although bacterial infection can induce IL-17D in fish and invertebrates, the role of mammalian IL-17D in antibacterial immunity has not been established. To determine whether IL-17D has a role in mediating host defense against bacterial infections, we studied i.p. infection by group A Streptococcus (GAS) in wild-type (WT) and Il17d ^-/- mice. Compared with WT animals, mice deficient in IL-17D experienced decreased survival, had greater weight loss, and showed increased bacterial burden in the kidney and peritoneal cavity following GAS challenge. In WT animals, IL-17D transcript was induced by GAS infection and correlated to increased levels of chemokine CCL2 and greater neutrophil recruitment. Of note, GAS-mediated IL-17D induction in nonimmune cells required live bacteria, suggesting that processes beyond recognition of pathogen-associated molecular patterns were required for IL-17D induction. Based on our results, we propose a model in which nonimmune cells can discriminate between nonviable and viable GAS cells, responding only to the latter by inducing IL-17D.

Dextromethorphan Attenuates NADPH Oxidase-Regulated Glycogen Synthase Kinase 3β and NF-κB Activation and Reduces Nitric Oxide Production in Group A Streptococcal Infection

Group A Streptococcus (GAS) is an important human pathogen that causes a wide spectrum of diseases, including necrotizing fasciitis and streptococcal toxic shock syndrome. Dextromethorphan (DM), an antitussive drug, has been demonstrated to efficiently reduce inflammatory responses, thereby contributing to an increased survival rate of GAS-infected mice. However, the anti-inflammatory mechanisms underlying DM treatment in GAS infection remain unclear. DM is known to exert neuroprotective effects through an NADPH oxidase-dependent regulated process. In the present study, membrane translocation of NADPH oxidase subunit p47^phox and subsequent reactive oxygen species (ROS) generation induced by GAS infection were significantly inhibited via DM treatment in RAW264.7 murine macrophage cells. Further determination of proinflammatory mediators revealed that DM effectively suppressed inducible nitric oxide synthase (iNOS) expression and NO, tumor necrosis factor alpha, and interleukin-6 generation in GAS-infected RAW264.7 cells as well as in air-pouch-infiltrating cells from GAS/DM-treated mice. GAS infection caused AKT dephosphorylation, glycogen synthase kinase-3β (GSK-3β) activation, and subsequent NF-κB nuclear translocation, which were also markedly inhibited by treatment with DM and an NADPH oxidase inhibitor, diphenylene iodonium. These results suggest that DM attenuates GAS infection-induced overactive inflammation by inhibiting NADPH oxidase-mediated ROS production that leads to downregulation of the GSK-3β/NF-κB/NO signaling pathway.

Reactive oxygen species generation mediated by NADPH oxidase and PI3K/Akt pathways contribute to invasion of Streptococcus agalactiae in human endothelial cells

BACKGROUND Streptococcus agalactiae can causes sepsis, pneumonia, and meningitis in neonates, the elderly, and immunocompromised patients. Although the virulence properties of S. agalactiae have been partially elucidated, the molecular mechanisms related to reactive oxygen species (ROS) generation in infected human endothelial cells need further investigation. OBJECTIVES This study aimed to evaluate the influence of oxidative stress in human umbilical vein endothelial cells (HUVECs) during S. agalactiae infection. METHODS ROS production during S. agalactiae-HUVEC infection was detected using the probe CM-H2DCFDA. Microfilaments labelled with phalloidin-FITC and p47phox-Alexa 546 conjugated were analysed by immunofluorescence. mRNA levels of p47phox (NADPH oxidase subunit) were assessed using Real Time qRT-PCR. The adherence and intracellular viability of S. agalactiae in HUVECs with or without pre-treatment of DPI, apocynin (NADPH oxidase inhibitors), and LY294002 (PI3K inhibitor) were evaluated by penicillin/gentamicin exclusion. Phosphorylation of p47phox and Akt activation by S. agalactiae were evaluated by immunoblotting analysis. FINDINGS Data showed increased ROS production 15 min after HUVEC infection. Real-Time qRT-PCR and western blotting performed in HUVEC infected with S. agalactiae detected alterations in mRNA levels and activation of p47phox. Pre-treatment of endothelial cells with NADPH oxidase (DPI and apocynin) and PI3K/Akt pathway (LY294002) inhibitors reduced ROS production, bacterial intracellular viability, and generation of actin stress fibres in HUVECs infected with S. agalactiae. CONCLUSIONS ROS generation via the NADPH oxidase pathway contributes to invasion of S. agalactiae in human endothelial cells accompanied by cytoskeletal reorganisation through the PI3K/Akt pathway, which provides novel evidence for the involvement of oxidative stress in S. agalactiae pathogenesis.

A novel enzyme with antioxidant capacity produced by the ubiquitous skin colonizer Propionibacterium acnes

The role of the skin microbiota in human health is poorly understood. Here, we identified and characterized a novel antioxidant enzyme produced by the skin microbiota, designated RoxP for radical oxygenase of Propionibacterium acnes. RoxP is uniquely produced by the predominant skin bacterium P. acnes, with no homologs in other bacteria; it is highly expressed and strongly secreted into culture supernatants. We show that RoxP binds heme, reduces free radicals, and can protect molecules from oxidation. Strikingly, RoxP is crucial for the survival of P. acnes in oxic conditions and for skin colonization of P. acnes ex vivo. Taken together, our study strongly suggests that RoxP facilitates P. acnes’ survival on human skin, and is an important beneficial factor for the host-commensal interaction. Thus, RoxP is the first described skin microbiota-derived mutualistic factor that potentially can be exploited for human skin protection.