Human neutrophils phagocytose and kill Acinetobacter baumanii and A. pittii

Acinetobacter baumannii is a common cause of health care associated infections worldwide. A. pittii is an opportunistic pathogen also frequently isolated from Acinetobacter infections other than those from A. baumannii. Knowledge of Acinetobacter virulence factors and their role in pathogenesis is scarce. Also, there are no detailed published reports on the interactions between A. pittii and human phagocytic cells. Using confocal laser and scanning electron microscopy, immunofluorescence, and live-cell imaging, our study shows that immediately after bacteria-cell contact, neutrophils rapidly and continuously engulf and kill bacteria during at least 4 hours of infection in vitro. After 3 h of infection, neutrophils start to release neutrophil extracellular traps (NETs) against Acinetobacter. DNA in NETs colocalizes well with human histone H3 and with the specific neutrophil elastase. We have observed that human neutrophils use large filopodia as cellular tentacles to sense local environment but also to detect and retain bacteria during phagocytosis. Furthermore, co-cultivation of neutrophils with human differentiated macrophages before infections shows that human neutrophils, but not macrophages, are key immune cells to control Acinetobacter. Although macrophages were largely activated by both bacterial species, they lack the phagocytic activity demonstrated by neutrophils

Inactivation of Staphylococcal Phenol Soluble Modulins by Serum Lipoprotein Particles

Staphylococcus aureus virulence has been associated with the production of phenol soluble modulins (PSM). PSM are known to activate, attract and lyse neutrophils. However, the functional characterizations were generally performed in the absence of human serum. Here, we demonstrate that human serum can inhibit all the previously-described activities of PSM. We observed that serum can fully block both the cell lysis and FPR2 activation of neutrophils. We show a direct interaction between PSM and serum lipoproteins in human serum and whole blood. Subsequent analysis using purified high, low, and very low density lipoproteins (HDL, LDL, and VLDL) revealed that they indeed neutralize PSM. The lipoprotein HDL showed highest binding and antagonizing capacity for PSM. Furthermore, we show potential intracellular production of PSM by S. aureus upon phagocytosis by neutrophils, which opens a new area for exploration of the intracellular lytic capacity of PSM. Collectively, our data show that in a serum environment the function of PSM as important extracellular toxins should be reconsidered

Defining motility in the Staphylococci

The ability of bacteria to move is critical for their survival in diverse environments and multiple ways have evolved to achieve this. Two forms of motility have recently been described for Staphylococcus aureus, an organism previously considered to be non-motile. One form is called spreading, which is a type of sliding motility and the second form involves comet formation, which has many observable characteristics associated with gliding motility. Darting motility has also been observed in Staphylococcus epidermidis. This review describes how motility is defined and how we distinguish between passive and active motility. We discuss the characteristics of the various forms of Staphylococci motility, the molecular mechanisms involved and the potential future research directions

Staphylococcus aureus infection dynamics

Staphylococcus aureus is a human commensal that can also cause systemic infections. This transition requires evasion of the immune response and the ability to exploit different niches within the host. However, the disease mechanisms and the dominant immune mediators against infection are poorly understood. Previously it has been shown that the infecting S. aureus population goes through a population bottleneck, from which very few bacteria escape to establish the abscesses that are characteristic of many infections. Here we examine the host factors underlying the population bottleneck and subsequent clonal expansion in S. aureus infection models, to identify underpinning principles of infection. The bottleneck is a common feature between models and is independent of S. aureus strain. Interestingly, the high doses of S. aureus required for the widely used "survival" model results in a reduced population bottleneck, suggesting that host defences have been simply overloaded. This brings into question the applicability of the survival model. Depletion of immune mediators revealed key breakpoints and the dynamics of systemic infection. Loss of macrophages, including the liver Kupffer cells, led to increased sensitivity to infection as expected but also loss of the population bottleneck and the spread to other organs still occurred. Conversely, neutrophil depletion led to greater susceptibility to disease but with a concomitant maintenance of the bottleneck and lack of systemic spread. We also used a novel microscopy approach to examine abscess architecture and distribution within organs. From these observations we developed a conceptual model for S. aureus disease from initial infection to mature abscess. This work highlights the need to understand the complexities of the infectious process to be able to assign functions for host and bacterial components, and why S. aureus disease requires a seemingly high infectious dose and how interventions such as a vaccine may be more rationally developed

Human skin commensals augment Staphylococcus aureus pathogenesis

All bacterial infections occur within a polymicrobial environment, from which a pathogen population emerges to establish disease within a host. Emphasis has been placed on prevention of pathogen dominance by competing microflora acting as probiotics1. Here we show that the virulence of the human pathogen Staphylococcus aureus is augmented by native, polymicrobial, commensal skin flora and individual species acting as ‘proinfectious agents’. The outcome is pathogen proliferation, but not commensal. Pathogenesis augmentation can be mediated by particulate cell wall peptidoglycan, reducing the S. aureus infectious dose by over 1,000-fold. This phenomenon occurs using a range of S. aureus strains and infection models and is not mediated by established receptor-mediated pathways including Nod1, Nod2, Myd88 and the NLPR3 inflammasome. During mouse sepsis, augmentation depends on liver-resident macrophages (Kupffer cells) that capture and internalize both the pathogen and the proinfectious agent, leading to reduced production of reactive oxygen species, pathogen survival and subsequent multiple liver abscess formation. The augmented infection model more closely resembles the natural situation and establishes the role of resident environmental microflora in the initiation of disease by an invading pathogen. As the human microflora is ubiquitous2, its role in increasing susceptibility to infection by S. aureus highlights potential strategies for disease prevention

Platelet GPIbα is a mediator and potential interventional target for NASH and subsequent liver cancer

Non-alcoholic fatty liver disease ranges from steatosis to non-alcoholic steatohepatitis (NASH), potentially progressing to cirrhosis and hepatocellular carcinoma (HCC). Here, we show that platelet number, platelet activation and platelet aggregation are increased in NASH but not in steatosis or insulin resistance. Antiplatelet therapy (APT; aspirin/clopidogrel, ticagrelor) but not nonsteroidal anti-inflammatory drug (NSAID) treatment with sulindac prevented NASH and subsequent HCC development. Intravital microscopy showed that liver colonization by platelets depended primarily on Kupffer cells at early and late stages of NASH, involving hyaluronan-CD44 binding. APT reduced intrahepatic platelet accumulation and the frequency of platelet-immune cell interaction, thereby limiting hepatic immune cell trafficking. Consequently, intrahepatic cytokine and chemokine release, macrovesicular steatosis and liver damage were attenuated. Platelet cargo, platelet adhesion and platelet activation but not platelet aggregation were identified as pivotal for NASH and subsequent hepatocarcinogenesis. In particular, platelet-derived GPIbα proved critical for development of NASH and subsequent HCC, independent of its reported cognate ligands vWF, P-selectin or Mac-1, offering a potential target against NASH.We thank D. Heide, J. Hetzer, R. Hillermann, C. Gropp, F. Muller, S. Prokosch, D. Kull, R. Dunkl, O. Seelbach, M. Bawohl, R. Maire, M. Bieri, C. Mittmann, H. HoncharovaBiletska, A. Fitsche, A. Adili, P. Munzer, T. Nussbaumer, F. Prutek, G. Dharmalingam and I. Singh for excellent technical assistance. We thank K. Nikolaou for the help with the human cohort recruitment and analysis. M. Malehmir was partially supported by grants from the University Zurich (Zurich Integrative Human Physiology (ZHIP) Sprint Fellowship) and from the Hartmann Muller Stiftung, Zurich. A.W. was supported by a grant from the Swiss National Science Foundation (320030_182764/1). M. Heikenwaelder was supported by an ERC Consolidator grant (HepatoMetaboPath), an EOS grant, SFBTR 209, SFBTR179, Research Foundation Flanders (FWO) under grant 30826052 (EOS Convention MODEL-IDI), Deutsche Krebshilfe projects 70113166 and 70113167, and the Helmholtz-Gemeinschaft, Zukunftsthema 'Immunology and Inflammation' (ZT-0027). This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement 667273 and the DFG (SFB/TR 240 (project 374031971) to B.N. and D. S.), ERC Consolidator grant 'CholangioConcept' (to L.Z.), and the German Research Foundation (DFG): grants FOR2314, SFB685 and the Gottfried Wilhelm Leibniz Program (to L.Z.). Further funding was provided by the German Ministry for Education and Research (BMBF) (eMed/Multiscale HCC), the German Universities Excellence Initiative (third funding line: 'future concept'), the German Center for Translational Cancer Research (DKTK) and the German-Israeli Cooperation in Cancer Research (DKFZ-MOST) (to L.Z. and M. Heikenwaelder). D. I. was supported by an EMBO Long-term Fellowship. J.M.L. is supported by Asociacion Espanola Contra el Cancer (Accelerator award: HUNTER), Spanish National Health Institute (SAF2013-41027), Generalitat de Catalunya (SGR 1162 and AGAUR, SGR-1358), the Samuel Waxman Cancer Research Foundation, the US Department of Defense (CA150272P3), the European Commission Horizon 2020 Program (HEPCAR, proposal number 667273-2), and the National Cancer Institute (P30 CA196521). D. A. M. is supported by CRUK grant C18342/A23390 and MRC grant MR/K001949/1. M. P. is supported by the German Research Foundation (DFG). M. G., T. G. and D. R. was supported by grants from the German Research Foundation (KFO274 and SFB/TR240 (project 374031971)). D. J. W. received a Wellcome Trust Strategic Award (098565/Z/12/Z) and funding from the Medical Research Council (MC-A654-5QB40). C.L.W. was funded by CRUK project Cancer Research UK Programme Grant C18342/A23390. H. G. A. has been supported by the Deutsche Forschungsgemeinschaft (SFB-TR209 'Liver Cancer').S