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Staphylococcus schweitzeri belongs to the Staphylococcus aureus -related complex and is mainly found in African wildlife; no infections in humans are reported yet. Hence, its medical importance is controversial. The aim of this work was to assess the virulence of S. schweitzeri in vitro. The capacity of African S. schweitzeri (n = 58) for invasion, intra- and extracellular cytotoxicity, phagolysosomal escape, coagulase activity, biofilm formation and host cell activation was compared with S. aureus representing the most common clonal complexes in Africa (CC15, CC121, CC152). Whole genome sequencing revealed that the S. schweitzeri isolates belonged to five geographical clusters. Isolates from humans were found in two different clades. S. schweitzeri and S. aureus showed a similar host cell invasion (0.9 vs. 1.2 CFU/Vero cell), host cell activation (i.e. expression of pro-inflammatory cytokines, 4.1 vs. 1.7 normalized fold change in gene expression of CCL5 ; 7.3 vs. 9.9 normalized fold change in gene expression of IL8 , A549 cells) and intracellular cytotoxicity (31.5% vs. 25% cell death, A549 cells). The extracellular cytotoxicity (52.9% vs. 28.8% cell death, A549 cells) was higher for S. schweitzeri than for S. aureus . Nearly all tested S. schweitzeri (n = 18/20) were able to escape from phagolysosomes. In conclusion, some S. schweitzeri isolates display virulence phenotypes comparable to African S. aureus. S. schweitzeri might become an emerging zoonotic pathogen within the genus Staphylococcus .

Staphylococcus aureus is a major human pathogen that causes a range of infections from acute invasive to chronic and difficult-to-treat. Infection strategies associated with persisting S. aureus infections are bacterial host cell invasion and the bacterial ability to dynamically change phenotypes from the aggressive wild-type to small colony variants (SCVs), which are adapted for intracellular long-term persistence. The underlying mechanisms of the bacterial switching and adaptation mechanisms appear to be very dynamic, but are largely unknown. Here, we analyzed the role and the crosstalk of the global S. aureus regulators agr, sarA and SigB by generating single, double and triple mutants, and testing them with proteome analysis and in different in vitro and in vivo infection models. We were able to demonstrate that SigB is the crucial factor for adaptation in chronic infections. During acute infection, the bacteria require the simultaneous action of the agr and sarA loci to defend against invading immune cells by causing inflammation and cytotoxicity and to escape from phagosomes in their host cells that enable them to settle an infection at high bacterial density. To persist intracellularly the bacteria subsequently need to silence agr and sarA. Indeed agr and sarA deletion mutants expressed a much lower number of virulence factors and could persist at high numbers intracellularly. SigB plays a crucial function to promote bacterial intracellular persistence. In fact, ΔsigB-mutants did not generate SCVs and were completely cleared by the host cells within a few days. In this study we identified SigB as an essential factor that enables the bacteria to switch from the highly aggressive phenotype that settles an acute infection to a silent SCV-phenotype that allows for long-term intracellular persistence. Consequently, the SigB-operon represents a possible target to develop preventive and therapeutic strategies against chronic and therapy-refractory infections.

Key Points Infective endocarditis (IE) is a major challenge for clinicians and a considerable burden for health-care systems In high-income countries over the past 5 decades, patients have been contracting IE at an increasingly old age, and the incidence of health-care-associated staphylococcal IE has risen An improved understanding of the mechanisms of vegetation formation, growth, and embolization will help to combat microbial resistance IE after transfemoral aortic valve implantation in elderly patients can be aggravated by immunosenescence Many factors that increase mortality in patients with IE have been identified, which will help to optimize treatment Mortality risk increases substantially when patients with IE develop septic shock Infection of the endocardium or prosthetic surfaces in the heart, if ineffectively treated, is associated with severe complications and a high mortality. In this Review, Karl Werdan and colleagues summarize the pathogen–host interactions and mechanisms of increased risk in patients with infective endocarditis, including immunosenescence in elderly patients, and the transition from local infection to systemic sepsis and shock. Patients with infective endocarditis (IE) form a heterogeneous group, ranging from those who are successfully treated with no adverse events, to those with severe complications and a high mortality. In this Review, we highlight pathogen–host interactions and the mechanisms underlying various risk factors for patients with IE. A temporal trend in the pattern of IE has been observed in high-income countries within the past 5 decades, with patients contracting IE at an increasingly old age, and a growing incidence of health-care-associated staphylococcal IE. Consequently, prevention strategies should no longer focus on prophylaxis of streptococcal bacteraemia during dental procedures, but instead encourage a more-general approach to reduce the incidence of health-care-associated IE. Much knowledge has been gained about the mechanisms of vegetation formation, growth, and embolization on damaged or inflamed cardiac valves, and on cardiac devices. Improved understanding of these mechanisms will help to combat the increasing problem of antimicrobial resistance. Two mechanisms of IE should increasingly be the focus of future research: the role of immunosenescence in elderly patients with IE, particularly after transcatheter aortic valve implantation, and the mechanisms that trigger septic shock, a condition that leads to a substantial increase in the risk of death in patients with IE.

Staphylococcus aureus is a common cause of hospital-acquired pneumonia associated with high mortality. Adequate clinical treatment is impeded by increasing occurrence of antibiotic resistances. Understanding the underlying mechanisms of its virulence during infections is a prerequisite to finding alternative treatments. Here, we demonstrated that an increased nuclease activity of a S. aureus isolate from a person with cystic fibrosis confers a growth advantage in a model of acute lung infection compared to the isogenic strain with low nuclease activity. Comparing these CF-isolates with a common MRSA-USA300 strain with similarly high nuclease activity but significantly elevated levels of Staphylococcal Protein A (SpA) revealed that infection with USA300 resulted in a significantly increased bacterial burden in a model of murine lung infection. Replenishment with the cell wall-bound SpA of S. aureus , which can also be secreted into the environment and binds to tumor necrosis factor receptor -1 (TNFR-1) to the CF-isolates abrogated these differences. In vitro experiments confirmed significant differences in spa -expression between USA300 compared to CF-isolates, thereby influencing TNFR-1 shedding, L-selectin shedding, and production of reactive oxygen species through activation of ADAM17.

Traditionally, Staphylococcus aureus has been considered an extracellular pathogen. However, among other factors, the frequent failure of antimicrobial therapy and the ability of the pathogen to cause recurrent disease have established the concept of eukaryotic invasion of the pathogen, thereby evading the host’s immune system. While Staphylococcus aureus has classically been considered an extracellular pathogen, these bacteria are also capable of being taken up by host cells, including nonprofessional phagocytes such as endothelial cells, epithelial cells, or osteoblasts. The intracellular S. aureus lifestyle contributes to infection development. The predominant recognition and internalization pathway appears to be the binding of the bacteria via a fibronectin bridge to the α5β1-integrin on the host cell membrane, followed by phagocytosis. Although osteoblasts showed high expression of α5β1-integrin and fibronectin, and bacteria adhered to osteoblasts to a high proportion, here we demonstrate by internalization assays and immunofluorescence microscopy that S. aureus was less engulfed in osteoblasts than in epithelial cells. The addition of exogenous fibronectin during the infection of cells with S. aureus resulted in an increased uptake by epithelial cells but not by osteoblasts. This contrasts with the previous conception of the uptake mechanism, where high expression of integrin and fibronectin would promote the bacterial uptake into host cells. Extracellular fibronectin surrounding osteoblasts, but not epithelial cells, is organized in a fibrillary network. The inhibition of fibril formation, the short interfering RNA-mediated reduction of fibronectin expression, and the disruption of the fibronectin-fibril meshwork all resulted in a significant increase in S. aureus uptake by osteoblasts. Thus, the network of fibronectin fibrils appears to strongly reduce the uptake of S. aureus into a given host cell, indicating that the supramolecular structure of fibronectin determines the capacity of particular host cells to internalize the pathogen. IMPORTANCE Traditionally, Staphylococcus aureus has been considered an extracellular pathogen. However, among other factors, the frequent failure of antimicrobial therapy and the ability of the pathogen to cause recurrent disease have established the concept of eukaryotic invasion of the pathogen, thereby evading the host’s immune system. In the current model of host cell invasion, bacteria initially bind to α5β1 integrin on the host cell side via a fibronectin bridge, which eventually leads to phagocytosis of S. aureus by host cells. However, in this study, we demonstrate that not the crude amount but the supramolecular structure of fibronectin molecules deposited on the eukaryotic cell surface plays an essential role in bacterial uptake by host cells. Our findings explain the large differences of S. aureus uptake efficacy in different host cell types as well as in vivo differences between courses of bacterial infections and the localization of bacteria in different clinical settings.

Background The prevalence of Staphylococcus aureus isolates carrying the Panton-Valentine leukocidin (PVL) gene is higher in Africa (≈50%) compared to Europe (< 5%). The study aimed to measure anti-PVL-antibodies in Africans and Germans in a multi-center study and to test whether detected antibodies can neutralize the cytotoxic effect of PVL on polymorphonuclear leukocytes (PMNs). Methods Sera from asymptomatic Africans ( n  = 22, Nigeria, Gabon) and Caucasians ( n  = 22, Germany) were used to quantify antibody titers against PVL and α-hemolysin (in arbitrary units [AU]) by ELISA. PMNs from one African and German donor were exposed to 5 nM recombinant PVL to measure the neutralizing effect of serial dilutions of pooled sera from African and Caucasian participants, or donor sera at 0.625 and 2.5% (v/v). Results Anti-PVL-antibodies were significantly higher in Africans than in Germans (1.9 vs. 0.7 AU, p  < 0.0001). The pooled sera from the study participants neutralized the cytotoxic effect of PVL on African and German PMNs in a dose dependent manner. Also, neutralization of PVL on PMNs from the African and German donors had a stronger effect with African sera (half-maximal inhibitory concentration (IC 50 ) = 0.27 and 0.47%, respectively) compared to Caucasian sera (IC 50  = 3.51 and 3.59% respectively). Conclusion Africans have higher levels of neutralizing anti-PVL-antibodies. It remains unclear if or at what level these antibodies protect against PVL-related diseases.

In the version of this Article originally published, the authors mistakenly used the same images for the Fig. 2d Per –/– upper Merge, DAPI and p-RPA2 (Ser33), and Fig. 3e upper 2 months, WT Per2 DAPI and Merge panels. The correct images from these experiments, and their correctly sized scale bars, are shown below. In addition, the full dataset of representative images for Figs 2d and 3e, and the numerical source data of the corresponding quantifications of Figs 2c and 3f, have been uploaded to Figshare ( https://doi.org/10.6084/m9.figshare.c.4353791.v1 ). In addition, the Methods section did not provide sufficient detail on how immunoblot experiments were conducted. Western blots were repeated three times using the antibodies stated in the Methods. PER2 blots were obtained using the PER2 antibody (Millipore, AB2202); except in the PER2 blots in the Repeat 1 experiments corresponding to Fig. 3g and 3k, where the PER2 antibody from BD Transduction (611138) was used. Repeats 1 and 2 were imaged using ECL and LI-COR methods, and Repeat 3 only used the LI-COR system. The images presented in the paper were from Repeat 3 and were stored electronically and as printouts, however the electronic versions were cropped as depicted in Supplementary Fig. 6. Repeat 1 images were stored electronically and Repeat 2 images only as printouts. In addition — with the exception of Figs 2g (ATM), 3g (PER2, Repeat 1A), 3k (PER2, PUMA, p21, BAX, BCL2) and Supplementary Fig. 1a of Repeat 1, in which actin immunoblots were loading controls processed from the same membranes used to detect the target proteins — in all other cases the actin blots were sample processing controls that were run in parallel using the same lysates and loading concentrations that were used for the detection of the target proteins. The electronic images from Repeat 1 and the printout images of Repeats 2 and 3 have been uploaded to Figshare ( https://doi.org/10.6084/m9.figshare.c.4353791.v1 ). Finally, there is an error in the protein size label of the p-CHK1 blot of Fig. 2f and the corresponding blot in Supplementary Fig. 6, which should read '55KD' instead of '50KD'.

Implant-related infections are a significant concern in orthopedic surgery. A novel anti-infective implant coating made of bioresorbable polymer with silver nitrate was developed. A controlled release of silver ions into the vicinity of the prosthesis can be triggered on-demand by extracorporeal shock waves to effectively combat all clinically relevant microorganisms. Microscopy techniques were used to examine the effects of shock wave application on coated titanium discs. Cytotoxicity was measured using a fibroblast proliferation assay. The anti-infective effect was assessed by monitoring the growth curves of three bacterial strains and by conventional culture. Microscopic analysis confirmed surface disruption of the coatings, with a complete release of silver in the focus area after shock wave application. Spectrometry detected an increase in silver concentration in the surrounding of the discs that surpassed the minimum inhibitory concentration (MIC) for both S. epidermidis RP62A and E. coli ATCC 25922. The released silver demonstrated an anti-infective effect, significantly inhibiting bacterial growth, especially at 6% and 8% silver concentrations. Cytotoxicity testing showed decreasing fibroblast viability with increasing silver concentration in the coating, with 6% silver maintaining viability above 25%. Compared to a commonly used electroplated silver coating on the market, the new coating demonstrated superior antimicrobial efficacy and lower cytotoxicity.

Bacterial biofilms on foreign surfaces are considered a primary cause of implant-related infections, which are challenging to treat. A new implant coating was developed, containing anti-infective silver within a biocompatible polymer carrier substance. In addition to its passive effect on the implant surface, highly concentrated anti-infective silver can be released as needed via the application of high-energy shock waves. This intervention could be applied transcutaneously in a clinical setting without the need for additional surgery. We investigated the inhibition of biofilm formation and the effectiveness of eradication after activation of the coating via shock waves in an in vitro biofilm model using Staphylococcus epidermidis RP62A. This was performed via scanning electron microscopy and quantitative microbiology. Additionally, we examined the cytotoxicity of the new coating on normal human fibroblasts and Saos-2 osteoblast-like cells, depending on the silver concentration. All studies were compared to uncoated titanium surfaces Ti6Al4V and a conventional electroplated silver coating. Cytotoxicity toward normal human fibroblasts and Saos-2 osteoblast-like cells increased with higher silver content but remained tolerable at 6%. Compared to uncoated Ti6Al4V and the electroplated silver coating, the new coating with a silver content of 4% and 6% exhibited a significant reduction in adherent bacteria by a factor of approximately 1000. This was also evident via microscopic examination of the surface morphology of the biofilms. Furthermore, following shock wave activation, no bacteria were detectable on either the implant or in the surrounding fluid after a 24 h period.