Time-resolved analysis of Staphylococcus aureus invading the endothelial barrier

The antivirulent Staphylococcal sRNA SprC regulates CzrB efflux pump to adapt its response to zinc toxicity

Bacterial regulatory RNAs (sRNAs) are important players to control gene expression. In Staphylococcus aureus, SprC is an antivirulent trans-acting sRNA known to base-pair with the major autolysin atl mRNA, preventing its translation. Using MS2-affinity purification coupled with RNA sequencing, we looked for its sRNA-RNA interactome and identified 14 novel mRNA targets. In vitro biochemical investigations revealed that SprC binds two of them, czrB and deoD, and uses a single accessible region to regulate its targets, including Atl translation. Unlike Atl regulation, the characterization of the SprC-czrB interaction pinpointed a destabilization of the czrAB cotranscript, leading to a decrease of the mRNA level that impaired CzrB zinc efflux pump expression. On a physiological standpoint, we showed that SprC expression is detrimental to combat against zinc toxicity. In addition, phagocyctosis assays revealed a significant, but moderate, increase of czrB mRNA levels in a sprC-deleted mutant, indicating a functional link between SprC and czrB upon internalization in macrophages, and suggesting a role in resistance to both oxidative and zinc bursts. Altogether, our data uncover a novel pathway in which SprC is implicated, highlighting the multiple strategies used by S. aureus to balance virulence using an RNA regulator.

Functional and Proteomic Dissection of the Contributions of CodY, SigB and the Hibernation Promoting Factor HPF to Interactions of Staphylococcus aureus USA300 with Human Lung Epithelial Cells

Staphylococcus aureus is a leading cause of severe pneumonia. Our recent proteomic investigations into S. aureus invasion of human lung epithelial cells revealed three key adaptive responses: activation of the SigB and CodY regulons and upregulation of the hibernation-promoting factor SaHPF. Therefore, our present study aimed at a functional and proteomic dissection of the contributions of CodY, SigB and SaHPF to host invasion using transposon mutants of the methicillin-resistant S. aureus USA300. Interestingly, disruption of codY resulted in a "small colony variant" phenotype and redirected the bacteria from (phago)lysosomes into the host cell cytoplasm. Furthermore, we show that CodY, SigB and SaHPF contribute differentially to host cell adhesion, invasion, intracellular survival and cytotoxicity. CodY- or SigB-deficient bacteria experienced faster intracellular clearance than the parental strain, underscoring the importance of these regulators for intracellular persistence. We also show an unprecedented role of SaHPF in host cell adhesion and invasion. Proteomic analysis of the different mutants focuses attention on the CodY-perceived metabolic state of the bacteria and the SigB-perceived environmental cues in bacterial decision-making prior and during infection. Additionally, it underscores the impact of the nutritional status and bacterial stress on the initiation and progression of staphylococcal lung infections.

Functional profiling of CHAP domain-containing peptidoglycan hydrolases of Staphylococcus aureus USA300 uncovers potential targets for anti-staphylococcal therapies

The bacterial pathogen Staphylococcus aureus employs a thick cell wall for protection against physical and chemical insults. This wall requires continuous maintenance to ensure strength and barrier integrity, but also to permit bacterial growth and division. The main cell wall component is peptidoglycan. Accordingly, the bacteria produce so-called peptidoglycan hydrolases (PGHs) that cleave glycan strands to facilitate growth, cell wall remodelling, separation of divided cells and release of exported proteins into the extracellular milieu. A special class of PGHs contains so-called 'cysteine, histidine-dependent amidohydrolase/peptidase' (CHAP) domains. In the present study, we profiled the roles of 11 CHAP PGHs encoded by the core genome of S. aureus USA300 LAC. Mutant strains lacking individual CHAP PGHs were analysed for growth, cell morphology, autolysis, and invasion and replication inside human lung epithelial cells. The results show that several investigated CHAP PGHs contribute to different extents to extracellular and intracellular growth and replication of S. aureus, septation of dividing cells, daughter cell separation once the division process is completed, autolysis and biofilm formation. In particular, the CHAP PGHs Sle1 and SAUSA300_2253 control intracellular staphylococcal replication and the resistance to β-lactam antibiotics like oxacillin. This makes the S. aureus PGHs in general, and the Sle1 and SAUSA300_2253 proteins in particular, attractive targets for future prophylactic or therapeutic anti-staphylococcal interventions. Alternatively, these cell surface-exposed enzymes, or particular domains of these enzymes, could be applied in innovative anti-staphylococcal therapies.

Host-induced cell wall remodeling impairs opsonophagocytosis of Staphylococcus aureus by neutrophils

The bacterial pathogen Staphylococcus aureus responds to the host environment by increasing the thickness of its cell wall. However, the impact of cell wall thickening on susceptibility to host defenses is unclear. Using bacteria incubated in human serum, we show that host-induced increases in cell wall thickness led to a reduction in the exposure of bound antibody and complement and a corresponding reduction in phagocytosis and killing by neutrophils. The exposure of opsonins bound to protein antigens or lipoteichoic acid (LTA) was most significantly reduced, while opsonization by IgG against wall teichoic acid or peptidoglycan was largely unaffected. Partial digestion of accumulated cell wall using the enzyme lysostaphin restored opsonin exposure and promoted phagocytosis and killing. Concordantly, the antibiotic fosfomycin inhibited cell wall remodeling and maintained the full susceptibility of S. aureus to opsonophagocytic killing by neutrophils. These findings reveal that host-induced changes to the S. aureus cell wall reduce the ability of the immune system to detect and kill this pathogen through reduced exposure of protein- and LTA-bound opsonins.

IMPORTANCE

Understanding how bacteria adapt to the host environment is critical in determining fundamental mechanisms of immune evasion, pathogenesis, and the identification of targets for new therapeutic approaches. Previous work demonstrated that Staphylococcus aureus remodels its cell envelope in response to host factors and we hypothesized that this may affect recognition by antibodies and thus killing by immune cells. As expected, incubation of S. aureus in human serum resulted in rapid binding of antibodies. However, as bacteria adapted to the serum, the increase in cell wall thickness resulted in a significant reduction in exposure of bound antibodies. This reduced antibody exposure, in turn, led to reduced killing by human neutrophils. Importantly, while antibodies bound to some cell surface structures became obscured, this was not the case for those bound to wall teichoic acid, which may have important implications for vaccine design.

CircTMEM165 facilitates endothelial repair by modulating mitochondrial fission via miR-192/SCP2 in vitro and in vivo

Constitutive explorations indicate a correlation between circular RNAs (circRNAs) and cardiovascular diseases. However, the involvement of circRNAs in endothelial recuperation and in-stent restenosis (ISR) remains underexplored. CircTMEM165 has first been reported to be highly expressed in hypoxic human umbilical vein endothelial cells (HUVECs). Here, we identified that circTMEM165 was downregulated in ISR patients, inversely correlating with ISR severity. Functionally, circTMEM165 was found to be abundant in endothelial cells, inhibiting inflammation, and adhesion. Particularly, we first observed that circTMEM165 could alleviate HUVECs apoptosis and mitochondrial fission induced by lipopolysaccharide (LPS). Mechanistically, circTMEM165, as a miR-192-3p sponge, enhancing SCP2 expression, which serves as a critical regulator of HUVECs biological functions. Moreover, in vivo, circTMEM165 attenuated intimal hyperplasia and facilitated repair following classic rat carotid artery balloon injury model. These findings investigated the circTMEM165-miR-192-3p-SCP2 axis as a critical determinant of endothelial health and a potential biomarker and therapeutic target for vascular disorders.

An Overview of Traditional Chinese Medicine in the Treatment After Radical Resection of Hepatocellular Carcinoma

According to the Barcelona Clinic Liver Cancer (BCLC) system, radical resection of early stage primary hepatocellular carcinoma (HCC) mainly includes liver transplantation, surgical resection, and radiofrequency ablation (RFA), which yield 5-year survival rates of about 70-79%, 41.3-69.5%, and 40-70%, respectively. The tumor-free 5-year rate for HCC patients undergoing radical resection only reach up to 13.7 months, so the prevention of recurrence after radical resection of HCC is very important for the prognosis of patients. The traditional Chinese medicine (TCM) takes the approach of multitarget and overall-regulation to treat tumors, it can also independently present the "component-target-pathway" related to a particular disease, and its systematic and holistic characteristics can provide a personalized therapy based on symptoms of the patient by treating the patient as a whole. TCM as postoperative adjuvant therapy after radical resection of HCC in Barcelona Clinic liver cancer A or B stages, and the numerous clinical trials confirmed that the efficacy of TCM in the field of HCC has a significant effect, not only improving the prognosis and quality of life but also enhancing patient survival rate. However, with the characteristics of multi-target, multi-component, and multi-pathway, the specific mechanism of Chinese medicine in the treatment of diseases is still unclear. Because of the positive pharmacological activities of TCM in combating anti-tumors, the mechanism studies of TCM have demonstrated beneficial effects on the regulation of immune function, chronic inflammation, the proliferation and metastasis of liver cancer cells, autophagy, and cell signaling pathways related to liver cancer. Therefore, this article reviews the mechanism of traditional Chinese medicine in reducing the recurrence rate of HCC after radical resection.

Antimicrobial effect of pimozide by targeting ROS-mediated killing in Staphylococcus aureus

In spite of the higher nosocomial and community-acquired infections caused by Staphylococcus aureus, emerging drug resistance is a leading cause of increased mortality and morbidity associated with the overuse of antimicrobials. It is an emergent need to find out new molecules to combat such infections. In the present study, we analyzed the antibacterial effect of pimozide (PMZ) against gram-positive and gram-negative bacterial strains, including methicillin-sensitive (MSSA) and methicillin-resistant (MRSA) S. aureus. The growth of MSSA and MRSA was completely inhibited at concentrations of 12.5 and 100 μg/mL, respectively, which is referred to as 1× minimum inhibitory concentration (MIC). The cell viability was completely eliminated within 90 min of PMZ treatment (2× MIC) through reactive oxygen species (ROS)-mediated killing without affecting cell membrane permeability. It suppressed α-hemolysin production and biofilm formation of different S. aureus strains by almost 50% at 1× MIC concentration, and was found to detach matured biofilm. PMZ treatment effectively eliminates S. aureus infection in Caenorhabditis elegans and improves its survival by 90% and is found safe to use with no hemolytic effect on human and chicken blood tissues. Taken together, it is concluded that PMZ may turn out to be an effective antibacterial for treating bacterial infections including MSSA and MRSA.

MRSA Isolates from Patients with Persistent Bacteremia Generate Nonstable Small Colony Variants In Vitro within Macrophages and Endothelial Cells during Prolonged Vancomycin Exposure

Staphylococcus aureus (especially methicillin-resistant S. aureus [MRSA]) is frequently associated with persistent bacteremia (PB) during vancomycin therapy despite consistent susceptibility in vitro. Strategic comparisons of PB strains versus those from vancomycin-resolving bacteremia (RB) would yield important mechanistic insights into PB outcomes. Clinical PB versus RB isolates were assessed in vitro for intracellular replication and small colony variant (SCV) formation within macrophages and endothelial cells (ECs) in the presence or absence of exogenous vancomycin. In both macrophages and ECs, PB and RB isolates replicated within lysosome-associated membrane protein-1 (LAMP-1)-positive compartments. PB isolates formed nonstable small colony variants (nsSCVs) in vancomycin-exposed host cells at a significantly higher frequency than matched RB isolates (in granulocyte-macrophage colony-stimulating factor [GM-CSF], human macrophages PB versus RB, P < 0.0001 at 48 h; in ECs, PB versus RB, P < 0.0001 at 24 h). This phenotype could represent one potential basis for the unique ability of PB isolates to adaptively resist vancomycin therapy and cause PB in humans. Elucidating the molecular mechanism(s) by which PB strains form nsSCVs could facilitate the discovery of novel treatment strategies to mitigate PB due to MRSA.

Staphylococcus aureus populations from the gut and the blood are not distinguished by virulence traits-a critical role of host barrier integrity

BACKGROUND

The opportunistic pathogen Staphylococcus aureus is an asymptomatically carried member of the microbiome of about one third of the human population at any given point in time. Body sites known to harbor S. aureus are the skin, nasopharynx, and gut. In particular, the mechanisms allowing S. aureus to pass the gut epithelial barrier and to invade the bloodstream were so far poorly understood. Therefore, the objective of our present study was to investigate the extent to which genetic differences between enteric S. aureus isolates and isolates that caused serious bloodstream infections contribute to the likelihood of invasive disease.

RESULTS

Here, we present genome-wide association studies (GWAS) that compare the genome sequences of 69 S. aureus isolates from enteric carriage by healthy volunteers and 95 isolates from bloodstream infections. We complement our GWAS results with a detailed characterization of the cellular and extracellular proteomes of the representative gut and bloodstream isolates, and by assaying the virulence of these isolates with infection models based on human gut epithelial cells, human blood cells, and a small animal infection model. Intriguingly, our results show that enteric and bloodstream isolates with the same sequence type (ST1 or ST5) are very similar to each other at the genomic and proteomic levels. Nonetheless, bloodstream isolates are not necessarily associated with an invasive profile. Furthermore, we show that the main decisive factor preventing infection of gut epithelial cells in vitro is the presence of a tight barrier.

CONCLUSIONS

Our data show that virulence is a highly variable trait, even within a single clone. Importantly, however, there is no evidence that blood stream isolates possess a higher virulence potential than those from the enteric carriage. In fact, some gut isolates from healthy carriers were more virulent than bloodstream isolates. Based on our present observations, we propose that the integrity of the gut epithelial layer, rather than the pathogenic potential of the investigated enteric S. aureus isolates, determines whether staphylococci from the gut microbiome will become invasive pathogens. Video Abstract.

Outer membrane vesicles of the oral pathogen Porphyromonas gingivalis promote aggregation and phagocytosis of Staphylococcus aureus

Staphylococcus aureus is an opportunistic Gram-positive bacterial pathogen that causes a wide variety of infectious diseases, including S. aureus bacteremia (SAB). Recent studies showed that rheumatoid arthritis (RA) is a risk factor for SAB, as RA patients appear to be more susceptible to SAB and display higher degrees of disease severity or complications, such as osteoarticular infections. On the other hand, Porphyromonas gingivalis is a Gram-negative bacterial oral pathogen, which is notable for its implication in the etiopathogenesis of RA due to its unique citrullinating enzyme PPAD and its highly effective proteases, known as gingipains. Both PPAD and gingipains are abundant in P. gingivalis outer membrane vesicles (OMVs), which are secreted nanostructures that originate from the outer membrane. Here we show that P. gingivalis OMVs cause the aggregation of S. aureus bacteria in a gingipain- and PPAD-dependent fashion, and that this aggregation phenotype is reversible. Importantly, we also show that the exposure of S. aureus to OMVs of P. gingivalis promotes the staphylococcal internalization by human neutrophils with no detectable neutrophil killing. Altogether, our observations suggest that P. gingivalis can eliminate its potential competitor S. aureus by promoting staphylococcal aggregation and the subsequent internalization by neutrophils. We hypothesize that this phenomenon may have repercussions for the host, since immune cells with internalized bacteria may facilitate bacterial translocation to the blood stream, which could potentially contribute to the association between RA and SAB.

Staphylococcal trafficking and infection - from 'nose to gut' and back

Staphylococcus aureus is an opportunistic human pathogen, which is a leading cause of infections worldwide. The challenge in treating S. aureus infection is linked to the development of multidrug-resistant strains and the mechanisms employed by this pathogen to evade the human immune defenses. In addition, S. aureus can hide asymptomatically in particular ‘protective’ niches of the human body for prolonged periods of time. In the present review, we highlight recently gained insights in the role of the human gut as an endogenous S. aureus reservoir next to the nasopharynx and oral cavity. In addition, we address the contribution of these ecological niches to staphylococcal transmission, including the roles of particular triggers as modulators of the bacterial dissemination. In this context, we present recent advances concerning the interactions between S. aureus and immune cells to understand their possible roles as vehicles of dissemination from the gut to other body sites. Lastly, we discuss the factors that contribute to the switch from colonization to infection. Altogether, we conclude that an important key to uncovering the pathogenesis of S. aureus infection lies hidden in the endogenous staphylococcal reservoirs, the trafficking of this bacterium through the human body and the subsequent immune responses.

Intracellular persistence of Staphylococcus aureus in endothelial cells is promoted by the absence of phenol-soluble modulins

A large proportion of clinical S. aureus isolates that carry an inactive Agr system are associated with persistent infection that is difficult to treat. Once S. aureus is inside the bloodstream, it can cross the endothelial barrier and invade almost every organ in the human body. Endothelial cells can either be lysed by this pathogen or they serve as a niche for its intracellular long-term survival. Following phagocytosis, several vesicles such as phagosomes and autophagosomes, target intracellular S. aureus for elimination. S. aureus can escape from these vesicles into the host cytoplasm through the activation of phenol-soluble modulins (PSMs) αβ. Thereafter, it replicates and lyses the host cell to disseminate to adjacent tissues. Herein we demonstrate that staphylococcal strains which lack the expression of PSMs employ an alternative pathway to better persist within endothelial cells. The intracellular survival of S. aureus is associated with the co-localization of the autophagy marker LC3. In cell culture infection models, we found that the absence of psmαβ decreased the host cell lysis and increased staphylococcal long-term survival. This study explains the positive selection of agr-negative strains that lack the expression of psmαβ in chronic infection due to their advantage in surviving and evading the clearance system of the host.