Heterogeneous Vancomycin-Intermediate Staphylococcus aureus Uses the VraSR Regulatory System to Modulate Autophagy for Increased Intracellular Survival in Macrophage-Like Cell Line RAW264.7

Adaptive physiological and metabolic alterations in Staphylococcus aureus evolution under vancomycin exposure

Staphylococcus aureus can develop antibiotic resistance and evade immune responses, causing infections in different body sites. However, the metabolic changes underlying this process are poorly understood. A variant strain, C1V, was derived from the parental strain C1 by exposing it to increasing concentrations of vancomycin in vitro. C1V exhibited a vancomycin-intermediate phenotype and physiological changes compared to C1. It showed higher survival rates than C1 when phagocytosed by Raw264.7 cells. Metabolomics analysis identified significant metabolic differences pre- and post-induction (C1 + SC1 vs. C1V + SC1V: 201 metabolites) as well as pre- and post-phagocytosis (C1 vs. SC1: 50 metabolites; C1V vs. SC1V: 95 metabolites). The variant strain had distinct morphological characteristics, decreased adhesion ability, impaired virulence, and enhanced resistance to phagocytosis compared to the parental strain. Differential metabolites may contribute to S. aureus ' resistance to antibiotics and phagocytosis, offering insights into potential strategies for altering vancomycin nonsusceptibility and enhancing phagocyte killing by manipulating bacterial metabolism.

Collaborative Cross mice have diverse phenotypic responses to infection with Methicillin-resistant Staphylococcus aureus USA300

Staphylococcus aureus (S. aureus) is an opportunistic pathogen causing diseases ranging from mild skin infections to life threatening conditions, including endocarditis, pneumonia, and sepsis. To identify host genes modulating this host-pathogen interaction, we infected 25 Collaborative Cross (CC) mouse strains with methicillin-resistant S. aureus (MRSA) and monitored disease progression for seven days using a surgically implanted telemetry system. CC strains varied widely in their response to intravenous MRSA infection. We identified eight 'susceptible' CC strains with high bacterial load, tissue damage, and reduced survival. Among the surviving strains, six with minimal colonization were classified as 'resistant', while the remaining six tolerated higher organ colonization ('tolerant'). The kidney was the most heavily colonized organ, but liver, spleen and lung colonization were better correlated with reduced survival. Resistant strains had higher pre-infection circulating neutrophils and lower post-infection tissue damage compared to susceptible and tolerant strains. We identified four CC strains with sexual dimorphism: all females survived the study period while all males met our euthanasia criteria earlier. In these CC strains, males had more baseline circulating monocytes and red blood cells. We identified several CC strains that may be useful as new models for endocarditis, myocarditis, pneumonia, and resistance to MRSA infection. Quantitative Trait Locus (QTL) analysis identified two significant loci, on Chromosomes 18 and 3, involved in early susceptibility and late survival after infection. We prioritized Npc1 and Ifi44l genes as the strongest candidates influencing survival using variant analysis and mRNA expression data from kidneys within these intervals.

Salmonella Enteritidis RfbD enhances bacterial colonization and virulence through inhibiting autophagy

Autophagy is a crucial innate immune response that clears pathogens intracellularly. Salmonella enterica serovar Enteritidis (S.E) has emerged as one of the most important food-borne pathogens. Here, we reported that dTDP-4-dehydro-β-ւ-rhamnose reductase (RfbD) was able to enhance bacterial colonization in vivo and in vitro by regulating autophagy. We screened the transposon mutant library of Salmonella Enteritidis strain Z11 by High-Content Analysis System, found that rfbD gene has an effect on autophagy. The Z11ΔrfbD-infected group showed greater expression of LC3-II than the Z11-infected group in HeLa, RAW264.7, and J774A.1 cells. Overall, the survival of Z11ΔrfbD in RAW264.7 cells was reduced after 8 h of infection compared to that of the Z11 wild-type strain. In addition, we observed that inhibition of autophagic flux significantly increased the survival of Z11ΔrfbD in RAW264.7 cells. Mice infection experiments revealed that Z11ΔrfbD virulence was significantly reduced, and bacterial load was reduced in the liver and cecum in mice model, and LC3-II expression was significantly increased. These findings indicate an important role of Salmonella Enteritidis protein as a strategy to suppress autophagy and provides new ideas for manipulating autophagy as a novel strategy to treat infectious diseases.

The Vancomycin Resistance-Associated Regulatory System VraSR Modulates Biofilm Formation of Staphylococcus epidermidis in an ica-Dependent Manner

The two-component system VraSR responds to the cell wall-active antibiotic stress in Staphylococcus epidermidis. To study its regulatory function in biofilm formation, a vraSR deletion mutant (ΔvraSR) was constructed using S. epidermidis strain 1457 (SE1457) as the parent strain. Compared to SE1457, the ΔvraSR mutant showed impaired biofilm formation both in vitro and in vivo with a higher ratio of dead cells within the biofilm. Consistently, the ΔvraSR mutant produced much less polysaccharide intercellular adhesin (PIA). The ΔvraSR mutant also showed increased susceptibility to the cell wall inhibitor and SDS, and its cell wall observed under a transmission electron microscope (TEM) appeared to be thinner and interrupted, which is in accordance with higher susceptibility to the stress. Complementation of vraSR in the ΔvraSR mutant restored the biofilm formation and the cell wall thickness to wild-type levels. Transcriptome sequencing (RNA-Seq) showed that the vraSR deletion affected the transcription levels of 73 genes, including genes involved in biofilm formation, bacterial programmed cell death (CidA-LrgAB system), glycolysis/gluconeogenesis, the pentose phosphate pathway (PPP), and the tricarboxylic acid (TCA) cycle, etc. The results of RNA-Seq were confirmed by quantitative real-time reverse transcription-PCR (qRT-PCR). In the ΔvraSR mutant, the expression of icaA and lrgAB was downregulated and the expression of icaR and cidA was upregulated, in comparison to that of SE1457. The transcriptional levels of antibiotic-resistant genes (pbp2, serp1412, murAA, etc.) had no significant changes. An electrophoretic mobility shift assay further revealed that phosphorylated VraR bound to the promoter regions of the ica operon, as well as its own promoter region. This study demonstrates that in S. epidermidis, VraSR is an autoregulator and directly regulates biofilm formation in an ica-dependent manner. Upon cell wall stress, it indirectly regulates cell death and drug resistance in association with alterations to multiple metabolism pathways.

IMPORTANCES. epidermidis is a leading cause of hospital-acquired catheter-related infections, and its pathogenicity depends mostly on its ability to form biofilms on implants. The biofilm formation is a complex procedure that involves multiple regulating factors. Here, we show that a vancomycin resistance-associated two-component regulatory system, VraSR, plays an important role in modulating S. epidermidis biofilm formation and tolerance to stress. We demonstrate that S. epidermidis VraSR is an autoregulated system that selectively responds to stress targeting cell wall synthesis. Besides, phosphorylated VraR can bind to the promoter region of the ica operon and directly regulates polysaccharide intercellular adhesin production and biofilm formation in S. epidermidis. Furthermore, VraSR may indirectly modulate bacterial cell death and extracellular DNA (eDNA) release in biofilms through the CidA-LrgAB system. This work provides a new molecular insight into the mechanisms of VraSR-mediated modulation of the biofilm formation and cell death of S. epidermidis.

Making the Most of the Host; Targeting the Autophagy Pathway Facilitates Staphylococcus aureus Intracellular Survival in Neutrophils

The success of Staphylococcus aureus as a human commensal and an opportunistic pathogen relies on its ability to adapt to several niches within the host. The innate immune response plays a key role in protecting the host against S. aureus infection; however, S. aureus adeptness at evading the innate immune system is indisputably evident. The “Trojan horse” theory has been postulated to describe a mechanism by which S. aureus takes advantage of phagocytes as a survival niche within the host to facilitate dissemination of S. aureus to secondary sites during systemic infection. Several studies have determined that S. aureus can parasitize both professional and non-professional phagocytes by manipulating the host autophagy pathway in order to create an intracellular survival niche. Neutrophils represent a critical cell type in S. aureus infection as demonstrated by the increased risk of infection among patients with congenital neutrophil disorders. However, S. aureus has been repeatedly shown to survive intracellularly within neutrophils with evidence now supporting a pathogenic role of host autophagy. By manipulating this pathway, S. aureus can also alter the apoptotic fate of the neutrophil and potentially skew other important signalling pathways for its own gain. Understanding these critical host-pathogen interactions could lead to the development of new host directed therapeutics for the treatment of S. aureus infection by removing its intracellular niche and restoring host bactericidal functions. This review discusses the current findings surrounding intracellular survival of S. aureus within neutrophils, the pathogenic role autophagy plays in this process and considers the therapeutic potential for targeting this immune evasion mechanism.

The Role of Macrophages in Staphylococcus aureus Infection

Staphylococcus aureus is a member of the human commensal microflora that exists, apparently benignly, at multiple sites on the host. However, as an opportunist pathogen it can also cause a range of serious diseases. This requires an ability to circumvent the innate immune system to establish an infection. Professional phagocytes, primarily macrophages and neutrophils, are key innate immune cells which interact with S. aureus, acting as gatekeepers to contain and resolve infection. Recent studies have highlighted the important roles of macrophages during S. aureus infections, using a wide array of killing mechanisms. In defense, S. aureus has evolved multiple strategies to survive within, manipulate and escape from macrophages, allowing them to not only subvert but also exploit this key element of our immune system. Macrophage-S. aureus interactions are multifaceted and have direct roles in infection outcome. In depth understanding of these host-pathogen interactions may be useful for future therapeutic developments. This review examines macrophage interactions with S. aureus throughout all stages of infection, with special emphasis on mechanisms that determine infection outcome.

Near-Infrared-Controlled Nanoplatform Exploiting Photothermal Promotion of Peroxidase-like and OXD-like Activities for Potent Antibacterial and Anti-biofilm Therapies

Nanozymes that mimic peroxidase (POD) activity can convert H₂O₂ into bactericidal free radicals, which is referred to as chemodynamic therapy (CDT). High glutathione (GSH) levels in the infectious tissue severely limit the performance of CDT. Herein, we report a near-infrared-controlled antibacterial nanoplatform that is based on encapsulating tungsten sulfide quantum dots (WS₂QDs) and the antibiotic vancomycin in a thermal-sensitive liposome. The system exploits the photothermal sensitivity of the WS₂QDs to achieve selective liposome rupture for the targeted drug delivery. We determined that WS₂QDs show a strong POD-like activity under physiological conditions and the oxidase-like activity, which can oxidate GSH to further improve the CDT efficacy. Moreover, we found that increased temperature promotes multiple enzyme-mimicking activities of WS₂QDs. This platform exerts antibacterial effects against Gram-positive Mu50 (a vancomycin-intermediate Staphylococcus aureus reference strain) and Gram-negative Escherichia coli and disrupts biofilms for improved penetration of therapeutic agents inside biofilms. In vivo studies with mice bearing Mu50-caused skin abscess revealed that this platform confers potent antibacterial activity without obvious toxicity. Accordingly, our work illustrates that the photothermal and nanozyme properties of WS₂QDs can be deployed alongside a conventional therapeutic to achieve synergistic chemodynamic/photothermal/pharmaco therapy for powerful antibacterial effects.