Staphylococcus epidermidis activates keratinocyte cytokine expression and promotes skin inflammation through the production of phenol-soluble modulins

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Point‐of‐care detection of neutrophils in live skin microsamples using chemiluminescence

Many skin diseases are defined by the presence of neutrophils, which are among the first cells to respond to infection and inflammation. Currently, neutrophil identification in the skin is costly and slow. The objectives of the present work are to investigate the feasibility of detecting the presence of neutrophils in live skin microsamples using chemiluminescence and develop a device and procedures that will enable preclinical and clinical investigations. Our approach consists of collecting skin microsamples and exposing them to reagents that activate neutrophils and amplify the light emission produced by chemiluminescence. Experiments using live pig skin with and without inflammation show that it is feasible to detect the presence of neutrophils in the skin. The proposed method is minimally invasive, simple, fast, and does not require user specialization. The developed system is compact in size with a small footprint, which makes it portable and suitable for point‐of‐care diagnostics.     

Metabolic efficiency reshapes the seminal relationship between pathogen growth rate and virulence

A cornerstone of classical virulence evolution theories is the assumption that pathogen growth rate is positively correlated with virulence, the amount of damage pathogens inflict on their hosts. Such theories are key for incorporating evolutionary principles into sustainable disease management strategies. Yet, empirical evidence raises doubts over this central assumption underpinning classical theories, thus undermining their generality and predictive power. In this paper, we identify a key component missing from current theories which redefines the growth–virulence relationship in a way that is consistent with data. By modifying the activity of a single metabolic gene, we engineered strains of Magnaporthe oryzae with different nutrient acquisition and growth rates. We conducted in planta infection studies and uncovered an unexpected non-monotonic relationship between growth rate and virulence that is jointly shaped by how growth rate and metabolic efficiency interact. This novel mechanistic framework paves the way for a much-needed new suite of virulence evolution theories.     

Fsr1, a striatin homologue,forms an endomembrane‐associated complex that regulates virulence in the maize pathogen Fusarium verticillioides

Fsr1, a homologue of mammalian striatin, containing multiple protein‐binding domains and a coiled‐coil (CC) domain, is critical for Fusarium verticillioides virulence. In mammals, striatin interacts with multiple proteins to form a STRIPAK (striatin‐interacting phosphatase and kinase) complex that regulates a variety of developmental processes and cellular mechanisms. In this study, we identified the homologue of a key mammalian STRIPAK component STRIP1/2 (striatin‐interacting proteins 1 and 2) in F. verticillioides, FvStp1, which interacts with Fsr1 in vivo. Gene deletion analysis indicates that FvStp1 is critical for F. verticillioides stalk rot virulence. In addition, we identified three proteins, designated FvCyp1, FvScp1 and FvSel1, which interact with the Fsr1 CC domain via a yeast two‐hybrid screen. Importantly, FvCyp1, FvScp1 and FvSel1 co‐localize to endomembrane structures, each having a preferred localization in the cell, and they are all required for F. verticillioides stalk rot virulence. Moreover, these proteins are necessary for the correct localization of Fsr1 to the endoplasmic reticulum (ER) and nuclear envelope. Thus, we identified several novel components in the STRIPAK complex that regulates F. verticillioides virulence, and propose that the correct organization and localization of Fsr1 are critical for STRIPAK complex function.     

Acclimation of Plasmopara halstedii (sunflower downy mildew) in relationship with trade-off between virulence and aggressiveness in a local pathogen population

The acclimation in relationship with virulence cost was analysed for seven Plasmopara halstedii (sunflower downy mildew) isolates including five progeny isolates of several races descending from two parental isolates of races 100 and 710. Aggressiveness criteria were analysed in one sunflower inbred line showing a high level of quantitative resistance. Isolates of races 100 and 3xx were characterised with shorter latent period and higher sporulation density than isolates of races 7xx. All isolates showed high percentage infection values and caused a large reduction in seedling size except for one isolate involved in dwarfing. The seven isolates were divided, according to their virulence and aggressiveness, into two main groups as more aggressive isolates of the 100 and 3xx races which do not overcome the sunflower differential host D3, and less aggressive isolates of 7xx races which can overcome D3. Consequently, the 100 and 3xx avirulent races had a virulence cost measured by differences in aggressiveness (from 45.5 to 76.3%) compared to 7xx virulent races carrying unnecessary virulence gene.     

Maximized virulence in a sterilizing pathogen: the anther-smut fungus and its co-evolved hosts

Host sterilization is a common feature of sexually transmitted diseases (STDs). Because host reproductive failure may free up resources for pathogen reproduction and transmission, theory predicts that selection on sterilizing pathogens will favour maximum virulence (i.e. complete sterilization). We examined patterns of infection in sexually transmitted anther-smut fungi (Microbotryum) on four of their host species in the Caryophyllaceae. Using controlled fungal matings and experimental inoculations, we compared disease expression in inoculations ranging from host-specific pathogens to hybrids and cross-species treatments. Our data support the existence of host-specific sibling species within the genus Microbotryum based on a low infection rate from cross-inoculations and reduced fitness for hybrid pathogens. These patterns of host specificity and reproductive isolation, however, were not absolute. We did observe some successful cross-species and hybrid infections, but the expression of disease was frequently incomplete, including only partial host sterilization and the failed dehiscence of pathogen spores. The prevalence of these maladapted disease phenotypes may greatly inhibit the emergence of novel host pathogen combinations. Infections by hybrid pathogen genotypes were intermediate, in terms of both infection rate and the normality of disease symptoms, between host-specific and cross-inoculated pathogens. In addition, the frequency with which hybrid and cross-inoculated anther-smut pathogens were able to infect but not sterilize new hosts supports the prediction that sterilizing STDs are under selection to maximize virulence in natural populations.     

Induction of alarmin S100A8/A9 mediates activation of aberrant neutrophils in the pathogenesis of COVID-19

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Non-toxic plant metabolites regulate Staphylococcus viability and biofilm formation: a natural therapeutic strategy useful in the treatment and prevention of skin infections

In the present study, the efficacy of generally recognised as safe (GRAS) antimicrobial plant metabolites in regulating the growth of Staphylococcus aureus and S. epidermidis was investigated. Thymol, carvacrol and eugenol showed the strongest antibacterial action against these microorganisms, at a subinhibitory concentration (SIC) of ≤ 50 μg ml^?1. Genistein, hydroquinone and resveratrol showed antimicrobial effects but with a wide concentration range (SIC = 50–1,000 μg ml^?1), while catechin, gallic acid, protocatechuic acid, p-hydroxybenzoic acid and cranberry extract were the most biologically compatible molecules (SIC ≥ 1000 μg ml^?1). Genistein, protocatechuic acid, cranberry extract, p-hydroxybenzoic acid and resveratrol also showed anti-biofilm activity against S. aureus, but not against S. epidermidis in which, surprisingly, these metabolites stimulated biofilm formation (between 35% and 1,200%). Binary combinations of cranberry extract and resveratrol with genistein, protocatechuic or p-hydroxibenzoic acid enhanced the stimulatory effect on S. epidermidis biofilm formation and maintained or even increased S. aureus anti-biofilm activity.     

Intraspecific competition and the evolution of virulence in a parasitic trematode

Intrahost competition between parasite genotypes has been predicted to be an important force shaping parasite ecology and evolution and has been extensively cited as a mechanism for the evolution of increased parasite virulence. However, empirical evidence demonstrating the existence and nature of intraspecific competition is lacking for many parasites. Here, we compared within-host competitiveness between genetic strains of Schistosoma mansoni with high (HIGH-V) or low (LOW-V) virulence to their intermediate snail host, Biomphalaria glabrata. Groups of snails were exposed to either one or the other of two parasite strains, or a mixed infection of both strains, and the resulting progeny were identified using a molecular marker. In two separate experiments investigating simultaneous and sequential infections, we demonstrated that the lifetime reproductive success of parasite strain HIGH-V was reduced in the presence of a faster replicating parasite genotype, LOW-V, regardless of whether it was in a majority or minority in the initial inoculum of the simultaneous exposure or of its relative position in the sequential exposure experiment. Thus, we demonstrate competition between parasite genotypes and asymmetry in competitive success between parasite strains. Moreover, since the less virulent strain investigated here had a competitive advantage, we suggest that a high frequency of multiple infections could favor the evolution of less, rather than more, virulent parasites in this system.     

Inhibitory role of neutrophils on influenza virus multiplication in the lungs of mice.

The protective role of neutrophils on intranasal infection of influenza virus was investigated in 3 strains of tumor-bearing mice with neutrophilic leukocytosis. In vitro multiplication of influenza virus was inhibited by neutrophils from both normal and tumor-bearing mice, and the inhibitory effect of neutrophils was augmented by an addition of fMLP to the culture. Pulmonary virus infectivities in the early phase after infection decreased in such ICR and BALB/c mice, and virus elimination in the late phase was accelerated in the ICR mice. However, no decrease in pulmonary virus infectivity was observed in tumor-bearing C57BL/6 mice. Intranasal administration of fMLP into normal and tumor-bearing C57BL/6 mice after infection significantly inhibited the virus propagation in the lungs. The decrease in neutrophil infiltration into the lung in tumor-bearing C57BL/6 mice was confirmed from histological observations of the lung and lung lavage after infection and from analysis of the neutrophil chemotactic activity induced by fMLP. This might be responsible for the high level of pulmonary virus titer in tumor-bearing C57BL/6 mice. Phagocytic activities of alveolar macrophages and productions of neutralizing antibody were suppressed in the 3 strains of tumor-bearing mice. These observations indicated that neutrophils could be significant effector cells as a host defense mechanism against influenza virus infection in vivo, and infiltration and functional activation of neutrophils could play a significant role in virus elimination from the infected site. Furthermore, the inhibition of virus propagation by neutrophils in vitro was almost completely abrogated by an addition of ZnSO4, suggesting that calprotectin could inhibit influenza virus multiplication.     

Activation of phosphoinositide-specific phospholipase C of rat neutrophils by the chemotactic aldehydes 4-hydroxy-2,3-trans-nonenal and 4-hydroxy-2,3-trans-octenal

A comparison has been made between the effects of 4-hydroxy-2,3-trans-nonenal (HNE) and 4-hydroxy-2,3-trans-octenal (HOE), two lipid peroxidation products, on the basal and GTPgammaS-stimulated activities of phosphoinositide-specific phospholipase C (PL-C) of rat polymorphonuclear leukocytes. PL-C activity was determined in vitro by measuring the hydrolysis of [³H] phosphatidylinositol-4,5-bis-phosphate (PtdIns-P₂) added as exogenous substrate to neutrophil plasma membranes. PL-C was activated by concentrations of HNE ranging from 10^?8 to 10^?6 M both in the presence and in the absence of 2 × 10^?5 M GTPgammaS; HOE stimulated the enzymatic activity between 10^?11 and 10^?8 M ; maximal stimulation was given by 10^?11 M HOE plus GTPgammaS. The aldehyde concentrations able to accelerate PtdIns-P₂ breakdown displayed a good correspondence with those which have been reported to stimulate the oriented migration of rat neutrophils. Pretreatment of neutrophils with pertussis toxin prevented the stimulation of PL-C by 10^?11 M HOE and by HOE plus GTPgammaS. Our results suggest that the chemotactic action of HNE and HOE might depend on the activation of PL-C; furthermore a regulatory G protein appears to be involved in the acceleration of PtdIns-P₂ turnover by HOE.     

VdMsb regulates virulence and microsclerotia production in the fungal plant pathogen Verticillium dahliae

The vascular wilt fungus Verticillium dahliae infects the roots of cotton plants and can seriously diminish the yield and quality of this and other dicotyledons. However, the key genes involved in V. dahliae infection and pathogenesis in cotton remain unclear. Msb encodes a transmembrane mucin that is highly conserved in the MAPK signal pathway. Msb has been implicated previously in pathogenicity in various aerial plant fungi. In this study, V. dahliae Msb (VdMsb) was found to be required for fungal virulence and microsclerotia production. Strains lacking VdMsb exhibited reduced conidiation and microsclerotia formation. Compared with wild-type and gene-complemented strains, the invasive growth and adhesive capacity of VdMsb deletion mutants were significantly decreased. These results suggest that VdMsb plays a role in development and virulence in V. dahliae.     

Genome characterization, analysis of virulence and transformation of Microbacterium nematophilum, a coryneform pathogen of the nematode Caenorhabditis elegans

A coryneform bacterium designated Microbacterium nematophilum has previously been reported to act as a pathogen for Caenorhabditis elegans. This bacterium is able to colonize the rectum of infected worms and cause localized swelling, constipation and slowed growth. Additional isolates and analysis of this bacterium are described here. Tests of pathogenicity on other Caenorhabditis nematodes show that M. nematophilum infection is lethal to most species in the genus, in contrast to its relatively mild effects on C. elegans. The size and geometry of the pathogen genome have been determined as a closed circular molecule of 2.85 Mb with high G+C content. Bacteria also harbor a 55 kb plasmid, pMN1, which is largely composed of a lysogenic bacteriophage genome. Mutagenesis experiments have yielded stable avirulent mutants of M. nematophilum. As a first step towards molecular genetic analysis, methods for low-efficiency transformation of M. nematophilum have been developed.     

分泌型蛋白介导白念珠菌与宿主相互作用分子机制的研究进展

白念珠菌是人类最常见的条件性致病真菌之一,主要定植于人体粘膜表面。在白念珠菌与宿主相互作用过程中,分泌型蛋白起着非常重要的作用。针对分泌蛋白功能及其作用机理的研究有助于阐明白念珠菌致病分子机制,并为诊断、预防和治疗真菌感染提供新的理论策略。本文综述了白念珠菌分泌型蛋白在介导病原与宿主相互作用分子机制方面的最新研究进展,概括了分泌蛋白在组织侵入损伤、营养获取、细胞壁维持以及免疫逃避等方面的功能,同时对未来值得重点关注的研究方向进行了探讨。     

Variation in resistance and virulence in the interaction between Arabidopsis thaliana and a bacterial pathogen

We examined patterns of variation and the extent of local adaptation in the interaction between the highly selfing annual weed Arabidopsis thaliana and its foliar bacterial pathogen Pseudomonas viridiflava by cross-infecting 23 bacterial isolates with 35 plant lines collected from six fallow or cultivated fields in the Midwest, USA. We used two measures of resistance and virulence: bacterial count in the leaf and symptom development four days after infection. We found variation in resistance in A. thaliana and virulence in P. viridiflava, as well as a significant difference in symptoms between two distinct genetic clades within P. viridiflava. We also observed that both resistance and plant development rate varied with field type of origin (cultivated or fallow), possibly through age-related resistance, a developmentally regulated general form of resistance. Finally, we did not observe local adaptation by host or pathogen, rather we found patterns of variation across populations that depended in part on P. viridiflava clade. These data suggest that the interaction between A. thaliana and P. viridiflava varies across space and is mediated by the selection regime of the host populations and differential performance of the P. viridiflava clades. This is one of a very limited number of studies examining a bacterial pathogen of wild plant populations and one of a few studies to examine patterns of variation in a plant-pathogen association that is not a highly specialized gene-for-gene interaction.