A PEST-like sequence in listeriolysin O essential for Listeria monocytogenes pathogenicity

Establishment and maintenance of an intracellular niche are critical to the success of an intracellular pathogen. Here, the pore-forming protein listeriolysin O (LLO), secreted by Listeria monocytogenes, was shown to contain a PEST-like sequence (P, Pro; E, Glu; S, Ser; T, Thr) that is essential for the virulence and intracellular compartmentalization of this pathogen. Mutants lacking the PEST-like sequence entered the host cytosol but subsequently permeabilized and killed the host cell. LLO lacking the PEST-like sequence accumulated in the host-cell cytosol, suggesting that this sequence targets LLO for degradation. Transfer of the sequence to perfringolysin O transformed this toxic cytolysin into a nontoxic derivative that facilitated intracellular growth.     

单核增生性李斯特杆菌感染和李氏溶血素

单核增生性李斯特杆菌病能引起绵羊、人和其他很多动物疾病,在免疫学检测上有重要意义,在研究胞内菌感染的分子机制上也是一个重要的模型。但由于当前血清学试验上的非特异性和非敏感性,使李氏杆菌病的诊断和流行病学调查存在困难。在所有致病性的李斯特杆菌中,李斯特溶血素是主要致病因子,现已经有用其做诊断抗原的报道。文章论述了近年来单核增生性李斯特杆菌及李氏溶血素的最新进展,对研究李氏杆菌病的发病机理有一定作用。     

Targeting QseC signaling and virulence for antibiotic development

Many bacterial pathogens rely on a conserved membrane histidine sensor kinase, QseC, to respond to host adrenergic signaling molecules and bacterial signals in order to promote the expression of virulence factors. Using a high-throughput screen, we identified a small molecule, LED209, that inhibits the binding of signals to QseC, preventing its autophosphorylation and consequently inhibiting QseC-mediated activation of virulence gene expression. LED209 is not toxic and does not inhibit pathogen growth; however, this compound markedly inhibits the virulence of several pathogens in vitro and in vivo in animals. Inhibition of signaling offers a strategy for the development of broad-spectrum antimicrobial drugs.     

Listeria intracellular growth and virulence require host-derived lipoic acid

Listeria monocytogenes is a Gram-positive intracytosolic pathogen that causes severe disease in pregnant and immunocompromised individuals. We found that L. monocytogenes lacking the lipoate protein ligase LplA1 was defective for growth specifically in the host cytosol and was less virulent in animals by a factor of 300. A major target for LplA1, the E2 subunit of pyruvate dehydrogenase (PDH), lacked a critical lipoyl modification when the DeltalplA1 strain was grown intracellularly, which suggests that abortive growth was due to loss of PDH function. Thus, the use of host-derived lipoic acid may be a critical process for in vivo replication of bacterial pathogens.     

Drosophila RNAi screen reveals CD36 family member required for mycobacterial infection

Certain pathogens, such as Mycobacterium tuberculosis, survive within the hostile intracellular environment of a macrophage. To identify host factors required for mycobacterial entry and survival within macrophages, we performed a genomewide RNA interference screen in Drosophila macrophage-like cells, using Mycobacterium fortuitum. We identified factors required for general phagocytosis, as well as those needed specifically for mycobacterial infection. One specific factor, Peste (Pes), is a CD36 family member required for uptake of mycobacteria, but not Escherichia coli or Staphylococcus aureus. Moreover, mammalian class B scavenger receptors (SRs) conferred uptake of bacteria into nonphagocytic cells, with SR-BI and SR-BII uniquely mediating uptake of M. fortuitum, which suggests a conserved role for class B SRs in pattern recognition and innate immunity.     

Lack of a role for iron in the Lyme disease pathogen

A fundamental tenet of microbial pathogenesis is that bacterial pathogens must overcome host iron limitation to establish a successful infection. Surprisingly, the Lyme disease pathogen Borrelia burgdorferi has bypassed this host defense by eliminating the need for iron. B. burgdorferi grew normally and did not alter gene expression in the presence of iron chelators. Furthermore, typical bacterial iron-containing proteins were not detected in cell lysates, nor were the genes encoding such proteins identified in the genome sequence. The intracellular concentration of iron in B. burgdorferi was estimated to be less than 10 atoms per cell, well below a physiologically relevant concentration.     

Inhibition Effect of Herbal Preservatives on Listeria monocytogenes on Chilled Pork

This study investigated the growth situation of Listeria monocytogenes on chilled pork and the effect of herbal preservatives on this pathogen. The inhibitions of herbal preservatives were identified. The minimum inhibitory concentrations （MIC） of cinnamon and clove were all 0.79 mg.mL^-1, while the rosemary was 1.58 mg.mL^-1. And the composite herbal preservatives were got through orthogonal experiment. The optimum proportion was as following on agar medium： 1.16 mg.mL^-1 cinnamon＋2.38 mg. mL^-1 rosemary＋3.17 mg. mLl clove （herb combination number 5）, while on chilled pork, the strong inhibition of L. monocytogenes was showed, which demonstrated that the surface application of herb combination resulted in an effective delay of L. monocytogenes growth.     

泡核桃干腐病病原菌分离鉴定及杀菌剂室内筛选

为明确泡核桃干腐病的病原和筛选合适的化学防治药剂,从云南省楚雄州大姚县核桃病害标本中分离和鉴定了病原菌,测定了8种杀菌剂的毒力。通过柯赫氏法则验证,确定分离得到的该菌株能侵染泡核桃,产生干腐症状。依据形态特征和rDNA-ITS序列分析,将病原鉴定为茶藨子葡萄座腔菌（Botryosphaeria dothidea）。室内毒力测定的结果表明：8种杀菌剂的EC50从大到小依次为氟啶胺0.0604mg/L、戊唑醇0.169 0mg/L、苯醚甲环唑0.1778mg/L、嘧菌酯0.4769mg/L、福美双2.0947mg/L、噻呋酰胺3.9610mg/L、异菌脲4.2190mg/L、霜脲氰101.7643mg/L。     

基因分型技术在单核细胞增生性李斯特菌监测溯源上的应用

单核细胞增生性李斯特菌Listeria monocytogenes是一种重要的食源性人畜共患病原菌,能引起人和多种动物流产、脑膜炎、肠胃炎、败血症、死胎等病症。与传统基于表型的分型方法相比,基因分型方法具有简单快速、分辨率高、敏感性强、重复性好等特点,在李斯特菌病病原菌的监测和溯源中具有重要的应用价值。对单核细胞增生性李斯特菌的3类基因分型方法:酶切技术,DNA测序技术和聚合酶链式反应（PCR）扩增技术进行了概述,从分型成本、样本通量、分辨力、灵敏度、重复性、快捷性和普及性等方面比较了3类基因分型方法的主要特点,重点评述了这些方法在单核细胞增生性李斯特菌暴发监测和溯源上的应用案例,为研究不同基因分型方法在单核细胞增生性李斯特菌暴发诊断、分型检测及感染溯源等方面的应用提供参考。     

布鲁氏菌胞内寄生的研究进展

布鲁氏菌是一种能够在哺乳动物巨噬细胞内生存和增殖的兼性厌氧菌。近年来,布鲁氏菌的研究主要集中在参与细胞内寄生过程中的毒力因子及其对宿主细胞的影响。主要论述布鲁氏菌如何逃避巨噬细胞的防御及其在细胞内寄生状况。     

大叶紫薇炭疽病病原的鉴定及生物学特性

为了明确大叶紫薇炭疽病的病原菌种类,为后续研究其发病规律及诊断防治提供理论依据,对海南出现的大叶紫薇炭疽病进行致病性测定、形态学鉴定和ITS、ACT、GAPDH、CHS序列分析,结果表明:引起海南大叶紫薇炭疽病的病原菌为隐秘刺盘孢（Colletotrichum aenigma）。生物学特性测定结果表明:大叶紫薇炭疽病原菌丝最适生长温度为 30 ℃,最适 pH 为8。黑暗条件有利于其菌丝生长,在PDA、PSA培养基上的生长速率较快。     

食品中单增李斯特菌检测技术研究进展

单增李斯特菌是一种重要的人畜共患食源性致病菌,如何有效控制食品(尤其是即食食品)中的单增李斯特菌,是食品安全的重要任务,其中快速、准确的检测技术是关键因素之一.作者对单增李斯特菌的传统检测法、免疫学检测法和分子生物学检测法进行综述,并对目前国内单增李斯特菌检测过程中所存在的问题进行探讨,以期为今后的研究提供参考.     

Monitoring the development of leaf rust pathogen on common wheat specimens

During 1995–2005 the leaf rust pathogen was monitored on common wheat specimens with identified Lr resistance genes. The number of pustules on the flag leaf surface of the host plant, pustule area, number of spores in it, and type of reaction are used as the main indices of pathogenesis of the pathogen. A number of regression models reflecting the main quantitative regularities of variables of the pathogen’s state are proposed.     

高良姜叶枯病病原菌的分离和鉴定

[目的]明确高良姜叶枯病病原菌.[方法]病原菌从高良姜感病组织上分离并依据柯赫氏法则进行致病性测定,病原菌的鉴定主要通过形态鉴定和ITS序列分析.[结果]高良姜叶枯病病原菌确定为可可毛色二孢（Lasiodiplodia theobromae）,属子囊菌门（Ascomycota）,座囊菌纲（Dothideomycetes）,葡萄座腔菌目（Botryosphaeriales）,葡萄座腔菌科（Botryosphaeriaceae）,毛色二孢属（Lasiodiplodia）.[结论]首次报道高良姜叶枯病病原菌为可可毛色二孢.     

The M43 domain-containing metalloprotease RcMEP1 in Rhizoctonia cerealis is a pathogenicity factor during the fungus infection to wheat

Wheat(Triticum aestivum L.) is an important staple crop for global human. The necrotrophic fungus Rhizoctonia cerealis is the causal pathogen of sharp eyespot, a devastating disease of wheat. Herein, we identified RcMEP1, a zinc metalloproteaseencoding gene from R. cerealis genomic sequences, and characterized its pathogenesis function. RcMEP1 expressed at markedly-high levels during R. cerealis infection process to wheat. The predicted protein RcMEP1 comprises of 287 amino acid residues and contains a signal peptide and a M43 metalloprotease domain harboring the active site motif(HEVGHWLGLYH). The assays of Agrobacterium tumefaciens-mediated transient expression in Nicotiana benthamiana leaves indicated that RcMEP1 is an apoplastic elicitor of cell death, and that the predicted signal peptide functions and is required for secretion and cell death-induction. The purified RcMEP1 protein and its M43 domain peptide were individually able to induce plant cell death and H2 O2 accumulation, and to inhibit expression of host chitinases when infiltrated into wheat and N. benthamiana leaves, while the M43 domain-deleting peptide and negative control lacked the capacity. Moreover, compared with the control pretreatment, the purified RcMEP1 protein or its M43-domain peptide resulted in enhanced pathogenesis in the inoculated wheat, whereas the M43 domain-deleting peptide failed. These results suggest that RcMEP1 acted as an important pathogenicity factor during R. cerealis infection to wheat and that its signal peptide and M43 domain are required for the secretion and pathogenesis of RcMEP1. This study provides insights into pathogenesis role of M43 domain-containing metalloproteases during R. cerealis infection to wheat.     

鸡冠花细菌性叶斑病菌的鉴定

笔者自鸡冠花Celosia cristatal.上发现一种细菌性叶斑病。它主要危害叶片,形成圆形枯斑,边缘淡褐色,使叶片枯萎。根据病原细菌的形态染色反应、培养性状、生理生化等方面的测试,鉴定该病原菌为Erwinia chrysanthemi pv.Chrysanthemi Burkholderet al.鸡冠花是该细菌的一个新的寄主。     

基于MALDI-TOF/TOF技术的单增李斯特菌四种血清型的快速鉴别

单增李斯特菌是一种重要的人畜共患病致病菌,其传统血清型鉴定方法具有耗时长、操作繁琐等缺点,现行的多重PCR方法无法精确判定其血清型。基于基质辅助激光解析/电离飞行时间质谱（MALDI-TOF/TOF）的快速、准确、高通量等特点,应用该技术建立了单增李斯特菌4种血清型的鉴别方法,以实现食品样品中单增李斯特菌4种血清型的高通量快速甄别。采用优化的MALDI-TOF/TOF条件对4种血清型的单增李斯特菌标准菌株和分离菌株进行检测,发现单增李斯特菌4种血清型的质谱特征峰。选取最优的支持向量机算法,建立基于1/2a、1/2b、1/2c和4b血清型差异的判别模型,运用该模型鉴别4种血清型的单增李斯特菌。初步建立了单增李斯特菌4种血清型的MALDI-TOF/TOF快速鉴别方法。以4种血清型的单增李斯特菌标准菌株为阳性对照、144株食品分离株为检测对象,运用该方法对单增李斯特菌1/2a、1/2b、1/2c、4b四种血清型鉴定符合率分别达到92.7%、90.3%、100%、100%,多重PCR方法的符合率为71.4%、87.0%、96.2%、95.0%。可见,建立的MALDI-TOF/TOF方法可对4种血清型的单增李斯特菌快速鉴别。与多重PCR方法相比,该方法具有快速、高通量、重现性好等特点,可用于食品中单增李斯特菌血清型的快速鉴定。     

土壤中山核桃干腐病抑制菌的筛选和鉴定

为了从土壤中筛选具有抑制山核桃Carya cathayensis于腐病菌的微生物,运用平皿对峙法从土壤中初筛得到对山核桃干腐病菌葡萄座腔菌Botryosphaeria dothidea具有拮抗作用的菌株5株,对峙培养发现菌株QZ2和QZ8抑菌效果显著,对峙试验显示QZ2,QZ8与病原菌之间有明显的抑菌圈,且QZ2孢子能完全覆盖在病原菌上生长而病原菌生长停止.通过形态特征观察及ITS序列分析,菌株QZ2被鉴定为棘孢木霉Trichoderma asperellum,主要通过重寄生以达到控病的效果;菌株QZ8为草酸青霉Penicillium oxalicum,主要通过代谢产生的抗菌素起作用.QZ2和QZ8是山核桃干腐病的潜在生防菌.