Iron depletion and virulence in Staphylococcus aureus

Abstract Staphylococcus aureus is able to grow in the presence of extremely low iron concentrations (0.04 μM). In iron-limiting conditions, this species develops alternative metabolic strategies such as highly efficient iron-uptake mechanisms which are only partially shared with S. epidermidis . Here we summarize the mechanisms induced by iron starvation in S. aureus in order to elucidate the virulence characteristics of this bacterium.     

Possible virulence factors of Staphylococcus aureus in a mouse septic model

Twenty clinical isolates of Staphylococcus aureus were examined to elucidate the virulence factors which are directly related to lethality in a mouse septic model. Heat or formalin treatment of the organism abolished the lethal activity of the live organism during challenge intravenously administered via the tail vein. Nevertheless, injection of ten times concentrated culture supernatant fluid (SUP) showed lethal activity in the mouse. However, there was no lethality when SUP was heated at 60 degrees C for 15 min. To examine variations of SUP lethality among strains, we collected 20 strains of S. aureus from four different hospitals. Then, we compared several factors for SUP lethality, which were the extracellular toxins and enzymes, such as toxic shock syndrome toxin 1, enterotoxin A, B, D, and hemolysins (alpha,beta,gamma), and also cytotoxic activity to human polymorphonuclear leukocytes and Vero cells. No difference was found among these factors except cytotoxic activity to Vero cells. Furthermore, we compared two strains in a mouse septic model according to the grade of bacteremia and lethal events. We found that mortality was higher with challenge by the strain whose SUP was lethal in comparison to the strain whose SUP was not lethal, even though the viable bacteria counts in the septic blood in both strains were not significantly different. This strongly supports the possibility that extracellular products, not the cell wall components, of S. aureus play the key role in the lethal event in this mouse septic model. In addition, among the extracellular products, those which have cytotoxic activity to Vero cells may contribute to the lethality in sepsis caused by S. aureus in this murine model.     

The use of monoclonal antibodies for studying the biological properties of Staphylococcus aureus endo-β-N-acetylglucosaminidase

Abstract Staphylococcus aureus endo- β - N -acetylglucosaminidase (SaG) has been suggested to function as a virulence determinant which interferes with the host cellular immune response. To further characterize the biological properties of SaG, monoclonal antibodies (mAbs) were raised against purified SaG. Four IgG₁ subclass mAbs were obtained, none of which reacted with the reduced, sodium dodecyl sulphate pretreated or boiled enzyme. The ability of the mAbs to react with the enzymes present in supernatants obtained from 197 S. aureus strains indicated that they recognized epitopes which are highly conserved; bacteriolytic enzymes produced by staphylococci other than S. aureus did not show any cross-reactivity. After pretreatment of SaG with mAbs (mAb-SaG molar ratios varying from 1 to 20), it was shown that all selected mAbs caused, at a mAb: SaG molar ratio of 10, a 90% inhibition of SaG bacteriolytic activity and a statistically significant reduction of its ability to interfere with phagocytosis to human polymorphonuclear leukocytes. All selected mAbs reacted with several commercially available exo- β - N -acetylglucosaminidases; mAb C1/10–11 also reacted with chicken and turkey egg muramidases and, at a mAb:SaG molar ratio of 10, inhibited their bacteriolytic activity by 97%. This suggests that one or more epitopes present in the above exo-glucosaminidases and muramidases share some degree of homology with others present in SaG.     

Silkworm apolipophorin protein inhibits Staphylococcus aureus virulence

Silkworm hemolymph inhibits hemolysin production by Staphylococcus aureus. We purified a factor in the silkworm hemolymph responsible for this inhibitory activity. The final fraction with the greatest specific activity contained 220- and 74-kDa proteins. Determination of the N-terminal amino acid sequence revealed that the 220- and 74-kDa proteins were apolipophorin I and apolipophorin II, respectively, indicating that the factor was apolipophorin (ApoLp). The purified ApoLp fraction showed decreased expression of S. aureus hla encoding α-hemolysin, hlb encoding β-hemolysin, saeRS, and RNAIII, which activate the expression of these hemolysin genes. Injection of an anti-ApoLp antibody into the hemolymph increased the sensitivity of silkworms to the lethal effect of S. aureus. Hog gastric mucin, a mammalian homologue of ApoLp, decreased the expression of S. aureus hla and hlb. These findings suggest that ApoLp in the silkworm hemolymph inhibits S. aureus virulence and contributes to defense against S. aureus infection and that its activity is conserved in mammalian mucin.     

金黄色葡萄球菌疫苗及其免疫治疗进展

具有多重抗生素耐药性的金黄色葡萄球菌是导致医院感染最常见的致病菌,而目前高致病性耐甲氧西林菌株(MRSA)在社区中的传播使得健康人群也面临极大威胁,因此针对金黄色葡萄球菌的疫苗和免疫治疗的研究迫在眉睫。多数的研究以金黄色葡萄球菌细胞壁锚定蛋白、荚膜多糖、外毒素等为靶点,虽然在一些临床前试验中显示出疫苗和免疫治疗对金葡菌感染具有保护性,但是目前临床试验结果却并不乐观,还没有一个经得起临床检验的疫苗。本文章从临床前试验和临床试验两个方面综述了目前关于金黄色葡萄球菌的疫苗和免疫治疗进展。     

纤溶酶原在金黄色葡萄球菌感染中的作用

金黄色葡萄球菌菌体表面有多种纤溶酶原受体,包括次黄嘌呤单核苷酸脱氢酶、核糖核苷酸还原酶、α-烯醇化酶和3-磷酸甘油醛脱氢酶等,它们均可以与纤溶酶原结合。与细菌结合的纤溶酶原可被宿主的纤溶酶原激活剂(组织型纤溶酶原激活剂和尿激酶型纤溶酶原激活剂)或葡萄菌属的纤溶酶原激活剂(葡激酶)激活为纤溶酶。细菌表面的纤溶酶有利于其降解宿主胞外基质,穿越组织屏障,因此哺乳动物的纤溶酶原可能在金黄色葡萄球菌感染宿主过程中起重要作用。     

快速检测金黄色葡萄球菌肠毒素A基因方法的建立与应用

目的建立一种快速准确定量检测金黄色葡萄球菌肠毒素A的方法。方法以femB、SEA基因分别作为金黄色葡萄球菌菌株、肠毒素A的靶序列,设计合成引物和TaqM an探针;收集腹泻患者大便标本分离的金黄色葡萄球菌68株,并定量检测其肠毒素A。结果TaqM an探针荧光聚合酶链反应检测金黄色葡萄球和肠毒素A的灵敏度均为1.0×102拷贝。68株金黄色葡萄球菌中检出产肠毒素A菌株11例(16.2%,11/68),CT值为13.5~20.6。结论TaqM an探针荧光聚合酶链反应能够准确快速检测金黄色葡萄球菌肠毒素A。     

Evolving superantigens of Staphylococcus aureus

Staphylococcus aureus bacteria utilize an extensive array of molecular countermeasures to manipulate the defensive microenvironment of the infected host and colonize potentially any tissue. The secreted polypeptides referred to as superantigens are unique among these countermeasures, because they target the multireceptor communication between T cells and antigen-presenting cells that is fundamental to initiating pathogen-specific immune clearance. Superantigens play a critical role in toxic-shock syndrome and food poisoning, yet their function in routine infections is not well understood. While an association of superantigens with cases of human autoimmune disease seems tantalizing, convincing data are not yet available. Blocking antigen-specific T-cell recognition is the primary evolutionary driving force behind superantigen selection, whereas superantigen-specific pathologies are by-products that are apparent only under select conditions.     

253株金黄色葡萄球菌耐药现状分析

目的 了解医院金黄色葡萄球菌临床分布情况及其对常用抗菌药物的耐药率,为临床合理使用抗菌药物提供依据.方法 回顾分析医院2010年5月至2011年4月检出的金黄色葡萄球菌,采用VITEK-AMS全自动微生物分析仪进行菌种鉴定和药敏分析.结果 共检出金黄色葡萄球菌253株,菌株的主要来源为痰130株(51.4％)、血液39株(15.4％)、创面24株(9.5％);菌株主要科室分布前3位是神内科35株(13.8％)、ICU30( 11.8％)、脑外科26株(10.3％);其中耐甲氧西林金黄色葡萄球菌( MRSA)为165株(65.2％),MRSA对多种抗菌药物耐药率＞70.0％,MSSA为88株(34.8％),对除青霉素、红霉素外的大多数抗菌药物敏感,未发现耐万古霉素菌株.结论 MRSA检出率高,耐药现状严重,应加强对金黄色葡萄球菌耐药性的监测,并根据药敏试验结果合理使用抗菌药物.     

Constitutive production of catalytic antibodies to a Staphylococcus aureus virulence factor and effect of infection

Antibodies that recognize microbial B lymphocyte superantigenic epitopes are produced constitutively with no requirement for adaptive immune maturation. We report cleavage of the Staphylococcus aureus virulence factor extracellular fibrinogen-binding protein (Efb) by catalytic antibodies produced with no exposure to the bacterium and reduction of the catalytic antibody activity following infection. IgG catalytic antibodies that specifically hydrolyzed Efb via a nucleophilic catalytic mechanism were found in the blood of healthy humans and aseptic mice free of S. aureus infection. IgG hydrolyzed peptide bonds on the C-terminal side of basic amino acids, including a bond located within the C3b-binding domain of Efb. Efb digested with the IgG lost its ability to bind C3b and inhibit complement-dependent antibody-mediated red blood cell lysis. In addition to catalysis, the IgG expressed saturable Efb binding activity. IgG from S. aureus-infected mice displayed reduced Efb cleaving activity and increased Efb binding activity compared with uninfected controls, suggesting differing effects of the infection on the antibody subsets responsible for the two activities. IgG from children hospitalized for S. aureus infection also displayed reduced Efb cleavage compared with healthy children. These data suggest a potential defense function for constitutively produced catalytic antibodies to a putative superantigenic site of Efb, but an adaptive catalytic response appears to be proscribed.     

A toxic shock syndrome toxin mutant of Staphylococcus aureus isolated by allelic replacement lacks virulence in a rabbit uterine model

The gene coding for toxic shock syndrome toxin-1 in S. aureus was inactivated by allelic replacement in two TSS-associated strains. One mutant derived from FRI1169 (a non-enterotoxigenic strain) lacked virulence in the rabbit uterine chamber infection model. This suggests that TSST-1 is the only determinant produced by this strain that can induce the symptoms of shock in rabbits. A novel method for allelic replacement involving transduction of plasmid integrants is described.     

Possible virulence factors of Staphylococcus sciuri

Staphylococcus sciuri is an opportunistic pathogen of controversial clinical significance. The factors that contribute to colonization and/or infection caused by this bacterium have not been studied intensively so far. The present research was carried out in order to study the presence of potential virulence factors in 121 human and animal isolates of this bacterium. Isolates were examined for biofilm formation, hemagglutination, presence of clumping factor, production of spreading factors and exotoxins, cytotoxicity and capacity to stimulate nitric oxide production. The results showed that S. sciuri is highly capable of biofilm production, that it displays strong proteolytic and DNase activities, produces hemolysins and stimulates nitric oxide production by rat macrophages. Although the present study showed existence of a wide spectrum of possible virulence determinants of S. sciuri, their exact contribution to virulence of this bacterium in vivo remains to be determined.     

金黄色葡萄球菌荚膜多糖研究进展

金黄色葡萄球菌作为引起人和动物发病的一种主要的致病菌,已严重影响到人们的身体健康和畜牧业的发展。致病性金黄色葡萄球菌多数含有荚膜成分,并且这种荚膜成分与金黄色葡萄球菌的毒力和抗噬菌作用有关。主要从金黄色葡萄球菌荚膜多糖的5型和8型血清学分类、分子结构、影响因素、表达调控等方面简要介绍了目前国内外关于金黄色葡萄球菌荚膜多糖的研究进展。     

金黄色葡萄球菌的分离及其抗药性的研究

从土壤中分离出金黄色葡萄球菌后,以其为出发菌株,采用梯度培养皿法,利用青霉素、四环素、红霉素、氯霉素和链霉素5种抗生素,对自然界中和经过NaNO2诱变的菌株进行了耐药性菌株的分离及抗性水平的确定。在自然界中分离的金黄色葡萄球菌只对青霉素(80μg/mL)和四环素(60μg/mL)有抗性,而对红霉素、氯霉素和链霉素则没有抗性。经过NaNO2诱变后,金黄色葡萄球菌对四环素(40μg/mL)的抗性降低,但对青霉素(120μg/mL)和其他3种抗生素的抗性均有所增加。     

Substrate specificity and energetics of antiseptic and disinfectant resistance in Staphylococcus aureus

The complete sequence coding for the 57-kDa major soluble antigen of the salmonid fish pathogen, Renibacterium salmoninarum, was determined. The gene contained an opening reading frame of 1671 nucleotides coding for a protein of 557 amino acids with a calculated M(r) value of 57,190. The first 26 amino acids constituted a signal peptide. The deduced sequence for amino acid residues 27-61 was in agreement with the 35 N-terminal amino acid residues determined by microsequencing, suggesting the protein is synthesized as a 557-amino acid precursor and processed to produce a mature protein of M(r) 54,505. Two regions of the protein contained imperfect direct repeats. The first region contained two copies of an 81-residue repeat, the second contained five copies of an unrelated 25-residue repeat. Also, a perfect inverted repeat (including three in-frame UAA stop codons) was observed at the carboxyl-terminus of the gene.     

金黄色葡萄球菌的快速检测方法

金黄色葡萄球菌是引起食物中毒常见的病原菌之一,其传统检测方法(选择性培养、生化鉴定)步骤多,操作复杂,耗时长、灵敏性不高。近年来以抗原抗体反应为基础的免疫学方法和以DNA为基础的分子生物学技术以其快速性、准确性已经成为微生物检测方法的发展方向。