Whole genome sequence to decipher the resistome of Shewanella algae,a multidrug-resistant bacterium responsible for pneumonia,Marseille, France

We characterize and decipher the resistome and the virulence factors of Shewanella algae MARS 14, a multidrug-resistant clinical strain using the whole genome sequencing (WGS) strategy. The bacteria were isolated from the bronchoalveolar lavage of a hospitalized patient in the Timone Hospital in Marseille, France who developed pneumonia after plunging into the Mediterranean Sea. Results: The genome size of S. algae MARS 14 was 5,005,710 bp with 52.8% guanine cytosine content. The resistome includes members of class C and D beta-lactamases and numerous multidrug-efflux pumps. We also found the presence of several hemolysins genes, a complete flagellum system gene cluster and genes responsible for biofilm formation. Moreover, we reported for the first time in a clinical strain of Shewanella spp. the presence of a bacteriocin (marinocin). Conclusion: The WGS analysis of this pathogen provides insight into its virulence factors and resistance to antibiotics.     

阴道来源的乳杆菌抑菌物质研究进展

乳杆菌是大多数健康女性阴道微生态中的优势菌群,对预防泌尿生殖系统感染性疾病起重要作用。能产生乳酸、过氧化氢、细菌素和生物表面活性物质等抑菌物质是乳杆菌成为潜在益生菌的重要基础。本文对阴道来源的乳杆菌抑菌物质相关研究进展作一综述。     

亚抑菌浓度茅苍术挥发油对金黄色葡萄球菌毒力因子表达的抑制作用初步研究

目的探索亚抑菌浓度茅苍术挥发油对金黄色葡萄球菌(Staphylococcus aureus)毒力因子如α溶血素等表达的抑制作用及其机制。方法采用微量肉汤稀释法测定茅苍术挥发油对4株金黄色葡萄球菌的最小抑菌浓度(minimum inhibitory concentration,MIC);吸光度测量等方法体外检测亚抑菌浓度茅苍术挥发油作用下金黄色葡萄球菌毒力因子产量的变化;采用Real-Time PCR法检测亚抑菌浓度挥发油对AgrA和Hla mRNA表达的影响。结果茅苍术挥发油可抑制金黄色葡萄球菌生长并呈现浓度依赖性,标准菌株ATCC25923的MIC为0.0625%(v/v),临床菌株的MIC为0.03125%(v/v)。亚抑菌浓度茅苍术挥发油作用后4株菌株凝固酶的分泌受到抑制,标准菌株ATCC25923的凝固酶效价只有对照组的1/4,差异有统计学意义(P<0.05),临床菌株的凝固酶效价都只有对照组的1/8,差异有统计学意义(P<0.05)。亚抑菌浓度茅苍术挥发油减弱了四株菌株的粘附能力,ATCC25923、SA1.5、SA2.3和SA4.12的粘附能力分别只有对照组的(53.71±6.56)%(P<0.01)、(53.10±9.39)%(P<0.01)、(74.70±9.00)%(P<0.01)和(45.62±21.22)%(P<0.01)。标准菌株ATCC25923和SA2.3的溶血活力受到亚抑菌浓度挥发油的显著抑制,溶血活力分别只有对照组的(18.48±23.88)%(P<0.01)和(1.63±4.18)%(P<0.01)。α-溶血素毒力基因Hla及其调控基因AgrA的表达受到了亚抑菌浓度挥发油的抑制,其表达水平分别只有对照组的(6.17±2.23)%(P<0.01)和(24.79±9.19)%(P<0.01)。结论茅苍术挥发油能抑制金黄色葡萄球菌的生长,并且对多种毒力因子的表达有抑制作用。     

牙菌斑生物膜的细菌生长抑制因子

牙菌斑生物膜中的细菌是龋病发生的先决条件,而口腔内存在多种细菌生长的抑制因子,它们对细菌的生长或菌斑的形成起一定抑制作用。细菌生长的抑制因子主要来自宿主和细菌本身产生的细菌素以及其他代谢产物,本文就致龋菌生长抑制因子的种类及作用的研究进展作一综述。     

牙龈卟啉单胞菌双组分信号转导系统的研究进展

牙龈卟啉单胞菌被认为是主要的牙周致病菌之一,与慢性牙周炎发生发展密切相关。面对复杂的口腔环境,牙龈卟啉单胞菌必须及时感知环境变化并作出反应,双组分信号转导系统在其中具有重要作用。双组分信号转导系统通常由组氨酸激酶和反应调节蛋白组成,通过控制蛋白的磷酸化状态调节信号传导。近年来,有关牙龈卟啉单胞菌的双组分信号转导系统陆续被报道。本文就牙龈卟啉单胞菌的双组分系统的组成和功能进行综述。     

Identical phosphatase mechanisms achieved through distinct modes of binding phosphoprotein substrate

Two-component signal transduction systems are widespread in prokaryotes and control numerous cellular processes. Extensive investigation of sensor kinase and response regulator proteins from many two-component systems has established conserved sequence, structural, and mechanistic features within each family. In contrast, the phosphatases which catalyze hydrolysis of the response regulator phosphoryl group to terminate signal transduction are poorly understood. Here we present structural and functional characterization of a representative of the CheC/CheX/FliY phosphatase family. The X-ray crystal structure of Borrelia burgdorferi CheX complexed with its CheY3 substrate and the phosphoryl analogue reveals a binding orientation between a response regulator and an auxiliary protein different from that shared by every previously characterized example. The surface of CheY3 containing the phosphoryl group interacts directly with a long helix of CheX which bears the conserved (E - X₂ - N) motif. Conserved CheX residues Glu96 and Asn99, separated by a single helical turn, insert into the CheY3 active site. Structural and functional data indicate that CheX Asn99 and CheY3 Thr81 orient a water molecule for hydrolytic attack. The catalytic residues of the CheX·CheY3 complex are virtually superimposable on those of the Escherichia coli CheZ phosphatase complexed with CheY, even though the active site helices of CheX and CheZ are oriented nearly perpendicular to one other. Thus, evolution has found two structural solutions to achieve the same catalytic mechanism through different helical spacing and side chain lengths of the conserved acid/amide residues in CheX and CheZ.     

From the Cover: Thuricin CD,a posttranslationally modified bacteriocin with a narrow spectrum of activity against Clostridium difficile

The last decade has seen numerous outbreaks of Clostridium difficile-associated disease (CDAD), which presented significant challenges for healthcare facilities worldwide. We have identified and purified thuricin CD, a two-component antimicrobial that shows activity against C. difficile in the nanomolar range. Thuricin CD is produced by Bacillus thuringiensis DPC 6431, a bacterial strain isolated from a human fecal sample, and it consists of two distinct peptides, Trn-α and Trn-β, that act synergistically to kill a wide range of clinical C. difficile isolates, including ribotypes commonly associated with CDAD (e.g., ribotype 027). However, this bacteriocin thuricin CD has little impact on most other genera, including many gastrointestinal commensals. Complete amino acid sequencing using infusion tandem mass spectrometry indicated that each peptide is posttranslationally modified at its respective 21st, 25th, and 28th residues. Solution NMR studies on [¹³C,¹⁵N] Trn-α and [¹³C,¹⁵N]Trn-β were used to characterize these modifications. Analysis of multidimensional NOESY data shows that specific cysteines are linked to the α-carbons of the modified residues, forming three sulfur to α-carbon bridges. Complete sequencing of the thuricin CD gene cluster revealed genes capable of encoding two S′-adenosylmethionine proteins that are characteristically associated with unusual posttranslational modifications. Thuricin CD is a two-component antimicrobial peptide system with sulfur to α-carbon linkages, and it may have potential as a targeted therapy in the treatment of CDAD while also reducing collateral impact on the commensal flora.