SOS response induction by beta-lactams and bacterial defense against antibiotic lethality

The SOS response aids bacterial propagation by inhibiting cell division during repair of DNA damage. We report that inactivation of the ftsI gene product, penicillin binding protein 3, by either beta-lactam antibiotics or genetic mutation induces SOS in Escherichia coli through the DpiBA two-component signal transduction system. This event, which requires the SOS-promoting recA and lexA genes as well as dpiA, transiently halts bacterial cell division, enabling survival to otherwise lethal antibiotic exposure. Our findings reveal defective cell wall synthesis as an unexpected initiator of the bacterial SOS response, indicate that beta-lactam antibiotics are extracellular stimuli of this response, and demonstrate a novel mechanism for mitigation of antimicrobial lethality.     

Peptidoglycan in the cell wall of the primary intracellular symbiote of the pea aphid

Primary intracellular symbiotes of the pea aphid, Acyrthosiphon pisum (Harris), when fixed with potassium permanganate, revealed a distinctly staining area between the cytoplasmic membrane and the outer cell-wall envelope. This area is thought to be analogous to the peptidoglycan complex of the Eubacteriales. In addition, the diagnostic bacterial peptidoglycan amino compounds, muramic acid and diaminopimelic acid, were detected in a hydrochloric acid hydrolyzate of isolated symbiotes.     

新疆某猪场分离的大肠杆菌对抗生素耐药性调查

【目的】调查新疆某规模化养猪场分离的大肠杆菌对临床常用抗生素的耐药情况。【方法】对养殖场粪样中分离出的大肠杆菌,采用微量肉汤稀释法,测定最小抑菌浓度。【结果】从该猪场共采集543份粪样,分离到454株大肠杆菌。分离的大肠杆菌对临床常用抗菌药物有不同程度的耐药。其中,对氨苄西林和阿莫西林/克拉维酸耐药率最高,达60.0%以上;对头孢噻呋最敏感,耐药率也达10.8%;3耐以上的菌株占64.5%。【结论】该猪场大肠杆菌对常用抗生素耐药情况较为严重,须在临床治疗细菌性疾病中避开使用不敏感的抗生素。     

肠道病原性大肠杆菌和宿主细胞间的相互作用

肠道病原性大肠杆菌(EPEC)属于胞外菌,主要通过粘附在肠上皮细胞上引起宿主的发病。EPEC形成基座、产生粘附和脱落(A/E)损伤的细菌因子、导致宿主信号转导改变的途径及其发病机制的遗传基础都已经得到广泛的研究。对近年来关于EPEC和宿主细胞间的相互作用的研究进展进行总结,并着重论述EPEC对于肠上皮细胞紧密连接的影响。     

A stochastic single-molecule event triggers phenotype switching of a bacterial cell

By monitoring fluorescently labeled lactose permease with single-molecule sensitivity, we investigated the molecular mechanism of how an Escherichia coli cell with the lac operon switches from one phenotype to another. At intermediate inducer concentrations, a population of genetically identical cells exhibits two phenotypes: induced cells with highly fluorescent membranes and uninduced cells with a small number of membrane-bound permeases. We found that this basal-level expression results from partial dissociation of the tetrameric lactose repressor from one of its operators on looped DNA. In contrast, infrequent events of complete dissociation of the repressor from DNA result in large bursts of permease expression that trigger induction of the lac operon. Hence, a stochastic single-molecule event determines a cell's phenotype.     

On the origin of bacterial resistance to penicillin: comparison of a beta-lactamase and a penicillin target

Structural data are now available for comparing a penicillin target enzyme, the D-alanyl-D-alanine-peptidase from Streptomyces R61, with a penicillin-hydrolyzing enzyme, the beta-lactamase from Bacillus licheniformis 749/C. Although the two enzymes have distinct catalytic properties and lack relatedness in their overall amino acid sequences except near the active-site serine, the significant similarity found by x-ray crystallography in the spatial arrangement of the elements of secondary structure provides strong support for earlier hypotheses that beta-lactamases arose from penicillin-sensitive D-alanyl-D-alanine-peptidases involved in bacterial wall peptidoglycan metabolism.     

利用GFP标记对OsWAK1蛋白胞外区的鉴定

水稻OsWAK1编码一细胞壁相联的受体类似蛋白激酶,对其推断的氨基酸进行预测,其结构组成包括胞外区、跨膜区和胞内激酶区。推断OsWAK1蛋白胞外区与配体识别并结合,是胞外信号传递到胞内的信号转导途径中的重要环节,因此OsWAK1蛋白的胞外区是OsWAK1发挥其生物学功能所必需的。将预测的OsWAK1蛋白胞外区与GFP构建为融合蛋白,通过融合蛋白在烟草细胞中的定位确定OsWAK1蛋白结构上含有预测的胞外区。     

植酸对大肠杆菌抑菌机理的研究

为了研究植酸对大肠杆菌的抑菌机理,测定了植酸对大肠杆菌的抑菌效果、最小抑菌浓度、细菌生长曲线、菌液碱性磷酸酶(AKP)含量及电导率,并观察了细菌超微结构。结果表明,植酸对大肠杆菌有较强的抑菌效果,且随着浓度的增大而增强,植酸对大肠杆菌的最低抑菌浓度(体积分数)为0.4%;与不添加植酸的对照相比,植酸改变了大肠杆菌的生长规律,使细胞破损严重,细胞壁和细胞膜通透性增加,细胞质外渗,菌液中AKP含量和电导率增大。     

Selective cleavage of D-Ala-D-Lac by small molecules: re-sensitizing resistant bacteria to vancomycin

Pathogenic enterococci are becoming resistant to currently available antibiotics, including vancomycin, the drug of last resort for Gram-positive infections. Enterococci pose a significant public health threat, not least because of the risk of transferring vancomycin resistance to the ubiquitous Staphylococcus aureus. Vancomycin resistance is manifested by cell wall peptidoglycan precursors with altered termini that cannot bind the antibiotic. Small molecules with well-oriented nucleophile-electrophile assembly and complementary chirality to the peptidoglycan termini were identified as catalytic and selective cleavers of the peptidoglycan precursor depsipeptide. These molecules were tested in combination with vancomycin and were found to re-sensitize vancomycin-resistant bacteria to the antibiotic.     

G protein signalling involved in host recognition and mycoparasitismrelated chitinase expression in Trichoderma atroviride

Mycoparasitic species of Trichoderma are commercially applied as biological control agents against various fungal pathogens. The mycoparasitic interaction is host specific and includes recognition, attack and subsequent penetration and killing of the host. Investigations on the underlying events revealed that Trichoderma responds to multiple signals from the host (e.g. lectins or other ligands such as low molecular weight components released from the host's cell wall) and host attack is ac…     

Chimeric NGF-EGF receptors define domains responsible for neuronal differentiation

To determine the domains of the low-affinity nerve growth factor (NGF) receptor required for appropriate signal transduction, a series of hybrid receptors were constructed that consisted of the extracellular ligand-binding domain of the human epidermal growth factor (EGF) receptor (EGFR) fused to the transmembrane and cytoplasmic domains of the human low-affinity NGF receptor (NGFR). Transfection of these chimeric receptors into rat pheochromocytoma PC12 cells resulted in appropriate cell surface expression. Biological activity mediated by the EGF-NGF chimeric receptor was assayed by the induction of neurite outgrowth in response to EGF in stably transfected cells. Furthermore, the chimeric receptor mediated nuclear signaling, as evidenced by the specific induction of transin messenger RNA, an NGF-responsive gene. Neurite outgrowth was not observed with chimeric receptors that contained the transmembrane domain from the EGFR, suggesting that the membrane-spanning region and cytoplasmic domain of the low-affinity NGFR are necessary for signal transduction.     

Single-Stranded DNA Binding Protein Encoded by the virE Locus of Agrobacterium tumefaciens

The transfer process of T (transfer)-DNA of Agrobacterium tumefaciens is activated after the induction of the expression of the Ti plasmid virulence (vir) loci by plant signal molecules such as acetosyringone. The vir gene products then act to generate a free transferable single-stranded copy of the T-DNA, designated the T-strand. Although some vir proteins are responsible for the synthesis of the T-strand, others may mediate T-strand transfer to plant cells as part of a DNA-protein complex. Here, a novel 69-kilodalton vir-specific single-stranded DNA binding protein is identified in Agrobacterium harboring a nopaline-type Ti plasmid. This protein binds single-stranded but not double-stranded DNA regardless of nucleotide sequence composition. The molecular size of the vir-specific single-stranded DNA binding protein and its relative abundance in acetosyringone-induced Agrobacterium suggested that it might be the product of the virE locus; molecular cloning and expression of the virE region in Escherichia coli confirmed this prediction.     

Structure of tracheal cytotoxin in complex with a heterodimeric pattern-recognition receptor

Tracheal cytotoxin (TCT), a naturally occurring fragment of Gram-negative peptidoglycan, is a potent elicitor of innate immune responses in Drosophila. It induces the heterodimerization of its recognition receptors, the peptidoglycan recognition proteins (PGRPs) LCa and LCx, which activates the immune deficiency pathway. The crystal structure at 2.1 angstrom resolution of TCT in complex with the ectodomains of PGRP-LCa and PGRP-LCx shows that TCT is bound to and presented by the LCx ectodomain for recognition by the LCa ectodomain; the latter lacks a canonical peptidoglycan-docking groove conserved in other PGRPs. The interface, revealed in atomic detail, between TCT and the receptor complex highlights the importance of the anhydro-containing disaccharide in bridging the two ectodomains together and the critical role of diaminopimelic acid as the specificity determinant for PGRP interaction.     

鸡大肠杆菌(HJ20株)与人大肠杆菌(RHU845)P型菌毛同源性分析

运用Goldkey电脑软件对鸡源大肠杆菌与人源大肠杆菌P型菌毛蛋白结构基因序列、氨基酸序列、二级结构进行了比较分析,二者结构基因序列相似性82.5%.二者P型菌毛的信号肽序列基本相同,氨基酸序列相似性83.7%,并且菌毛蛋白在二级结构上存在较多的相似性.     

禽致病菌ESBLs和AmpC酶的检测及药敏分析

用全自动微生物鉴定系统(VITEK-32)鉴定了禽分离致病菌,分别进行了β-内酰胺酶(BLA)、超广谱β-内酰胺酶(ESBLs)、AmpC酶的检测,并用试管两倍稀释法测定了各种抗生素对非产酶菌、产ESBLs菌及产AmpC菌的抗菌活性。结果表明,鉴定分离的20株致病菌有大肠埃希菌15株、阴沟肠杆菌1株、铜绿假单胞菌1株、法氏柠檬酸杆菌1株、肺炎克雷伯菌1株及鹑鸡肠球菌1株,其中法氏柠檬酸杆菌、肺炎克雷伯菌及鹑鸡肠球菌系兽医上首次检出。报道所分离的20株致病菌均产β-内酰胺酶,其中产ESBLs 9株,同时产ESBLs和AmpC酶1株。产酶菌株对抗生素的耐药性严重,而抗生素/抑制剂联用能降低药物对细菌的MICs。     

Expression of streptococcal M protein in Escherichia coli

The structural gene for group A streptococcal M protein, the fibrillar surface molecule enabling the organism to resist phagocytosis, has been cloned into Escherichia coli. The molecule produced by Escherichia coli is slightly larger than the M protein isolated by solubilization of the streptococcal cell wall, but is similar in size to that secreted by streptococcal protoplast and L forms. Immunologically, the molecule synthesized by Escherichia coli has the same type-specific determinants as the streptococcal M protein.     

利用放线菌固态发酵生产农用抗生素的初步研究

采用杯碟法研究了4株拮抗性放线菌固态和液态发酵产物对辣椒疫霉病菌(Phytophthoracapsici)、金黄色葡萄球菌(Staphylococcusaureaus)、埃希氏大肠杆菌(Escherichiacoli)及青霉(Penicillium)4株供试靶标菌的抑菌活性。结果表明,利用放线菌固态发酵生产农用抗生素的思路是可行的。供试的04,07和08号3株放线菌大米固态发酵产物与黄豆粉液态发酵产物对靶标菌金黄色葡萄球菌(Staphylococcusaureaus)的相对抑菌环宽度分别为4.0mm/g与0.7mm/mL,对埃希氏大肠杆菌(Escherichiacoli)的相对抑菌环宽度分别为5.2mm/g与1.1mm/mL,供试菌固态发酵抗生素活性远大于液态发酵,表明通过固态发酵提高抗生素得率的设想在微生物合成阶段是可以实现的。同时还发现,固态与液态两种发酵模式对某些抗生素的合成有极显著影响。