Anti-biofilm and anti-adherence properties of novel cyclic dipeptides against oral pathogens

Microorganisms embedded in a biofilm are significantly more resistant to antimicrobial agents and the defences of the human immune system, than their planktonic counterpart. Consequently, compounds that can inhibit biofilm formation are of great interest for novel therapeutics. In this study, a screening approach was used to identify novel cyclic dipeptides that have anti-biofilm activity against oral pathogens. Five new active compounds were identified that prevent biofilm formation by the cariogenic bacterium Streptococcus mutans and the pathogenic fungus Candida albicans. These compounds also inhibit the adherence of microorganisms to a hydroxylapatite surface. Further investigations were conducted on these compounds to establish the structure–activity relationship, and it was deduced that the common cleft pattern is required for these molecules to act effectively against biofilms.     

TCP pilus biosynthesis in Vibrio cholera O1: gene sequence of tcpC encoding an outer membrane lipoprotein

The nucleotide sequence of the tcpC gene has been determined. It encodes a 53995-Da protein precursor with a signal sequence and cleavage site typical of a number of outer membrane lipoproteins, which are cleaved by the equivalent of signal peptidase II (Lsp) of Escherichia coli. The location of the tcpC gene is such that it is predicted to be translationally coupled to the 5' and 3' flanking genes, tcpY and tcpD, respectively, indicating that it forms part of an operon. Together with the lipoprotein signal sequence and the several hydrophobic domains it seems likely that TcpC is a surface-anchored trans-outer membrane lipoprotein.     

An efficient microtest to study adherence of bacteria to mammalian cells

A simple, fast and highly reproducible microtest was developed for in vitro adherence studies. A rat epithelial cell line was investigated for the adherence of clinical and subclinical ovine and bovine Staphylococcus aureus strains isolated from mastitis. Staphylococcus aureus strains differed in their ability to adhere to epithelial cells, the degree of adherence being dependent on the concentration of bacteria used in the test.     

Adherence of human neutrophils changes Ca signaling during activation with opsonized particles

Changes in the cytosolic free Ca²⁺ concentration ([Ca²⁺]_i) upon activation of human neutrophils by opsonized particles (serum-treated zymosan; STZ) were evaluated by three different methods: (i) measurement of total fluorescence changes in indo-1 loaded neutrophils activated in suspension; (ii) measurement of fluorescence changes in individual indo-1 loaded neutrophils in a flow cytometer and (iii) measurement of fluorescence changes in individual fura-2 loaded neutrophils adherent to serum-coated coverslips. Our study shows that the opsonized particle-induced change in [Ca²⁺]_i in neutrophils is altered during adherence of the cells to a serum-coated surface. These observations might be of importance for neutrophil function in vivo, since adherence is a prerequisite for diapedesis and chemotaxis.     

双歧杆菌的粘附特性及其对肠道致病菌的体外拮抗作用

本文采用体外细胞培养法, 从实验室现有的20株不同生境来源的双歧杆菌中筛选具有较强粘附能力的菌株, 并通过混合培养和牛津杯方法, 研究了具有粘附特性的双歧杆菌对肠道致病菌的体外拮抗作用。结果显示, 长寿老人源菌株A03和I06的粘附能力最强, 其菌液对金黄色葡萄球菌及大肠杆菌均具有显著的抑制性, 但是菌体及中和后的发酵液均没有抑菌性, 说明受试菌主要通过其代谢产物中的有机酸来发挥其抑菌性能; 此外, 通过分析比较受试菌和肠道致病菌分别与Caco-2细胞粘附后释放的乳酸脱氢酶量, 证实双歧杆菌与致病菌对细胞的作用具有本质上的区别, 双歧杆菌的粘附能减缓致病菌对细胞所造成的损害。     

Adherence and invasion of avian pathogenic <Emphasis Type="Italic">Escherichia coli</Emphasis> to avian tracheal epithelial cells

Avian septicemia is a systemic disease where bacteria attach and invade the avian respiratory tract and enter the bloodstream and vital organs. Avian pathogenic Escherichia coli (APEC) cause this extraintestinal disease utilizing several virulence factors that have been identified. Adhesion to the trachea is the critical initial step for septic APEC pathogenicity. We investigated the ability of APEC to associate with models of tracheal epithelium. The microorganism was able to adhere to an avian tracheal explant model of infection. In addition, a primary cell culture, derived from chicken tracheal epithelium, was developed and demonstrated the ability of APEC to attach to and invade avian tracheal cells in vitro. These results are compatible with the nature of the disease and are important to the understanding of the initial point of entry of APEC in the avian model of septic infections.     

Microcystins -LA, -YR, and -LR action on neutrophil migration

Microcystins (MCs) produced by some freshwater cyanobacterial species possess potent liver toxicity as evidenced by acute neutrophil infiltration. Here, we investigate the ability of three structurally distinct toxins (MC-LA, MC-LR, and MC-YR) to evoke neutrophil recruitment per se and their effects on migration pathways. Intravital microscopic studies showed that topical application of only MC-LR enhanced the numbers of rolling and adhered leukocytes in the endothelium of postcapillary mesenteric venules. The latter effects may be dependent upon induction of the synthesis and expression of l-selectin and β2-integrin in neutrophils, as assessed by flow cytometry and RT-PCR, respectively. Conversely, the three toxins promoted direct locomotion of neutrophils and enhanced their migration in response to fMLP, as measured by Boyden chamber assays, and increased intracellular calcium, a messenger in the chemotaxic process. In conclusion, our results show that MCs act on specific pathways of neutrophil recruitment, indicating their potential effect on neutrophils activation.     

CR1-mediated ATP Release by Human Red Blood Cells Promotes CR1 Clustering and Modulates the Immune Transfer Process

Humans and other higher primates are unique among mammals in using complement receptor 1 (CR1, CD35) on red blood cells (RBC) to ligate complement-tagged inflammatory particles (immune complexes, apoptotic/necrotic debris, and microbes) in the circulation for quiet transport to the sinusoids of spleen and liver where resident macrophages remove the particles, but allow the RBC to return unharmed to the circulation. This process is called immune-adherence clearance. In this study we found using luminometric- and fluorescence-based methods that ligation of CR1 on human RBC promotes ATP release. Our data show that CR1-mediated ATP release does not depend on Ca²⁺ or enzymes previously shown to mediate an increase in membrane deformability promoted by CR1 ligation. Furthermore, ATP release following CR1 ligation increases the mobility of the lipid fraction of RBC membranes, which in turn facilitates CR1 clustering, and thereby enhances the binding avidity of complement-opsonized particles to the RBC CR1. Finally, we have found that RBC-derived ATP has a stimulatory effect on phagocytosis of immune-adherent immune complexes.     

EHEC的新型粘附因子研究进展

肠出血性大肠杆菌（enterohemorrhage E-coli,EHEC）是一种重要的人畜共患病,世界各地包括中国都有不同规模的暴发流行。EHEC有多种血清型,其中毒力最强血清型是0157：H7。EHEC0157：H7感染除可使人发生常规腹泻外,还可在5％-10％的病例中引发严重并发症,甚至死亡。该菌是重要的食源性致病菌,危害严重,缺乏有效的防治手段,而抗生素治疗可能会加剧溶血性尿毒症（haemoluticuraemicsyndrome,HUS）。由于以上特点EHEC0157：H7成为世界公共卫生问题,引起微生物学家和公共卫生工作者的广泛关注。目前,临床针对EHEC感染只是对症治疗和适当的抗茵治疗。粘附是EHEC感染宿主细胞的第一步,没有这一步,细菌和宿主肠道细胞之间不会发生任何的相互作用,而且对于许多病原菌来说,粘附具有宿主特异性。本文概述了EHEC的流行病学及粘附机理,并对近年在EHEC研究中的发现一些新型粘附因子和一些假设的定植因子的研究背詈及作用机理作一综述。