Combating Biofilm Associated Infection In Vivo: Integration of Quorum Sensing Inhibition and Photodynamic Treatment based on Multidrug Delivered Hollow Carbon Nitride Sphere

Recently, quorum sensing (QS) inhibitors (QSIs) have been combined with antibiotics to enhance antibiofilm efficacy in vitro and in vivo. However, targeting QS signals alone is not enough to prevent bacterial infections. Drug resistance and recurrence of biofilms makes it difficult to eradicate. Herein, photodynamic therapy (PDT) is selected to unite QSIs and antibiotics. A synergistically antibiofilm system, which combines QSIs, antibiotics, and PDT based on hollow carbon nitride spheres (HCNSs) is envisaged. First, HCNS provides the multidrug delivering ability, enabling QSIs and antibiotics to be released in sequence. Subsequently, multistage releases sensitize bacteria effectively, potentiating the chemotherapeutic effects of the antibiotics. Finally, the integration of QSIs and PDT not only minimizes the possibility of drug resistance, but also overcomes the problem of limited mass and extension of PDT. Even after 48 h of incubation, the bacterial biofilm is obviously inhibited. And its biofilm disperse efficiency exceeds 48% (compared with QSI‐potentiated chemotherapy group) and 40% (compared with PDT group). Besides, the inhibition of the QS system influences phenotypes related to virulence factor production and surface hydrophobicity, which weaken biofilm invasion and formation. Eventually, this system is applied to disperse bacterial biofilm in vivo. Overall, PDT and QS modulation are devoted to eradicate drug resistance and recurrence of the biofilm.     

基于门限签名方案的BQS系统的服务器协议

利用冗余复制技术,BQS(Byzantine quorum system)系统在异步信道上提供了能容忍f台服务器拜占庭失效的存储服务.COCA系统和CODEX系统设计了一种结合门限签名方案和BQS系统的服务器协议,完成了TSS-BQS(threshold signature schemes-BQS)系统.与普通BQS系统相比,具有更易于支持Proactive Recovery,简化客户端密钥管理和客户端通信的优点.基于相同的系统模型和信道假设,提出了一种新的服务器协议,满足TSS-BQS系统的安全要求;而且与已有协议相比,该协议只需更少的通信轮数,在读/写并发情况下执行效果 更优.     

TSS-BQS系统的Graceful Degradation机制

将门限签名方案分别应用于两种类型的BQS系统(Masking BQS系统和Dissemination BQS系统),可以得到两种TSS- BQS系统(文中称为TSS- mBQS系统和TSS- dBQS系统).TSS-mBQS系统的性能优于TSS- dBQS系统.由此,作者提出了TSS- BQS系统的Graceful Degradation机制:系统由n=3fd+1台服务器组成,在初始阶段以TSS-mBQS状态运行,容忍fm=[fd/2]台Byzantine失效服务器;随着系统运行,可能失效的服务器数量增大,则以降低性能为代价,切换到TSS- dBQS状态,容忍fd台Byzantine失效服务器.在不影响容错能力的前提下,Graceful Degradation机制提高了已有TSS- BQS系统的平均性能.文中完成的Graceful Degradation机制能够在不中断存储服务、不影响客户端的前提下完成状态切换,客户端也不需要知道系统的运行状态(处于TSS- mBQS或TSS- dBQS状态).     

Analyzing User-Perceived Dependability and Performance Characteristics of Voting Algorithms for Managing Replicated Data

User-perceived dependability and performance metrics are very different from conventional ones in that the dependability and performance properties must be assessed from the perspective of users accessing the system. In this paper, we develop techniques based on stochastic Petri nets (SPN) to analyze user-perceived dependability and performance properties of quorum-based algorithms for managing replicated data. A feature of the techniques developed in the paper is that no assumption is made regarding the interconnection topology, the number of replicas, or the quorum definition used by the replicated system, thus making it applicable to a wide class of quorum-based algorithms. We illustrate this technique by comparing conventional and user-perceived metrics in majority voting algorithms. Our analysis shows that when the user-perceiveness is taken into consideration, the effect of increasing the network connectivity and number of replicas on the availability and dependability properties perceived by users is very different from that under conventional metrics. Thus, unlike conventional metrics, user-perceived metrics allow a tradeoff to be exploited between the hardware invested, i.e., higher network connectivity and number of replicas, and the performance and dependability properties perceived by users.     

Dental Chatter: Bacterial Cross-Talk in the Biofilm of the Oral Cavity

Dental biofilms are composed of hundreds of bacterial species. These biofilms are diverse biological structures due to the heterogeneity of the many different types of supports in the oral cavity. The bacteria immobilized in these biofilms are exposed to rapid environmental changes such as pH, temperature, nutrition and anti-plaque agents. One mode in which these bacteria adapt in the dental biofilm is by quorum sensing. This cell-cell communication regulates diverse sets of adhesion modes, physiological changes, virulence properties, allowing the bacteria to persist in the dental biofilm under rapid environmental changes. In this review, we will concentrate mostly on the cariogenic bacterium Streptococcus mutans as one of the pivotal microorganisms in the supra-gingival biofilm that plays a major role in dental caries.     

Spoilage of refrigerated (4 °C) Litopenaeus vannamei: cooperation between Shewanella species and contribution of cyclo‐(L‐Pro‐L‐Leu)‐dependent quorum sensing

The spoilage potential of Shewanella putrefaciens and S. baltica isolated from spoiled refrigerated Litopenaeus vannamei was evaluated by in vitro assays for trimethylamine oxide reduction, extracellular hydrolytic enzymes and biofilm formation, and in vivo inoculation into surface‐sterilised shrimp followed by microbial, biochemical and sensory analyses during storage for 5 days at 4 °C. S. baltica displayed higher spoilage potential than S. putrefaciens both in vitro and in vivo. Shrimp co‐inoculated with them had one‐day shorter shelf life than those mono‐inoculated, based on the results of bacterial density, volatile base nitrogen, trimethylamine, volatile organic compounds and sensory analysis, which strongly suggests cooperation of Shewanella species in shrimp spoilage. Exogenous cyclo‐(L‐Pro‐L‐Leu) boosted bacterial growth, extracellular protease and collagenase activities, and biofilm formation of S. putrefaciens and S. baltica at least before they entered the stationary phase, indicating that cyclo‐(L‐Pro‐L‐Leu)‐dependent quorum sensing, a recently suggested communication mechanism between them, contributes to the cooperation.     

维氏气单胞菌中AHLs介导的群体感应现象及大蒜提取物的干扰作用

以发酵鱼糜中分离的1株维氏气单胞菌为对象,分析该菌中N-酰基高丝氨酸内酯(AHLs)介导的群体感应现象,研究大蒜提取物作为群体感应抑制剂对该菌群体感应及腐败能力的干扰作用.结果表明,维氏气单胞菌至少产生3种AHLs信号分子,即C6-HSL、C7-HSL和C8-HSL.在细菌快速生长阶段,AHLs分子的活性不断增加;当细...     

真菌群体感应分子法尼醇及其作用机制

群体感应(quorum sensing,QS)是取决于细胞密度的微生物通信机制,可调节细菌毒力因子分泌、生物膜形成、感受态和生物发光等行为。真菌群体感应系统10年前在法尼醇控制致病多态性真菌白色念珠菌中的细丝化研究中被发现。研究显示法尼醇作为群体感应分子(QSM)对宿主和其他微生物发挥多种作用;还发现芳香醇酪醇是控制白色念珠菌生长、形态发生和生物膜形成的另一群体感应分子。在酿酒酵母中,发现另两种芳香醇苯乙醇和色氨酸是在氮饥饿条件下调节形态发生的群体感应分子。此外,类似于群体感应的种群密度依赖性行为已在几种其他真菌中描述。本综述总结了目前发现群体感应效应的几种关键真菌物种,并重点阐述了研究较多的白色念珠菌和法尼醇作用的微观机制研究进展。     

钝顶螺旋藻提取物对细菌群体感应的抑制作用

以mini-Tn5突变株Chromobacterium violaceum CV026为报告菌检测系统,研究钝顶螺旋藻甲醇提取物的群体感应抑制活性及对大菱鲆腐败菌Shewanella putrefacens生物膜形成的影响。结果表明:螺旋藻75%甲醇提取物(0.125～1.000g/100mL)不仅能显著降低Chromobacterium violaceum CV026细菌紫色菌素的产生,而且能显著抑制外源信号分子N-已酰化高丝氨酸内酯(10μmol/L C6-HSL)诱导的报告菌紫色菌素的增加。当螺旋藻提取物添加质量浓度为1.000g/100mL时,对报告菌紫色菌素的抑制率达87.67%,对Shewanella putrefacens生物膜的形成抑制率达77.05%,与对照差异均达显著水平(P<0.05)。抑菌实验表明,在给定的质量浓度范围内,螺旋藻提取物对报告菌的生长无显著影响;螺旋藻提取物抑制紫色色素的产生与生物膜的形成不是通过抑制细菌的生长来实现的,而与抑制信号分子诱导的群体感应现象有关;螺旋藻提取物具有较强的细菌群体感应抑制活性,可作为细菌群体感应抑制剂用于新鲜食品及其制品的贮藏与保鲜。