Helicobacter pylori Adapts to Chronic Infection and Gastric Disease via pH-Responsive BabA-Mediated Adherence

International audienceThe BabA adhesin mediates high-affinity binding of Helicobacter pylori to the ABO blood group antigen-glycosylated gastric mucosa. Here we show that BabA is acid responsive-binding is reduced at low pH and restored by acid neutralization. Acid responsiveness differs among strains; often correlates with different intragastric regions and evolves during chronic infection and disease progression; and depends on pH sensor sequences in BabA and on pH reversible formation of high-affinity binding BabA multimers. We propose that BabA's extraordinary reversible acid responsiveness enables tight mucosal bacterial adherence while also allowing an effective escape from epithelial cells and mucus that are shed into the acidic bactericidal lumen and that bio-selection and changes in BabA binding properties through mutation and recombination with babA-related genes are selected by differences among individuals and by changes in gastric acidity over time. These processes generate diverse H. pylori subpopulations, in which BabA's adaptive evolution contributes to H. pylori persistence and overt gastric disease

Psykisk ohälsa - interventioner och möjligheter för evidensbaserad omvårdnad

Inledning: Psykisk ohälsa är ett växande problem som ses hos både individer och i samhället i stort, det medför stora kostnader och lidande för individer och anhöriga. Många av de med psykisk ohälsa söker hjälp i primärvården men primärvården är dåligt rustade för att hjälpa dessa personer. Distriktssköterskor träffar en stor del av befolkningen och därmed många människor med psykisk ohälsa. Med anledning av detta önskar uppsatsen beskriva distriktssköterskans arbete med patienter som upplever psykisk ohälsa. Syfte: Syftet med denna studie är att sammanställa och analysera forskning om distriktssköterskors omvårdnad riktad till patienter som upplever psykisk ohälsa, ur ett primärvårdsperspektiv. Metod: Forskningsplanen är utformad som en systematisk litteraturstudie med både kvalitativa och kvantitativa data, Mixed methods. Sökning av vetenskapliga artiklar utfördes i databaserna CINAHL och PubMed, tio artiklar valdes ut till en pilotstudie. Fyra interventionsstudier respektive sex beskrivande kvalitativa och kvantitativa artiklar inkluderades. Resultat: Resultatet visade att interventioner för utbildning i själv-hjälp upplevdes som positiva och hade i varierad utsträckning effekt. Utifrån andra interventioner sågs att sjuksköterskor och distriktssköterskor hade en samordnande funktion. Förutsättningar i omvårdnaden identifierades utifrån att distriktsköterskor och sjuksköterskor var involverade i vården av patienter med upplevd psykisk ohälsa och att ett kunskapsbehov fanns. Diskussion: Distriktssköterskor och sjuksköterskor är och bör vara involverade i arbetet med psykisk ohälsa. Kompetens, position och tillgänglighet möjliggör för och gör distriktssköterskor lämpliga att arbeta med psykisk ohälsa

Congestion control in wireless cellular networks

Through the introduction of the third generation of mobile cellular network technologies a major step towards a ubiquitious and wireless access to the Internet has been taken. There are however still challenges due to the different characteristics and prerequisites of wired and wireless networks. An important network element is congestion control. The purpose of congestion control is to ensure network stability and achieve a reasonably fair distribution of the network resources among the users. TCP is a well-established protocol, which offers reliable transport of data and applies congestion control. With regards to TCP it is of interest to follow up on proposed changes to the protocol and to learn how to tune wireless networks for optimal TCP performance, since its usage is wide spread. We have performed a study of buffer management for TCP with High Speed Downlink Packet Access (HSDPA) and evaluated the effect of reducing the lower bound of the retransmit timeout interval in an environement with varying capacity. A number of the features that TCP consist of introduce arbitrarily delay, therefore reliable transport is sometimes traded for less delay variations by applications with strict timing requirements. Until recently UDP has been the main alternative to TCP. UDP does not provide any service guarantees, nor congestion control, but does on the other hand not introduce any delay in itself. There are however concerns that increased usage of UDP would cause network instability and starve the TCP flows that reduce their send rate when competition intensifies. Therefore a new transport protocol called the Datagram Congestion Control Protocol (DCCP) is being designed to provide applications that do not desire the service model of TCP with an alternative. Currently, DCCP includes two profiles for congestion control, TFRC and TCP-like. For these new algorithms verifying the design, identifying weaknesses and suggesting improvements, as I have done, is important in order to drive the development forward. Through the studies that comprise this thesis, I contribute to the stable operation of the future Internet and the merging with wireless cellular data architectures.Godkänd; 2005; 20070102 (haneit

TCP/IP technology for modern network environments

To facilitate the merging of wireless access technologies and the traditional Internet, the core protocols for data communication should be robust and have low overhead. In this thesis, we propose refinements to the Transmission Control Protocol (TCP) that improve its cost efficiency over wireless links.TCP is unable to distinguish between congestion and error induced losses, reordered, or delayed segments. A reordering robust TCP would make it possible to simplify network elements, now performing explicit actions to prevent reordering, and open up for deployment of new technologies that naturally cause reordering. We propose TCP-Aix; a set of TCP modifications that improves the robustness of TCP to reordering and delay spikes. TCP-Aix decouples loss recovery and congestion control actions. We also present an algorithm called the winthresh algorithm for computing a duplicate acknowledgment threshold based on TCP buffer space and current send window size. The results show that TCP-Aix with the winthresh algorithm is able to maintain almost constant performance even in scenarios frequently displaying long reordering durations. It is also fair towards competing standards-compliant TCP flows.In wireless networks, where the links out of efficiency constraints are more error prone than wired links, the error and the reordering sensitivity of TCP have motivated link layer protocols that perform retransmissions and enforce in-order delivery. We investigate the potential gains of using a reordering robust TCP, like TCP-Aix, with a wireless link layer that allows out-of-order delivery, compared to using in-order delivery with a standardscompliant TCP. We found that the smoothness of TCP is strongly affected by the link layer configuration. In-order delivery leads to burstier traffic and larger network layer buffering needs, than out-of-order delivery and TCP-Aix. The interference and power consumption in foremost wireless networks make it important to reduce the communication overhead. The TCP receiver acknowledges each or every second segment. We study how to reduce the acknowledgment frequency while preserving throughput performance also in wireline networks where frequent acknowledgments generally are not problematic. To preserve throughput, the sender should use byte counting and be involved in determining the acknowledgment frequency. The results show that acknowledging four segments per send window is sufficient to maintain throughput performance also in wireline scenarios. This indicates that a lower acknowledgment frequency than provided through the delayed acknowledgment algorithm is possible today for general usage.A key service to the successful merging of traditional Internet technology and wireless cellular networks is Voice over IP (VoIP). Channels to be shared by both VoIP and TCP-based traffic is being considered for wireless cellular systems. It is challenging to provide VoIP over a shared wireless cellular channel, because VoIP is a low bitrate service with high demands on channel availability to bound the delay. The scheduling algorithm, controlling access to the channel, is central to achieve efficiency as well as to satisfy user demands. We study how a scheduler for a mix of VoIP and interactive (TCP-based) traffic should be designed for High Speed Downlink Packet Access (HSDPA). In particular, we find that slowly increasing the priority of a VoIP session relative TCP-based services is important to take advantage of the varying network conditions.Godkänd; 2008; 20080520 (ysko)</p