Tues 10th November, 8pm GMT

Tuesday’s #microtwjc (8pm GMT) will be looking at this paper:

Active Transport of Phosphorylated Carbohydrates Promotes Intestinal Colonization and Transmission of a Bacterial Pathogen

Brandon Sit , Shauna M. Crowley , Kirandeep Bhullar, Christine Chieh-Lin Lai, Calvin Tang, Yogesh Hooda, Charles Calmettes, Husain Khambati, Caixia Ma, John H. Brumell, Anthony B. Schryvers, Bruce A. Vallance , Trevor F. Moraes

 

Abstract

Efficient acquisition of extracellular nutrients is essential for bacterial pathogenesis, however the identities and mechanisms for transport of many of these substrates remain unclear. Here, we investigate the predicted iron-binding transporter AfuABC and its role in bacterial pathogenesis in vivo. By crystallographic, biophysical and in vivo approaches, we show that AfuABC is in fact a cyclic hexose/heptose-phosphate transporter with high selectivity and specificity for a set of ubiquitous metabolites (glucose-6-phosphate, fructose-6-phosphate and sedoheptulose-7-phosphate). AfuABC is conserved across a wide range of bacterial genera, including the enteric pathogens EHEC O157:H7 and its murine-specific relative Citrobacter rodentium, where it lies adjacent to genes implicated in sugar sensing and acquisition. C. rodentium ΔafuA was significantly impaired in an in vivo murine competitive assay as well as its ability to transmit infection from an afflicted to a naïve murine host. Sugar-phosphates were present in normal and infected intestinal mucus and stool samples, indicating that these metabolites are available within the intestinal lumen for enteric bacteria to import during infection. Our study shows that AfuABC-dependent uptake of sugar-phosphates plays a critical role during enteric bacterial infection and uncovers previously unrecognized roles for these metabolites as important contributors to successful pathogenesis.

Author Summary

Essentially all Gram-negative pathogens are reliant on specific transport machineries termed binding protein-dependent transporters (BPDTs) to transport solutes such as amino acids, sugars and metal ions across their membranes. In this study we investigated AfuABC, a predicted iron-transporting BPDT found in many bacterial pathogens. We show by structural and functional approaches that AfuABC is not an iron transporter. Instead, AfuABC is a trio of proteins that bind and transport sugar-phosphates such as glucose-6-phosphate (G6P). In doing so, we present the first structural solution of a G6P-specific transport protein and add to the few known unique machineries for sugar-phosphate uptake by bacteria. Furthermore, we show that AfuABC is required by the intestinal pathogen C. rodentium to effectively transmit between mice and re-establish infection, leading us to propose that the transport of sugar-phosphates is an important part of general bacterial pathogenesis.

 

Discussion points to follow…

#microtwjc 10/03/2015 8pm

Hi all

Sorry for the brief hiatus but hopefully we are back up and running and on Tues we will be looking at this paper

A Novel Mechanism of Bacterial Toxin Transfer within Host Blood Cell-Derived Microvesicles

Ståhl A-l, Arvidsson I, Johansson KE, Chromek M, Rebetz J, et al. (2015) A Novel Mechanism of Bacterial Toxin Transfer within Host Blood Cell-Derived Microvesicles. PLoS Pathog 11(2): e1004619. doi: 10.1371/journal.ppat.1004619

Abstract

Shiga toxin (Stx) is the main virulence factor of enterohemorrhagic Escherichia coli, which are non-invasive strains that can lead to hemolytic uremic syndrome (HUS), associated with renal failure and death. Although bacteremia does not occur, bacterial virulence factors gain access to the circulation and are thereafter presumed to cause target organ damage. Stx was previously shown to circulate bound to blood cells but the mechanism by which it would potentially transfer to target organ cells has not been elucidated. Here we show that blood cell-derived microvesicles, shed during HUS, contain Stx and are found within patient renal cortical cells. The finding was reproduced in mice infected with Stx-producing Escherichia coliexhibiting Stx-containing blood cell-derived microvesicles in the circulation that reached the kidney where they were transferred into glomerular and peritubular capillary endothelial cells and further through their basement membranes followed by podocytes and tubular epithelial cells, respectively. In vitro studies demonstrated that blood cell-derived microvesicles containing Stx undergo endocytosis in glomerular endothelial cells leading to cell death secondary to inhibited protein synthesis. This study demonstrates a novel virulence mechanism whereby bacterial toxin is transferred within host blood cell-derived microvesicles in which it may evade the host immune system.

Author Summary

Shiga toxin-producing enterohemorrhagic Escherichia coli are non-invasive bacteria that, after ingestion, cause disease by systemic release of toxins and other virulence factors. These infections cause high morbidity, including hemolytic uremic syndrome with severe anemia, low platelet counts, renal failure, and mortality. The most common clinical isolate is E. coli O157:H7. In 2011 an E. coli O104:H4 strain caused a large outbreak in Europe with high mortality. After Shiga toxin damages intestinal cells it comes in contact with blood cells and thus gains access to the circulation. In this study we have shown that the toxin is released into circulating host blood cell-derived microvesicles, in which it retains its toxicity but evades the host immune response. Our results suggest that these microvesicles can enter target organ cells in the kidney and transfer toxin into these cells as well as between cells. Such a mechanism of virulence has not been previously described in bacterial infection.

Discussion Points

1. Is the paper well/clearly written?
2. Were the experiments appropriate?  Were there any extras you would like to see in the paper?  Were any stats used appropriate?
3. What impact will the results have on a wider field?  Where else might you look for this mechanism?
4. Any other further experiments you would like to do?
5. Any other comments?

Hope to see you there…

#microtwjc week 53 – more Salmonella, but this time from an evolution/vaccine perspective

Hi all

The next #microtwjc will take place on Tues 12th August at 8pm BST (and won’t clash with the Great British Bake Off this series!)

We will be looking at another Salmonella paper but this paper focuses on population dynamics: both a mechanism to study the dynamics and how vaccination interacts with them.  The paper can be found here

Independent Bottlenecks Characterize Colonization of Systemic Compartments and Gut Lymphoid Tissue by Salmonella

Chee Han Lim, Sabrina Voedisch, Benjamin Wahl, Syed Fazle Rouf, Robert Geffers, Mikael Rhen, Oliver Pabst

Abstract

Vaccination represents an important instrument to control typhoid fever in humans and protects mice from lethal infection with mouse pathogenic serovars of Salmonella species. Mixed infections with tagged Salmonella can be used in combination with probabilistic models to describe the dynamics of the infection process. Here we used mixed oral infections with taggedSalmonella strains to identify bottlenecks in the infection process in naïve and vaccinated mice. We established a next generation sequencing based method to characterize the composition of tagged Salmonella strains which offers a fast and reliable method to characterise the composition of genome-tagged Salmonella strains. We show that initial colonization ofSalmonella was distinguished by a non-Darwinian selection of few bacteria setting up the infection independently in gut associated lymphoid tissue and systemic compartments. Colonization of Peyer’s patches fuels the sustained spread of bacteria into mesenteric lymph nodes via dendritic cells. In contrast, infection of liver and spleen originated from an independent pool of bacteria. Vaccination only moderately reduced invasion of Peyer’s patches but potently uncoupled bacterial populations present in different systemic compartments. Our data indicate that vaccination differentially skews the capacity of Salmonella to colonize systemic and gut immune compartments and provide a framework for the further dissection of infection dynamics.

 

Author Summary

Pathogens have evolved strategies to invade, replicate and spread within their hosts. On the contrary, vertebrates have developed sophisticated immune defence mechanisms that limit, and ideally clear, the infection. This dynamic interplay between host and pathogens determines the course of the infection and the development of clinical disease. Knowledge on particularly vulnerable steps in the infection process, i.e. the “Achilles heel” of a pathogen, may guide the development of anti-infective therapies and vaccines. However, for most pathogens we lack detailed information on the dynamics of the infection process. Here we determined bottlenecks, i.e. critical steps during pathogen invasion and spread, after oral Salmonella infection in non-manipulated and vaccinated mice. We infected mice with mixtures of tagged Salmonella strains and analysed the strain composition in different compartments by high throughput sequencing. This information allowed us to estimate the number of Salmonella invading a given tissue and to describe routes of pathogen dissemination. We show that vaccination only modestly reduces invasion of intestinal lymphoid tissue but had a profound effect on the spread of Salmonella to systemic compartments.

 

Discussion Points

1. Was the paper clearly written, figures clear etc?
2. Was the method sound? How novel was it? Does it have other applications?
3. Are the conclusions supported by the results
4. What further work would you do? Would you use the method to study something else? What questions does it raise about vaccination?

 

#microtwjc week 45

Hi all.

Tuesday’s #microtwjc paper is this one:

Clonal Expansion during Staphylococcus aureus Infection Dynamics Reveals the Effect of Antibiotic Intervention

Gareth McVicker, Tomasz K. Prajsnar, Alexander Williams, Nelly L. Wagner, Michael Boots, Stephen A. Renshaw, Simon J. Foster

Abstract:

To slow the inexorable rise of antibiotic resistance we must understand how drugs impact on pathogenesis and influence the selection of resistant clones. Staphylococcus aureus is an important human pathogen with populations of antibiotic-resistant bacteria in hospitals and the community. Host phagocytes play a crucial role in controlling S. aureus infection, which can lead to a population “bottleneck” whereby clonal expansion of a small fraction of the initial inoculum founds a systemic infection. Such population dynamics may have important consequences on the effect of antibiotic intervention. Low doses of antibiotics have been shown to affect in vitro growth and the generation of resistant mutants over the long term, however whether this has any in vivo relevance is unknown. In this work, the population dynamics of S. aureus pathogenesis were studied in vivo using antibiotic-resistant strains constructed in an isogenic background, coupled with systemic models of infection in both the mouse and zebrafish embryo. Murine experiments revealed unexpected and complex bacterial population kinetics arising from clonal expansion during infection in particular organs. We subsequently elucidated the effect of antibiotic intervention within the host using mixed inocula of resistant and sensitive bacteria. Sub-curative tetracycline doses support the preferential expansion of resistant microorganisms, importantly unrelated to effects on growth rate or de novo resistance acquisition. This novel phenomenon is generic, occurring with methicillin-resistant S. aureus(MRSA) in the presence of β-lactams and with the unrelated human pathogen Pseudomonas aeruginosa. The selection of resistant clones at low antibiotic levels can result in a rapid increase in their prevalence under conditions that would previously not be thought to favor them. Our results have key implications for the design of effective treatment regimes to limit the spread of antimicrobial resistance, where inappropriate usage leading to resistance may reduce the efficacy of life-saving drugs.

Author Summary:

Staphylococcus aureus is a major cause of human disease, made even more notable due to the spread of antibiotic resistance. We used a combination of animal models to study the spread of bacteria between organs during an infection and the resulting effect of antibiotic intervention. We found that S. aureus infection is highly clonal, following a “bottleneck” in which very few bacterial cells found each abscess. Despite previous in vitro research, the effect of antibiotics on S. aureus infection was poorly understood. We utilized our systemic infection models to study intervention with sub-curative antibiotic doses, such as one might encounter upon failing to complete an antibiotic course. We have shown that such doses are able to support the preferential expansion of antibiotic-resistant organisms during a mixed infection. This selection is due to the clonal pattern of infection, occurring despite a lack of effect on growth rate or on the spontaneous generation of resistance. Furthermore, it is generic to multiple pathogen species, including Pseudomonas aeruginosa, and antibiotic classes, such as with methicillin-resistant S. aureus (MRSA) in the presence of oxacillin. Given the current debate in the field, our results have important implications for the design of properly-controlled treatment regimes.

Discussion Points

1. Was the paper clearly written, presented etc. Did it all make sense?
2. Were the methods sound? Was there anything extra that you would have done? How were the stats?
3. Were the conclusions supported by the results?
4. How much of this is new? What are the practical implications?
5. What experiments would you do next?

Hope to see you on Tuesday 18th March, 8pm GMT 🙂

#microtwjc 31 Subglacial bacteria and Eukarya

For next weeks #microtwjc session (8pm BST 23rd July) I thought we would cool things down a little and discuss sequencing bacteria and eukarya in ice taken from a lake in Antarctica. The paper was recently published in PLOS one and is available from the following link http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0067221

Abstract:
Lake Vostok, the 7th largest (by volume) and 4th deepest lake on Earth, is covered by more than 3,700 m of ice, making it the
largest subglacial lake known. The combination of cold, heat (from possible hydrothermal activity), pressure (from the
overriding glacier), limited nutrients and complete darkness presents extreme challenges to life. Here, we report
metagenomic/metatranscriptomic sequence analyses from four accretion ice sections from the Vostok 5G ice core. Two
sections accreted in the vicinity of an embayment on the southwestern end of the lake, and the other two represented part
of the southern main basin. We obtained 3,507 unique gene sequences from concentrates of 500 ml of 0.22 mm-filtered
accretion ice meltwater. Taxonomic classifications (to genus and/or species) were possible for 1,623 of the sequences.
Species determinations in combination with mRNA gene sequence results allowed deduction of the metabolic pathways
represented in the accretion ice and, by extension, in the lake. Approximately 94% of the sequences were from Bacteria and
6% were from Eukarya. Only two sequences were from Archaea. In general, the taxa were similar to organisms previously
described from lakes, brackish water, marine environments, soil, glaciers, ice, lake sediments, deep-sea sediments, deep-sea
thermal vents, animals and plants. Sequences from aerobic, anaerobic, psychrophilic, thermophilic, halophilic, alkaliphilic,
acidophilic, desiccation-resistant, autotrophic and heterotrophic organisms were present, including a number from
multicellular eukaryotes.

Discussion points:

1. Was the paper well written, easy to understand/follow and the data presented well?

2. Were the methods appropriate? Anything else you would have liked the authors to do?

3. Are the results useful? Do they help us to understand microbial communities?

4. What next?