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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



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…

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

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


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…

Hi all

Happy New Year and welcome/ welcome back to #microtwjc. Cholera_bacteria_SEM

Next week, on Tues 20th Jan at 8pm GMT we will be looking at this paper:

Insights into Vibrio cholerae Intestinal Colonization from Monitoring Fluorescently Labeled Bacteria

Yves A. Millet, David Alvarez, Simon Ringgaard, Ulrich H. von Andrian, Brigid M. Davis, Matthew K. Waldor

PLoS Pathog 10(10): e1004405. doi: 10.1371/journal.ppat.1004405



Vibrio cholerae, the agent of cholera, is a motile non-invasive pathogen that colonizes the small intestine (SI). Most of our knowledge of the processes required for V. cholerae intestinal colonization is derived from enumeration of wt and mutant V. cholerae recovered from orogastrically infected infant mice. There is limited knowledge of the distribution of V. choleraewithin the SI, particularly its localization along the villous axis, or of the bacterial and host factors that account for this distribution. Here, using confocal and intravital two-photon microscopy to monitor the localization of fluorescently tagged V. cholerae strains, we uncovered unexpected and previously unrecognized features of V. cholerae intestinal colonization. Direct visualization of the pathogen within the intestine revealed that the majority of V. choleraemicrocolonies attached to the intestinal epithelium arise from single cells, and that there are notable regiospecific aspects to V. cholerae localization and factors required for colonization. In the proximal SI, V. cholerae reside exclusively within the developing intestinal crypts, but they are not restricted to the crypts in the more distal SI. Unexpectedly, V. cholerae motility proved to be a regiospecific colonization factor that is critical for colonization of the proximal, but not the distal, SI. Furthermore, neither motility nor chemotaxis were required for proper V. choleraedistribution along the villous axis or in crypts, suggesting that yet undefined processes enable the pathogen to find its niches outside the intestinal lumen. Finally, our observations suggest that host mucins are a key factor limiting V. cholerae intestinal colonization, particularly in the proximal SI where there appears to be a more abundant mucus layer. Collectively, our findings demonstrate the potent capacity of direct pathogen visualization during infection to deepen our understanding of host pathogen interactions.


Author Summary

Vibrio cholerae is a highly motile bacterium that causes the diarrheal disease cholera. Despite our extensive knowledge of the genes and processes that enable this non-invasive pathogen to colonize the small intestine, there is limited knowledge of the pathogen’s fine localization within the intestine. Here, we used fluorescence microscopy-based techniques to directly monitor where and how fluorescent V. cholerae localize along intestinal villi in infected infant mice. This approach enabled us to uncover previously unappreciated features of V. cholerae intestinal colonization. We found that most V. cholerae microcolonies appear to arise from single cells attached to the epithelium. Unexpectedly, we observed considerable differences between V. cholerae fine localization in different parts of the small intestine and found that V. choleraemotility exerts a regiospecific influence on colonization. The abundance of intestinal mucins appears to be an important factor explaining at least some of the regiospecific aspects of V. cholerae intestinal localization. Overall, our findings suggest that direct observation of fluorescent pathogens during infection, coupled with genetic and/or pharmacologic manipulations of pathogen and host processes, adds a valuable depth to understanding of host-pathogen interactions.


Discussion Points

  1. Was the paper well written? Clear? Easy to follow?
  2. Were the methods appropriate? Were there any methods/experiments that you thought were missing? Were the stats appropriate?
  3. Were the conclusions supported by the results? What impact do you think these results will have on the wider V cholera field?
  4. What experiments would you like to see done in the future to build upon this work?
  5. Anything else?  Please comment in the box below

Looking forward to see you there (just search for #microtwjc on the night and the tweets should come up automatically).  Please spread the word to your colleagues – the more the merrier 🙂

This week, Tues 25th November, we will be looking at this paper 

Shed GP of Ebola Virus Triggers Immune Activation and Increased Vascular Permeability

Beatriz Escudero-Pérez, Valentina A. Volchkova, Olga Dolnik, Philip Lawrence, Viktor E. Volchkov mail


Discussion points

  1. Is the paper well written?
  2. Do the results support the conclusions?
  3. What work would you like to see done in the future?


Hope to see you there on Tuesday



dishHi 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


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?