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 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 week 24: A dilema of choices!

So people here is next week’s paper for discussion.

Microanatomy at Cellular Resolution and Spatial Order of Physiological Differentiation in a Bacterial Biofilm

I had a hard choice and I have decided on one of two stories (the other one was on phages) that caught my attention at the BACNET13 meeting I attended in Poland recently.

The wonderful images produced by the Hengge lab while dissecting the role of c-di-GMP in biofilm formation won. You will need to use the online material as well as the paper for this one.

We have discussed c-di-GMP and Biofilms sometime back and it is a subject that started my own journey into the fascinating world of Caulobacter crescentus as a young Post-Doc. Regine Hengge gave an excellent talk on this story at BACNET. The field of c-di-GMP itself played a central role at this meeting. What was clear to me is that the field has begun to move on from the biochemical characterisation of the components involved to returning to the underlying question of what c-di-GMP is regulating, why and how? Clearly exciting times are ahead for the field.

As per usual our discussion will focus on:

1) Did the paper read well?

2) Could you understand the regulatory network?

3) Would you have done anything differently?

4) where next?

#microtwjc Week 10 – the #SGMwarw edition

Next week’s #microtwjc paper comes from the September 2012 issue of the SGM’s ‘Microbiology’ and is titled:

Molecular characterization of a novel mosaic tet(S/M) gene encoding tetracycline resistance in foodborne strains of Streptococcus bovis

Simona Barile, Chiara Devirgiliis, and Giuditta Perozzi

(Microbiology September 2012 158:2353-2362; published ahead of print June 21, 2012, doi:10.1099/mic.0.058206-0 )

The abstract:

The presence of antibiotic-resistance (AR) genes in foodborne bacteria of enteric origin represents a relevant threat to human health in the case of opportunistic pathogens, which can reach the human gut through the food chain. Streptococcus bovis is a human opportunistic pathogen often associated with infections in immune-compromised or cancer patients, and it can also be detected in the environment, including fermented foods. We have focused on the molecular characterization of a tetracycline (Tet)-resistance gene present in 39 foodborne isolates of S. bovis phenotypically resistant to this drug. The gene was identified as a novel tet(S/M) fusion, encoding a mosaic protein composed of the N-terminal 33 amino acids of Tet(S), in-frame with the Tet(M) coding sequence. Heterologous expression of the mosaic gene was found to confer Tet resistance upon Escherichia coli recipients. Moreover, the tet(S/M) gene was found to be transcriptionally inducible by Tet under the endogenous tet(S) promoter in both S. bovis and E. coli. Nucleotide sequencing of the surrounding genomic region of 16.2 kb revealed large blocks of homology with the genomes of Streptococcus infantarius and Lactococcus lactis. A subregion of about 4 kb containing mosaic tet(S/M) was flanked by two copies of the IS1216 mobile element. PCR amplification with primers directed outwards from the tet(S/M) gene identified the presence of a 4.3 kb circular form corresponding to the intervening chromosomal region between the two IS1216 elements, but lacking a replication origin. The circular element shared extensive overall homology with a region of the multidrug-resistance plasmid pK214 from Lc. lactis, containing tet(S), as well as the IS1216 transposase-containing element and intervening non-coding sequences. Linear reconstruction of the insertion events likely to have occurred within this genomic region, inferred from sequence homology, provides further evidence of the chromosomal rearrangements that drive genomic evolution in complex bacterial communities such as the gut and food microbiota.

 

A few discussion points to consider (if you have any other points please comment below)

1. Was the paper well written, clearly laid out and easy to follow?
2. Were the experiments well designed?  Were there any experiments you would have liked to see there that weren’t?
3. How does this work contribute to our knowledge of antibiotic resistance and are there any practical suggestions/outcomes/considerations that stem from this work?
4. If you were the researchers what future work would you want to do?

 

We hope you can join us next week, Tues 11th September, 8pm UK time for #microtwjc 🙂

Photo

With thanks to CRV Arnhem for making this available via a Creative Commons licence