Friday, April 29, 2011

1 The Friday Four

In this week's Friday Four, we'll look at how some bacteria avoid antibiotics by shutting down and hiding until it's safe to come out again,  students who go bacteriophage hunting,  disrupting bacteria's communication or quorum sensing in future antibacterial treatments,  tests which use bacteria's scent to detect not only their presence but species, strain, and their antibiotic resistance profile.

CO message to readers: The Friday Four postings will be on hiatus for at least the month of May during Lyme Awareness Month.

1) 'Going off the grid' helps some bacteria hide from antibiotics


ScienceDaily (2011-04-25) -- Call them the Jason Bournes of the bacteria world. Going "off the grid," like rogue secret agents, some bacteria avoid antibiotic treatments by essentially shutting down and hiding until it's safe to come out again.


I want to keep this one short and sweet: What if those few Borrelia burgdorferi left behind in collagen that some researchers say are not viable or non-dividing are just basically in stasis instead? What if they have shut down their metabolic processes and only look mostly dead? (This is starting to remind me of the scene in that movie, The Princess Bride, where Westley is... Oh, never mind, if you haven't seen it, I don't want to spoiler it for you. It's a fun movie. I will tell you the Bourne series is one of the best action series in my opinion - along those lines, I like Memento too...)

Source Reference:
Xiaoxue Wang, Younghoon Kim, Seok Hoon Hong, Qun Ma, Breann L Brown, Mingming Pu, Aaron M Tarone, Michael J Benedik, Wolfgang Peti, Rebecca Page, Thomas K Wood. Antitoxin MqsA helps mediate the bacterial general stress response. Nature Chemical Biology, 2011; DOI: 10.1038/nchembio.560

2) Phage hunting students find new bacteriophages in soils of St. Louis suburbs


ScienceDaily (2011-04-25) -- Twelve students who had participated in an unusual biology course as freshmen have found two bacteriophages, viruses that prey exclusively on bacteria, in the soil of two suburbs of St. Louis, Missouri. As the finders, they had the naming rights; the new phages are called Angelica and Uncle Howie.


This is as awesome as being an amateur astronomer. If you're an amateur astronomer, if you find an object in the sky no one has discovered before, it can be named after you or you can decide what you want to name it. Here, students are discovering their own bacteriophages in the dirt and naming them anything they want.

I posted this mainly because I think it's cool, and I wish I had gotten the opportunity to do this in school, too. Well, who knows... maybe I'll go back to school someday, just to be able to take a course like this and name my own bacteriophage Camp Other. If I did, though, I'd try to find one that consumed Borrelia burgdorferi.

Source Reference:
Pope WH, Jacobs-Sera D, Russell DA, Peebles CL, Al-Atrache Z, et al. Expanding the Diversity of Mycobacteriophages: Insights into Genome Architecture and Evolution. PLoS ONE, 2011; 6 (1): e16329 DOI: 10.1371/journal.pone.0016329

3) Bacteria interrupted: Disabling coordinated behavior and virulence gene expression


ScienceDaily (2011-04-22) -- New research reveals a strategy for disrupting the ability of bacteria to communicate and coordinate the expression of virulence factors. The study may lead to the development of new antibacterial therapeutics.


Bonnie Bassler is up to it again. I love her presentation on TED, and if you haven't seen it, you really should set aside 18 minutes of your time to watch her video on how to get bacteria to talk and how to get them to shut up.

And recently she was on a team that did more research on how to stop bacterial infections by shutting up them up.  Four points in turn outlined their strategy for how one could stop bacterial infection by stopping quorum sensing:

  1. Quorum-sensing (QS) antagonists represent potential antibacterial therapeutics
  2. They can bind LuxR-family transcription factors in competition with autoinducers
  3. The antagonists stabilize a closed conformation incapable of binding operator DNA
  4. This inhibition strategy may be generalizable to other multidomain receptors

Which means that there are antagonists which can bind to certain factors that normally autoinducers would bind to - the antagonists are competition for them,  much like Saccharomyces bouldarii can be competition for other yeasts and C. difficle. When the antagonists bind to the factors, they will not bind to operator DNA.

So to sum up: If you can stop autoinducers, you can stop the bacteria from communicating. You can shut it up. If you shut it up, you can tell it to stop having sex and the immune system police will evict it, much like a loud annoying neighbor.

You think I'm kidding, and making this story up? I'm not - I'm merely telling the story to illustrate a point: In order for gene transcription to be activated in the bacteria, the cell must encounter autoinducers secreted by other cells in its environment.

Here's a basic diagram of how Gram-negative bacteria engages in quorum sensing (noting that Borrelia burgdorferi is not exactly Gram-negative or Gram-positive here, it is somewhat closer to Gram-negative so I include that model here):

What you need to imagine here is that this oval represents a bacterium, and that initially a small number of bacteria are doing this all at the same time in their host, whether that be human or not.

Here the LuxI protein makes the autoinducers (green pentagons) which then diffuse freely outside. Each bacterium doing the same, the concentration of external autoinducer is a measure of the size of the population (quorum).

When the autoinducer concentration is high (meaning the bacteria has reproduced to a certain population)  the autoinducer binds to a cognate receptor LuxR (cognate means having the same form and ad hoc characteristics to bind specifically to the molecule it receives).

This is quorum sensing.

The complex auto inducer-Lux R then binds at target gene promoters and activate their effect (transcription) which has behavioral consequences.

In other words, once the bacteria reaches a certain threshold, the level of autoinducers is very high, and the number of bacteria goes up. The high autoinducer level means more bacteria, and more bacteria means more autoinducers. It's a self-perpetuating feedback loop. If you can prevent the loop from even getting started, bacterial numbers will remain low.

So, you're probably wondering, does Borrelia burgdorferi engage in quorum sensing, and if so, can we get it to shut up also?

This has actually been somewhat under debate. Some research has stated that Borrelia burgdorferi has an autoinducing cognate receptor called LuxS, but it doesn't have the necessary autoinducer to bind to it, which in this case would be AI-2.

More recent research has shown that there might be a more complicated method for Borrelia burgdorferi involved for synthesizing its own autoinducers... Might.

To draw from this Polish research paper from 2009 (

"...the studies of von Lackum et al.[62] demonstrated that B. burgdorferi encodes functional Pfs and LuxS enzymes for the breakdown of toxic products of methylation reactions. According to these observations, B. burgdorferi was shown to synthesize the final product, 4,5-dihydroxy-2,3-pentanedione (DPD) during laboratory cultivation. DPD undergoes spontaneous rearrangements to produce a class of pheromones collectively named autoinducer 2 (AI-2). The addition of in vitro-synthesized DPD to the culture of B. burgdorferi manifested in differential expression of a distinct subset of proteins, including the outer surface lipoprotein VlsE. Although many bacteria for regeneration of methionine can utilize the other LuxS product, homocysteine, B. burgdorferi did not show such an ability. It is hypothesized that B. burgdorferi produces LuxS for the express purpose of synthesizing DPD, and utilizes a form of that molecule as an AI-2 pheromone to control gene expression [4]."

Those cited papers are:

[62] Von Lackum K, Babb K, Riley SP, Wattier RL, Bykowski T, Stevenson B: Functionality of Borrelia burgdorferi LuxS: the Lyme disease spirochete produces and responds to the pheromone autoinducer-2 and lacks a complete activated-methyl cycle. Int J Med Microbiol 2006, 296, 92-102 -and-
[4] Babb K, von Lackum K, Wattier RL, Riley SP, Stevenson B: Synthesis of autoinducer 2 by the lyme disease spirochete, Borrelia burgdorferi. J Bacteriol 2005, 187, 3079-3087

I need to read more about it, at this point the above is currently hypothetical and an in vitro test, so the answer to your question is (unless you know something I don't): the jury is still out on this one.
Source Reference:
Guozhou Chen, Lee R. Swem, Danielle L. Swem, Devin L. Stauff, Colleen T. O'Loughlin, Philip D. Jeffrey, Bonnie L. Bassler, Frederick M. Hughson. A Strategy for Antagonizing Quorum Sensing. Molecular Cell, Volume 42, Issue 2, 199-209, 22 April 2011 DOI: 10.1016/j.molcel.2011.04.003

4) Get a whiff of this: Low-cost sensor can diagnose bacterial infections


Colorimetric sensor array
overlaid on petri dish
ScienceDaily (2011-04-28) -- Bacterial infections really stink. And that could be the key to a fast diagnosis. Researchers have demonstrated a quick, simple method to identify infectious bacteria by smell using a low-cost array of printed pigments as a chemical sensor. In only a few hours, the array not only confirms the presence of bacteria, but identifies a specific species and strain. It even can recognize antibiotic resistance -- a key factor in treatment decisions.

Comments: So the abstract for this paper is as follows:
"Rapid identification of both species and even specific strains of human pathogenic bacteria grown on standard agar has been achieved from the volatiles they produce using a disposable colorimetric sensor array in a Petri dish imaged with an inexpensive scanner. All 10 strains of bacteria tested, including Enterococcus faecalis and Staphylococcus aureus and their antibiotic-resistant forms, were identified with 98.8% accuracy within 10 h, a clinically important time frame. Furthermore, the colorimetric sensor arrays also proved useful as a simple research tool for the study of bacterial metabolism and as an easy method for the optimization of bacterial production of fine chemicals or other fermentation processes."
The full text requires paid access, however, just looking at what is known here between the article and abstract, I have to wonder how accurate a test this could be to detect Borrelia burgdorferi. I could see this rapid strain identification being useful for identifying bacteria for bacteriophage treatments and also for detecting the presence of bacteria on specific surfaces in hospitals or from open wounds. This wouldn't work well for something that is deeply embedded in collagen, but it might work from a synovial fluid sample better than current detection tests for Bb there.

Source Reference:
James R. Carey, Kenneth S. Suslick, Keren I. Hulkower, James A. Imlay, Karin R. C. Imlay, Crystal K. Ingison, Jennifer B. Ponder, Avijit Sen, Aaron E. Wittrig. Rapid Identification of Bacteria with a Disposable Colorimetric Sensing Array.Journal of the American Chemical Society, 2011; : 110427110353066 DOI: 10.1021/ja201634d

1 comment:


    **** soil in University City, Mo. Both Clayton and University City are suburbs of St. Louis.****

    I lived in U.City for most of my young life and my (now) ex husband was from Clayton.

    Small world department!


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