Advertisement

The Great Escape

By Richard P. Grant The Great Escape 3D4Medical / Photo Researchers, Inc. The paper L.A. Knodler et al., “Dissemination of invasive Salmonella via bacterial-induced extrusion of mucosal epithelia.” PNAS, 107:17733-38, 2010. Free F1000 Evaluation The finding When the Salmonella bacterium infects eukaryotic cells, it becomes encased in membrane-bound vacuoles. How it escapes from these vacuoles and infects other cells was a mystery until now

By | February 1, 2011

The Great Escape

3D4Medical / Photo Researchers, Inc.

The paper

L.A. Knodler et al., “Dissemination of invasive Salmonella via bacterial-induced extrusion of mucosal epithelia.” PNAS, 107:17733-38, 2010. Free F1000 Evaluation

The finding

When the Salmonella bacterium infects eukaryotic cells, it becomes encased in membrane-bound vacuoles. How it escapes from these vacuoles and infects other cells was a mystery until now. Olivia Steele-Mortimer and colleagues at NIH’s National Institute of Allergy and Infectious Diseases in Hamilton, Montana, found that these bacteria don’t all behave the same way, even when infecting the same cell—and that very few actually escape the vacuoles at all.

The cytosol

First author Leigh Knodler noticed “balls of cells” sitting on top of the monolayer of cultured Salmonella-infected gut epithelial cells in electron micrographs. These epithelial cells had been extruded from the monolayer and were laden with bacteria swimming free in the cytosol. This bacterial population, however, divided almost five times as fast as vacuole-dwelling-bacteria.

The escape

The researchers found that only a small number of bacteria manage to escape the vacuole, probably through transient defects in membrane assembly. Once free, they express virulence-associated genes, grow much faster, and ultimately force their host cell out of the epithelium. The host cell suffers inflammatory cell death, releasing the bacteria into the lumen of the gut.

The signal

“The big challenge,” according to F1000 Member Francisco Garcia-del Portillo, is to find out how individual bacteria decide their fate. Knodler is trying to answer this question by identifying the signals Salmonella uses to escape into the cytosol and become this virulent, rapidly replicating form.

F1000 evaluators: G. Tran Van Nhieu (Institut Pasteur)F. Garcia-del Portillo (Centro Nacional de Biotecnología - CSIC)

Comments

Avatar of: Edo McGowan

Edo McGowan

Posts: 19

January 31, 2011

Sewer plants expose bacteria to chlorine and resistance to chlorine thus evolves. As these bacteria are cycled down long rivers, the re-up-take and repeated discharge of water as it cycles through numerous cities enhances this tendency. This is also enhanced by sewage sludge washed off from farmed fields into water resources, something during storm events has been demonstrated (see: Can. J. Microbiol. 50(8): 653?656 (2004) and that US/EPA has exempted from regulation. That Salmonella actually become chlorine resistant is well known (see: http://onlinelibrary.wiley.com/doi/10.1046/j.1472-765X.1998.00432.x/pdf). When chlorine resistant Salmonella meet phagocytic cells, they are engulfed into phagosomes and then a form of chlorine is released within the phagosome to help destroy the intruder. But for chlorine resistant pathogens, there is an increased chance for survival. Additionally, if the immune system is compromised by this strategy on the part of the Salmonella, then bacteriostatic antibiotics, which merely arrest bacterial growth but are not bacteriocidal, and thus rely on a competent immune system for the final destruction are thwarted. If Salmonella which are chlorine resistant are the attacking pathogen, the job of recovery which when coupled by the mechanisms discussed in The Scientist, is likely prolonged and the illness exacerbated. As can be seen in the article The Great Escape, Salmonella have other ways to circumvent the immune system and thus sustain infection. Consequently, a combination of these survival strategies merely means longer recovery times for those with bacterial infections. Salmonella are found in sewage sludge and are in fact, one of the suggested indicators. Thus a combined onslaught by Salmonella armed in this way will see treatment failures increase, especially for a combination of up-regulated resistance and virulence genes in Salmonella. See also Chang on enhanced virulence in response to chlorine: http://cat.inist.fr/?aModele=afficheN&cpsidt=19219794\n\nDr Edo McGowan

Follow The Scientist

icon-facebook icon-linkedin icon-twitter icon-vimeo icon-youtube
Advertisement

Stay Connected with The Scientist

  • icon-facebook The Scientist Magazine
  • icon-facebook The Scientist Careers
  • icon-facebook Neuroscience Research Techniques
  • icon-facebook Genetic Research Techniques
  • icon-facebook Cell Culture Techniques
  • icon-facebook Microbiology and Immunology
  • icon-facebook Cancer Research and Technology
  • icon-facebook Stem Cell and Regenerative Science
Advertisement
Rainin Instrument
Rainin Instrument
Advertisement
PITTCON
PITTCON
Life Technologies