This week’s paper reports on the characterisation of a gene, pgp1, that is important for the helical shape of the bacterium Campylobacter jejuni.

The authors first identified the gene by screening for hypofluorescent C. jejuni mutants  with calcofluor white (which reacts with certain carbohydrate linkages and fluoresces under UV light).  (The researchers in previous work had shown that hypofluorescent mutants “exhibit changes in pathogenesis, virulence, fundamental and/or stress survival phenotypes”).  They then investigated the functional consequences of loss of this gene for C. jejuni by creating a non-polar pgp1 targeted deletion strain .

Having identified that the pgp1 gene is required for the helical shape of C. jejuni and having identified that it plays a role in motility and biofilm formation they went on to characterise the muropeptide content of the C. jejuni strain and determine how this is altered by loss of pgp1 function.

Then they looked at the effect the pgp1 gene had on how C. jejuni interacts with host cells, finding that the deletion strain showed a decreased ability to colonise one day old chicks but that in vitro there was little difference between the deletion strain and the wild type strain when it came to invasion and intracellular survival in epithelial and macrophage cell line.  Finally, they showed that the deletion strain did produce an increased epithelial cell Nod1  response compared to the wild type and increased IL-8 production by epithelial cells.

In the discussion the authors state that “identification and characterisation of pgp1 provides a critical first step in understanding how shape and PG modifications impact C. jejuni pathogenesis“.  They conclude by saying that the deletion strain “will be a valuable tool to continue to study the effects of the loss of C. jejuni helical shape on its biology and pathogenesis“.

Discussion points

These are points/questions that occurred to me as I read the paper.  If you have anything else you think would be interesting to discuss please post in the comments below.

  • Was the paper written clearly and logically with the results informing the discussion?
  • Much of this paper is by necessity descriptive, as the authors discuss how they characterised the gene.  Once they identified its role in C. jejuni biology was there a clear hypothesis for its role in C. jejuni pathogenesis?
  • Have the authors shown sufficiently that it is pgp1‘s role in helical shape formation that is directly affecting C. jejuni‘s pathogenesis?
  • Are there any other experiments you would like to have seen done?