Enterohemorrhagic E. coli
Reference:
Campellone, K.G., Roe, A.J., Løbner-Olesen, A., Murphy,
K.C.,
Magoun, L., Brady, M.J., Donohue-Rolfe, A.J., Tzipori, S., Gally, D.L.,
Leong, J.M. and Marinus, M. G. (2007) Increased adherence and actin
pedestal formation by dam-deficient
enterohemorrhagic Escherichia coli
O157:H7. Molec. Microbiol. 63, 1468-1481.
Enterohemorrhagic Escherichia coli
(EHEC) are highly-infectious pathogens capable of causing severe
diarrheal illnesses. As a critical step during their colonization, EHEC
adhere intimately to intestinal epithelial cells and generate F-actin
‘pedestal’ structures that elevate them above surrounding cell
surfaces. Intimate adhesion and pedestal formation result from delivery
of the EHEC type III secretion system (TTSS) effector proteins Tir and
EspFU into the host cell and expression of the bacterial outer membrane
adhesin, intimin. To investigate a role for DNA methylation during the
regulation of adhesion and pedestal formation in EHEC, we deleted the dam (DNA adenine methyltransferase)
gene from EHEC O157:H7 and demonstrate that this mutation results in
increased interactions with cultured host cells. EHECΔdam exhibits dramatically elevated
levels of adherence and pedestal formation when compared to wild type
EHEC, and expresses significantly higher protein levels of intimin, Tir
and EspFU. Analyses of GFP fusions, Northern blotting, RT-PCR, and
microarray experiments indicate that the abundance of Tir in the dam
mutant is not due to increased transcription levels, raising the
possibility that Dam methylation can indirectly control protein
expression by a post-transcriptional mechanism. In contrast to other
dam-deficient pathogens, EHECΔdam
was capable of robust intestinal colonization of experimentally
infected animals.