Request for information about Ecoli O157

Don Chen chend at
Fri Jan 28 00:51:11 EST 1994


I've been doing some reading on the E. coli O157 infections
which have been of concern to consumers in the Pacific NW.
I've some questions which someone may have either answers or
which someone can point me to sources who may have answers.

1.  I have read that the Shiga-like toxin (Slt) genes reside
within temperate lambdoid phages which can be shifted to the 
lytic state via UV irradiation.  While Southern blots have 
shown that a lambda/Pvu probe reveals multiple bands in genomic
bands of E. coli that are verocytotoxigenic, I am unsure what
this says about the amount of the wild-type lambda DNA that is 
contained within these temperate phages.  What, if any, of the 
lambda genome is missing?  Where within the phage do the Slt
gene(s) lie?

2.  If these phages are lambdoid, does this mean that these
phages are necessarily inserted at the att site or at other
secondary sites?  If the latter, is there a simple way of
determining where the insertion(s) may be?

3.  Cattle, both dairy and beef, have been implicated as the 
reservoirs for O157, yet when fecal samples are cultured as soon
as 4-5 days after an initial positive test, it appears that the
bacteria are no longer present.  In addition, samples that test
positive are mostly from immature cattle, calves and heifers.
It appears that either the cattle are able to clear the bacteria
or that the bacteria have sequestered themselves such that fecal
samples are no longer positive (by plating or serology).  Is there
research which looks at the reasons why only immature cattle test 
positive?  Do mature cattle have an immunity to the toxigenic
effects of the bacteria?

4.  There are at least two variants of the Slt genes that reside in
cattle.  While there is immunity between some phages, there is none
between others.  In at least two CDC strains, both genes can be
isolated from two separate phages.  Can someone remind me how the
immunity can occur between some but not all lambdoid phages?

5.  The Slt genes are related to the toxin gene from Shigella as
well as the eukaryotic ricin gene from plants.  Does anyone know
of similarities to other toxin genes?

6.  Along with the Slt genes on the chromosome, there seems to be
a 60 Mda plasmid which appears to be necessary for pathogenesis.
There may be an Omp protein which is expressed from this plasmid,
but I am not aware of research which has looked at other possible
proteins expressed;  does anyone know where I can look?

That's all for now.  Thanks for any help you can afford me.

Don Chen

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