[paul.fr]

If we all have E.coli present in our bodies, at what stage does it's presence start to become a health concern, how does it get to this stage and why?

[WylieE]

I know, it's not a plant question. . .

There are good E.coli and there are bad E.coli.

All belong to the same genus Escherichia and the species coli.
However, there are different strains.  Just like each human has slightly different DNA, so does each strain of E.coli. 

The bad one we hear about all the time 0157:H7 contains a gene encoding for a toxin, Shiga-like toxin.  This toxin is what causes damage to the intestine.
 
So 'normal' E.coli is probably about 0.1% of the bacteria in your intestine.  However even a little bit of E.coli 0157 you could have problems.

Colleen

[Carol-A]

But 0.1% of 1kg is 1 gram, and there are 10,000,000,000,000 E.coli in 1 gram!! It is thought they contribute to our vitamen K levels, as well as protecting from harmful bacteria.

[Sajib]

E.coli has different strains. Some are pathogenic and some are non-pathogenic.Among the pathogenic E.coli ETEC and EPEC(enterotoxigenic and enteropathogenic)are common.Enterotoxigenic e.coli acause diarrhoea. 

[nilmot]

Also, having E.coli in places they shouldn't be at could also causes concern. This actually goes for many flora in human e.g. S. aureus

[Heronumber0]

It seems that E. coli with an infectivity plasmid (a piece of DNA in a circular shape that lives outside of the bacterial chromosome) is able to invade deeper tissues like spleen and liver etc... these guys are dangerous and pathogenic (able to cause disease).

[Quantum_Vaccuum]

the bad e.coli was generated from cow manure that ran into the river, and into the lettece and plants, at first it was found in hamburgers and they thought it was unhealthy things in the meat, but it was in the veggies, therfore, that is the real cause of bad E.Coli, and not many people will actully die or even get injured, out of 10000 people infected, 1.4% died, and only 23% actuly showed symptoms.

[cheryl j]

One thing that puzzles me about Ecoli O157:H7 is why cattle farmers dont seem to be a high risk group. Having lived on a beef cattle farm, manure inevitably gets on the bottom of boots, on clothes, on farm equipment, etc. I did read that grass fed cattle have a lower incidence than grain fed, and before being sent to feed lots, cattle are grass fed. Still you'd think there would be a higher incidence of infection with people who work with the animals.

[Mackay]

Katie Couric of CBS news did an extensive report on microbes and feed lot animals.. What she found was pretty scary.
Aside from bad strains of e-coli she found lots of MRSA, not only in the cattles environment but in the workers also. They were MRSA carriers
and some brought it home to their families causing serious illness.

She also reported on cattle ranches that did not use any antibiotics in the feed. There was NO MRSA found there... this was true for pig farms also.

Due to high levels of MRSA and ecoli in the meat supply many nations have gone to irradiating the meat to kill the pathogens.

the only safe meat is from grass fed beef that has never seen antibiotic feed.

Grass fed beef is also nutritionally better for you being higher is the good omega fats.