Thks for link.
@Shajir Bran, thks for yr nicely detailed attachment.
I thought a condensed but (hopefully) fairly accurate summary of the pathogenic nature of E.coli might be useful so I hv extracted/compiled some info. from several references (the originals are linked at end of each section and contain far more detail). –
Over 700 antigenic types (serotypes) of E. coli are recognized based on O, H, and K antigens. At one time serotyping was important in distinguishing the small number of strains that actually cause disease. Thus, the serotype O157:H7 (O refers to somatic antigen; H refers to flagellar antigen) is uniquely responsible for causing HUS (hemolytic uremic syndrome). Nowadays, particularly for diarrheagenic strains (those that cause diarrhea) pathogenic E. coli are classified based on their unique virulence factors and can only be identified by these traits. Hence, analysis for pathogenic E. coli usually requires that the isolates first be identified as E. coli before testing for virulence markers.
Pathogenic strains of E. coli are responsible for three types of infections in humans: urinary tract infections (UTI), neonatal meningitis, and intestinal diseases (gastroenteritis). The diseases caused (or not caused) by a particular strain of E. coli depend on distribution and expression of an array of virulence determinants, including adhesins, invasins, toxins, and abilities to withstand host defenses. For example some classified toxins are –
Food-wise, the last variety of the three types of infection referred above appears most relevant here, ie intestinal diseases (gastroenteritis) -
Five classes (virotypes) of E. coli that cause diarrheal diseases are now recognized: (1) enterotoxigenic E. coli (ETEC), (2) enteroinvasive E. coli (EIEC), (3) enterohemorrhagic E. coli (EHEC), (4) enteropathogenic E. coli (EPEC), and (5) enteroaggregative E. coli (EAEC).
The EHEC group is also variously (and somewhat approx.) referred to as VTEC (verocytotoxic E. coli ) and STEC ("Shiga toxin-producing” E. coli)
Each class falls within a serological subgroup and manifests distinct features in pathogenesis
The group of immediately current interest is No.5 –
(5) Enterohemorrhagic E. coli (EHEC)
EHEC are recognized as the primary cause of hemorrhagic colitis (HC) or bloody diarrhea, which can progress to the potentially fatal hemolytic uremic syndrome (HUS). EHEC are characterized by the production of verotoxin or Shiga toxins (Stx). Although Stx1 and Stx2 are most often implicated in human illness, several variants of Stx2 exist.
There are many serotypes of Stx-producing E. coli , but only those that have been clinically associated with HC are designated as EHEC. Of these, O157:H7 is the prototypic EHEC and most often implicated in illness worldwide. The infectious dose for O157:H7 is estimated to be 10 - 100 cells; but no information is available for other EHEC serotypes. EHEC infections are mostly food or water borne and have implicated undercooked ground beef, raw milk, cold sandwiches, water, unpasteurized apple juice and vegetables
EHEC are considered to be "moderately invasive". Nothing is known about the colonization antigens of EHEC but fimbriae are presumed to be involved. The bacteria do not invade mucosal cells as readily as Shigella, but EHEC strains produce a toxin that is virtually identical to the Shiga toxin. The toxin plays a role in the intense inflammatory response produced by EHEC strains and may explain the ability of EHEC strains to cause HUS.
( http://www.textbooko...net/e.coli.html )
(I did note that several of the other groups apparently have much higher infectious doses, eg >= 10
Here is a 2nd, USA extract also focussing on Group5 above –
Some kinds of E. coli cause disease by making a toxin called Shiga toxin. The bacteria that make these toxins are called “Shiga toxin-producing” E. coli, or STEC for short. You might hear them called verocytotoxic E. coli (VTEC) or enterohemorrhagic E. coli (EHEC); these all refer generally to the same group of bacteria. The most commonly identified STEC in North America is E. coli O157:H7 (often shortened to E. coli O157 or even just “O157”). When you hear news reports about outbreaks of “E. coli” infections, they are usually talking about E. coli O157.
In addition to E. coli O157, many other kinds (called serogroups) of STEC cause disease. These other kinds are sometimes called “non-O157 STEC.” E. coli serogroups O26, O111, and O103 are the non-O157 serogroups that most often cause illness in people in the United States.
and with direct relevance to the 2011 incident in Europe (O104:H4) –
Certain strains of E. coli, such as O157:H7, O104:H4, O121, O26, O103, O111, O145,and O104:H21, produce potentially lethal toxins. Food poisoning caused by E. coli usually results from eating unwashed vegetables or undercooked meat. O157:H7 is also notorious for causing serious and even life-threatening complications such as hemolytic-uremic syndrome. This particular strain is linked to the 2006 United States E. coli outbreak due to fresh spinach. The O104:H4 strain is, though rarer, still more dangerous because it is just as, if not more so, virulent. Antibiotic and supportive treatment protocols for it are not as well-developed (it has the ability to be very enterohemorrhagic like O157:H7, causing bloody diarrhea, but also is more enteroaggregative, meaning it adheres well and clumps to intestinal membranes). It is the strain behind the ongoing and deadly June 2011 E. coli outbreak in Europe. Severity of the illness varies considerably; it can be fatal, particularly to young children, the elderly or the immunocompromised, but is more often mild. Earlier, poor hygienic methods of preparing meat in Scotland killed seven people in 1996 due to E. coli poisoning, and left hundreds more infected.
E. coli can harbour both heat-stable and heat-labile enterotoxins. The latter, termed LT, contain one A subunit and five B subunits arranged into one holotoxin, and are highly similar in structure and function to cholera toxins. The B subunits assist in adherence and entry of the toxin into host intestinal cells, while the A subunit is cleaved and prevents cells from absorbing water, causing diarrhea. LT is secreted by the Type 2 secretion pathway.
( http://en.wikipedia....scherichia_coli )
Some more comments (including conspiracy theories) specifically on the O104 situation can be seen here –
Rgds / Charles.C