E. coli, one of the commensals in the human gut microbiota,
inhabits the intestinal tract without causing injury
to the host. However, several pathogenic E. coli strains
express virulence factors and cause disease in humans. In
1976, Hoekstra et al. found membrane fragments (OMVs)
in the culture supernatant of normally growing E. coli,
consisting of practically unmodified outer membrane
(Hoekstra et al. 1976). Later, the heat/labile enterotoxin
(LT) activity was found in the newly synthesized OMVs
released from E. coli (Gankema et al. 1980; Wai et al.
1995). In addition, Kollings and Matthews demonstrated
the presence of DNA in OMVs purified from E. coli
O157:H7, and using that DNA, they were able to identify
the virulence genes eae, stx1, stx2, and uidA. Also, they
confirmed that the Shiga toxins 1 and 2 were contained
within the vesicles by western blot