Pm. Fratamico et al., STUDIES ON ESCHERICHIA-COLI SEROTYPE 0157 H7 STRAINS CONTAINING A 60-MDA PLASMID AND ON 60-MDA PLASMID-CURED DERIVATIVES/, Journal of Medical Microbiology, 39(5), 1993, pp. 371-381
Seventeen strains of Escherichia coli serotype O157:H7 producing Shiga
-like toxin were examined for the presence of plasmids and for the abi
lity to adhere to HEp-2 and Intestine 407 cells. All of the strains po
ssessed a common 60-MDa plasmid. To determine the role of the 60-MDa p
lasmid, plasmid-cured strains were compared with the parent strains fo
r their ability to produce pili and to adhere to epithelial cells in c
ulture. The total cell lysate protein and outer-membrane protein (OMP)
profiles were also compared. Both the parent strains and their plasmi
d-cured derivatives produced pili. Immunofluorescence assay results in
dicated that the plasmid-cured and parent strains adhered equally well
to HEp-2 and Intestine 407 cells; overall adherence was greater with
intestinal cells than HEp-2 cells. SDS-PAGE of polypeptides synthesise
d in an E. coli system in vitro showed that plasmid DNA encodes c. 35
proteins. SDS-PAGE of OMP preparations demonstrated that the 60-MDa pl
asmid appears to be involved in the synthesis of a 33-kDa OMP. Two str
ains cured of the 60-MDa plasmid, one that possessed no plasmids and o
ne that still contained a 2.2-MDa plasmid, produced exopolysaccharide
(EPS) when cultured on solid medium at 25 degrees C. Two other strains
, which were cured of the 60-MDa plasmid but contained a 4.5-MDa plasm
id, did not produce visible amounts of EPS. Gas chromatography analysi
s showed that the EPS consisted of fucose, glucose and galactose in an
approximate molar ratio of 2.0:0.9:1.1 and also had 7% of a uronic ac
id sugar as part of its structure.