| dc.description.abstract | Escherichia coli O157:H7 is an emerging food-borne and water-borne pathogen that belongs to
Enterohemorrhaghic pathogenic group of bacteria. E. coli O157:H7 colonizes the gastrointestinal
tract and is responsible for hemorrahagic colitis, renal failure, bloody diarrhoea, hemolytic
uremic syndrome, thrombocytopenia, hemolytic anemia and other systemic problems.
E. coli O157:H7 is responsible for outbreaks of Enterohemorrhaghic E. coli infections and
causes significant mortality and morbidity globally. Factor V (Mr-330,00Da) is a procofactor
that upon activation to FVa profoundly enhances thrombin generation and fibrin clot formation
as part of prothrombinase. The fibrin clot immobolizes the pathogen and allows the immune
system to target and destroy the bacterium. Our research has shown that pathogenic Escherichia
coli O86a:K61 secretes the protease OmpT as part of outer membrane vesicles (OMVs), which
inactivates coagulation Factor V and in so doing, induces a hemorrhagic state. To further
characterize the effect of OmpT on the coagulation, this study has employed a genetic approach
using wild type, an OmpT deletion mutant, and an over-expressing OmpT construct in
pathogenic E. coli O157:H7. Although the growth of the three strains in liquid culture was not
significantly different over time in nutrient rich media, OmpT over expression retarded cell
growth in nutrient deficient media (p<0.05). Wild type cells and OmpT over expressing cells
produced significantly larger numbers of different size ranges of outer membrane vesicles than
OmpT deletion mutant (p<0.05). Wild type cells and outer membrane vesicles prolonged both
the prothrombin time and activated partial thromboplastin time in normal human plasma, and this
effect was enhanced with OmpT over expressing cells and abolished in the OmpT deletion
mutant. Wild type cells and outer membrane vesicles inactivated Factor V, but not other factors
(fibrinogen, FII and FX), in normal human plasma to a 250kDa product and the effect was
increased in OmpT overexpressing strain and abolished in the OmpT deletion mutant. The effect
of OmpT was direct and did not involve the host plasminogen system. In summary, this research
indicates that OmpT has a role in OMV biogenesis and composition, and disrupting the
coagulation process and fibrin barrier formation during the host innate immune response and in
doing so may permit enhanced bacterial survival within host environments. The research will
also lead to a greater understanding of the mechanism of action of E. coli virulence factors and
positively impact healthcare environments through the development of novel and robust
vaccines, antimicrobial drugs, diagnostic methods, and medical treatments. | en |
