There are currently five categories of Escherichia coli that have been unequivocally associated with diarrhea in epidemiological and volunteer studies and at least three other categories of diarrheagenic E. coli have been proposed in the last decade.
Enteropathogenic
E. coli (EPEC), the first
category of E. coli that showed epidemiological association with
diarrheal disease, is an important cause of morbidity and mortality
in children, particularly in developing countries. 
Central
to the pathogenicity of this and related organisms is the ability to adhere
intimately to host cell epithelia and cause effacement of gut microvilli,
a striking pathophysiology (right), known as attaching-and-effacing.
A chromosomally located pathogenicity island, the locus of enterocyte
effacement, encodes all the genes required to produce this phenotype.
In addition to this locus, EPEC strains carry a large virulence plasmid.
Genes on this plasmid include those that encode a bundle-forming pilus
responsible for localized adherence of the bacteria to tissue culture
cells and a plasmid encoded regulator. Several other virulence
genes have been identified outside these loci. On-going studies
are being conducted to examine the molecular divergence of virulence loci
from different EPEC clones with a view to better understanding the pathogenesis,
evolution and epidemiology of the pathogen.
Enteroaggregative E. coli (EAEC),
another category of diarrheagenic E. coli, are an emerging cause
of persistent and acute diarrhea. EAEC adhere to epithelial cells
in a characteristic stacked-brick pattern (left). 
Recent evidence suggests that EAEC infection accounts for a significant
proportion of diarrhea cases in both developing and developed countries.
EAEC infections are acquired orally, probably through contaminated food
and water. E. coli belonging to this category are heterogeneous
with respect to virulence gene content and their pathogenic mechanisms
are only beginning to be elucidated. There is growing evidence to suggest
that EAEC infections are under-diagnosed due to difficulties in delineating
the organisms from other E. coli. We are interested in using
molecular methods to study EAEC isolates from cases of diarrhea with a
view to identifying conserved and significant factors that can be used
in the development of diagnostic tools for food analysis, patient monitoring
and to improve the understanding of pathogenesis.
Epidemiology and Antibiotic Resistance: Ongoing collaborative surveys are defining the pathogenic role of E. coli and hope to improve the awareness, diagnosis, intervention strategies and treatment protocols in disease. These studies are also providing evidence that factors such as antibiotic misuse and urban overcrowding are increasing the prevalence of antibiotic resistance among enteric bacteria. In addition to conducting research to estimate the magnitude of this problem, dermine the biological bases, identify risk factors and seek solutions, it is also important to provide information for health practitioners and the general public because many of the contributing factors are socio-cultural.
2002-2003 Lab Members
Tamia Harris, Katie Unger, 'Becca Bockow, Iruka Okeke, Vernon Caldwell, Adaobi Nwaneshiudu
In the background: Escherichia coli
Back to Iruka Okeke or Haverford College