Download E. coli is the most common cause of urinary tract infection and

Clinical Microbiology
(MLCM- 201)
Prof. Dr. Ebtisam.F. El Ghazzawi
Medical Research Institute (MRI)
Alexandria University
OUTCOMES
By the end of this lecture the Student should be able
to understand Gram Negative Rods Related to
Enteric Tract (Types, pathogens and laboratory
Diagnostic tests)
The
Enterobacteriaceae
are
a
large
heterogeneous group of gram negative rods
whose natural habitat is the intestinal tract of
humans and animals.
The family includes many genera (Escherichia,
Shigella, Salmonella, Enterobacter, Klebsiella,
Serratia, Proteus and others).
Some enteric organisms, e.g. Escherichia
coli are part of the normal flora and
incidentally cause disease, while others, the
Salmonellae and Shigellae are regularly
pathogenic for humans.
The
Enterobacteriaceae
are
facultative
anaerobes or aerobes, ferment glucose and
a wide range of carbohydrates, oxidase
negative and reduce nitrate to nitrite and
produce a variety of toxics and other
virulence factors.
Enterobacteriaceae, enteric gram-negative
rods may also be called coliforms.
They cause a variety of diseases with
different pathogenic mechanisms.
The clinical manifestations of infections
with E. coli and other enteric bacteria
depend on the site of infection and cannot
be differentiated by symptoms or signs from
processes caused by other bacteria.

Urinary tract infection: E. coli is the most
common cause of urinary tract infection and
account for 90% of first urinary tract infections
in young women. The symptoms and signs
include urinary frequency, dysuria, hematuria,
and pyuria. Frank pain is associated with
upper tract infection. U.T.I can result in
bacteremia with clinical signs and sepsis.

E. coli-associated diarrheal diseases: E. coli
that cause diarrhea are extremely common
worldwide. Enteropathogenic E. coli (EPEC) is
an important cause of diarrhea in infants
especially in developing countries. The result
of
EPEC
infection
is
watery
diarrhea.
Enterotoxigenic E. coli (ETEC) is a common
cause of “traveler’s” diarrhea and a very
important cause of diarrhea in infants in
developing countries.
Care in the selection and consumption of
foods potentially contaminated with ETEC
is highly recommended to help prevent
traveler’s
diarrhea.
Antimicrobial
prophylaxis can be effective but may
result in increased antibiotic resistance in
the bacteria and probably should not be
uniformly recommended.
Once
diarrhea
develops,
antibiotic
treatment effectively shortens the duration
of disease. Enterohemorrhagic E. coli
(EHEC)
has
been
associated
with
hemorrhagic colitis, a severe form of
diarrhea,
and
with
hemolytic
uremic
syndrome, a disease resulting in acute
renal
failure,
hemolytic
thrombocytopenia.
anemia
and
Enteroinvasive E. coli (EIEC) strains are
nonlactose or late lactose fermenters and
are nonmotile. EIEC produce disease by
invading
intestinal
mucosal
epithelial
cells. The disease occurs most commonly
in children in developing countries and in
travelers to these countries.
Enteroaggregative E.coli (EAEC) causes acute
and chronic diarrhea (> 14 days in duration) in
persons
in
developing
countries.
These
organisms are also the cause of food-born
illnesses in industrialized countries. They are
characterized by their characteristic pattern of
adherence to human cells.
Sepsis: when normal host defenses are
inadequate, E. coli may reach the blood
stream and cause sepsis. New borns may
be highly susceptible to E. coli sepsis
because they lack IgM antibodies. Sepsis
may occur secondary to urinary tract
infection.
Meningitis: E. coli is one of the leading
causes of meningitis in infants.
Specimens suspected of containing E. coli
are grown on blood agar plate and on
differential media such as Mac-Conkey’s agar
or Ethylene methylene blue agar (EMB).
E. coli which ferments lactose forms pink
colonies.
On EMB agar E. coli colonies have a
characteristic green sheen.
E. coli can be distinguished from other
lactose fermenting gram negative rods by:
a. Its production of indole from Tryptophan.
b. It is motile.
c. It uses acetate as the only source of
carbon.
d. It decarboxylates lysine.
Assignment
Staphylococcus Aureous
Study Questions
Complete the following questions:
•
The
Enterobacteriaceae
are
a
large
heterogeneous group of gram negative rods
whose natural habitat is ………….of humans
and animals.
•
The family includes many genera (………,
……., ………,…………, Klebsiella,…………)
E. coli can be distinguished from other lactose
fermenting gram negative rods by:
a)
b)
c)
d)
Recommended Textbooks
Manual of Clinical Microbiology, Vols. 1 and 2: Eighth
Edition Patrick R. Murray