Download Escherichia coli

Babylon university
College of Medicine
Microbiology Dept.
Prof.Dr.Ilham AL-Saedi
Enterobacteriaceae
 The Enterobacteriaceae is a large family of Gram-negative
bacteria that includes many of the more familiar pathogens,
such as Salmonella, Escherichia coli, Yersinia pestis,
Klebsiella and Shigella.
 Other disease-causing bacteria in this family include
Proteus, Enterobacter, Serratia, and Citrobacter.
 Characteristics of enterobacteriaceae:
 Members of the Enterobacteriaceae are rod-shaped, and
are typically 1-5 μm in length. Like other proteobacteria,
enterobacteria have Gram-negative stains, and they are
facultative anaerobes, fermenting sugars to produce lactic
acid and various other end products [lactose fermenters:
produce pink-red colonies on MacConkey agar (Escherichia
coli, Klebsiella, Citrobacter Enterobacter, Serratia. [nonlactose fermenters: pale-colour colonies on MacConkey agar
(Salmonella, Shigella, Proteus).
 Most also reduce nitrate to nitrite. Most have many flagella
used to move about, but a few genera are non-motile. They
are not spore-forming. Catalase reactions vary among
Enterobacteriaceae.
 Grow readily on MacConkey (MAC) and eosin methylene blue
(EMB) agars
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 Grow readily at 35oC except Yersinia (25o-30oC)
 Motile by peritrichous flagella except Shigella and Klebsiella
which are non-motile
 Do not form spores.
 Many members of this family are a normal part of the gut
flora found in the intestines of humans and other animals,
while others are found in water or soil, or are parasites on a
variety of different animals and plants.
 Most members of Enterobacteriaceae have peritrichous,
type I fimbriae involved in the adhesion of the bacterial
cells to their hosts.
 Some enterobacteria produce endotoxins. Endotoxins reside
in the cell cytoplasm and are released when the cell dies and
the cell wall disintegrates.
 Some members of the Enterobacteriaceae family produce a
systemic infection into the blood stream when all the dead
bacterial cells release their endotoxins. This is known as
endotoxic shock, and can be rapidly fatal.
 Identification of enterobacteriaceae:
 To identify different genera of Enterobacteriaceae, a
microbiologist may run a series of tests in the lab. These
include a range of tubes cultures and agar plates cultures
such as:
 Phenol red
 Tryptone broth
 Phenylalanine
agar
for
detection
of
production
of
deaminase, which converts phenylalanine to phenylpyruvic
acid
 Methyl red or Voges-Proskauer tests depend on the
digestion of glucose. The methyl red tests for acid
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endproducts.
The
Voges
Proskauer
tests
for
the
production of acetylmethylcarbinol.
 Catalase test on nutrient agar tests for the production of
catalase enzyme, which splits hydrogen peroxide and
releases oxygen gas.
 Oxidase test on nutrient agar tests for the production of
the enzyme oxidase, which reacts with an aromatic amine
to produce a purple color.
 Nutrient gelatin tests to detect activity of the enzyme
gelatinase.
 In a clinical setting, three species make up 80 to 95% of all
isolates identified. These are Escherichia coli, Klebsiella
pneumoniae and Proteus mirabilis.
 Major Genera of enterobacteriaceae:
Escherichia coli, Shigella, Salmonella, Citrobacter, Yersinia,
Klebsiella, Enterobacter, Serratia, Proteus and Morganella.
 Natural Habitats of enterobacteriaceae:
 Environmental sites (soil, water, and plants)
 Intestines of humans and animals
 Modes of Infection of enterobacteriaceae:
 Contaminated food and water (Salmonella spp., Shigella spp.,
Yersinia enterocolitica, Escherichia coli O157:H7)
 Endogenous (urinary tract infection, primary bacterial
peritonitis, abdominal abscess)
 Abnormal host colonization (nosocomial pneumonia)
 Transfer between debilitated patients
 Insect (flea) vector (unique for Yersinia pestis)

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 Enterobacteriaceae: Types of Infectious Disease:
 Intestinal (diarrheal) infection
 Extraintestinal infection
- Urinary tract (primarily cystitis)
- Respiratory (nosocomial pneumonia)
- Wound (surgical wound infection)
- Bloodstream (gram-negative bacteremia)
- Central nervous system (neonatal meningitis)
 Urinary
tract
infection:
Escherichia
coli,
Klebsiella
pneumoniae, Enterobacter spp., and Proteus mirabilis
 Pneumonia:
Enterobacter
spp.,
Klebsiella
pneumoniae,
Escherichia coli, and Proteus mirabilis
 Wound
Infection: Escherichia coli, Enterobacter spp.,
Klebsiella pneumoniae, and Proteus mirabilis
 Bacteremia: Escherichia coli, Enterobacter spp., Klebsiella
pneumoniae, and Proteus mirabilis.
 Intestinal Infection:
- Shigella sonnei (serogroup D)
- Salmonella serotype Enteritidis
- Salmonella serotype Typhimurium
- Shigella flexneri (serogroup B)
- Escherichia coli O157:H7
- Yersinia enterocolitica.
Escherichia coli
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 E. coli is
the head
of the large bacterial family,
Enterobacteriaceae, the enteric bacteria, is one of the most
important enterobacteriaceae species; it is a gram negative
rod, facultative anaerobic and non-sporulation. Usually
motile. It can grow in media with glucose as the sole organic
constituent. It produces polysaccharide capsule, positive
test
for
indole,
lysine
decarboxylase
and
mannitol
fermentation and produces gas from glucose. This bacterium
is predominant among aerobic commensal bacteria in healthy
human intestine.
 The bacterium can grow in the presence or absence of O2.
Under anaerobic conditions it will grow by means of
fermentation.
 E. coli uses mixed acid fermentation in anaerobic conditions,
producing lactate, succinate, ethanol, acetate and carbon
dioxide producing characteristic "mixed acids and gas" as
end products.
 However, it can also grow by means of anaerobic respiration,
since it is able to utilize NO3, NO2 or fumarate as final
electron acceptors for respiratory electron transport
processes. In part, this adapts E. coli to its intestinal
(anaerobic) and its extraintestinal (aerobic or anaerobic)
habitats.
 Antigenic structure of E.coli:

somatic (O) antigen, capsular (K) antigen, flagellar (H)
antigen.
 pilli: help in attachment and virulence:
- bind to D-mannose residues on surface of cells.
- Pyelonephritis associated pilli (pap).
- Intestinal colonization factor antigen.
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 Virulence factors :
- Adherence to uroepithelial cells by Pap pilli.
- Capsule (K-antigen).
- E.coli produce Exotoxins e.g. Hemolysins ,Enterotoxins
causes diarrheas, Heat labile HL, Heat stable HS and
Vero toxins like Shigella toxins.
- Sidrophore-help
survival
of
E.coli
in
iron-poor
environment of human body fluids.
 Diseases caused by E. coli:
1. Urinary tract infection (UTI).
-Urethritis:
- Commonest cause (70%-90%).
- More common in females due to shorter urethra.
-
105 bacteria/ml of urine is significant
- Common cause of hospital-acquired UTI due to urinary
catheters.
- Cystitis: (infection of bladder)
 Pain (dysuria)
 Frequency of maturation
 More common in females due to shorter urethra
- Pyelonephritis: (infection of kidney)
 Fever (chills)
 Flank pain
2. Intestinal infections:
a. Enterotoxigenic E. coli (ETEC):
 Virulence due to enterotoxins
 Act on small intestine
 Watery diarrhea (common couse of travelar
diarrhea)
 Transmitted by contamination food and water
-Produce Heat stable /Heat labile toxins
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-Adheres to epithelium of small intestine.
-Present with Nausea, Vomiting and Lose stool
-H L like cholera toxin
-Causes accumulation of fluids
-Adhesive factors
- Fimbriae specific receptor in the intestinal
epithelium CFA
-Mortality in children < 5 years
b. Enteropathogenic E. coli (EPEC):
 Adhere to enterocytes, cause destruction of
microvilli of small intestine.
 Infantile and childhood diarrhea (20% of bottlefed)
 Stool: watery, non-purulent, no blood.
c. Enteroinvasive E. coli(EIEC):
 Cause invasion of enterocytes in large intestine
 Necrosis, ulceration and inflammation
 Stool: scanty, purulent and blood stain
d. Enterohemorrhagic E. coli (EHEC)
 Due to verotxin –causes destruction of microvilli
in large intestine.
 Produced by E. coli O157:H7
 Hemorrhagic colitis with copious bloody stool
without pus cells
e.
enteroaggragative E. coli EAggEC)
f. Diffuse-aggregative E. coli.
3. Meningitis in newborns: form mothers genital tract
(colonized with E.coli)
4. Opportunistic infections
 Peritonitis due to intestinal trauma
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 Wound infections
 Bacteremia gram-negative septic shock
5. Hospital-acquired infection: common cause
 Lab diagnosis of E. coli:
- Specimens: urine, stool, pus
- Culture on :
 MacConkey agar-lactose fermenter
 ENB agar- green metallic sheen
 Indole +, citrate –
 TSI: slant acid, butt –acid
 Treatment of E.coli diseases:
- UTI:
use
antibiotics
after
C/S:
Trimethoprim-
Sulphamethoxazole).
-
Diarrhea: oral rehydration + ciprofloxacin
- Meningitis: ceftriaxone (3rd generation cephalosporin).
- Other diseases C/S: increasing resistance in E. coli
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