Escherichia Flashcards
Colon bacillus
E coli
E Coli
Previously considered as a harmless member of the colon biota
• First described by______
• Associated with wide range of clinical syndromes
• Primary marker of___ in water
Theodore Escherich in 1885
fecal contamination
• Closely related to Shigella in terms of DNA homology but can be easily
differentiated through______
• E. coli is____ fermenter
• Shigella is_____ fermenter
lactose fermentation:
lactose
non-lactose
Escherichia coli (Colon bacillus)
Characteristics
• Motile, possess an adhesive
fimbriae and sex pili
• Has _____antigens
O, H and K
Escherichia coli (Colon bacillus)
General laboratory findings
Fermenter of: (4)
Glucose, lactose, trehalose and xylose
Associated with diarrhea of infants (major cause!) and adults in tropical and subtropical areas
Acquired via ingestion of contaminated food and water
ETEC
Most common cause of diarrheal disease commonly referred
as TRAVELLER’S DIARRHEA/TOURIST’S,
DIARRHEA/ “MUNTEZUMA’S REVENGE”
ETEC
10^6 - 10^10 (1000000 - 10000000000) organisms is the infective dose of organisms in immunocompetent individuals.
Enterotoxigenic E.coli (ETEC)
• Serves as a protective mechanism against colonization and disease initiation
• Patients suffering from_____ - higher risk compared to normal persons
ETEC
Stomach acidity
achlorhydria
Colonization of ETEC in the small intestine mediated by fimbriae
Releases toxins in the small intestine
• Heat - Labile (LT) toxin
• Heat - stable (ST) toxin
Enterotoxigenic E.coli (ETEC)
Pathophysiology
- consists of 2 subunits, one A subunit and five B subunit.
B subunit binds to the GM, ganglioside receptor, the same receptor used by cholera toxin to bind on the epithelial cells in the small intestine.
The whole toxin is endocytosed by the epithelial cells of the intestine
LT toxin (heat labile)
Pathophysiology
The increased levels of CAMP stimulate the intestinal cells to hyper secret fluids and electrolytes into the lumen of the intestine.
This results in watery diarrhea (similar to cholera).
Enterotoxigenic E.coli (ETEC)
Enterotoxigenic E.coli (ETEC)
Pathophysiology
• Binds to the transmembrane guanylate peptide cyclase receptor found on the surface of the intestine.
• Binding results in an increased accumulation of cyclic guanosine monophsophate (cGMP) which also causes hyper-secretion of fluid and electrolytes.
• This results in watery diarrhea
Heat - stable (ST) toxin
Diagnosis
Characteristic symptoms such as watery diarrhea, abdominal cramps, and nausea
Isolation of lactose fermenting organisms on selective and differential media
Biochemical tests
Multiplex PCR
Enterotoxigenic E.coli (ETEC)
Note: The presence of colonies on EMB that exhibit a “green
metallic sheen” does not definitively indicate that presence of
Escherichia coli since some (2)
species are also able to produce the same type of colony
characteristic on EMB
Citrobacter and Enterobacter
Associated with dysentery (watery diarrhea with blood, leukocytes, and mucus) similar to Shigella spp.
Occur in adults and children
Direct person-to-person transmission via fecal oral route
Clinical infection characterized by: fever, sever abdominal cramps, malaise, and watery diarrhea.
Enteroinvasive E.coli (ElEC)
Pathophysiology
• Plasmid mediated bacterial invasion (pinv genes) mediate the colonization of
EIC into the colonic epithelium
•____ lyses phagocytic vacuole and replicate into the cell cytoplasm
• Movement within the cytoplasm and into the adjacent cells is regulated by formation of actin filaments
• This destroys colonic epithelium cells and results in inflammation that could progress to colonic ulceration.
Enteroinvasive E.coli (EIEC)
Fecal - oral route
Manifestation:
• Fever, severe abdominal cramps, malaise and watery diarrhea (with blood)
• Clinical symptoms similar to Shigella spp. (Must be differentiated from
Shigella species)
Virulence test:
Enteroinvasive E.coli (EIEC)
SERENY TEST
Similarities of EIEC with Shigella
• Both are gram negative, facultative anaerobic and non-spore-forming bacilli
• Non-motile
• Non-lactose fermenters
• Negative for lysine decarboxylation
• Cross reactions between 0 antigens
Differentiation is done thru:
• Their infective dose
• EIEC - has higher infective dose (____)
• Shigella - as few as____ organisms
• Acetate or mucate utilization as carbon source
- EIEC is positive
10^6
10
Non-toxigenic and non-invasive
strain that causes diarrhea
Enteropathogenic E.coli (EPEC)
Pathophysiology is based on its adhesive properties
Major cause of infant diarrhea in impoverished countries
Characterized by watery
amounts of mucus but no blood!
Enteropathogenic E.coli (EPEC)
Pathophysiology
Infection is initiated by ____
attachment to the epithelial cells of the small intestine with subsequent effacement (destruction)
of the microvillus(attachment/effacement).
Bundle-forming pili (BFP)- mediates the initial aggregation of EPEC that leads to the formation of micro-colonies on the epithelial cell surface.
Enteropathogenic E.coli (EPEC)
Enteropathogenic E.coli (EPEC)
Pathophysiology
Attachment is followed by the active secretion of proteins into the host epithelial cells through the type Ill secretion of EPEC
• __-inserted into the host’s epithelial cell membrane and functions as a receptor for an outer membrane bacterial adhesin, intimin.
• Binding of intimin to Tir - results in polymerization of actin and accumulation of cytoskeletal elements beneath the attached bacteria, loss of cell surface integrity, and death.
Translocated intimin receptor (Tir) -
Pathophysiology
Attachment is followed by the active secretion of proteins into the host epithelial cells through the type Ill secretion of ____
______- causes loss of intestinal barrier function through disruption of tight junctions and induces host cell death through apoptosis.
Enteropathogenic E.coli (EPEC)
-Escherichia colil secreted protein F (EspF)
Causes hemorrhagic diarrhea and colitis
Enterohemorrhagic E.coli (EHEC)
EHEC strain 0157: H7-associated with hemorrhagic diarrhea, colitis, and hemolytic uremic syndrome (HUS)
Classic symptoms - watery diarrhea that progresses to bloody diarrhea with abdominal cramps, low grade fever or an absence of fever.
Stool contains no leukocytes - distinguishes it with dysentery caused by Shigella or ElEC infections
Risk factors - consumption of processed meats such as undercooked hamburgers served at fast food restaurants, unpasteurized dairy products and apple cider, bean sprouts, and spinach.
EHEC
Pathophysiology: Hemorrhagic diarrhea and colitis
_____ 0157:7 (a.k.a STEC) produces two toxins: verotoxin 1 and verotoxin 2
Enterohemorrhagic E.coli (EHEC)
Classic symptoms - watery diarrhea that progresses to bloody diarrhea with abdominal cramps, low grade fever or an absence of fever.
Stool contains no leukocytes - distinguishes it with dysentery caused by Shigella or ElEC infections
Risk factors - consumption of processed meats such as undercooked hamburgers served at fast food restaurants, unpasteurized dairy products and apple cider, bean sprouts, and spinach.
EHEC
Verotoxin 1 -phage encoded toxin identical to the shiga toxin (Stx) produced by Shigella dysenteriae type 1.
It produces damage to Vero Cells (African Green Monkey kidney cells).
Biologically similar to, but immunologically similar from both Stx and verotoxin 1
Enterohemorrhagic E.coli (EHEC)
Pathophysiology: Hemolytic Uremic Syndrome (HUS)
Endothelial cells appear to be particularly important target cells for Shiga toxins.
The toxin is transported retrograde in membrane-bound vesicles to the endoplasmic reticulum.
The A subunit induces depuration in ribosomal RNA; this leads to cessation of protein synthesis and death of the cell.
Enterohemorrhagic E.coli (EHEC)
Shiga-toxin binding to proteins on the surface of glomerular endothelium and
inactivating a metalloproteinase
called von
Willebrand factor-cleaving protease (VWFCP).
Once the
VWFCP is disabled, multimers of von Willebrand Factor
(vWF) form and initiate platelet activation and cause micro thrombi
The arterioles and capillaries of the body become obstructed by the resulting complexes of activated platelets which have adhered to endothelium via large multimeric vWF
Enterohemorrhagic E.coli (EHEC)
The growing thrombi lodged in smaller vessels destroy red blood cells (RBCs) as they squeeze through the narrowed blood vessels, forming schistocytes, or fragments of sheared RBCs This mechanism, known as microangiopathic hemolysis.
The consumption of platelets as they adhere to the thrombi lodged in the small vessels can lead to severe thrombocytopenia
Kidney Failure - Due to reduced blood flow leading to Ischemia and also due to the direct damage caused by the toxin to the renal endothelial cells
Enterohemorrhagic E.coli (EHEC)
EHEC
Thus
the
symptoms of
HUS
thrombocytopenia,
microangiopathic hemolytic anemia, and kidney failure.
Enterohemorrhagic E.coli (EHEC)
Laboratory Diagnosis
Stool culture with serotyping
Isolation using MAC using____ instead of lactose
Demonstration of a four-fold increase or greater in Shiga-toxin neutralizing antibody titer in patients’ sera with HUS
sorbitol
Laboratory Diagnosis
MUG test (4-methylumbelliferyl-ß-D-glucoronide)
rarely produces the enzyme, whereas 92% of other E.coli strains do produce it.
EHEC 0157:7
Note: Sorbitol-negative and MUG-negative colonies are subcultured for serotyping using anti serum for the detection of
E.coli 0157:H7
Implicated in persistent watery diarrhea in infants in developing countries and in travelers to these countries
On of the few bacteria associated with chronic diarrhea and growth retardation in children
Enteroaggregative E.coli (EAEC)
Characterized by their auto-agglutination
“stacked-brick” arrangement”.
Enteroaggregative E.coli (EAEC)
Pathophysiology
The “stacked-brick” arrangement is mediated by______ that are similar to the bundle-forming pilus (BFP) of EPEC.
After adherence of EAEC to the surface of the intestine, mucus secretion is stimulated leading to the formation of a thick biofilm.
Thick biofilm - protects the aggregated bacteria from antibiotics and phagocytic cells.
Enteroaggregative E.coli (EAEC)
aggregative adherence fimbriae I (AAF1) adhesin
Enteroaggregative E.coli (EAEC)
Pathophysiology
Two toxins are also produced:
•_______-antigenically related to the heat-stable toxin of ETEC
•_______
Both toxins induce fluid secretion
Enteroaggregative heat stable toxin
Plasmid encoded toxin
Watery diarrhea with no white blood cells and red blood cells present
EAEC
Most common cause of UTI, mostly occurring among females
Originate from the large intestine a sresident biota, contaminate the urethra, and ascend into the bladder and may migrate to the kidney or prostate
Uropathogenic E.coli
Uropathogenic E.coli
- primary virulence factor which uropathogenic strain used to adhere to epithelial cells and not be washed off with urine flow
- characterized as a hemolysin that can lyse whle blood cells and innion onagocylosis and chemolaxis
- allows uropathogenic strains to chelate iron
Pili
Cytolysins
Aerobatin
Meningitis - caused by E.coli (and also group B streptococci!)
Acquired in the birth canal during delivery
May also result if contamination of the amniotic fluid occurs.
Septicemia- originates from infections in the urinary tract or gastrointestinal tract
Encapsulated strains of E.coli (possess K1 Ag) - mostly associated with neonatal meningitis and septicemia
Extra-intestinal Infections
Bacteremia - E.coli is a clinically significant isolate in blood cultures from adults.
Bacteremia in adults may result from
urogenital tract infection or from Gl source.
Extra-intestinal Infections
• Formerly called E.coli atypical or
enteric group lI
• Yellow pigmented colonies
• Isolated from CSF, wounds and blood
E. hermannii
• Isolated from humans with infected wounds
• Half of the strains produced yellow-pigmented colonies
E. vulneris
• Associated with diarrheal disease in children
E. albertii
