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54 Cards in this Set

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  • Back
What is the gram stain, oxygen requirements and shape of the enterobacteriaceae?
They are gram negative rods with rapid growth under both aerobic and anaerobic conditions
Describe the abilities of E. coli, shigella, and salmonella to ferment lactose and glucose
All of the three can ferment glucose, but only escherichia can ferment lactose
What are the antigens commonly found with the enterobacteriaceae?
O antigen, H antigen (flagella), K antigen (polysaccharide capsule)
What are the major cellular antigens of E. coli?
LPS (O antigen), capsule (K antigen), flagella, pili/fimbriae
What capsule antigen is most important for disseminated E. coli infections?
The K1 antigen
What role does the pili of E. coli play in it's virulence?
It aides in the adherence to the mucosal surfaces
What type of fimbriae are associated with enterotoxigenic E. coli?
CFA fimbriae
What type of fimbriae is found in all normal flora intestinal isolates and UTI isolates of E. coli?
Type 1 fimbriae
What are the types of exotoxins secreted by E. coli?
1) Enterotoxins 2) Shiga-like toxins 3) hemolysin
What are the two types of enterotoxins produced by E. coli and what strains produce them?
The enterotoxins are the heat-labile toxin (LT) and the heat-stable toxin (ST); they are NOT found in normal flora E. coli but instead are produced by the enterotoxigenic E. coli (ETEC)
What exotoxin of E. coli has the same mechanism of action as the cholera toxin? What is the MOA?
The heat-labile enterotoxin has the same mechanism of action as cholera toxin - it activates adenylate cyclase and causes fluid secretion
What type of E. coli produce the Shiga-like toxin?
The shiga-like toxin is produced by enterohemorrhagic E. coli EHEC); it is NOT produced by normal flora E. coli
What symptoms are produced by the entertoxin?
Watery diarrhea (such as traveler's diarrhea)
What is the disease caused by the shiga-like toxin?
Enterohemorrhagic colitis
What sort of disease is caused by the shiga-like toxin?
The shiga-like toxin has activity identical to the shiga toxin from Shigella and inhibits protein synthesis in target cells; it causes hemolytic uremic syndrome with a bloody diarrhea and destruction of renal endothelium
What is the normal habitat of E. coli?
The intestinal tract of animals and humans
How does E. coli cause urinary tract infections and invasive disease?
One's own normal intestinal flora spreads to these body areas
How does E. coli cause intestinal infections?
These are caused by the fecal-oral spread of new unique strains of E. coli that have acquired additional virulence factors on plasmids of phage
Describe the transmission of the enterohemorrhagic E. coli. What kind of toxin does it produce?
The transmission of the EHEC is via animal-to-human transmission; it makes the shiga-like toxin
Describe the transmission of the enterotoxigenic E. coli. What kind of toxin does it produce?
The transmission of the ETEC is via human-to-human transmission; it produces the enterotoxins
What strain or E. coli is responsible for bloody diarrhea and kidney failure?
What are the clinical manifestations of enterohemorrhagic E. coli?
It begins as a watery diarrhea followed by bloody diarrhea; children may develop HUS (kidney failure and hemolytic anemia)
What is the difference between the diarrhea of EHEC and dysentery of Shigella species?
Shigella dysentery shows pus in the stools and fever, both of which are NOT seen in EHEC hemorrhagic colitis
Describe the pathogenesis of enterohemorrhagic colitis
The shiga-like toxin causes destruction of the epithelial cells in the colon leading to bloody diarrhea and shiga-like toxin circulation into the bloodstream which allows for destruction of renal endothelial and glomeruli (local infection with systemic toxemia)
What is important about the treatment of enterohemorrhagic e. coli?
It should NOT be treated with an antibiotic because it will enhance the Shiga-toxin release, making the HUS worse
What populations usually see enterotoxigenic E. coli infections?
Infants and children in developing countries or tourists to those countries
Describe the clinical manifestations of enterotoxigenic E. coli infection (ETEC)
A watery diarrhea that may produce a severe cholera-like disease with absent fever
Describe the pathogenesis of ETEC
It is similar to cholera toxin and shows production of one or both of the enterotoxins (LT or ST) with no invasion (bacteria remain localized in the small intestines)
What are the two main species of shigella?
S. dysenteriae and S. sonnei
What are the major cellular antigens of Shigella?
The major cellular antigens are LPS (O-antigen), and invasion plasmid antigens that are essential for the entry into intestinal epithelial cells
Describe the toxin produced by Shigella
The Shiga toxin is a lethal toxin which kills target cells by inhibiting protein synthesis causing a bloody diarrhea with local infection and a killing of renal endothelial cells with a systemic infection
Why is S. dysenteriae more pathogenic than S. sonnei?
It produces nearly 1000 times more shiga toxin
Where is shigella commonly found?
It is commonly found in the intestinal tract of humans with disease but is NOT NORMAL FLORA and has no animal carriers
How is Shigella transmitted?
It is transmitted by the fecal-oral route and is largely a pediatric disease (caused by S. sonnei)
Describe the clinical manifestations of Shigellosis including which species is the cause
Shigellosis is generally caused by S. sonnei, flexneri and boydii and produces a watery diarrhea that is NOT the classical dysentery
Describe the pathogenesis of shigellosis
The bacteria invade the colonic epithelial cells and reproduce intracellularly, small amounts of Shiga toxin are produced
Describe the clinical manifestations of bacterial dysentery and name the causative species
Bacterial dysentery is caused by S. dysenteriae with symptoms of small volume bloody diarrhea and mucoid discharge with fever as well as hemolytic uremic syndrome and extensive ulceration in severe cases
Describe the pathogenesis of bacterial dysentery
The bacteria invade the colonic epithelium and replicate intracellularly with production of large amounts of the Shiga toxin; large amounts of leukocytes and red cells appear in the stools
How is shigella diagnosed and what is important to consider when treating?
It is diagnosed based on stool cultures and should NOT be treated with antibiotics when showing signs of HUS
Which serotypes of Salmonella cause food poisoning (gastroenteritis)
S. typhimurium and S. enteritidis
What serotypes of Salmonella cause typhoid fever?
S. typhi and a. paratyphi
What are the major cellular antigens of shigella?
LPS endotoxin (O antigen) and adhesion and invasion antigens required for growth inside macrophages
What type of salmonella has enterotoxins?
S. enteritidis
What is the primary reservoir for salmonella and how do humans become infected?
The major reservoir is the intestinal tract of animals, with humans becoming infected through the ingestion of contaminated water or food and high rate of secondary spread via human to human contact
What are the most common sources of salmonella?
Poultry and eggs (salmonella inside the yolk and egg white) as well as pet reptiles
Describe the gastroenteritis caused by salmonella
It has an incubation period following infection and shows a nausea and vomiting that progresses to abdominal pain and diarrhea with fever
Describe the pathogenesis of a salmonella infection
The ingested bacteria invade and replicate in epithelial cells of the small and large intestines, as well as the macrophages; there is NO bloodstream invasion except in compromised patients
What is Reiter's Syndrome?
An autoimmune linked syndrome which is a response to an infection in another part of the body with symptoms of arthritis of large joints, inflammation of the eyes, and urethritis; associated with chlamydia trachomatis, salmonella, shigella, yersinia, or campylobacter
What is the distinctive antigen of salmonella typhi?
The Vi capsular antigen which aids in bloodstream spread
What causes typhoid fever?
Salmonella typhi
Describe the pathogenesis of typhoid fever
The bacteria invade the submucosa via M cells and multiply within the macrophages and spread to the bloodstream, liver, spleen and bone marrow all the while asymptomatic!
What happens in the pathogenesis of typhoid after the bacteria spread to the liver?
Increased numbers in the liver lead to a sustained bacteremia with high fever spreading to the kidney, gallbladder, peyers patches and skin
How does the carrier state of typhoid occur?
A chronic infection in the gallbladder with the bacteria constantly shed in the bile/feces
What are the two vaccines for typhoid fever and who should receive them?
Travelers to developing countries should receive them; one is a purified Vi capsular polysaccharide and the other is a live attenuated S. typhi strain