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Questions and Answers
What is the net result of the LT mechanism described in the text?
What is the net result of the LT mechanism described in the text?
Which molecule causes permanent activation of adenyl in the LT mechanism?
Which molecule causes permanent activation of adenyl in the LT mechanism?
What is the function of a-hemolysin in certain E. coli strains?
What is the function of a-hemolysin in certain E. coli strains?
What is the primary function of a contact secretion system possessed by certain E. coli?
What is the primary function of a contact secretion system possessed by certain E. coli?
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Which type of E. coli strain is known to have intimin as an important adhesin?
Which type of E. coli strain is known to have intimin as an important adhesin?
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How are pathogenic E. coli strains classified based on their serology and pathogenic behavior?
How are pathogenic E. coli strains classified based on their serology and pathogenic behavior?
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What are the two principal disease manifestations of Salmonella enterica?
What are the two principal disease manifestations of Salmonella enterica?
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Why are small children more likely to have a bad outcome when infected with Salmonella enterica?
Why are small children more likely to have a bad outcome when infected with Salmonella enterica?
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Where is Salmonella enteritis chiefly contracted from?
Where is Salmonella enteritis chiefly contracted from?
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What makes Enteric (typhoid) fever caused by S.enterica serotype Typhi a potentially very dangerous systemic infection?
What makes Enteric (typhoid) fever caused by S.enterica serotype Typhi a potentially very dangerous systemic infection?
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Why is Salmonella enteritis considered more dangerous than typical salmonella?
Why is Salmonella enteritis considered more dangerous than typical salmonella?
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What is the mechanism that allows Salmonella enterica to cross the lining of the gut?
What is the mechanism that allows Salmonella enterica to cross the lining of the gut?
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What is the advantage of using a treponemal test?
What is the advantage of using a treponemal test?
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Why are treponemal tests not useful for screening?
Why are treponemal tests not useful for screening?
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What makes it difficult to interpret treponemal test results in infants?
What makes it difficult to interpret treponemal test results in infants?
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Which is the drug of choice for Borrelia infections?
Which is the drug of choice for Borrelia infections?
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Where was Lyme disease first observed?
Where was Lyme disease first observed?
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What is a characteristic symptom of the first stage of Lyme disease?
What is a characteristic symptom of the first stage of Lyme disease?
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What is the old name for Mycoplasma pneumoniae?
What is the old name for Mycoplasma pneumoniae?
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Which of the following statements is true about Ureaplasma urealyticum?
Which of the following statements is true about Ureaplasma urealyticum?
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What is the unique means of motility for spirochetes?
What is the unique means of motility for spirochetes?
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What is the principal pathologic finding in syphilis?
What is the principal pathologic finding in syphilis?
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Which stage of syphilis is characterized by a long time course, Type IV hypersensitivity damage, and spontaneous remission?
Which stage of syphilis is characterized by a long time course, Type IV hypersensitivity damage, and spontaneous remission?
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What makes Treponema pallidum difficult to grow except in tissue culture at low oxygen concentration?
What makes Treponema pallidum difficult to grow except in tissue culture at low oxygen concentration?
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Which type of E.coli is associated with 'traveller's diarrhea'?
Which type of E.coli is associated with 'traveller's diarrhea'?
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Which E.coli type is a major cause of diarrheal illness in small children and causes damage by injecting cytoskeletal inhibition?
Which E.coli type is a major cause of diarrheal illness in small children and causes damage by injecting cytoskeletal inhibition?
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Which E.coli type has a reservoir in cattle and produces Shiga toxin?
Which E.coli type has a reservoir in cattle and produces Shiga toxin?
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Which E.coli type pathogenesis is dependent on LT and ST toxins and CFA-type pili?
Which E.coli type pathogenesis is dependent on LT and ST toxins and CFA-type pili?
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Which E.coli type causes malabsorptive diarrhea by disrupting the cytoskeletons of microvilli on intestinal lining cells?
Which E.coli type causes malabsorptive diarrhea by disrupting the cytoskeletons of microvilli on intestinal lining cells?
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Which E.coli type is non-invasive and damages readily reversible?
Which E.coli type is non-invasive and damages readily reversible?
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Study Notes
E. coli
- Similar molecules seen in other organisms as well
- LT (Heat-Labile Toxin) ADP-ribosylates a G protein, causing permanent activation of adenyl cyclase and resulting in efflux of water from the cell
- ST (Heat-Stable Toxin) has an overall effect similar to LT but works via cGMP
- Hemolysins, such as a-hemolysin, similar to those of staph and strep, are channel formers
- Contact secretion system: a molecular "syringe" possessed by certain E. coli, allowing for the injection of macromolecules into cells and causing major cytoskeletal rearrangement
- Intimin: an important adhesin found in certain E. coli serogroups
Pathogenic E. coli Strains
- Classified into four groups based on serology and pathogenic behavior:
- Enterotoxigenic E. coli (ETEC)
- Enteropathogenic E. coli (EPEC)
- Enterohemorrhagic E. coli (EHEC)
- Enteroinvasive E. coli (EIEC)
Enterotoxigenic E. coli (ETEC)
- Causes traveler's diarrhea or Montezuma's revenge
- Important cause of infant diarrhea in developing countries
- Acts on cyclic nucleotides
- Pathogenesis dependent on LT and ST toxins and CFA (colony formation antigen)-type pili
- Non-invasive, damage readily reversible
Enteropathogenic E. coli (EPEC)
- A major cause of diarrheal illness in small children
- No toxins in the classic sense, but damaging substances involved
- Contact secretion system injects cytoskeletal inhibiting agents, leading to decrease in surface area and absorption
- Disrupts cytoskeletons of microvilli on intestinal lining cells, causing attachment and effacement (A/E) lesions
- Malabsorptive diarrhea, reversible
Enterohemorrhagic E. coli (EHEC)
- Mainly O157:H7
- Reservoir in cattle
- Shiga toxin plus A/E lesions
- Very low infectious dose (100-200 cells)
- Causes bloody diarrhea leading to dysentery and HUS (Hemolytic Uremic Syndrome) in about 10% of cases
- HUS: glomerulus contains many receptors for toxin, leading to renal failure and death
Salmonella
- Similar in many respects to E. coli
- About 2000 named serotypes, formerly considered species, now all classified as "S. enterica"
- Two principal disease manifestations: enteritis (so-called "Salmonella food poisoning") and enteric fever (historic name "typhoid fever")
- People most likely to have a bad outcome: small children (immune system has yet to develop) and elderly people (due to poor stomach acid)
- Requires an actual organism infection, better referred to as food-borne infection
- Can be transmitted through contaminated foodstuffs, dairy products, eggs, poultry, and plant material
Salmonella Enteritis
- Mechanism of pathogenesis unclear, but contracted chiefly from contaminated foodstuffs
- Symptoms (nausea, vomiting, maybe fever, etc.) may be due to inflammation or enterotoxin activity
- Considerable spectrum of severity
Salmonella Enteric (Typhoid) Fever
- Totally human, due to S. enterica serotype Typhi
- Can grow in bile, highly bile resistant, and readily survives macrophages
- Systemic infection with a weeks-long time course, can be very damaging
- Important to understand the survival and growth of the organism in macrophages
Borrelia
- Large, microaerophilic, and will grow on artificial media
- Many are carried by arthropods (most often ticks or lice)
- Two most important conditions: relapsing fever and Lyme disease
- Relapsing fever: due to B. hermsii, carried by body lice, fever comes and goes over months
- Lyme disease: caused by B. bergdorferi, found in land with vegetation, and carried by Ixodes ticks (eastern and western deer ticks)
- First stage: rash (bull's eye, erythema migrans)
- Second stage: cardiac and/or nervous symptoms, usually resolve in weeks
- M. pneumoniae responsible for about 10% of pneumonia ("walking" pneumonia)
Ureaplasma urealyticum
- Identified with urethritis (males) and possibly a variety of other conditions, exact role/significance unclear
- Commonly seen resident flora organism in the GU tract
Spirochetes (Order Spirochetales)
- Gram negative organisms with unusual spiral morphology and unique means of motility (endoflagella within periplasmic space)
- Motility sometimes called "spinning and flexing"
- Bending in the middle
- Commonly seen in many animals, including humans, especially in the oral cavity
- Can be difficult to visualize under light microscope, hard to see and stain due to very thin structure
Treponema pallidum and Syphilis
- Strictly human, difficult to grow except in tissue culture at low oxygen concentration
- Abscess-like structure that is triggered by type 4 hypersensitivity
- Syphilis is a classic granulomatous disease in many respects
- Three stages: primary, secondary, and tertiary, with latent phase between secondary and tertiary
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Description
Test your knowledge about the mechanism of bacterial toxins, focusing on ADP-ribosylation of G proteins and its effects on cellular processes. Explore how these toxins lead to the efflux of water from cells and the activation of adenylate cyclase and cAMP. Additionally, learn about the role of cGMP in the process.
