Pathogenesis Flashcards
Virulence is measured by______, or the dose needed to cause symptoms in 50% of hosts
ID50 (Infective dose); cause symptoms in 50%
Pathogenicity Island
-Several genes that direct invasion are clustered together on the chromosome contain DRs (direct repeats) and ISs (insertion sequences)
- can contain genes that cause systematic disease
- appear to have been horizontally transmitted via conjugation or transduction
Why does is seem that most pathogenicity islands have been horizontally transmitted via conjugation or transduction?
- Unique GC/AT rations
- Codon biases
- Flanked by inverted repeats
- Found in specific strains of a species
Which of the following is evidence that a pathogenicity island was initially acquired by horizontal transfer?
A. It contains genes for core, fundamental biological processes such as transcription.
B. It has a GC percentage different from the rest of the genome.
C. It is passed on to daughter bacteria during cell division.
D. It contains genes for a sex pilus.
B. It has a GC percentage different from the rest of the genome.
Which of the following statements about virulence factors is true?
They increase the ability of a pathogen to cause disease
Some intracellular pathogens can use unipolar structures to mediate host cell actin polymerization. This gives the microbe motility within the host cell. In order for a pathogen to avoid being killed by the phagolysosome, which mechanism relies most upon motility?
escape of the phagosome, for example by capsule interactions
How do capsules prevent phagocytosis
blocks opsonization - no access of receptors to opsonins –> MOST IMPORTANT
blocks antibody, complement interaction
mimics “self molecules”
- prevents stimulation of antibody complement responses
Suppose a suspected virulence gene is deleted from a pathogenic organism. If the gene product did indeed decrease virulence, the modified organism will have
a higher LD50 than the unmodified, gene-containing organism.
- remember the inverse relationship higher Ld50 or id 50 means it takes a higher dose for same effect
Through a search of the genetic databases it is found that a protein expressed by a microbial pathogen resembles a host protein. What is this resemblance most likely to indicate?
The microbial protein mimics the host protein’s function.
A localized, focal point of infection found within a patient’s catheter is most likely employing which virulence mechanism?
biofilm
The bacterial pathogens Salmonella and Shigella can live either inside a host cell or independently of a host cell. Such pathogens are known as what?
facultative intracellular pathogens
- intracellular when it’s need
Which type of secretion system resembles conjugation machinery?
Type IV secretion
AB toxin
A subunit - toxic activity (2 domain A1 - toxic activity, A2 fixes to B)
B subunit - binding activity (Binds GM1)
- triggers endocytosis ends up at ER the A1 peptide is released and will modify a G Protein by using NAD+and adding ribose ADP to the alpha subunit to prevent the deactivating through the hydrolysis of GTP and so it stays active producing a ton of cAMP which keeps Cl- channels open they leave the cell and so does water to try to regulate osmolarity. –> diarrhea
The cholera toxin, an AB exotoxin, attaches an ADP-ribose group to the host’s stimulatory G factor (Gs). The normal function of Gs is to stimulate the host’s adenylate cyclase, which produces the second messenger molecule cAMP. This toxin-mediated ADP-ribosylation of Gs has which of the following effects?
constant activation of Gs, causing an increase in cAMP levels and resulting in increased ion transport from the infected host cell
The cholera toxin, an AB exotoxin, creates a(an)
________ environment in the intestinal lumen when compared to the cytoplasm of the intestinal cells.
hypertonic
What characteristic of V. cholerae allows it to cause widespread epidemics?
V. cholerae can survive in marine environments and can thereby spread to many areas where people live.
What aspect of V. cholerae allows it to spread quickly from one person to many people?
People infected with V. cholerae produce copious fecal particles containing V. cholerae cells.
A gene coding for __________ proteins is likely to be found in a genomic island of a pathogenic bacterial strain and NOT found in a nonpathogenic strain.
host cell attachment
The pathogenic strain of Escherichia coli, E. coli O104:H4, expresses the Shiga toxin and is highly resistant to many antibiotics. How did the E. coli O104:H4 strain originally obtain the genes for the Shiga toxin and antibiotic resistance?
horizontal gene transfer
A hypothetical drug with which of the following effects would be the most useful in treating the diarrhea caused by cholera?
increases the GTPase activity of the ADP-ribosylated stimulatory G factor (Gs)
How do phagocytes overcome the immune protection that the bacterial capsule gives to pathogens?
They bind to the Fc region of antibodies that opsonize the capsule.
The ability of HIV to use a capsular protein to bind to the host cell CCR5 receptor is an example of which type of virulence factor?
Nonpilus adhesins
Which of the following information could not be gained from a genomic study of a pathogenic strain and a nonpathogenic strain of the same species of bacteria?
genes that are expressed when the pathogenic bacteria infect a host
Hosts differ in how susceptible they are to certain infections due to differences in
cell surface receptors.
The pathogen Listeria monocytogenes produces exotoxins that disrupt membranes. What is the purpose of the membrane disruption caused by Listeria monocytogenes?
to allow the bacteria to escape the phagosome and grow in the cytoplasm of the host
An obligate intracellular pathogen like Rickettsia compares to a facultative one like Salmonella in that it
cannot grow outside the host cell.
The image below shows Staphylococcus aureus colonies growing on an agar plate. What exotoxin-mediated process is shown in this image?
colonies budding off “eggs” are clearing around them
