Virulence factors of Staph and Strep
- Dashboard
- Virulence factors of Staph and Strep
Most Recent Score Report
| Questions Correct | Questions Answered | Time Spent | Status | Attempt Date | |
|---|---|---|---|---|---|
| -- | -- | -- | -- | -- |
Previous Score Reports
| Questions Correct | Questions Answered | Time Spent | Status | Attempt Date | |
|---|---|---|---|---|---|
| -- | -- | -- | -- | -- |
Virulence factors of Staph and Strep
Array
(
[passage] => WP_Post Object
(
[ID] => 554586
[post_author] => 12815
[post_date] => 2024-12-23 17:58:00
[post_date_gmt] => 2024-12-23 22:58:00
[post_content] => Practice Passage (Question 1-6)
*This passage is the property of Khan Academy and has been reformatted into an AAMC-style interface in their entirety by MedLife Mastery. MedLife Mastery does not endorse and is not an affiliate of Khan Academy.
Staphylococcus aureus and group A streptococci are both gram-positive cocci, although S. aureus strains are facultative anaerobes, whereas group A streptococci are aerotolerant anaerobes. Both organisms depend on a myriad of cell-surface and secreted virulence factors for host colonization and disease production. These cell-surface virulence factors include a variety of proteins referred to as microbial surface components recognizing adhesive matrix molecules (MSCRAMMs). These molecules facilitate the attachment to host cells or interfere with host immune responses through antiphagocytic effects. Both organisms also produce large numbers of secreted virulence factors, including families of superantigens (SAgs) and cytolysins.
Nearly all S. aureus strains can produce one or more SAg proteins, including toxic shock syndrome toxin-1 (TSST-1), a small protein that can trigger a massive immune response that results in toxic shock syndrome (TSS). TSS is a rare but potentially life-threatening illness that is characterized by the rapid onset of symptoms, including high fever, low blood pressure, a rash resembling sunburn, and organ dysfunction.
When staphylococci come in contact with a mucosal surface, they secrete α-cytolysins, which bind to receptors on the surface of the target cell and form oligomers (clusters) that insert into the lipid bilayer, creating transmembrane pores. This allows TSST-1 to reach the deeper mucosal layers, where T cells reside. TSST-1 binds nonspecifically to T cells’ surface receptors, activating T cells to release highly inflammatory molecules, such as interleukin-1 (IL-1) and tumor necrosis factor (TNF), beginning the cascade of clinical TSS symptoms.
Treatment of TSS involves an antibiotic course, provision of fluids, and intravenous immunoglobulin (IVIg). IVIg is a purified antibody collected and pooled from multiple donors; it acts to neutralize TSST-1. In some toxin-mediated staphylococcal infections, a second antibiotic, clindamycin, is added to the treatment regimen for its anti-protein synthesis effects.
Adapted from Brosnahan et al. Gram-positive bacterial superantigen outside-in signaling causes toxic shock syndrome. FEBS J. Dec 2011; 289(23): 4649-4667
[post_title] => Virulence factors of Staph and Strep
[post_excerpt] =>
[post_status] => publish
[comment_status] => closed
[ping_status] => closed
[post_password] =>
[post_name] => virulence-factors-staph-strep
[to_ping] =>
[pinged] =>
[post_modified] => 2024-12-23 17:58:00
[post_modified_gmt] => 2024-12-23 22:58:00
[post_content_filtered] =>
[post_parent] => 0
[guid] => https://medlifemastery.com/?post_type=passage&p=554586
[menu_order] => 0
[post_type] => passage
[post_mime_type] =>
[comment_count] => 0
[filter] => raw
)
[questions] => Array
(
[0] => Array
(
[quiz_unique_key] => 602779517
[question] => S. aureus differs from group A streptococci in which way?
[value] => Array
(
[answer] => 2
[description] => Reason for Correct Answer:
The first paragraph states that S. aureus strains are facultative anaerobes, whereas group A streptococci are aerotolerant anaerobes.
An aerotolerant anaerobe can survive in conditions containing oxygen (aerotolerant) but doesn’t utilize oxygen (anaerobe).
Facultative anaerobes are also sometimes referred to as “facultative aerobes,” and an aerobic organism can use oxygen.
Facultative anaerobes (aka facultative aerobes) like S. aureus can utilize oxygen but can also adapt and continue to grow in the absence of oxygen. They are different from obligate aerobes, which are microorganisms that require oxygen for their growth and survival.
)
[answers] => Array
(
[0] => Array
(
[each_answer] => A. S. aureus cannot tolerate oxygen-containing environments.
)
[1] => Array
(
[each_answer] => B. S. aureus can utilize oxygen but does not require it.
)
[2] => Array
(
[each_answer] => C. S. aureus requires oxygen to survive.
)
[3] => Array
(
[each_answer] => D. S. aureus can survive in oxygen-containing environments.
)
)
)
[1] => Array
(
[quiz_unique_key] => 1403770772
[question] => Which are examples of mucosal surfaces that S. aureus might penetrate?
I. Skin surfaces and open wounds
II. The inner lining of the bladder
III. The nasal passages
IV. Heart valves
[value] => Array
(
[answer] => 2
[description] => Reason for Correct Answer:
Although Staph can enter non-mucosal and mucosal surfaces, the passage describes the bacterium penetrating mucosal surfaces and this question is asking which surfaces that could include. Mucosa is found in specific places in the body.
Mucosa, also known as a mucous membrane, is a specialized type of tissue that lines various cavities and surfaces within the body. Mucosal surfaces are characterized by the presence of mucous-producing cells and are typically moist. In many mucosal surfaces, the outermost layer or lining of the mucosa is made up of epithelial tissue. This epithelium forms the interface between the external environment (such as the contents of the digestive tract or the air in the respiratory tract) and the internal tissues of the body.
Mucosal surfaces are found lining the gastrointestinal tract and the respiratory tract, including the oral and nasal passages, as well as the genitourinary cavity.
Mucosal surfaces are therefore found in the inner lining of the bladder (II) and the nasal passages (III).
)
[answers] => Array
(
[0] => Array
(
[each_answer] => A. I and IV only
)
[1] => Array
(
[each_answer] => B. II and III only
)
[2] => Array
(
[each_answer] => C. II, III, and IV only
)
[3] => Array
(
[each_answer] => D. I and II only
)
)
)
[2] => Array
(
[quiz_unique_key] => 1403770772
[question] => What structural feature of alpha-cytolysins most contributes to their ability to aid in cell penetration?
[value] => Array
(
[answer] => 1
[description] => Reason for Correct Answer:
The passage says that α-cytolysin forms oligomers that “insert into the lipid bilayer, creating transmembrane pores.” Like other pore-forming toxins, they must have a structure that allows them to interact with lipid membranes effectively.
α-Cytolysins typically have an amphipathic structure, meaning they have both hydrophilic (water-attracting) and hydrophobic (water-repelling) regions. This amphipathic nature is crucial for their interaction with lipid bilayers.
The hydrophilic heads of alpha-cytolysins are typically involved in receptor binding and initial interactions with the target cell’s membrane. These regions are attracted to the aqueous environment surrounding the cell.
The hydrophobic tails of α-cytolysins, on the other hand, can more easily penetrate the lipid bilayer of the cell membrane. Lipid bilayers consist of a hydrophobic core made up of fatty acid tails of phospholipids. The hydrophobic tails of the toxin can embed themselves into this lipid bilayer, disrupting this organization and creating a channel or pore.
)
[answers] => Array
(
[0] => Array
(
[each_answer] => A. Hydrophobic tail
)
[1] => Array
(
[each_answer] => B. Hydrophilic head
)
[2] => Array
(
[each_answer] => C. Beta-sheet secondary structure
)
[3] => Array
(
[each_answer] => D. Disulfide bonds
)
)
)
[3] => Array
(
[quiz_unique_key] => 1403770772
[question] => What is a likely effect of IVIg treatment?
[value] => Array
(
[answer] => 2
[description] => Reason for Correct Answer:
The passage says that IVIg works to neutralize TSST-1, not to reduce the replication of bacteria.
TSST-1 is not responsible for mucosal barrier destruction – that is α-cytolysin. So, IVIg would not help with this. TSST-1 is, however, responsible for the clinical symptoms of toxic shock syndrome (TSS).
Neutralizing TSST-1 would halt the resultant inflammatory cascade that causes the clinical symptoms of low blood pressure (hypotension), rash, and organ dysfunction.
The answer choice consistent with this is reduced vascular leakage and hypotension.
)
[answers] => Array
(
[0] => Array
(
[each_answer] => A. Reduced replication of S. aureus
)
[1] => Array
(
[each_answer] => B. Reduced vascular leakage and hypotension
)
[2] => Array
(
[each_answer] => C. Enhanced T cell proliferation cell binding.
)
[3] => Array
(
[each_answer] => D. Restoration of mucosal barriers
)
)
)
[4] => Array
(
[quiz_unique_key] => 1403770772
[question] => When comparing two patients with TSS, the patient with higher-affinity T cell binding to TSST-1 would most likely require:
[value] => Array
(
[answer] => 3
[description] => Reason for Correct Answer:
The detrimental effects of TSST-1 are caused by its immune cell activation.
The patient in question would have a more pronounced response to TSST-1.
Antibiotics, although they will eliminate the causative pathogen, do not always ameliorate toxin-mediated processes.
A more pronounced response to the TSST-1 would require more supportive care, i.e., more aggressive fluid resuscitation
)
[answers] => Array
(
[0] => Array
(
[each_answer] => A. higher-dose antibiotics.
)
[1] => Array
(
[each_answer] => B. a longer course of antibiotics.
)
[2] => Array
(
[each_answer] => C. more intensive rehydration.
)
[3] => Array
(
[each_answer] => D. lower-dose IVIg.
)
)
)
[5] => Array
(
[quiz_unique_key] => 1325138223
[question] => What is the likely identity of an MSCRAMM?
[value] => Array
(
[answer] => 2
[description] => Reason for Correct Answer:
The passage defines MSCRAMMs as “microbial surface components recognizing adhesive matrix molecules” that can “facilitate attachment to host cells.” It also mentions that MSCRAMMs are proteins.
So, they’re like to be proteins that bind to adhesive cell matrix molecules.
Adhesive matrix molecules are host proteins found in the extracellular matrix (ECM) of tissues that play a critical role in cell adhesion, tissue integrity, and various cellular processes. These molecules are essential for maintaining the structural and functional integrity of tissues. They include various proteins, glycoproteins, and proteoglycans.
Keratin is not a cell matrix molecule but is a fibrous structural protein found in the skin, hair, and nails.
Adhesive matrix molecules include things like fibronectin, collagen, laminin, elastin, heparin sulfate, mucins, and hyaluronic acid. MSCRAMMs like fibronectin-binding protein and collagen-binding protein could bind to these.
)
[answers] => Array
(
[0] => Array
(
[each_answer] => A. Lipopolysaccharide
)
[1] => Array
(
[each_answer] => B. Fibronectin-binding protein
)
[2] => Array
(
[each_answer] => C. Keratin-binding protein
)
[3] => Array
(
[each_answer] => D. Collagen
)
)
)
)
[total_question] => 6
[correct_answers] => Array
(
[554586|1] => B
[554586|2] => B
[554586|3] => A
[554586|4] => B
[554586|5] => C
[554586|6] => B
)
[hide_display_feedback_settings] =>
[hide_solutions] =>
)