Flashcards in Exam #4: Bacterial Infections of the URT Deck (40):
List the anatomical structures that form the upper respiratory tract.
Essentially, everything from the mouth, ears, eyes, & nose down to the epiglottis (with the epiglottis included)
What infections are associated with upper respiratory pathogens?
What is the function of the upper respiratory tract?
- Regulates the temperature & water content of inspired air
- Membranes are constantly being bombarded by pathogens
What is the function of the ciliated epithelium in the URI?
- Cilia beat roughly 1,000/min
- The beating cilia form the mucociliary escalator
Thus, a URT pathogen must avoid being caught in the mucociliary escalator & swallowed to cause disease
What stops the mucociliary escalator?
- Viral infection
*Thus, pathogens are stuck in the lower airway & can lead to severe pneumonia
What respiratory tissues are considered sterile?
- Mastoid air cells
- Middle ear
- Bronchi & bronchioles
Why is the normal flora of the URT important in the hospital setting?
- Normal flora in the nose (s. aureus) will increase with prolonged time in the hospital setting
- Epidemiologic issue
What is special about the conjunctiva?
Conjunctiva should be sterile because of lysozyme & eyelid blinking, but you're going to find that there are a number of pathogens in that region; however, these pathogens do NOT usually colonize
What are the normal flora that are present in the nose?
- Staphylococcus epidermidis
- Staphylococcus aureus (increase in hospital setting, which will have epidemiologic implications)
What are the characteristics of staphylococcus epidermidis & aureus?
- Gram (+)
- Cocci clusters
- Facultative anaerobes
*Look like a cluster of grapes*
What are the characteristics of coryebacterium?
- Gram (+)
- Non-spore forming
Found in nasal secretions & nares
What bacteria are part of the normal flora of the nasopharynx?
- Streptococcus (viridans group)
- Moraxella catarrhalis
What are the characteristics of moraxella catarrhalis?
- Gram (-)
- Diploid coccobacillus
What is unique about the bacteroides group that form the normal flora of the nasopharynx?
Only anaerobe in the URT
What are the pathogens that typically infect the nasopharynx. What season are they associated with increasing?
*Note that all of these pathogens increase in the winter months & ALL can be part of the normal flora.
What differentiates Streptococcus from Staphylococcus?
Streptococcus are Catalase (-)
What are the characteristics of the streptococci?
- Gram (+)
- Cocci in chains
- Catalase (-)
What are the Group A strep?
S. Pyogenes (Beta-hemolytic)
What are the Group B Strep?
S. Agalactiae (Beta-hemolytic)
What are the Group D Strep?
What is the one alpha-hemolytic streptococcus?
If you see anything that is alpha-hemolytic, think strep. pneumoniae*
What are the symptoms of streptococcal pharyngitis (strep throat)? What is it caused by? What are the characteristics of the causative organism?
- Symptoms of strep throat include:
○ Redness of the throat
○ Patches of adhering pus
○ Scattered tiny hemorrhages
- Strep throat is caused by Streptococus Pyogenes, which is: Catalase negative, Beta-hemolytic, & Group A
What does a rapid strep test target?
Group A antigen, which is part of the cell wall antigen of Streptococcus pygoens
What is the M-protein?
M-protein= a virulence factor associated with streptococcus pyogens that causes the degradation of complement C3b
- Thus, M-protein is anti-phagocytic
*This is ESSENTIAL for virulence; if strep does NOT have M-protein, it is not virulent
80 strains= v. difficult to make a vaccine
What is special about the capsule in streptococcus pyogenes?
- Some strains are capsulated & some are not
- The capsule in capsulated strains is made of hyaluronic acid and inhibits phagocytosis/ aids in adherence to epithelial cells
Functions to inhibit phagocytosis & increases virulence
What are streptococcal pyrogenic exotoxins (SPEs)?
Superantigens that cause an upregulation/ activation of immune response via non-specific association of TCR & MHC
- SPE-A, SPE-B...etc
- These are the causative agents of scarlet fever, toxic shock, & necrotizing fasciitis
What symptoms are caused by streptococcal pyrogenic exotoxins?
What diseases can streptococcal pyrogenic exotoxins cause?
- Scarlet fever= the only one associated with strep throat
- Toxic Shock Syndrome
- Necrotizing fasciitis
*Scarlet fever= the only one associated with strep throat
What is blood agar?
Jelly that is used to culture organisms (like normal agar), which contains RBCs
What antibiotics should be used to treat streptococcal pharyngitis?
Why has vaccination for strep throat been impractical?
There are 80 serotypes of M-proteins that are NOT cross-reactive
Why is it important to treat this patients with strep throat with antbiotics?
SPE's from streptococcus pyogens can lead to the development of more serious diseases including:
- Scarlet Fever
- Acute Rheumatic Fever
- Necrotizing Fasciitis
*Want to avoid these condtiions*
What are the symptoms of Scarlet Fever?
- Redness of the skin
- White coating of the tongue
- Desquamation of the hands & feet
What are the symptoms of Rheumatic Fever?
- Joint pain
- Chest pain (arrhythmia)
- Skin nodules
- Uncontrollable jerky movements (neurotoxicity)
- Can result in severe heart damage, heart failure, heart valve damage, and subacute endocarditis
*Caused by immune response to S. pyogenes; by the time the patient has rheumatic fever, he or she has already cleared the primary infection (strep throat i.e. strep. pyogenes) Rheumatic fever cannot be controlled by antibiotics, must immunosuppress. Also, if someone gets Rheumatic fever, each subsequent exposure to strep is worse.
How is rheumatic fever treated?
How does necrotizing fasciitis present?
- Complete tissue destruction
How does streptococcus pyogenes cause acute glomerulonephritis? When does it occur?
- Childhood, begins 1-4 weeks after streptococcal pharyngitis
- 3-6 weeks after skin infection
- Immune response leads to the deposition of antigen-antibody complexes in the glomeruli
What are the symptoms of acute glomerulonephritis?
- Decreased serum complement levels (immune complexes result in the activation of complement)
How does strep throat lead to acute rheumatic fever?
Antibodies to s. pyogens antigen co-recognize an epitope in tissue, causing inflammatory autoimmune attack