22 Bacterial Pathogens I - Respiratory Infections Flashcards
Most commonly affected body sites by bacterial pathogens?
- Respiratory tract
- Skin and soft tissues
- GI tract
- Genitourinary tract
T or F: Upper respiratory tract infections are more severe than lower resp. tract. infections
F
Upper respiratory tract infections are LESS severe than lower resp. tract. infections
T or F: Most bacteria have a preference wrt whether they infect either the upper or lower resp tract
T
How are resp tract infections transmitted? (2)
- Droplet transmission
2. Airborne transmission
What does Streptococcus pyogenes (“Group A Strep”) cause?
Streptococcal pharyngitis (aka “Strep throat”)
Streptococcal pharyngitis (aka “Strep throat”) is caused by what kind of bacteria (Gram stain? Shape?)
Gram positive cocci
How is Streptococcal pharyngitis (aka “Strep throat”) transmitted?
Respiratory droplet transmission
Most common age range affected by Strep throat?
5-15 yrs
Go through the pathogenesis of Strep throat.
- Strep enters upper resp tract (throat)
- It attaches to epithelial cells
- It multiplies in throat and uses anti-phagocytic capsule to evade host defenses
- It secretes hemolysin and other exotoxins (but doesn’t penetrate into deeper tissues)
- Symptoms appear (inflammation and sore throat, pus, swollen lymph nodes)
T or F: Strep throat often requires medical intervention
F
Strep throat is self-limiting
Why’re antibiotics usually used for strep throat despite it being a self-limiting illness? (2)
- prevent pt from becoming an asymptomatic carrier
2. prevent more severe complications from arising
List possible complications from untreated strep throat. (3)
- Scarlet fever
- Glomerulonephritis
- Rheumatic Fever
Symptoms of scarlet fever?
- Strep throat symptoms (sore throat, pus, swollen lymph nodes)
- Skin rash
The skin rash of scarlet fever is caused by…
certain strains of Strep that produce “Erythrogenic Exotoxin”
What does the erythrogenic exotoxin associated w/ certain strains of Strep specifically damage in the body? What occurs as a result?
Small blood vessels > high fever, red rash on face, trunk, and arms, as well as an inflamed “strawberry” tongue
A “strawberry tongue” is associated w/…
scarlet fever (a potential complication of Strep throat)
What occurs during glomerulonephritis?
Immune complexes made of Strep antigens + anti-Strep antibodies accumulate in the glomeruli (blood vessels) of the kidneys > fever, blood in urine, increased bp
When does glomerulonephritis occur?
During the RECOVERY stage of UNTREATED Strep throat
How is glomerulonephritis similar to scarlet fever?
Aside from both being complications of untreated Strep throat, they’re also both caused by only SOME strains of Strep pyogenes.
What is rheumatic fever?
- A complication of Strep infection
- An autoimmune disease where antibodies formed against Strep proteins CROSS-REACT w/ antigens found in the heart and joint tissues
Strep pyogenes can also cause necrotizing fasciitis. What is this?
“Flesh-eating disease” > a destructive tissue infection caused by various bacterial species, including Strep pyogenes
In order for Strep pyogenes to cause necrotizing fasciitis, how must it be transmitted?
Entry into skin via cuts (NOT by resp droplets)
In necrotizing fasciitis, what type of tissue is initially degraded by bacterial enzymes? What occurs afterwards?
Connective tissue is degraded first.
After tissue separation, the bacteria invade into deeper muscle tissues > tissue necrosis, high fever, rapidly-spreading inflammation occur
T or F: Streptococcus pyogenes is v. common, relatively mild, and easily treated.
T
When do serious complications of Strep infections tend to occur?
When the infection is left untreated
T or F: Sore throats are always caused Strep throat.
F
Sore throats can be due to viral infections too
How can Strep throat be diagnosed?
Throat swab > look for hemolytic colonies on blood agar media
Streptococcal pharyngitis (aka “Strep throat”) is a(n) ______ resp. tract infection.
upper
Bacterial pneumonias are infections of the _____ resp. tract, and include: (2)
lower
Lobar and bronchial pneumonia
What does lobar pneumonia affect?
a section of the lung
What does bronchial pneumonia affect?
patches of lung around bronchial tubes that convey air into lungs
Pneumonia in general leads to what? (2)
- Inflammation of lungs
2. Filling of air-spaces w/ fluids
~80% of bacterial pneumonias are caused by these 3 bacteria:
- Streptococcus pneumoniae
- Mycoplasma pneumoniae
- Haemophilus influenzae
Risk factors for pneumonia? (5)
- Elderly
- Immunocompromised
- Smoking
- Chronic resp diseases (e.g asthma, emphysema, etc.)
- Being on a ventilator
What structural feature of pneumonia-causing bacteria allow them to evade phagocytosis (and hence, are virulence factors in pneumonia)?
Bacterial capsules
What does a bacterial pneumonia require for treatment?
- Aggressive antibiotic treatment
- Fever suppression
- +/- breathing assistance in severe cases
What causes tuberculosis?
Mycobacterium tuberculosis
Tuberculosis is an infection of the ____ respiratory tract
lower
Name the three respiratory tract bacterial infections, and which part of the tract (upper or lower) ea affect.
- Strep throat (upper)
- Bacterial pneumonia (lower)
- Tuberculosis (lower)
What staining technique can be used to detect mycobacterium tuberculosis? Why should this stain be used?
Acid-fast stain
This bacterium has mycolic acid in its cell wall
T or F: Mycobacterium contains most of the usual virulence factors seen in other bacteria, such as exotoxins, pili, and capsules (hence why it’s particularly dangerous)
F
Mycobacterium tuberculosis actually LACKS most of the usual virulence factors seen in other bacteria
Tuberculosis disease symptoms are due to…
the HOST’S immune response to M. tb, not to the bacterium itself.
Two forms of TB:
- Primary tuberculosis
2. Secondary tuberculosis
Describe a primary tuberculosis infection sequence.
- Airborne and/or droplet transmission from infected host
- Phagocytes ingest M. tb in lungs > M. tb survives and multiply INSIDE phagocytes
- Phagocytes die > break open > release live M. tb > cycle repeats
- After ~3 weeks, helper T cells activated > macrophages are stimulated
- Stimulated macrophages kill M.tb or create a Ghon complex (aka “tubercle”) > M.tb is enclosed in tubercle structure and prevents further spread
What happens w/ the tubercles in 95% of primary cases of tuberculosis?
What is the health state of these pts?
The tubercules HEAL by fibrosis and calcification
Pts are usually asymptomatic and NOT infectious (no free bacteria in the lungs)
What occurs in 5% of primary tuberculosis cases?
How many die if left untreated?
Who’s most likely to suffer from primary TB complications?
- Cell-mediated immune response fails due to a lack of Th cell activation
- M.tb spreads to other organs (“extrapulmonary TB”)
- Various organ tissues get damaged due to by-products of macrophage attacks (necrotic cavities containing M.tb in lungs and other organs)
Up to 50% die if left untreated
Kids and immunocompromised are most likely to suffer from primary TB complications
What is secondary tuberculosis?
REACTIVATION of dormant Mycobacterium tuberculosis via rupture of Ghon complexes (“tubercules”)
How long after a primary TB infection may a secondary TB infection occur?
Reactivation is dependent on what?
May occur years after primary infection
Reactivation is dependent on overall health and any underlying conditions
What types of tests are used to diagnose TB?
- Direct tests
a. acid-fast staining + microscopy
b. growth of M.tb in lab culture
c. NAATs (PCR) - Indirect tests
a. Tuberculin skin test (Mantoux test)
b. Interferon Gamma Release Assay (IGRA) > detects presence of Th cells due to M.tb
What are direct tests used for in diagnosing TB?
They’re used for looking for M.tb bacteria in resp tract specimens (i.e. they’re looking for an ACTIVE infection)
What are indirect tests used for in diagnosing TB?
They’re used to measure EXPOSURE to M.tb bacteria (i.e. they can only tell you if you’ve been exposed to M.tb; they can’t be used to indicate an active infection)
You have a
- negative PCR and culture
- positive IGRA/skin test
What can this say about your disease status? (2 possibilities)
The bacteria have been cleared by the immune sys > no symptoms and no transmission
OR
The bacteria are being ctrled by the immune sys via Ghon complexes (“tubercules”) > reactivation can occur (which would make the PCR and culture positive)
You have a
- positive PCR and culture
- positive IGRA/skin test
What does this say about your disease status?
Tuberculosis is ACTIVE (M.tb is growing inside you) > symptomatic and transmissible infection
How was TB treated pre-1950s?
Long-term care in sanatorium/clinic
How is TB treated now?
Anti-Mycobacterial drugs that must be given continuously for 6-9 months of daily treatment
Minimum infectious dose of M.tb?
~10 bacterial cells (= VERY HIGH infectious potential)
T or F: The TB vaccine is highly effective at preventing TB
F
Despite their low effectiveness, in what types of settings are TB vaccines usually used?
Settings where the incidence of TB is high
What kinds of ppl are at higher risks for TB (re)infection? (3)
- Immunocompromised (esp HIV/AIDS)
- Lower SES
- Those routinely in contact w/ inds who have TB
Since patient compliance is s.times a problem with proper drug treatment for TB, what is usually done?
Directly observed treatment
