Gram (-) Bacilli - Respiratory Tract Flashcards
List the gram (-) bacilli that commonly infect the respiratory tract (3)
Bordetella pertussis
H Flu
Legionella
What disease does Bordetella cause?
Whooping Cough - Pertussis
B. pertussis transmission
Respiratory droplets
Highly contagious
B. pertussis infection pathway
It attaches to respiratory epithelium using pili
Once attached, it doesn’t invade. Instead, it releases several toxins that cause systemic effects.
Pilus is made of filamentous hemagglutinin
Antibodies against its pilus help protect against infection
What are the 3 main toxins released by B. pertussis?
Pertussis Toxin
Adenylate Cyclase Toxin
Tracheal Toxin
Pertussis Toxin
Ribosylates Gi thus disabling it (inhibits Gi)
Since we are inhibiting an inhibitory G protein, we see and increase in cAMP
The ADP-ribosylation of Gi also disables chemokine receptors for lymphocytes. This makes lymphocytes unable to enter lymphoid tissue - they get stuck in bloodstream, causing lymphocytosis
Adenylate Cyclase Toxin
Increases cAMP directly by acting like adenylate cyclase
Same mechanism as Edema Factor (B. anthracis)
Tracheal Toxin
Part of the peptidoglycan wall of pertussis
Damages ciliated cells in respiratory epithelium
Pertussis presentation
Catarrhal Stage - Initially presents with nonspecific symptoms - presents with conjunctival injection and lacrimation for 1-2 weeks
Paroxysmal Stage - 2 weeks - 2 months. Patients develop characteristic cough. Usually in children. Intense bout of coughing that leaves kid so out of breath that when he does breathe in it makes a characteristic whooping sound on inspiration
Convalescent Stage - about 3 months. Gradual reduction of symptoms. Used to sometimes be called the “100 Day Cough” in its entirety.
Tx Pertussis
Macrolides are useful to remove it from respiratory tract. Not that effective at symptom reduction if toxin is already circulating body. So start Tx early.
Pertussis prevention
2 vaccines
1) Killed - no longer available in USA
2) Acellular - purified antigens of the bacteria make up the vaccine.
Usually given to kids with diphtheria toxoid and tetanus toxoid as part of DTaP vaccine.
What does H flu look like?
Characteristic coccobacilliary shape
What agar does H flu grow on?
Chocolate Agar - requires the addition of 2 special factors though
Factor 5 - NAD (nicotinamide)
Factor 10 - hemotin
How is H flu transmitted?
Aerosol transmission
What can H flu cause?
1) Pneumonia - droplets hit resp system first
2) Epiglottitis - inflamed epiglotis, inspiratory stridor, drooling
Usually in kids. “Cherry red epiglotis”
3) Otitis Media
4) Meningitis - only caused by capsular form of H flu, specifically only the B strain (Type B capsule)
5) Sepsis, Septic arthritis (usually more common in Pts without spleen)
It is encapsulated
H flu vaccine
Contains type B capsular antigen
Contains a polysaccharide of the H flu capsule conjugated to the diphtheria toxoid - increased immunogenicity for stronger IgG response
Best time to vaccinate = 2-18 months of age
Tx for H flu
B-Lactam antibiotic
For meningitis or a systemic disease it’s Cephtriaxone
If a kid is diagnosed with H. meningitis then Rifampin is used for prophylaxis of close contacts.
Unique feature of Legionella on gram staining
Does not gram stain well. Technically gram (-)
You need to use silver stain to visualize it
How do you grow Legionella?
On buffered charcoal yeast extract
- make sure it’s in the presence of Cysteine and Iron
What 2 diseases does Legionella cause?
Legionairre’s Disease - very serious, potentially fatal
Pontiac Fever - less severe
Pontiac Fever
Caused by Legionella
Fever + malaise
Self-limiting
Legionairre’s Disease presentation
Caused by Legionella
More commonly in smokers
Causes Atypical pneumonia
Patchy infiltrate with consolidation of 1 lobe on CXR (highly variable on CXR tho)
Unique features about this atypical pneumonia:
1) Hyponatremia (40C, 104F)
What bacteria can cause an atypical pneumonia?
Legionella
Mycoplasma Pneumoniae
Chlamydophila Pneumoniae
How do you diagnose Legionella?
Culture respiratory sputum (3-5 days though)
Rapid urine antigen test (less sensitive, but still used)
Tx Legionella
Macrolides (like other atypical pneumonias)
OR
Fluoroquinolones (fewer side effects)