Gram (-) Bacilli - Respiratory Tract

Question 1

List the gram (-) bacilli that commonly infect the respiratory tract (3)

Answer 1

Bordetella pertussis
H Flu
Legionella

Question 2

What disease does Bordetella cause?

Answer 2

Whooping Cough - Pertussis

Question 3

B. pertussis transmission

Answer 3

Respiratory droplets

Highly contagious

Question 4

B. pertussis infection pathway

Answer 4

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

Question 5

What are the 3 main toxins released by B. pertussis?

Answer 5

Pertussis Toxin

Adenylate Cyclase Toxin

Tracheal Toxin

Question 6

Pertussis Toxin

Answer 6

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

Question 7

Adenylate Cyclase Toxin

Answer 7

Increases cAMP directly by acting like adenylate cyclase

Same mechanism as Edema Factor (B. anthracis)

Question 8

Tracheal Toxin

Answer 8

Part of the peptidoglycan wall of pertussis

Damages ciliated cells in respiratory epithelium

Question 9

Pertussis presentation

Answer 9

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.

Question 10

Tx Pertussis

Answer 10

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.

Question 11

Pertussis prevention

Answer 11

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.

Question 12

What does H flu look like?

Answer 12

Characteristic coccobacilliary shape

Question 13

What agar does H flu grow on?

Answer 13

Chocolate Agar - requires the addition of 2 special factors though

Factor 5 - NAD (nicotinamide)

Factor 10 - hemotin

Question 14

How is H flu transmitted?

Answer 14

Aerosol transmission

Question 15

What can H flu cause?

Answer 15

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

Question 16

H flu vaccine

Answer 16

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

Question 17

Tx for H flu

Answer 17

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.

Question 18

Unique feature of Legionella on gram staining

Answer 18

Does not gram stain well. Technically gram (-)

You need to use silver stain to visualize it

Question 19

How do you grow Legionella?

Answer 19

On buffered charcoal yeast extract

• make sure it’s in the presence of Cysteine and Iron

Question 20

What 2 diseases does Legionella cause?

Answer 20

Legionairre’s Disease - very serious, potentially fatal

Pontiac Fever - less severe

Question 21

Pontiac Fever

Answer 21

Caused by Legionella

Fever + malaise

Self-limiting

Question 22

Legionairre’s Disease presentation

Answer 22

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)

Question 23

What bacteria can cause an atypical pneumonia?

Answer 23

Legionella

Mycoplasma Pneumoniae

Chlamydophila Pneumoniae

Question 24

How do you diagnose Legionella?

Answer 24

Culture respiratory sputum (3-5 days though)

Rapid urine antigen test (less sensitive, but still used)

Question 25

Tx Legionella

Answer 25

Macrolides (like other atypical pneumonias)

OR

Fluoroquinolones (fewer side effects)