Intracellular Bacteria

Question 1

Examples of intracellular bacteria (3 total)

Answer 1

Mycobacterium (TB)
- facultative

Legionella pneumophila
- facultative

Chlamydia (pneumoniae & psittaci)
- obligate

Question 2

Intracellular pathogens that replicate in specialized vacuoles

Answer 2

Legionella

Chlamydia pneumoniae

Question 3

Why are antibodies not very helpful against intracellular pathogens?

Answer 3

Antibiotics must penetrate host cells to reach the site of infection.

Question 4

Why plays a major role in controlling and clearing intracellular pathogens?

Answer 4

Cell-mediated adaptive immunity

Question 5

Intracellular pathogens that replicate in the host cell cytoplasm

Answer 5

Rickettsia (gram - cocobacillus with host-actin based motility)

• GI block (Listeria, Shigella)

Question 6

facultative intracellular Gram - rods that causes acute pneumonia

Answer 6

Legionella pneumophila (opportunistic pathogen)

Question 7

Legionella is spread via

Answer 7

inhalation of contaminated water

• not spread person to person

Question 8

If Legionella is so prolific in water systems, why aren’t more people sick with it?

Answer 8

Typically affects only those with compromised immune systems (advanced age, smokers/COPD, intubation, immunosuppression)

Question 9

If an immunoCOMPETENT (healthy) person is infected with Legionella, what is usually the result?

Answer 9

“Pontiac” fever (flu-like w/fever, upper respiratory, but no pneumonia)

Can recover w/o treatment in a week

Question 10

In environment, extracellular Legionella are viable. It can persist in _____ and also grows within _______

Answer 10

biofilms; fresh-water amoeba

Question 11

Extracellular Legionella is cultivable or non-cultivable

Answer 11

NON-cultivable

Question 12

Where does Legionella survive and grow in humans?

Answer 12

Macrophages

- inside Legionella-containing vacuoles (modified phagosomes)

Question 13

Immune response to Legionella

Answer 13

• similar to M. Tuberculosis

1. Infected macrophages release IL-12 (cytokine)
2. Neutrophils and new macrophages are recruited
3. TNF-a from macrophages control infection
4. Th1 response causes T cells to release IFN-gamma to clear infection

Question 14

How is Legionella diagnosed?

Answer 14

• Difficult to diagnose (stains poorly, not enough in sputum)

Best method is to culture on buffered charcoal-yeast extract agar using urine sample

Question 15

Treatment for Legionella infection

Answer 15

Macrolides (azithromycin)

Question 16

Obligate intracellular gram - bacterium that causes chronic walking penumonia

Answer 16

Chlamydia pneumoniae

Question 17

How is C. pneumoniae transmitted?

Answer 17

spread person to person by respiratory droplets

• asymptomatic rates are high

Question 18

What pathogen is very hard to distinguish C. pneumoniae from?

Answer 18

Mycobacterium pneumoniae

• Not M. tuberculosis!

Question 19

Treatment for C. pneumoniae

Answer 19

Doxycycline (penetrates and accumulates inside host cells)

Question 20

C. pneumoniae exist in what 2 forms

Answer 20

1. Elementary bodies: metabolically inert but infectious

2. Reticulate bodies: metabolically active, replicative but not infectious

Question 21

Where does C.penumoniae survive and grow in humans?

Answer 21

Macrophages and epithelial cells

- inside Chlamydia containing vacuole called inclusion body

Question 22

How does C. pneumoniae survive in macrophages?

Answer 22

modifies phagosomal membrane to block fusion w/ lysosome

Question 23

What Chlamydia spp. can infect birds and humans and cause psittacosis?

Answer 23

C. psittaci

Question 24

psittacosis is usually presented with

Answer 24

upper respiratory illness and infiltrates on CXR