Atypical Pneumonia

Question 1

Chlamydia Structure

Answer 1

• Contain DNA, RNA, and 70S ribosomes
• Divide by binary fission
• Small genome (~ 1 Mbp)
• Carry plasmids; infected by bacteriophages
• Cell envelope
• Similar to Gram negative bacteria (two membranes; LPS)
• No detectable peptidoglycan

Question 2

Chlamydia Developmental Cycle

Answer 2

1. Attachment and phagocytosis of EB
2. RB forms and begins reorganization and synthetic diversion
3. Multiplication of RB by binary fusion
4. Chlamydia antigens expressed on cell surface
5. Continued multiplication and conversion of RB to EB
   
   • Development of large cytoplasmic inclusion
6. Multiplication stops
7. Release of extracellular infectious EB

Question 3

Compare and contrast elementary bodies and reticulate bodies of Chlamydia

Answer 3

-Elementary body (EB)
-Small, dense; 0.25um
-Extracellular
-Infectious form
-Metabolically inactive
-Disulfide cross-liked outer membrane proteins
Reticulate body (RB)
-Large, 0.6 - 1.0um
-Intracellular
-Replicative form
-Metabolically active
-Osmotically fragile

Question 4

List the etiologic agents associated with atypical pneumonia.

Answer 4

Bacterial Agents
	-Mycoplasma pneumoniae
	-Chlamydia pneumoniae
	-Chlamydia psittaci (Psittacosis)
	-Coxiella burnetti (Q fever)
Viral agents
	-Adenovirus
	-Parainfluenza virus
	-Epstein-Barr virus
	-Respiratory syncytial virus

Question 5

Chlamydia pneumoniae Pathogenesis

Answer 5

Entry
	-“Parasite-specified endocytosis”
	-Rapid internalization
	-Receptor-mediated endocytosis
	-Clathrin-coated pits
	-Probably multiple mechanisms for entry
•Cytopathic effect on host cells
•Immune pathogenesis
	-Acute and chronic inflammation
	-Tissue damage caused by host response
	-Scarring of conjunctivae
	-Fallopian tube scarring
	-Role for “heat shock” proteins?
Establishment of persistent infections?

Question 6

Chlamydia pneumoniae Transmission and Symptoms

Answer 6

Transmission
	-Person-to-person transmission via respiratory secretions
	-No animal reservoir
Symptoms
	-Community-acquired pneumonia

Question 7

Chlamydia psittaci: Pathogenesis

Answer 7

• Zoonotic infection
• Wasting disease of birds: “Parrot fever”
• Spontaneous abortion in sheep
• Birds are the major zoonotic reservoir (over 400 different species)

Question 8

Chlamydia psittaci: Transmission

Answer 8

• Occupational hazard – poultry industry workers, veterinarians, exotic bird owners
• Inhalation of aerosolized organisms in dried feces or respiratory tract secretions
• Direct contact with infected bird (most infected birds are asymptomatic)

Question 9

Chlamydia psittaci Symptoms

Answer 9

• Psittacosis – primary atypical pneumonia
• Can lead to spontaneous abortion
• Abrupt onset
• Fever, headache, myalgia, mild cough
• Abnormal chest exam
• Confusion/altered conscious state

Question 10

Chlamydia Treatment

Answer 10

-Psittacosis and pneumonia – doxycycline, macrolides (azithromycin, erythromycin)

Question 11

Structure of a typical Mycoplasma cell and Pathogenic species

Answer 11

• Normal flora
  
  • Oropharynx: M. salivarium, M. orale
  • Urinary tract: M. hominis, M. fermentans
• Human pathogens
  
  • M. pneumoniae, M. hominis, M. genitalium, Ureaplasma
• Structure
  
  • small: 0.1-0.25 um
  • Lack cell wall; no peptidoglycan- Resistant to penicillin
  • Unit membrane contains sterols
  • Pleomorphic; filterable

Question 12

Mycoplasma Nutrition

Answer 12

–limited biosynthetic capacity

• Facultative aerobes (except M. pneumoniae)
• Grow slowly (gt = 6 h)
• Require sterols

Question 13

Mycoplasma pneumoniae Pathogenesis

Answer 13

• Infections of the conducting airways primarily in older children and young adults
• “Walking pneumonia”: Flu-like symptoms, Non-productive cough
• Self-limiting chronic nature
• Entry via respiratory route
  
  • Bacteria attach to epithelial cells of lower respiratory tract
  • Tight association but no invasion
  • Bacterial attachment factor: P1 adhesin
  • Cell membrane receptor: neuraminic acid-containing glycoprotein
• Induction of ciliostasis – deterioration of cilia in the respiratory epithelium, both structurally and functionally
• Production of CARDS toxin
  
  • Homology to pertussis toxin S1 subunit
  • ADP-ribosyltransferase activity
  • Causes vacuolation and ciliostasis in cultured cells
• Immune pathology vs. immune protection
  
  • Bacteria are phagocytized by activated macrophages; cytokine production → local inflammation
  • Vigorous CMI → severe clinical disease

Question 14

Mycoplasma Symptoms and Transmission

Answer 14

Transmission
-Transmission through close contact with contaminated respiratory droplets
-2-3 week incubation period
Symptoms
-Generalized aches and pains
-Fever
-Cough – usually non-productive
-Sore throat
-Headache/myalgias
-Nasal congestion
-General malaise

Question 15

Mycoplasma Treatment

Answer 15

• Antimicrobial therapy shortens period of symptoms
• Antibiotics of choice
• Tetracycline
• Erythromycin or azithromycin
• Evidence of emerging macrolide resistance
• β-lactam antibiotics are not effective
• No vaccine available