3.6.4. Atypical CAP

Question 1

Name the following difference between typical and atypical community acquired penumonia (CAP):

Speed of Onset

Answer 1

TYPICAL

rapid onset (acute)

ATYPICAL

gradual onset over days-to-weeks (insidious)

(constitutional symptoms predominate over respiratory ones)

Question 2

Name the following difference between typical and atypical community acquired penumonia (CAP):

Symptoms

Answer 2

TYPICAL

fever, chills

productive cough, with PMNs seen in sputum

ATYPICAL

low-grade fever (100-101 F, ~38 C)

nagging cough, often not productive

Question 3

Name the following difference between typical and atypical community acquired penumonia (CAP):

Gram stain

Answer 3

TYPICAL

may have a positive blood culture with agents visible in Gram staining

ATYPICAL

patients are ambulatory (contributes to definition of “walking pneumonia”), no gram stain

Question 4

Name the following difference between typical and atypical community acquired penumonia (CAP):

Responsible Agents (most common = more important)

Answer 4

TYPICAL

Associated agents:

Strep pneumoniae

Staph aureus (especially after the flu)

Gram negative opportunistic pathogens:

Klebsiella pneumoniae

Pseudomonas aeruginosa

Enterobacter

Viruses:

H. influenza (typically type b)

Adenovirus (in acute resp. syndrome)

ATYPICAL

Associated agents: all have ATYPICAL cell walls, and can be recognized because they don’t Gram stain

• Chlamydia pneumoniae (an obligate intracellular pathogen)
• Mycoplasma pneumoniae (no cell wall)
• Mycobacterium tuberculosis (acid fast; produces sputum that may be bloody)

Endemic mycoses:

• Histoplasmosis
• Blastomycosis
• Coccidioides

Question 5

How does the xray of atypical CAP appear compared to the symptoms?

Answer 5

CXR may show greater involvement than expected from physical symptoms

Question 6

Define Walking Pneumonia

Answer 6

A type of pneumonia caused by mycoplasmas, with symptoms similar to but milder than those of bacterial or viral pneumonia. It spreads easily and typically affects school-age children and adults under 40.

Question 7

Describe the properties of Chlamydiae organisms

i.e. genome size, gram stain, cell wall, etc

Answer 7

• Obligate intracellular bacteria
  
  • contain DNA, RNA, and 70S ribosomes
  • divide via binary fission
  • small genome (~1 Mbp)
  • carry plasmids that were once from bacteriophages
• Cell envelope
  
  • similar to Gram (-) bacteria (has two phospholipid membranes and LPS)
  • no DETECTABLE peptidoglycan present

Question 8

Name the two developmental forms of Chlamydia

Describe some of their properties

Answer 8

• Elementary Body (EB)
  
  • Small and dense (0.25 um in size)
  • extracellular
  • INFECTIOUS FORM
  • Metabolically inactive
  • disulfide cross-linked outer membrane proteins
• Reticulate Body (RB)
  
  • Large (0.6 - 1.0 um)
  • intracellular
  • REPLICATIVE form (R for Replicative)
  • Metabolically active
  • osmotically fragile

Question 9

How does Chlamydia spread and cause infection (at the cellular level).

Answer 9

• 1) Entry of EBs
  
  • rapid internalization at the bases of villi
  • uptake done via clathrin-coated pits, and likely other mechanisms
  • once in the cell, EBs become RBs.
• 2) Then, endosomes containing RBs fuse and release them into the cell
• 3) Multiplication/Replication
• 4) Lysis/spread

Question 10

Describe the developmental cycle of Chlamydia

(Hint) Stages at 0, 8, 24, 30, and 35-40 hrs

Question 11

Name some examples of disease types Chlamydia can cause and which species is responsible for each

(Hint: 4 general types, 3 species)

Question 12

Give some examples of diseases Chlamydia may cause along with their causative species

Question 13

What is psittacosis and what causes it?

Answer 13

• abrupt onset with fever, headache, myalgia, mild cough (generalized constitutional symptoms)
• abnormal chest exam
• UNIQUE SYMPTOM: confusion or altered conscious state
• Diagnose with culture from respiratory secretions, or serology (include microimmunofluorescence)
• typically caught from infected birds, it is a bacterial infection by C. psittaci

Question 14

Why are Chlamydia and mycoplasma considered atypical organisms?

Answer 14

• Mycoplasma does not have a cell wall
• Chlamydia is an obligate intracellular organism
• Both are technically bacteria, but they have small genomes, so they can’t encode for all the stuff they need (esp ATP-essential proteins/enzymes)

Question 15

What are the two most common species of Chlamydia that cause respiratory disease?

Answer 15

• C. pneumoniae
• C. psittaci

Question 16

Describe the distribution and frequency in pulmonary disease of C. pneumoniae. How is it spread, does it have an animal reservoir?

Answer 16

• C. pneumoniae
  
  • There is a WORLDWIDE distribution
  • Seroprevalence of > 60% among adults (60% of us have encountered this at some point in our lives…)
  • C. pneumoniae causes 10% of community-acquired cases of pneumonia (10% of cases are specifically due to this, with the rest a mix of viral/bacterial/etc…)
  • Person-to-person transmission occurs via respiratory secretions (can’t dodge the snot-bullet)
  • NO ANIMAL RESERVOIR exists

Question 17

Describe the spread of C. psittaci, who is at risk, who harbors this bacteria?

Answer 17

• C. psittaci
  
  • zoonotic infection (“parrot fever”) - many species of birds can harbor this bacteria, but they’re often asymptomatic
  • transmissible to humans via inhalation of aerosolized organisms in dried feces or respiratory tract secretions
  • OCCUPATIONAL RISKS: poultry industry workers, veterinarians, exotic bird owners

Question 18

Describe the unique properties of Mycoplasma species and describe their cellular features

Answer 18

• 1- They are the smallest bacteria (0.1 - 0.25 micrometers)
• 2- They can pass through 0.45 um filters that otherwise restrict other bacteria (are dubbed “filterable”)
• 3- They lack a cell wall; no peptidoglycan present
• 4- They are surrounded by lipid bilayer membranes that contain sterols (like humans - our cells are actually where these guys take their resources from)

Question 19

Describe the growth requirements of mycoplasma (growth as in a lab or on an agar plate). Do they take up gram stains? Why are they so sticky?

Answer 19

• 4- They are surrounded by lipid bilayer membranes that contain sterols (like humans - our cells are actually where these guys take their resources from)
  
  • results in a pleomorphic shape that has a P1 adhesin at the tip, which allows it to stick to whatever surface it’s on. HOWEVER, they can only grow UNDER THE SURFACE of agar on plates. *** This results in a “fried egg appearance” - look for this buzzword for lab cultures to consider mycoplasma. These fried-egg colonies require serum for growth ***
    
    • The P1 adhesin attaches near the cilia on host respiratory epithelia and causes bronchial irritation that closely resembles asthma attacks
    • definitely worth seeking medical attention if a nagging cough presents
  • this cellular container doesn’t Gram stain
  • allows them to make small subsurface colonies

Question 20

What are the species of mycoplasma that typically cause human disease?

Answer 20

• Typical niches for the Mycoplasmatales family (to include Mycoplasma and Ureaplasma)
  
  • human pathogens:
    
    • M. pneumoniae
    • M. hominis
    • M. genitalium and Ureaplasma species (both can cause urethritis and complications of pregnancy)

Question 21

How do we try and diagnose Mycoplasma infection? What tests are available?

Answer 21

• Mycoplasma pneumoniae (no cell wall)
  
  • goal of your DDx: eliminate alternatives (basically process of elimination to confirm M. pneumoniae)
  • culture = difficult and restricted to specialized labs, so not often recommended…
  • serology = greater than or equal to a 4x rise in specific IgM antibodies to M. pnemoniae
  • test for cold agglutinins (not specific
  • NAAT = nucleotide sequencing, not available clinically…

Question 22

What is the cold agglutinin test? Is it specific?

Answer 22

• test for cold agglutinins (not specific)
  
  • IgM antibodies bind the “I” antigen on human RBCs, and are produced 1-2 weeks after the initial infection
  • first, prep the blood sample with heparin to prevent clotting, then rerigerate.
  • then, when refrigerated, IgM will agglutinate said “I” antigen, BUT THIS RESPONSE IS ONLY SEEN IN 50% OF PATIENTS

Question 23

How do we test for chlamydia infections? What labs do we look for?

Answer 23

• C. pneumoniae (obligately intracellular)
  
  • culture = difficult and restricted to specialized labs (same as mycoplasma)
  • serology
• IgM: greater than or equal to 1:64
• IgA: 4-fold increase in acute and convalescent serums (measure these serums 4 weeks apart)
• NAAT

Question 24

What is Bordetella pertussis? What are its virulence factors and bacteriologic traits? (i.e. gram - or +, general shape)

Answer 24

• Bordetella pertussis (causative agent of Whooping Cough, but can also cause atypical pneumonia)
  
  • Seen in adults after previous vaccination has worn off, and manifests as a “cold” and nagging cough
  • virulence factors include the pertussis toxin and special adhesion molecules, which allow this microbe to persist in the host’s respiratory epithelium
  • look for these bacteriologic traits: short, Gram negative rods that form “safety pin” shapes

Question 25

What are some treatment options for Mycoplasma pneumoniae?

Answer 25

• Mycoplasma pneumoniae
  
  • tetracycline
  • macrolides (erythromycin or azithromycin)
  • there is increasing evidence of emerging macrolide resistance…!
  • beta-lactam antibiotics are NOT effective! these bad boys don’t have cell walls, so these antibiotics can’t inhibit cell wall synthesis if there aren’t any to begin with…
  • no vaccine available, either :(

Question 26

What are some treatment options for Chlamydia pneumoniae?

Answer 26

• C. pneumoniae
  
  • Doxycycline
  • Macrolides (same as mycoplasma)

Question 27

What are some preventive measures for Bordetella pertussis?

Answer 27

• Bordetella pertussis
  
  • children are vaccinated and boosted from 6 months to 6 years
  • this means that children younger than 6 mos (they’re ineligible for the vaccine) are susceptible… So, boost the mom and adolescents to build that herd immunity!