Micro - Atypical pneumonia (Chlamydia, Legionella, Mycoplasma) Flashcards
3 bugs that cause atypical pneumonia
Chlamydia pneumoniae, Legionella pneumophila, Mycoplasma pneumoniae
Which bug causing atypical pneumonia has a biphasic lifecycle? Describe it.
Chlamydia
- EB is inert and enters cells, inhibiting the phagolysosome
- Transforms into metabolically active, obligate intracellular parasite RB
- RB replicates, forming mature EB daughter cells
- EB released from cell to infect others
What is unique about chlamydia?
Resembles gram - organisms but cell wall lacks peptidoglycan and muramic acid
How do we know peptidoglycan is involved in formation of chlamydia cell wall although not present in finished structure?
- Chlamydia is sensitive to ampicillin, which inhibits transpeptidase that crosslinks peptidoglycan during cell wall synthesis
- Chlamydia infection stimulates Nod1 and Nod2 activated pathways (Nod1 and Nod2 are PRRs that detect peptiodglycan)
Legionella is (G+, G-), (aerobic, anaerobic), (shape)
G- aerobic (remember it lives in H2O) bacilli
Why is Legionnaire’s becoming more recognized?
It is now looked for anytime a pt has a pneumonia
When is Legionnaire’s more common?
Summer and early fall
What is unique about Mycoplasma?
Smallest free living organisms and lack a cell wall
What does mycoplasma require from host?
Cholesterol
Which two bugs causing atypical pneumonia are IC pathogens and which is an EC pathogen?
IC - Chlamydia, Legionella
EC - Mycoplasma
Two virulence factors of mycoplasma
- Polarized adhesin molecule which allows it to stick to respiratory epithelium without entering cell
- Diacyl-lipoprotein stimulates inflammation via macrophage TLR2 and TLR6
What is unique about mycoplasma’s diacyl-lipoprotein?
Most bacteria have triacyl-lipoprotein
What causes symptoms of mycoplasma infection?
Host immune response (although it also clears infection; host immune response also causes sx of sepsis!)
Virulence factor of chlamydia
Type three secretions - in host cytosol, inhibit different pathways
Where does legionella replicate?
Inside alveolar macrophages
Virulence factor of legionella
- Able to avoid phagolysosome in phagocytic cells
- Injects host cells with bacterial proteins that transform its vesicular mechanisms into a specialized vacuole that resembles bacterial ER, facilitating legionella replication
Hallmark of chlamydial infection
Some have no to mild disease while some have severe disease
What is psittacosis?
RTI caused by Chlamydia psittaci acquired via dried bird feces
Incubation period of C. pneumoniae
7-21 days
What % of CAP is caused by C. pneumoniae?
6-10%
C. pneumoniae is associated with what other disease?
Coronary artery disease
C. pneumoniae binds serum lipoproteins –> immune complexes –> inflammation –> atherosclerosis
Ocular, respiratory tract, and genital infections caused by C. trachomatis is due to infection of:
Squamocolumnar cells of mucous membranes
What is trachoma?
Chronic conjunctivitis caused by C. trachomatis immunotypes A-C
C. trachomatis is the most common cause of:
Preventable blindness worldwise
STI’s in developed countries
C. trachomatis immunotypes D-K cause ___ infections and are associated with what disease?
Genital tract infx
Squamous cell carcinoma of cervix
2 neonatal diseases caused by Chlamydia and how to prevent them
Neonatal pneumonia and neonatal inclusion conjunctivitis; erythromycin
3 diseases that can be caused by chlamydia and mycoplasma
- Atypical pneumonia
- Nongonococcal urethritis
- Pelvic inflammatory disease
Big problem with chlamydia infections?
Up to 50% are asymptomatic so they continue to be spread
Disease caused by C. trachomatis immunotypes L1-L3?
Lymphogranuloma venerum - infection of endothelial and lymphatic cells
2 diseases caused by Legionella
- Atypical pneumonia
2. Pontiac disease
Who is at increased risk of Legionella infection?
Elderly, heavy smokers, alcoholics, chronic lung disease pts, immunocompromised, males
Incubation period for Legionnaire’s?
2-10 days
What is Pontiac fever?
Milder form of Legionnaire’s that presents within 2 days, does NOT result in pneumonia, has flu-like sx, and clears within 5 days
3 diseases caused by Mycoplasma/Ureaplasma?
- Atypical pneumonia (M. pneumoniae)
- Nongonococcal urethritis (Ureaplasma urealyticum)
- Postpartum fever and PID (M. hominis)
When is Mycoplasma pneumonia more common?
Summer and early fall
Mycoplasma pneumoniae is most common cause of:
Pneumonia in pt 5-20 yo
Two symptoms that point to Chlamydial pneumonia?
Hoarseness
Sinus tenderness
Two symptoms that point to atypical pneumonia?
HA
Pharyngeal erythema without exudate
Why don’t most patients with Chlamydial infection have fever?
More common in first few days of infection so generally absent by time of clinical presentation
Key symptom of mycoplasma infection?
Dry cough that is persistent and progressive
Chlamydial vs. Legionnaire’s symptoms
Chlamydia generally has no fever but has hoarseness; Legionnaire’s has high fever
Mode of transmission and reservoir for various Chlamydia spp?
C. pneumoniae - Inhalation, humans
C. psittaci - Direct contact or inhalation, birds
C. trachomatis - Sex or birth, humans
Where is Legionella found?
Heated water (hot tubs, air conditioning units, hot water tanks)
How is Legionella transmitted? Reservoir?
Inhalation of contaminated mist/vapor; water is reservoir - NOT spread human to human, so typically Legionella infection occurs in a single, isolated case
Places where Legionella infection is more likely?
Hospital, cruise ship, hotel
What causes 50% of all pneumonias in summer?
M. pneumoniae
Mycoplasma pneumonia vs. viral pneumonia
Mycoplasma incubation is 3 weeks, while viral is 3 days
M. pneumonia most common in what setting and more severe in what group?
Closed setting
Males
For which cause of atypical pneumonia are lab tests not very useful?
M. pneumoniae
Diagnostic criteria for Chlamydia
- IgM titer 1:16
- 4 fold increase in IgG
- PCR assay for C. pneumoniae DNA
Key diagnostic tool for Legionella
Urine antigen test - detects Legionella in urine samples
+ urine antigen test + pneumonia =
Legionnaire’s
Another way to diagnose Legionnaire’s
Isolate Legionella from lung biopsy, sputum sample, lavage
Which cause of atypical pneumonia has high incidence of mixed infection?
Chlamydia (up to 60%)
DOC chlamydia
Doxy
CI doxy
Under 9 yo
Pregnancy
How long to treat chlamydial infection?
10-14 days after fever resolves
Important feature of treating Legionella
Delaying tx increases mortality!!!!!!! (like sepsis)
3 weeks of progressive dry cough =
Mycoplasma pneumonia
When to give prophylactic tx for Mycoplasma
Pt with underlying condition (SCD, Ab deficiency) in household with recent Mycoplasma exposure
