Respiratory Tract Infections The Atypical Pathogens by AmnaKhan

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									Respiratory Tract Infections The Atypical Pathogens and Mycobacterium tuberculosis

Dr. Ross Davidson Rm 309, MacKenzie Building QE II HSC ph: 473-5520

Community Acquired Pneumonia
etiology
S.pneumoniae

H.influenzae

Other

Anaerobes
L.pneumophilia M.pneumoniae C.pneumoniae

Respiratory Tract Infections
• Legionella pneumophila - 1st described in 1996 (Philadelphia) - gram negative bacilli - intracellular pathogen - widespread in environment (soil, water, taps, showers) - widespread spectrum of illness

• L.pneumophila -14 serotypes • L.micdadei • Approx 40 Legionella spp.

Respiratory Tract Infections

• Legionella - thin faintly staining -very easy to miss on gram stain -acridine orange stain may be useful • Motile • Fastidious , BCYE agar • require L-cysteine for growth • stimulated by 5% CO2

Respiratory Tract Infections
Legionella (lab diagnosis)

• DFA testing Sens 25-70% Spec > 95% • Urinary Ag Sens 70-80% Spec > 99%

Culture Sens 80-90% Spec 100% Serology Sens 70-80% Spec 95%

Respiratory Tract Infections
• Legionella • Routine susceptibility not done • In-vitro results do not often correlate with clinical response

• Predictably susceptible to the fluoroquinolones • Macrolides are excellent alternative

Respiratory Tract Infections
• Atypical Pathogens

-Mycoplasma pneumoniae -Chlamydaphyla pneumoniae • Routine susceptibility testing not performed • Not susceptible to cell wall active agents • Highly susceptible to the macrolides and fluoroquinolones

Mycoplasma pneumoniae
• Smallest free living organisms • Totally lack cell wall • sterol needed for growth; cholesterol in membrane

• Detection - culture - PCR

Chlamydia pneumoniae
• Unique cell wall structure.

- considered a virulence factor - inhibits phagolysosome fusion in phagocytes. - resembles gram-negative bacteria - contains an outer lipopolysaccharide membrane - lacks peptidoglycan in its cell wall.

Chlamydia pneumoniae • Unique biphasic life cycle • EB (elementary bodies) - infective form - attach to susceptible host
• RB (reticulate bodies) - divide by binary fission - after division, reorganize into EB

Chlamydia life cycle

M.tuberculosis
• Slightly curved or straight bacilli • Known as “acid-fast” bacteria - high concentration of mycolic acids in their cell walls - can withstand decolourization with acidified alcohol

Mycobacterial cell wall

AFB smear

AFB (shown in red) are tubercle bacilli

Mycobacteria
• Most will grow on relatively simple media • Some are fastidious, some cannot be cultured • Most relatively slow to grow

• Aerobic, non-spore forming, non-motile • Genus includes obligate pathogens and environmental organisms

M.tuberculosis complex
• M.tb complex includes M.tuberculosis, M.bovis, M.africanum, M.microti, and M.canettii • Discrete group of organisms with >95% DNA-DNA homology

TB Transmission
• Infectious disease cause by the bacterium, Mycobacterium tuberculosis • Spread by airborne droplets, “droplet nuclei,” 1 to 5 microns in size • Droplet nuclei generated when a person with TB disease coughs, sneezes, speaks, or sing • TB infection occurs when a susceptible person inhales droplet nuclei containing the bacteria becomes established in the body

Probability TB Will Be Transmitted
• Infectiousness of person with TB • Environment in which exposure occurred • Duration of exposure • Virulence of the organism

M.tuberculosis
• 50%-infective dose < 10 bacilli • In Canada, level III laboratories are recommended. • Laboratory personal must wear protective gowns, gloves, masks (N95 or respirator)

M.tuberculosis
• M.tuberculosis may cause both pulmonary and extra-pulmonary disease • Patients with pulmonary or suspected pulmonary disease must be isolated
• Negative pressure rooms and respiratory precautions


								
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