Respiratory Tract Infections The Atypical Pathogens

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