Micro 21: Bacterial Respiratory Tract Infections
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44 terms
Terms | Definitions |
|---|---|
 Streptococci | gram positive cocci -> non motile, no spore, catalase negative -> Metabolism: fermentative with lactic acid production -> O2 requirements: facultative anaerobes |
| Pyogenic streptococcus group | S. pyogenes, S. agalactiae |
| Mutans streptococcus group | S. mutans |
| Mitis streptococcus group | S. mitis, S. pneumoniae |
| Lipoteichoic acid | group polysaccharide -> basis for Lancefield classification (groups A - W, no I or J) -> not useful for S. pneumoniae |
| Strep Lab ID | catalase negative (facultative anaerobes), growth enhanced by CO2, nutritionally fastidious (Blood Agar + yeast extract + peptone) |
| Group A strep -> Strep pyogenes | causes Pharyngitis "strep throat" -> induces pus formation due to LEUKOCIDIN production -> has hyaluronic acid capsule (not seen as antigen -> invisibility cloak) -> M protein extends through capsule -> has streptolysin (causes b-hemolysis), pyrogenic exotoxins, streptokinase (dissolves nucleic acids in solution), hyaluronidase -> Beta hemolysis, Bacitracin sensitive (A disc) -> lab kit test is available |
| Streptococcus pneumoniae | causes pneumonia, sinusitis, otitis media -> no cell wall carbohydrate for Lancefield classification -> gram positive diplococci -> Optochin sensitive (P disc) -> alpha hemolysis -> most common cause of community acquired pneumonia (normal flora in healthy individuals 5-40%) -> can infect exogenously (person to person droplets) or endogenously (predisposed by influenza), no animal reservoir |
| Strep pneumonia | capsule, IgA protease, pneumolysin, autolysin, transformation -> goes to blood stream in 15-30% of cases |
| Pneumolysin | inhibits ciliated epithelial cell activity, cytotoxic for alveolar and endothelial cells -> causes inflammation and decreases PMN effectiveness |
| Prevention of pneumonia | polyvalent capsular polysaccharide vaccine (pneumovax, Pnu-immune) -> immunizes against 23 of most common serotypes -> used in high risk individuals -> also 7 valent conjugated vaccine that triggers T cell dependent response -> one of the most rapidly increasing antibiotic resistance |
| Corynebacterium diphtheria | pleomorphic (Chinese letters -> acute angles) gram positive rod -> no spores -> 4 biotypes (gravis, mitis, belfanti and intermedium) -> other types of same genus are normal members of flora -> prevented by toxoid vaccine -> endemic in subtropical and tropical countries -> outbreaks in countries with breakdown in health care infrastructure |
| C. jeikeium | Corynebacterium associated with bacteremia, IV catheter colonization |
| C. minutissimum | Corynebacterium associated with RTI's, wound infections |
| Corynebacterium diphtheria | normal flora unless it produces toxin -> Pharyngitis can be severe enough to block airway -> suffocation |
| Diphtheria exotoxin | genes acquired via lysogenic conversion -> responsible for local and systemic symptoms -> inflammation and formation of pseudomembrane, damage to organs -> bull neck |
| Pseudomembrane | layer of dead cells -> if you disturb it will bleed profusely |
| Lab diagnosis of Corynebacterium diphtheria | screen using Tellurite agar -> black colonies -> G+ rods -> on blood agar will pump out pyrazinamidase, cystinase -> look for toxigenicity (Elek, EIA, PCR) |
| Elek test | streak of non-toxigenic strain -> use filter paper and antitoxin -> see lines of precipitin for toxigenic strain -> quick simple, cheap test for Corynebacterium diphtheria |
| Haemophilus influenza (does not cause influenza) | causes otitis media, pneumonia, epiglottitis -> MOST COMMON cause of swelling of epiglottis (90%) -> Gram negative, pleomorphic, facultative anaerobe -> normal flora of upper RT -> serotypes A-F -> B is most commonly associated with invasive disease (2-4% of people), non typeable strains carried by 50-80% of people -> # |
| Pathogenesis of haemophilus influenza | Pili, non-pilus adhesins (P2 outer membrane protein attaches to sialic acid containing mucin oligosaccharides), LPS (impairs ciliary function), antiphagocytic capsule composed of polyribose ribitol phosphate (PRP), IgA protease (30 different proteases identified) |
| Lab diagnosis of H. influenza | coagulase negative, catalase positive -> requires chocolate agar with X (Hemin) and V (AND) factor -> both released from blood following gentle heating -> only species that requires both! |
| Bordetella pertussis | small gram negative coccobacillus -> upper RT bacteria -> causes whooping cough in unvaccinated children -> adhesion to respiratory mucosa and forms biofilm (FHA, PT, Fimbriae) -> growth and toxin release (PT, ACT, TCT) -> local & systemic pathology (TCT, PT, DNT, LOS) -> bacterial clearance |
| Whooping cough | incubation for 1 week -> catarrhal (common cold) for 1-2 weeks -> paroxysmal (cough, vomiting) for 2 weeks -> convalescence = goes away in 6-7 weeks |
| Culture and identification of Bordetella | nasopharyngeal swab (NOT cotton -> FA in cotton inhibit Bordetella; NOT throat -> organism is very susceptible to drying) -> Bordet-Gengou agar -> charcoal blood agar and cephalosporin -OR- PCR |
| Bordetella vaccine | whole cell (formalin inactivated), acellular components (FHA, PT) -> lower rate of side effects, AP = acellular pertussis (DTaP) -> symptoms don't tend to appear in adults |
| Klebsiella pneumoniae (class enterobacteriaceae) | gram negative bacillus (large capsule Mucoid appearance) -> part of normal flora (5% of healthy people) -> two high affinity iron uptake systems (aerobactin and enterochelin) -> causes necrotizing pneumonia -> culture to diagnose |
| Necrotizing pneumonia | necrotization of lung tissue in response to LPS -> in immunocompromised individuals -> putrid odor to breath and sputum -> red currant jelly sputum |
| Legionella pneumophila (80% of infections due to L. pneumophila serogroup 1) | gram negative motile rod (invisible on sputum gram stain from active case -> picks up Safranin) -> non spore forming, heat resistant (can survive 50C for 30 min) -> associated with epidemics (inhalation of contaminated aerosols -> person to person is rare) -> causes legionnaire's disease (pneumonia) and Pontiac fever (self limiting) |
| Legionella pneumophila | uptake is via phagocytosis -> prevent fusion of phagosome-lysosome -> much of damage is host inflammatory response -> intracellular growth -> endotoxin? Extracellular protease? |
| Pseudomonas | environmental opportunist -> gram negative rods strictly aerobic, highly motile with multiple flagella, versatile metabolism, non-hemolytic, Mucoid colonies on conventional agar -> pyocyanin and fluorescein (gives green color to colorless media) -> smells like grapes! -> Ubiquitous in still fresh water sources -> otitis externa = swimmers ear -> dangerous for burn victims, CF patients -> causes necrotizing bronchial pneumonia |
| CF | pseudomonas aeruginosa and Burkholderia cepacia are bona fide pathogens -> both have elevated patterns of drug resistance -> abnormal mucus constitutes ready-made biofilm for these organisms -> chronic inflammation causes accumulation of WBC debris (makes things work) -> often fatal |
| Mycobacterium | grow in long parallel chains "cords" of bacilli -> aerobic, non spore forming, resist drying but still sensitive to heat -> grows slowly in lab (2-8 weeks) |
| Mycobacterium TB cell wall | arabinogalactan (embedded in peptidoglycan layer -> Mycolic acid attached = covered in wax -> variable in length -> wax makes it waterproof and resists drying -> still heat sensitive) and lipoarabinomannan (embedded in cytoplasmic membrane, has a few of these attachment organelles) |
| HIV patients | resistance to TB dependent on subset of CD4+ helper T cells that produce IFN alpha (immunocompetent are resistant to TB) |
| Pathogenesis of TB | intracellular survival in alveolar macrophages -> prevent oxidative burst and inhibit phagosome-lysosome fusion (role of sulfolipids), resist lysosomal enzymes and ROS (cell wall lipids, LAM, secretion of SOD), escape phagosome (into cytoplasm) -> LAM and mycolic acids -> secretes siderophores (exochelins -> very high affinity for ferric ions) |
| Culture of TB | Lowenstein-Jensen agar, oleic acid-albumin broth -> test for antimicrobial susceptibility -> MDR strains becoming increasingly important |
| Microscopy of mycobacterium sputum | use Ziehl-Neelsen stain (acid fast bacilli), Rhodamine-auramine fluorescent stain (faster and more reliable) |
| Latent dormant TB | has positive PPD, +/- X ray (coin lesion) -> has NO disease |
| Tuberculin test | look to see if person has been exposed -> measure induration after 48-72 hours (positive result is > 10mm) -> use cell-free supernatant from old cultures |
| Treat TB | use combination therapy -> antimycotic agents |
| First line treatments of TB | Isoniazid, rifampin, streptomycin, ethambutol |
| Second line treatment of TB | para-aminosalicylic acid, cycloserine, flouroquinolones |
| Prevention of TB | prophylactic antimycotic -> BCG vaccine -> live attenuated M. bovis strain |
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