Bacterial Pneumonia PDF

lower respiratory tract infection (Bacterial pneumonia) By Dr. Amany M. Tawfeik Medical Microbiology & Immunology department Asthma: Bronchial Asthma is an obstructive disease characterized by bronchoconstriction, increased mucus production, hyp...

lower respiratory tract infection (Bacterial pneumonia) By Dr. Amany M. Tawfeik Medical Microbiology & Immunology department Asthma: Bronchial Asthma is an obstructive disease characterized by bronchoconstriction, increased mucus production, hypertrophied bronchial smooth muscle, and airway hyperactivity to stimuli such as cold air and inhaled exogenous antigens. A number of asthma patients also have atopic disease, such as eczema, related to environmental allergen exposure (type I hypersensitivity). Inhaled corticosteroids decrease mucus and proinflmmatory cytokines in the lungs, and bronchodilators to relax bronchial smooth muscle, are used for treatment. Mast cell stabilizers inhibit release of inflammatory cytokines and histamine Infectious agents may cause interstitial or intra-alveolar pneumonias. Bronchopneumonia involves alveoli and bronchioles with a patchy distribution throughout the lung, whereas lobar pneumonia is infection of the alveoli in an entire lobe of the lung = typical pneumonias. The microbes causing atypical pneumonias induce primarily bronchopneumonia with interstitial infection throughout the lung parenchyma Typical pneumonias: Rapid onset, more sever symptoms, productive cough and dense consolidation in chest X- ray Klebsiella pneumonia Pseudomonas aeruginosa Atypical pneumonias: Slower onset, less sever symptoms, non productive cough and patchy interstitial pattern in chest X- ray Coxiella burnetti Fungi. II: Pneumonia according to source of infection: A. Nosocomial (hospital acquired) pneumonia: It occurs 48 hours or more after admission to hospital. It was not present at the time of admission. Common causes: - Gram negative bacilli e.g E. coli, Klebsiella pneumonia, Pseudomonas aeruginosa, Serratia marcescens, Acinetobacter spp. and Enterobacter spp. - Gram positive cocci especially Staphylococcus aureus. B. Community acquired pneumonia: The patient has not recently (more than 14 days) in a hospital. The most common cause is Streptococcus pneumonia Bacterial causes of typical pneumonias: 1- Streptococcus pneumonia 2- Haemophilus influenza 3- Klebsiella pneumonia Other bacterial causes of typical pneumonias: 4- Pseudomonas aeruginosa 5- Bacillus anthracis 6- Yersinia pestis Klebsiella pneumonia: Distinguishing Features: Gram-negative rods with large polysaccharide capsule Mucoid, lactose-fermenting colonies on MacConkey agar Oxidase negative Reservoir: human colon and upper respiratory tract Transmission: endogenous Pathogenesis : capsule (impedes phagocytosis); endotoxin (causes fever, inflammation, and shock [septicemia]) Disease(s) Pneumonia – Community-acquired, most often older men; most commonly those with chronic lung disease, alcoholism, or diabetes (but this is not the most common cause of pneumonia in alcoholics; S. pneumoniae is.) – Endogenous; assumed to reach lungs by inhalation of respiratory droplets from upper respiratory tract – Frequent abscesses make it hard to treat; fatality rate high – Sputum is generally thick and bloody (currant jelly) but not foul smelling as in anaerobic aspiration pneumonia Diagnosis: culture of sputum MacConkey`s agar; mucoid lactose fermenter Treatment: third-generation cephalosporin Pseudomonas aeruginosa Distinguishing Features Oxidase-positive, Gram-negative rods, aerobic; motile. Pigments: pyocyanin (blue-green) exopigment on nutrient agar and fluorescein Grape-like odor Non–lactose fermenting colonies on MacConkey Biofilm Reservoir: ubiquitous in water and soil Transmission: water aerosols, raw vegetables, flowers Diagnosis: Gram stain and culture Treatment: antipseudomonal penicillin and an aminoglycoside (Susceptibilities important and drug resistance very common; Intrinsic resistance plasmid- mediated) Pathogenesis Endotoxin causes inflammation in tissues and gram-negative shock in septicemia Pseudomonas exotoxin A ADP ribosylates eEF-2, inhibiting protein synthesis (like diphtheria toxin) Liver is primary target Capsule/slime layer allows formation of pulmonary microcolonies; difficult to remove by phagocytosis Disease(s): Neutropenic patients: pneumonia and septicemia (often superinfection, i.e., infection while on antibiotics) Chronic granulomatous disease: pneumonias, septicemias; [diabetic] osteomyelitis (diabetic foot) Otitis externa: swimmers, diabetics, those with pierced ears Cystic fibrosis: early pulmonary colonization, recurrent pneumonia Bacillus anthracis: Distinguishing Features: Large, boxcar-like, gram-positive, spore-forming rods Capsule is polypeptide (poly-d-glutamate) Potential bioterrorism agent Reservoir: animals (zoonosis), skins, soils Transmission: contact with infected animals or inhalation of spores (bioterrorism) Pathogenesis: Capsule polypeptide, antiphagocytic, immunogenic Anthrax toxin includes 3 protein components: – Protective antigen (B component) – Lethal factor kills cells – Edema factor is an adenylate cyclase Diseases: Inhalation of spores, most commonly from contaminated animals or animal products Pulmonary (woolsorter’s disease): life-threatening pneumonia; cough, fever, malaise, and ultimately facial edema, dyspnea, diaphoresis, cyanosis, and shock with mediastinal hemorrhagic lymphadenitis Diagnosis: Mediastinal widening on chest x-ray Gram stain and culture of blood, respiratory secretions or lesions Colonies show a halo of projections, sometimes referred to as “medusa head” appearance. Serology PCR Treatment: ciproflxacin or doxycycline. Prevention: toxoid vaccine (AVA, acellular vaccine adsorbed) is given to those in high risk occupations such as military Comparative Microbiology Major encapsulated organisms Some Killers Have Pretty Nice Capsules: Strep pneumoniae Klebsiella pneumoniae Haemophilus inflenzae Type b (a-d) Pseudomonas aeruginosa Neisseria meningitidis Cryptococcus neoformans (the yeast) Yersinia pestis: Distinguishing Features Small gram-negative rods with bipolar staining Facultative intracellular parasite Reservoir: zoonosis; rodents; potential biowarfare agent Transmission: wild rodents flea bite lead to sylvatic plague; human-to-human transmission by respiratory droplets Pathogenesis: Coagulase-contaminated mouth parts of flea Endotoxin and exotoxin Envelope antigen (F-1) inhibits phagocytosis. Type III secretion system suppresses cytokine production and resists phagocytic killing Disease: Pneumonic plague. It develops as a result of inhalation of droplets infected with Y. pestis passed from person to person. Highly contagious – Hemoptysis, chest pain, dyspnea Diagnosis: Clinical specimens and cultures are hazardous Serodiagnosis or direct immunofluorescence “Safety pin” staining on blood stain Treatment: aminoglycosides Prevention: animal control and; killed vaccine (military) Bacterial causes of Atypical Pneumonia : Slower onset , less severe symptoms, non productive cough, patchy interstitial pattern in chest x- ray. Causative agents: 1-Mycoplasma pneumoniae. 2- Chlamydia pneumoniae. 3-. Chlamydia psittaci. 4-Legionella pneumophila 5- Coxiella burnetti. 1- Mycoplasma pneumoniae: Distinguishing Features Extracellular, tiny, flexible No cell wall; not seen on Gram-stained smear Membrane with cholesterol but does not synthesize cholesterol Requires cholesterol for in vitro culture Reservoir: human respiratory tract Transmission: respiratory droplets; close contact: families, military recruits, medical school classes, college dorms Pathogenesis Surface parasite: not invasive Attaches to respiratory epithelium via P1 protein Inhibits ciliary action Produces hydrogen peroxide, superoxide radicals, and cytolytic enzymes, which damage the respiratory epithelium, leading to necrosis and a bad, hacking cough (walking pneumonia) M. pneumoniae functions as superantigen, elicits production of IL-1, IL-6, and TNF-α Disease: walking pneumonia Pharyngitis Most common atypical pneumonia (along with viruses) in young adults Diagnosis: Primarily clinical diagnosis; PCR/nucleic acid probes ELISA and immunofluorescence sensitive and specific Fried-egg-shaped colonies on sterol-containing media, 10 days Positive cold agglutinins (autoantibody to RBCs) test is nonspecific and is positive in only 65% of cases Treatment: erythromycin, azithromycin, clarithromycin; no cephalosporin or penicillin Family: Chlamydiaceae Family Features: Obligate intracellular bacteria Cannot make ATP Cell wall lacks muramic acid Elementary body/reticulate body Not seen on Gram stain Genera of Medical Importance: Chlamydia trachomatis Chlamydophila pneumoniae Chlamydophila psittaci  Chlamydiaceae pneumoniae: Atypical pneumonia: sputum with intracytoplasmic inclusions Chlamydiaceae psittaci: Atypical pneumonia: exposure to parrots -Lab diagnosis: PCR, nucleic acid amplification test. + 4- Legionella pneumophila Distinguishing Features Stain poorly with standard Gram stain; gram-negative Fastidious requiring increased iron and cysteine for laboratory culture (BCYE, buffered charcoal, yeast extract) Facultative intracellular Reservoir: rivers/streams/amebae; air-conditioning water cooling tanks Transmission: aerosols from contaminated air-conditioning; no human-to human transmission Predisposing Factors: smokers age >55 with high alcohol intake; immunosuppressed patients such as renal transplant patients Pathogenesis: facultative intracellular pathogen; endotoxin Disease(s) Legionnaires disease (“atypical pneumonia”): associated with air conditioning systems (now routinely decontaminated); pneumoniasevere pneumonia (often unilateral and lobar); hyponatremia; mental confusion; diarrhea (no Legionella in GI tract) Pontiac fever: pneumonitis mild fl-like syndrome; no fatalities Diagnosis: Urinary antigen test (serogroup 1) DFA (direct fluorescent antibody) on biopsy Treatment: floroquinolone (levoflxacin) or macrolide (azithromycin) with rifampin (immunocompromised patients); Prevention: routine decontamination of air-conditioner cooling tanks 5- Coxiella burnetii Distinguishing Features: obligate intracellular, spore-like characteristics Transmission: inhalation from dried placental material; zoonosis (sheep and goats); possible bioterrorism agent Pathogenesis: obligate intracellular, live inside phagolysosomes Disease(s): Q fever: atypical pneumonia, hepatitis, or endocarditis Diagnosis: serologic detection of Phase II LPS antigen (for acute disease) and Phase I and Phase II LPS antigens (for chronic disease) Treatment: doxycycline