Microbiology of Pneumonia and Pathogens

Lower Respiratory Tract Infection (Bacterial Pneumonia)

• Lower respiratory tract infection, specifically bacterial pneumonia, is a significant health concern.
• Identifying the causative agents and characteristics of pneumonia is crucial for effective treatment.

Types of Pneumonia

• Typical Pneumonia:
  • Rapid onset, more severe.
  • Productive cough and dense consolidation in chest X-ray.
  • Common pathogens include Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, Klebsiella pneumoniae, and Pseudomonas aeruginosa.
  • Classification of pathogens is based on characteristics such as Gram staining and morphology.
• Atypical Pneumonia:
  • Slower onset, less severe symptoms.
  • Non-productive cough and patchy interstitial pattern in chest X-ray.
  • Common pathogens include Mycoplasma pneumoniae, Chlamydia pneumoniae, Chlamydophila psittaci, Legionella pneumophila, and Coxiella burnetii.

Bacterial Causes of Pneumonia, Further Defined

• Typical:
  • Streptococcus pneumoniae
  • Haemophilus influenzae
  • Klebsiella pneumoniae
  • Pseudomonas aeruginosa
  • Bacillus anthracis
  • Yersinia pestis
• Atypical:
  • Mycoplasma pneumoniae
  • Chlamydia pneumoniae
  • Chlamydia psittaci
  • Legionella pneumophila
  • Coxiella burnetii

Pneumonia by Infection Source

• Nosocomial Pneumonia:
  • Develops 48 hours or more after hospital admission.
  • Common causative agents: Gram-negative bacilli (e.g., E. coli, Klebsiella, Pseudomonas, Serratia, Acinetobacter, Enterobacter) and Gram-positive cocci (e.g., Staphylococcus aureus).
• Community-Acquired Pneumonia:
  • Develops outside of a hospital setting.
  • Common causative agent: Streptococcus pneumoniae.

Key Characteristics of Klebsiella Pneumoniae

• Gram-negative rods
• Large polysaccharide capsule
• Mucoid, lactose-fermenting colonies on MacConkey agar
• Oxidase negative
• Reservoir: human colon and upper respiratory tract
• Transmission: endogenous (through inhalation of respiratory droplets)
• Pathogenesis: capsule impedes phagocytosis; endotoxin causes fever, inflammation, and shock.

Key Characteristics of Pseudomonas aeruginosa

• Oxidase-positive, Gram-negative rods, aerobic, and motile.
• Pigments: pyocyanin (blue-green) and fluorescein.
• Grape-like odor
• Non-lactose fermenting colonies on MacConkey agar.
• Biofilm formation.
• Reservoirs: ubiquitous in water and soil.
• Transmission: water aerosols, raw vegetables, flowers.
• Important to note that drug resistance is very common.
• Treatment: antipseudomonal penicillin and an aminoglycoside, with consideration for susceptibilities.

Key Characteristics of Bacillus anthracis

• Large, boxcar-like, gram-positive, spore-forming rods.
• Capsule is polypeptide (poly-d-glutamate).
• Potential bioterrorism agent.
• Reservoir: animals (zoonosis), skins and soils.
• Transmission: contact with infected animals or spore inhalation (bioterrorism).
• Pathogenesis: includes capsule (antiphagocytic), anthrax toxin (protective antigen, lethal factor, edema factor).

Key Characteristics of Yersinia pestis

• Small gram-negative rods with bipolar staining.
• Facultative intracellular parasite.
• Reservoir: rodents.
• Transmission: wild rodents via flea bite (sylvatic plague), or human-to-human respiratory droplets.
• Pathogenesis: coagulase-contaminated flea mouthparts, endotoxin, envelope antigen, Type III secretion system.
• Disease: Pneumonic Plague (highly contagious), with symptoms including hemoptysis, chest pain, and dyspnea.
• Diagnosis: clinical, serological, and PCR methods.
• Prevention: animal control, vaccination.

Key Characteristics of Mycoplasma pneumoniae

• Extracellular, tiny, flexible.
• No cell wall.
• Does not stain with Gram.
• Requires cholesterol for in vitro culture.
• Reservoir: human respiratory tract.
• Transmission: respiratory droplets.
• Pathogenesis: surface parasite, inhibits ciliary action, causes damage to respiratory epithelium through secretion of harmful compounds.

Key Characteristics of Chlamydia pneumoniae

• Obligate intracellular bacteria.
• Cannot make ATP.
• Cell wall lacks muramic acid.
• Not seen on Gram stain.
• Reservoir: human respiratory tract.
• Transmission: respiratory droplets.
• Pathogenesis: intracellular growth infecting smooth muscle, endothelial cells, and coronary arteries and macrophages.
• Disease: atypical walking pneumonia, bronchitis, scant sputum, prominent dry cough, and hoarseness; sinusitis.
• Diagnosis: serology, complement fixation, and microimmunofluorescence.
• Treatment: macrolides and tetracycline.

Key Characteristics of Legionella pneumophila

• Stains poorly with standard Gram stain, Gram negative.
• Fastidious: requires increased iron and cysteine for growth (BCYE, buffered charcoal).
• Facultative intracellular.
• Reservoir: water sources (e.g., rivers, streams, and cooling towers).
• Transmission: aerosolized droplets.
• Pathogenesis: facultative intracellular pathogen, endotoxin.
• Disease: Legionnaires disease (atypical pneumonia).
• Diagnosis: urinary antigen test (serogroup 1).
• Treatment: floroquinolones, macrolides, or rifampin (for immunocompromised patients).

Key Characteristics of Coxiella burnetii

• Obligate intracellular, spore-like characteristics.
• Transmission: dried placental material; zoonotic and potential bioterrorism agent.
• Pathogenesis: obligate intracellular, live within phagolysosomes.
• Disease: Q fever (atypical pneumonia, hepatitis, or endocarditis).
• Diagnosis: serological detection of Phase II and Phase I LPS antigens.
• Treatment: doxycycline.

This quiz explores various bacterial pathogens associated with pneumonia, particularly focusing on organisms like Klebsiella pneumoniae and Pseudomonas aeruginosa. Test your knowledge on their characteristics, transmission methods, and associated diseases. Ideal for students studying microbiology or clinical pathology.