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Bacterial Respiratory Pathogens Notes

Bacterial Respiratory Pathogens

Overview

  • Module Focus: This module will cover respiratory pathogens. The lecture specifically focuses on bacterial respiratory pathogens.
  • Types of Infections: The lecture will address both upper and lower respiratory tract infections, using Klebsiella and Pseudomonas as examples.

Respiratory Tract Infections

  • Definition: Respiratory tract infections are infectious diseases affecting the respiratory tract.
  • Classification:
    • Upper Respiratory Tract Infection: Affects the upper part of the respiratory system.
    • Lower Respiratory Tract Infection: Affects the lower part of the respiratory system.

Anatomy of the Respiratory Tract

  • Upper Respiratory Tract: Consists of:
    • Nose
    • Nasal cavity
    • Pharynx
  • Lower Respiratory Tract: Consists of:
    • Larynx
    • Trachea
    • Bronchi
    • Lungs

Upper Respiratory Tract Infections

  • Cause: Typically caused by an acute infection.
  • Common infections include:
    • Tonsillitis
    • Pharyngitis
    • Laryngitis
    • Sinusitis
    • Otitis media
    • Common cold

Lower Respiratory Tract Infections

  • Definition: Inflammation of air passages within the lungs.
  • Affected Areas: Trachea (windpipe) and bronchi (airways).
  • Types:
    • Bronchitis
    • Pneumonia

Defenses of the Respiratory Tract

  • Defense Mechanisms:
    • Nasal hair
    • Cilia
    • Mucus
    • Involuntary responses (coughing, sneezing, swallowing)
    • Macrophages
    • Secretory IgA

Normal Microbiota of the Respiratory Tract

  • Location: Primarily limited to the upper respiratory tract.
  • Common Bacteria: Gram-positive bacteria (Streptococci and Staphylococci).
  • Pathogenic Bacteria: Present as normal biota but can cause disease if the host is immunocompromised or transferred to other hosts.
  • Examples:
    • Streptococcus pyogenes
    • Haemophilus influenzae
    • Streptococcus pneumoniae
    • Neisseria meningitidis
    • Staphylococcus aureus

Focus on Bacteria

  • The lecture will primarily focus on bacterial infections, while viral infections will be covered by other lecturers.

Sinusitis

  • Common Name: Sinus infection
  • Causes: Allergy, infections, or structural problems, often following a common cold.
  • Symptoms:
    • Nasal congestion
    • Pressure above the nose or in the forehead
    • Headache or toothache
    • Facial swelling and tenderness
    • Discharge: opaque with green or yellow color in bacterial infections, clear in cases of allergy.

Acute Otitis Media (Ear Infection)

  • Association: Common sequel of rhinitis
  • Mechanism: Viral upper respiratory tract infections lead to inflammation of the Eustachian tubes, causing fluid buildup in the middle ear, which can lead to bacterial multiplication.
  • Process: Bacteria migrate along the Eustachian tube, multiply rapidly, leading to pus production and fluid secretion (effusion).
  • Chronic Otitis Media: Fluid remains in the middle ear for extended periods, possibly caused by biofilm bacteria.
  • Symptoms:
    • Sensation of fullness or pain in the ear
    • Loss of hearing
  • Complications: Untreated infections can lead to eardrum rupture

Pharyngitis

  • Definition: Inflammation of the throat.
  • Symptoms:
    • Pain and swelling
    • Reddened mucosa
    • Swollen tonsils
    • White packets of inflammatory products
    • Swollen mucous membranes
    • Foul-smelling breath
  • Incubation Period: 2-5 days.

Diphtheria

  • Symptoms:
    • Sore throat
    • Lack of appetite
    • Low-grade fever
    • Pseudomembrane formation on the tonsils or pharynx

Diseases Affecting Both Upper and Lower Respiratory Tracts

  • Examples:
    • Whooping cough (bacteria)
    • Respiratory Syncytial Virus (RSV) (virus)
    • Influenza (virus)

Whooping Cough

  • Also known as: Pertussis
  • Causative Agent: Bordetella pertussis (bacteria)
  • Symptom Phases:
    • Catarrhal Stage:
      • Incubation of 3 to 21 days
      • Cold-like symptoms (runny nose)
      • Lasts 1 to 2 weeks
    • Paroxysmal Stage:
      • Severe and uncontrollable coughing
      • Violent coughing spasms can cause burst blood vessels in the eyes or vomiting
    • Convalescent Stage:
      • Long recovery phase (weeks or months)
      • Increased susceptibility to secondary infections

Lower Respiratory Tract Infections Caused by Bacteria

  • Affected Areas: Bronchi, bronchioles, and lungs.
  • Examples:
    • Pneumonia
    • Tuberculosis (to be covered in the next lecture)

Pneumonia

  • Definition: Inflammatory condition of the lung with fluid filling the alveoli.
  • Causes: Various microorganisms (viral pneumonias are generally milder than bacterial).
  • Types: Community-acquired vs. nosocomial pneumonias.
  • Symptoms:
    • Begins with upper respiratory tract symptoms (runny nose and congestion)
    • Headache
    • Fever
    • Chest pain
    • Cough
    • Discolored sputum
  • Typical Bacteria:
    • Streptococcus pneumoniae
    • Staphylococcus aureus
    • Group A Streptococcus
    • Klebsiella pneumoniae
    • Haemophilus influenzae
    • Moraxella catarrhalis
    • Anaerobes
    • Gram-negative organisms

Klebsiella pneumoniae

  • Characteristics:
    • Gram-negative
    • Non-motile
    • Lactose fermenting (exceptions: K. ozaenae & K. rhinoscleromatis)
    • Rod-shaped
    • Facultative anaerobic
    • Polysaccharide capsule (highly mucoid colonies on plates)
  • Significance: Important pathogen in nosocomial infections.
  • Habitat:
    • Widely found in nature (soil, water, plants)
    • Human microbiota (mouth, nasopharynx, skin & intestinal tract)
  • Transmission: Spreads easily and rapidly, but not through the air.
  • Infections: Can lead to severe infections such as pneumonia, bloodstream infections, wound infections, urinary tract infections, and meningitis.
  • Hospital Setting:
    • Frequently causes nosocomial infections/outbreaks
    • Significant proportion of hospital-acquired soft tissue & urinary tract infections, pneumonia, septicemia
  • Transmission Reservoirs:
    • Gastrointestinal tract
    • Contaminated hands of employees or patients
  • Risk Factors:
    • Patients requiring catheters or ventilators
    • Patients administered broad-spectrum antibiotics, disrupting normal microbiota

Klebsiella – Virulence Factors

  • Antigens:
    • Lipopolysaccharide (O antigen)
    • Capsular polysaccharide (K antigen)
    • 77 K antigens and 12 O antigens described - structural variability helps classify serotypes

Klebsiella pneumoniae – Capsule

  • Function:
    • Encases the entire cell surface
    • Accounts for the large appearance of the organism on Gram stain
    • Increases virulence
    • Physical barrier to evade host immune response
    • Protects the cell from desiccation

Pseudomonas aeruginosa

  • Characteristics:
    • Gram-negative
    • Found widely in nature (soil and water)
    • Encapsulated
    • Aerobic–facultatively anaerobic
    • Rod-shaped
    • Non-spore forming
  • Pathogenicity: Can cause disease in plants and animals, including humans.
  • Opportunistic Pathogen: Commonly associated with cystic fibrosis patients.
  • Impact in Nosocomial Setting:
    • 30% prevalence among hospital-acquired pneumonia (HAP)
    • 66% prevalence among ventilator-acquired pneumonia (VAP)
  • Virulence Factors:
    • Efflux pumps (antibiotic resistance)
    • Extracellular polysaccharide (biofilm formation)
    • Multiple secretion systems (delivery of toxins)
    • Biofilm formation
    • Quorum sensing (QS) systems
    • Flagellins
    • Pyoverdine (PVD) siderophore
    • Type 4 pili
    • Lipopolysaccharide (LPS) & outer membrane proteins (OMPs)
    • Type III secretion system (T3SS)
    • Type VI secretion system (T6SS)

Pseudomonas aeruginosa and Cystic Fibrosis

  • Major cause of lung infections in people with cystic fibrosis

Pseudomonas aeruginosa – Acute Versus Chronic Infection

  • Can cause both acute and chronic infections depending on the host and environment conditions.

Recommended Reading

  • Prescott's Microbiology, By Joanne Willey, Kathleen Sandman and Dorothy Wood
  • Kot, B., Piechota, M., Szweda, P. et al. 2023. Virulence analysis and antibiotic resistance of Klebsiella pneumoniae isolates from hospitalised patients in Poland. Sci Rep 13, 4448.
  • Jurado-Martín, I.; Sainz-Mejías, M.; McClean, S. 2021. Pseudomonas aeruginosa: An Audacious Pathogen with an Adaptable Arsenal of Virulence Factors. Int. J. Mol. Sci., 22, 3128.
  • Purushothama V. Dasaraju and Chien Liu. Chapter 93 - Infections of the Respiratory System. Medical Microbiology. 4th edition.