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.