Chapter 21
Microbial Diseases of the Respiratory System
Structure of the respiratory system
Upper respiratory system
Nose
Pharynx (throat)
Middle ear and auditory tubes
Larynx (voice box)
Lower respiratory system
Trachea (windpipe)
Bronchial tubes
- Lungs (alveoli sac)
Respiratory System
Function of the respiratory system:
Upper respiratory system: Collects air, filters contaminants from the air, and delivers it to the lower respiratory organs
Lower respiratory system: Exchange of gases
The Normal Microbiota
Upper Respiratory System: The normal microbiota prevents the growth of pathogenic organisms. Some normal microbiota are opportunistic pathogens.
Haemophilus influenzae, Staphylococcus aureus, Neisseria meningitidis, Diphtheroids (colonize the nose and nasal cavity)
Lower Respiratory System: Typically microorganisms are not present
How the microbes are prevented of reaching the lungs?
Particles (microbes) are removed from larynx, trachea and bronchial tubes by ciliary escalator (first line of defense)
Cilia propel particles upward
Microbes reaching the lungs are removed by phagocytosis
VIRAL DISEASES OF THE UPPER RESPIRATORY SYSTEM
The Common Cold - Rhinitis
Caused by 200 different viruses (Rhinoviruses, Coronaviruses)
Immunity is accumulated during the lifetime
Symptoms: sneezing, nasal secretion, congestion
Primary infection is in the throat but can spread to the lower respiratory system and the middle ear
The Common Cold
Virus is transmitted by air and hands to the nose mucous membrane
Recovery time is about one week
Antibiotics are not useful
Ear Infection Acute Otitis Media
Result of rhinitis
Viral infection causes inflammation of eustachian tubes accumulation of fluid
Becomes the site of bacterial infection Streptococcus pneumoniae; Haemophilus influenzae
Treatment: Broad-spectrum antibiotics
Streptococcal pharyngitis (Strep throat)
Causative agent: S. pyogenes
Symptoms: Inflammation of throat mucous membrane, lymph nodes (tonsillitis), difficulty swallowing
May progress to scarlet or rheumatic fever and endocarditis
Transmitted by respiratory secretion
Treatment: penicillin
Strep Throat Diagnosis
Pharyngeal swab samples
Blood Agar Streak
Quick Strep: ELISA in a small tube .can be done in a physicians office.
Only about 30% people diagnosed with Strep Throat actually have a S. pyogenes
Major Problem people recovering from Strep throat are contagious even with antibiotic therapy
Virulence Factors of S. pyogenes
Includes:
Polysaccharides- protection against lysozyme
Lipoteichoic acid adherence to epithelial cells in the pharynx
M protein a spiky surface projections resistance against phagocytosis
Hyaluronic acid capsule adherence
Toxins - streptolysins cytotoxic to tissue cells
Rheumatic Fever
May develop two to three weeks after a Group A streptococcal infection strep throat
Antibodies developed against streptococcal M protein cross react with the heart tissue and joints
Damage to heart valves
Diphtheria
Used to be the leading cause of fatal infectious diseases of children
Caused by Corynebacterium diphteriae
Gr+ non-endospore irregular rods pleomorphic morphology
Symptoms: Sore throat, fever, grayish membrane in the throat (can block the passage of air)
Lysogenized bacteria produce powerful toxin
Treatment: penicillin and erythromycin + antitoxin
Vaccine available DTP
Virulence Factors of
Corynebacterium diphteriae
Exotoxin is the A-B toxin
B (binding) component attaches to the receptor on the surface of the host cell
The toxin enters the cell inside the endocytic vacuole
Two components separate A-chain enters the cytoplasm
The active enzyme (chain A) disrupts the normal function of the host proteins
Cell death follows
Bacterial Diseases Of The Lower Respiratory System
Pertusis (Whooping Cough)
Caused by Bordetella pertussis - aerobic Gr- coccobacili
Bacteria affect the ciliated escalator system (prevent the movement of mucus) - mucus accumulates in trachea
Infants can suffer from the brain damage caused by severe coughing
Transmitted by droplets
Treatment: Combination antibiotic therapy
Vaccine is available - DTP
Viral Diseases of the Lower Respiratory System
Influenza (Flu)
Caused by Influenza virus
The virus contains RNA (8 RNA segments), protein and lipid layer
Lipid layer is holding two types of spikes (protein N and H) - antigens
The immune response is directed towards these spikes.
Influenza Vaccines
The circulating virus must be identified in February every year there is a different vaccine composition
Contains three most important strains of virus
The existing vaccine does not provide long-term immunity against all viral strains
Why is it difficult to produce a universal flu vaccine?
The structure of spikes
changes - evading the immune response
- Mutations occur via two main processes
1. Antigenic drift minor change
2. Antigenic shift major change; Involves two strains
Antigenic shift
Happens when ducks, swine and humans live close together
The swine harbors two different virus strains
The hybrid virus is formed not recognized by the human immune system
Influenza
Pathogenesis
Symptoms chills, fever, headache, and muscular aches.
Flu patients are susceptible to secondary bacterial infections - damage to the lung epithelium
Epidemiology
Influenza is transmitted via inhalation of airborne viruses
Complications occur most often in the elderly, children, and those with chronic diseases
10,000-20,000 Americans die annually of the flue.
In 1918 epidemics 20 million people died.
Tuberculosis
Caused by: Mycobacterium tuberculosis, Gr+ slender rods, sometimes filamentous
Very resistant to drying and disinfectants (cell wall contains large amounts of lipids)
Signs and Symptoms
Initial symptoms include minor cough and mild fever
Later symptoms include difficulty breathing, chest pain, wheezing, and coughing up blood
Long term (chronic) infection
Infection process- Primary infection
Bacilli penetrate the alveoli
Macrophages ingest the bacterium (not always destroyed)
M. tuberculosis can survive inside the macrophage
A layer of macrophages at the infection site is formed - tubercle (lump)
Tubercle may remain dormant for years
The lesion may heal - become calcified
The tubercle may become a source of a new infection Secondary tuberculosis
Tubercle grows forming air-filled cavity. Bacteria start multiplying outside the macrophages
The disease is spread through aerosol droplets
Tuberculosis Diagnosis
Tuberculin skin test - injection of a protein released by M. tuberculosis when grown in a liquid medium.
Tuberculin causes hypersensitivity reaction in the person who is infected with the M. tuberculosis
Doesnt distinguish between active disease, chronic carriers, or those who have been vaccinated
Treatment: streptomycin, isoniazid, rifampin, and pyarazin amid
Six month antibiotic treatment (3 - 4 drugs)
BCG vaccine - introduced in the 1920s. (Bacillus of Calmette - Guerin) - live but avirulent strain.
Bacterial pneumonias
Pneumonia pulmonary infection
Pneumococcal pneumonia
Hemophilus influenzae
Mycoplasma pneumoniae
Pneumococcal pneumonia
Caused by Streptococcus pneumoniae - Gr+ ovoid bacteria in pairs, thick capsule.
Infection of both bronchi and alveoli
Symptoms: Breathing difficulty, high fever, chest pain
Bacteria can enter the blood stream and infect the meninges
Treatment: Penicillin
Legionellosis
Caused by: Legionella pneumophila
Discovered in 1976. Members of American Legion contracted pneumonia caused by unknown microbe
L. pneumophila can be found in various natural environments, water lines, air conditioning systems, shower heads, decorative fountains
Bacterium resistant to chlorine and high temperatures
FUNGAL DISEASES OF THE LOWER RESPIRATORY SYSTEM
Histoplasmosis
Causative agent: Histoplasma capsulatum dimorphic fungus
When grown in soil and artificial media it forms filamentous mycelium
When grown in tissue produces yeast-like cells
Infected lung shows lesions resembling tuberculosis
In US the diseases is localized in Mississippi and Ohio
The disease is acquired by inhalation of airborne spores (bird droppings provide the favorable environment for the fungus)