Study Guide – Respiratory Infections (Chapter 22)
1) Immune Defense Mechanisms of the Respiratory Tract
The respiratory tract has multiple layers of defense that prevent microbes from entering and establishing infection.
Physical and Mechanical Defenses
Mucous membranes line the respiratory tract
Goblet cells secrete mucus
Mucus traps dust, bacteria, viruses, and particles
Mucociliary escalator
cilia beat upward
moves trapped microbes toward the throat
microbes are then swallowed or expelled (mucus when sick is brought upwards from the lungs filled with microbes)
Chemical Defenses
Lysozyme
breaks down bacterial cell walls
Defensins
antimicrobial peptides that kill microbes
Surfactant
helps reduce surface tension in lungs
also contributes to antimicrobial defense
Secretory IgA antibodies
prevent microbes from attaching to mucosal surfaces
Immune Cell Defenses
MALT (mucosa-associated lymphoid tissue)
includes tonsils and adenoids
monitors pathogens entering upper respiratory tract
Alveolar macrophages
located in lower respiratory tract
engulf and destroy inhaled microbes
Normal Microbiota
Upper respiratory tract normally contains microbes such as:
Staphylococcus aureus
Streptococcus
Haemophilus
Neisseria
2) What is Pneumonia?
Pneumonia is an infection/inflammation of the lower respiratory tract, specifically the lung parenchyma and alveoli.
Key Features
alveoli fill with:
pus
blood
fluid
gas exchange becomes impaired
oxygenation decreases
Symptoms
cough
fever
chills
shortness of breath
chest pain
productive cough with sputum
sometimes cyanosis
Diagnosis Clues
crackling or bubbling lung sounds
white shadows on chest x-ray
Treatment
Depends on cause:
bacterial → antibiotics
fungal → antifungals
viral → generally no effective treatment listed in slides
3) Three Bacterial Pathogens that Cause Pneumonia
The three major bacterial causes discussed are:
Streptococcus pneumoniae
Klebsiella pneumoniae
Mycoplasma pneumoniae
Similarities
All cause:
cough
fever
respiratory distress
inflammation in lungs
Differences
Streptococcus pneumoniae
4) Characteristics of the Bacteria
Gram-positive cocci
arranged in pairs (diplococci) or short chains
major cause of hospitalized adult pneumonia
causes about 60% of hospitalized adult pneumonias
5) Symptoms / Pathology / Treatment
Symptoms
cough
fever
chest pain
pinkish sputum
Pathology
fluid accumulates in alveoli
difficult breathing
impaired oxygen exchange
Complications
If bacteria enter bloodstream:
septicemia
endocarditis
meningitis
Treatment
antibiotics
vaccine prevention available
6) Who is Most Susceptible?
The slide mainly emphasizes:
hospitalized adults
individuals vulnerable to bloodstream spread complications
7) Serotypes
There are more than 90 serotypes.
These are based on differences in the capsular polysaccharide antigens.
This is important because immunity is serotype specific.
8) Virulence Factors
Polysaccharide Capsule
Most important virulence factor.
Functions:
prevents phagocytosis
interferes with C3b opsonization
Pneumolysin
toxin
damages ciliated respiratory epithelium
9) Vaccines
PPSV23
Contains 23 serotypes
PCV13
Contains 13 serotypes
conjugated to diphtheria toxoid protein
Choice depends on:
age
health conditions
Klebsiella pneumoniae
10) Characteristics
Gram-negative rod
large capsule
forms large mucoid colonies
normal intestinal microbiota in some people
11) Symptoms / Pathology / Treatment
Symptoms
Similar to pneumococcal pneumonia
Pathology
tissue necrosis
lung abscesses
bacteremia
sepsis
endotoxic shock
Treatment
antibiotics
resistant strains developing
surgery may be needed to drain abscesses
12) Who is Most Susceptible?
Mostly:
immunocompromised
debilitated individuals
hospitalized patients
ventilator-associated infections
13) Virulence Factors
Capsule
Main virulence factor
Function:
interferes with phagocytosis
Also endotoxin contributes to systemic inflammation.
Mycoplasma pneumoniae
14) Characteristics
no cell wall
causes walking pneumonia
atypical pneumonia
common in children and young adults
15) Symptoms / Pathology / Treatment
Symptoms
Usually mild
persistent cough
fever
fatigue
Pathology
attaches to respiratory epithelium
interferes with cilia
causes cells to slough off
Treatment
Because it lacks a cell wall:
penicillin ineffective
use macrolides
azithromycin (Z-pack)
16) Who is Most Susceptible?
children
young adults
elderly
immunocompromised
people with lung disease
Streptococcus pyogenes (Strep Throat)
17) Symptoms / Pathogenesis / Treatment
Symptoms
sore throat
redness
fever
pus patches
tiny hemorrhages
painful swallowing
Treatment
penicillin
amoxicillin
beta-lactams
Important to treat due to complications.
18) Lancefield Groups
Lancefield grouping is based on cell wall carbohydrates.
Streptococcus pyogenes = Group A strep (GAS)
19) Characteristics
Gram-positive cocci
chains
catalase negative
beta hemolytic
20) Virulence Factors
Very important exam section.
M protein
attachment
prevents C3b opsonization
many strains (~80 types)
Capsule
hides from immune system
Streptolysins O and S
lyse RBCs and WBCs
causes beta hemolysis
C5a peptidase
blocks phagocyte recruitment
Streptokinase
dissolves clots
DNase / hyaluronidase / proteases
tissue spread
SPE exotoxins
superantigens
scarlet fever
toxic shock
flesh-eating disease
Influenza (Seasonal Flu)
21) Risk Factors / Susceptible Groups
High-risk groups:
adults >65
children <5
pregnant women
chronic disease patients
22) Symptoms / Severity
fever
headache
chills
body aches
sore throat
dry cough
nasal congestion
Most resolve in 1–2 weeks, but can progress to pneumonia.
23) Structure of Virus
enveloped virus
8 segments of negative-sense ssRNA
budding release
does not always kill host cell
24) Hemagglutinin vs Neuraminidase
Hemagglutinin (H)
spike protein
binds sialic acid receptors
allows viral attachment
Neuraminidase (N)
assists entry
helps virus bud out of cell
These are major antigens.
25) Influenza A vs B vs C
A
most virulent
infects humans + animals
pandemics
B
milder
humans/mammals
C
mildest
less clearly disease-causing
26) Antigenic Drift vs Shift
Drift
small mutations
caused by error-prone RNA polymerase
seasonal outbreaks
Shift
reassortment of RNA segments
major change
pandemics
Mycobacterium tuberculosis
27) Characteristics
rod-shaped
obligate aerobe
acid-fast
waxy mycolic acid cell wall
survives in macrophages
28) Who is Most Susceptible?
Especially:
immunocompromised
AIDS patients
people in high-risk populations
29) Signs / Symptoms / Pathogenesis
Symptoms
(active disease)
chronic cough
respiratory spread
systemic illness
Pathogenesis
inhaled into lungs
engulfed by alveolar macrophages
survives inside them
granulomas form
tubercles form
30) Two Stages of Disease
Latent TB (LTBI)
~90%
no symptoms
not contagious
granuloma formation
Active TB
5–10% reactivate
symptomatic
contagious
31) Treatment / MDR-TB
Treatment
long antibiotic therapy
MDR-TB
multidrug-resistant tuberculosis
Means TB strain is resistant to multiple antibiotics.
The slides specifically note MDR strains are rising.