LOWER RESPIRATORY Flashcards
SOURCES OF LOWER RESPIRATORY TRACT SAMPLES
Expectorated sputum
Induced sputum
Endotracheal aspirate
Bronchial washings
BALs
Bronchial brushings
Ideal sputum specimen collection occurs
first thing in the morning, with no food ingestion for 1–2
hours prior.
Rinsing the mouth with water before collection and collecting directly into a sterile
specimen container aid in
avoiding contaminating the sample with saliva
Sputum is collected
through the following methods:
Expectorated sputum
Induced sputum
Endotracheal aspirate
Expectorated sputum is expelled by
a deep cough of the patient
Induced sputum collection uses
an aerosol spray that reaches the lungs, inducing a deep
cough
Endotracheal aspirate samples are
collected via mechanical suction from patients with a
tracheostomy tube.
Bronchoscopy procedures visualize
the lungs by passing a tube with a light source and camera
down a patient’s throat and into the lungs.
Bronchoscopes are used for collection of the following
lower respiratory tract specimens
Bronchial washings
Bronchial brushings
BALs
Bronchial washings are collected from
the bronchial tube
A measured amount of sterile
saline is passed through (washings)
the scope, and then it is gently suctioned back out
For washing The suctioned
saline is placed into
a sterile container because it contains the cells and fluids needed for
analysis.
Bronchoalveolar lavage samples are collected from
the smaller bronchoalveolar pathways
via the same process as bronchial washings. Multiple lavage samples may be collected from
several sites during one procedure
Bronchial brushings are collected by
passing a brush through the bronchoscope and
gently abrading the surface of the airway mucosa and bronchial lesions to collect cells for
analysis
Quantitative and semiquantitative results from Gram stains of lower respiratory tract specimens
are used to
evaluate the quality of samples before culture and aid in the diagnostic and treatment
process for patients suspected of lower respiratory tract infections
Expectorated and induced
sputum samples must
meet specific Gram stain criteria to be considered acceptable for culture
For sputum, Observed in 10–20 fields under low power, the following criteria indicate an acceptable specimen
<10 squamous epithelial cells and ≥10 WBCs per field. Regardless of the number of white cells
present, samples with more than 25 epithelial cells per low-power field will be rejected.
For sputum, unacceptable samples indicate
that a sample did not originate in the lower respiratory tract and is contaminated
by saliva and oral flora
Physicians interpret semiquantitative results for bacteria in
conjunction with quantitative WBC and epithelial cell results to determine the following:
presence or absence of infection, the presumptive cause of infection, and the severity of infection
ORAL FLORA GPCs
S. aureus
S. epidermidis
S. pneumo
S. pyogenes
S. mitis
S. salivarius
S. mutans
E. faecalis
ORAL FLORA GPRs
Corynebacterium
Actinomycetes
Lactobacillus
ORAL FLORA Gram-positive buds, hyphae, or pseudohyphae
Candida species
ORAL FLORA GNC
Neisseria species
ORAL FLORA GNRs
H. influenzae
E. coli
S. aureus colony morphology
soft, opaque or pale gold, and circular
S. epidermidits colony morphology
opaque, gray, smooth, raised, with no hemolysis
S. pneumoniae colony morphology
alpha-hemolytic, convex, mucoid or “water drop”
S. pyogenes colony morphology
grayish-white, transparent to translucent, matte or glossy, large zone of
hemolysis
S. mitis colony morphology
alpha-hemolytic, broken glass appearance
S. salivaris colony morphology
small, colorless, smooth or rough, nonhemolytic or weakly alpha-
hemolytic
S. mutans colony morphology
small white to gray, rough, nonhemolytic or alpha-hemolytic
E. faecalis colony morphology
circular, smooth, nonhemolytic
Corynebacterium colony morphology:
small to medium, gray, white, or yellow, nonhemolytic
Actinomycetes colony morphology:
white, rough, crumbly texture, occasionally pigmented red
Lactobacillus colony morphology:
small to medium, gray, alpha-hemolytic
Candida colony morphology:
creamy, white, dull, grows upward with foot-like projections
Neisseria colony morphology:
small, white to gray-brown, smooth, butter-like, translucent, possible green
hue underneath
H. influenzae: on chocolate agar colony morphology:
❖ Unencapsulated strain — small, smooth, and translucent
❖ Encapsulated strain — larger, mucoid, with a mouse nest odor
E. coli colony morphology:
circular, dull gray, smooth, convex
COMMON LOWER RESPIRATORY TRACT PATHOGENS
S. aureus
S. pneumo
H. influenzae
K. pneumo
Legionella
Candida
Mycoplasma pneumoniae
Mycobacterium tuberculosis
GPCs in lower resp tract:
Staphylococcus
❖ S. aureus: soft, opaque or pale gold, and circular
❖ S. epidermidis: opaque, gray, smooth, raised, with no hemolysis
GNRs in lower respiratory tract
o H. influenzae: on chocolate agar
❖ Unencapsulated strain — small, smooth, and translucent
❖ Encapsulated strain — larger, mucoid, with a mouse nest odor
o K. pneumoniae: small to medium, grayish-white, translucent or opaque. circular, dome
shaped, mucoid, nonhemolytic
o Legionella: green or iridescent pink, circular with entire edge, convex, glistening, with a
ground-glass appearance on buffered charcoal yeast extract agar
Mycoplasma pneumoniae in lower respiratory tract
o Organisms do not stain well due to the lack of a rigid cell wall.
o Pinpoint, granular, “fried egg” appearance on media enriched with cholesterol and fatty
acids.
Mycobacterium tuberculosis in lower respiratory tract
o Mycolic acid in the cell wall resists Gram stain. Appear as slim rods, gram variable or
bright red using an acid-fast stain.
o Off-white to buff, dry, rough, raised, and wrinkled on Löwenstein–Jensen medium.
Fungi in lower respiratory tract
o Yeasts: Gram-positive buds, hyphae, or pseudohyphae
❖ Candida: creamy, white, dull, grows upward with foot-like projections
o Other fungi: fluorescent white buds, hyphae, or pseudohyphae with KOH reagent and
calcofluor-white stain
❖ Variable growth on Sabouraud’s dextrose agar for up to 6 weeks after inoculation.
Legionnaires’ disease and Pontiac pneumonia are lower respiratory infections caused by
Legionella bacteria
Legionella bacteria’s natural habitat is
freshwater lakes and ponds, and it becomes pathogenic when it is able to grow in human-made water systems such as air conditioners, shower heads, hot water heaters, and large plumbing systems.
Legionella in lower respiratory tract
- Heat shock protein 60: aids in invasion
- Outer membrane protein: prevents phagocytosis
- Type IV pili: entry into macrophages for spread and survival.
Primary infections caused by M. tuberculosis take place in
the lungs causing pneumonia-like
symptoms
If left untreated, tuberculosis can
become disseminated and spread to other organ
systems in the body
M. tuberculosis in lower respiratory tract
- No endotoxins or exotoxins, toxic effects on cells from lipids and phosphatides
- Cord factor: destroys cell mitochondria, inhibits leukocyte migration
- Waxy layer and mycolic acid cell wall: delay hypersensitivity, induce multidrug-resistant
variants
Opportunistic fungi such as Aspergillus and Cryptococcus species aspirated into the lungs can cause
pneumonia and lead to sepsis in immunocompromised patients.
Bacterial lung abscesses are
commonly a
polymicrobial infection predominantly comprised of anaerobic oropharyngeal or
gastric normal flora aspirated into the lungs
DIRECT AND MOLECULAR TECHNIQUES FOR DETECTING RESPIRATORY PATHOGENS
immunochromatographic
or immunofluorescent assays
Direct-fluorescent antibody
testing
real-time PCR
Multiplex PCR
isothermal loop-mediated amplification
S. pyogenes, or group A Streptococcus, is the respiratory pathogen responsible for
upper respiratory
infections including strep throat and pharyngitis
B. pertussis is responsible for
whooping cough
immunochromatographic
or immunofluorescent assays
Rapid test kits have been created for the detection of S. pyogenes
Positive results are enough evidence to diagnose infection,
whereas negative results need to be confirmed with a throat culture
Direct-fluorescent antibody
testing
serologic test for the presence of IgG antibodies to B. pertussis. Although helpful in
diagnosing an infection of B. pertussis, a diagnosis will be delayed because this method is best when
a patient is tested between 2 and 8 weeks of symptom onset
Traditional culture or molecular
methods allow for a timelier diagnosis for B. pertussis than antibody testing
The most common molecular method used to detect S. pyogenes and B. pertussis is
real-time PCR
Multiplex PCR methods are
also used to detect
B. pertussis, along with multiple other respiratory pathogens.
highly specific isothermal loop-mediated amplification method can also be used in
detecting B. pertussis
infections between 0 and 3 weeks of symptom onset
COMMON PNEUMONIA-CAUSING PATHOGENS
S. aureus
S. pneumo
H. influenzae
K. pneumo
M. pneumo
Lower respiratory tract infections can manifest into
various disease states including tracheitis,
acute or chronic bronchitis, and community- or hospital-acquired pneumonia.
The mode of
transmission for these pathogens is through
the inhalation of respiratory droplets from an infected
person.
S. aureus in pneumonia
o Exotoxins: hemolysins, leukocidins, spreading factor by coagulase and hyaluronidase,
nuclease, protease, and lipase
o Beta-lactamase: penicillin resistance, MRSA: methicillin resistance
S. pneumo in pneumonia
o Pneumolysin: antiphagocytic capsular protein
o Several adhesion factors and immunogenic cell wall membrane
H. influenzae in pneumonia
o Encapsulated strains: resistant to phagocytosis and complement-mediated lysis
K. pneumo in pneumonia
o Encapsulated to inhibit phagocytosis and complement-mediated lysis
o Lipopolysaccharide endotoxin causing inflammation
o Fimbriae for adhesion and siderophores that acquire host iron for organism survival
M. pneumoniae in pneumonia
o P1 membrane protein: acts as a cytohesin to ciliated epithelial cells
o Community-acquired respiratory distress syndrome toxin: damages respiratory
epithelium and ciliary activity by releasing cytokines and inflammatory mediators.
