chapter 19 (module 7) Flashcards
19.1 The Respiratory Tract and Its Defenses
-resp tract is the most common place for infectious agents to gain access to the body
components of upper resp tract
mouth, nose, nasal cavity and sinuses above it, throat/pharynx, epiglottis, and larynx
components of lower resp tract
trachea, bronchi, bronchioles, lungs
________ are attached to the bronchioles and are small balloon like structures; sites of oxygen exchange in lungs
alveoli
anatomical features of resp system that protect from infection
- nasal hairs serve to trap particles
- cilia on the epithelium of trachea and bronchi propel particles up and out of resp tract (ciliary escalator)
- mucus on the surface of mucous membranes lining the resp tract is a natural trap for invading microorganisms
- ->once trapped, involuntary responses like coughing, sneezing, and swallowing can move them out of sensitive areas
(FIRST LINE DEFENSES)
small piece of cartilage that partially covers the larynx; its job is to help prevent inhalation of food and fluids into your lungs
Epiglottis
_______ occurs when infection or injury causes the epiglottis to swell, which may result in the inability to draw air into the lungs
sx: fever, extremely sore throat, muffled or hoarse voice, stridor (high pitched breathing sound on inhalation), and difficulty breathing and swallowing
name some serious infections besides epiglottitis, that have been decreased in incidence since the intro of Hib vaccine (Haemophilus influenzae b.)
Meningitis, otitis media, and pneumonia
second and third lines of defense that also protect the resp tract
complement action, antimicrobial peptides, and increased levels of cytokines all help battle pathogens in the lungs
- macrophages inhabit the alveoli of the lungs and the cluster of the lymphoid tissues (tonsils) in the throat (pharynx)
- secretory IgA against specific pathogens can be found in the mucus secretions as well
19.2 Normal Biota of Resp. Tract
latest research shows that a healthy upper resp. system harbors thousands of commensal microorganisms and that even the LUNGS have a normal, if limited, biota
- –> part of this normal biota can cause serious disease especially in immunocompromised people, including:
- S. pyogenes
- S. aureus
- Streptococcus pneumoniae
- Neisseria meningitidis
- Haemophilus influenzae
Yeasts, especially Candida albicans, also colonize the mucosal surfaces of the mouth
-other fungi can be found
- biota in lung differs in patients suffering from lung disorders such as COPD, asthma, and cystic fibrosis
- smokers vs nonsmokers appear to have different biota
reduces the chances of pathogens establishing themselves in the same area by competing with them for resources and space (in resp system)
microbial antagonism
19.3
Upper Resp Tract Diseases Caused by Microorganisms
Pharyngitis
inflammation of the throat, pain and swelling experienced by host (ranging from mod to severe for pain depending on causative agent
Pharyngitis
Viral sore throats are generally ______ and sometimes lead to __________
mild
hoarseness
Pharyngitis
Bacterial sore throats are generally more ________ than those caused by viruses, and are more likely to be accompanied by _____, ______, and _____
painful
nausea
headache
fever
Clinical signs of pharyngitis (sore throat)
reddened mucosa, swollen tonsils, sometimes white packets of inflammatory products visible on the walls of the throat, especially in streptococcal disease
- the mucous membranes may be swollen, affecting swallowing and speech
- often pharyngitis results in foul smelling breath
incubation period for most sore throats
generally 2-5 days
Streptococcus pyogenes
gram + coccus that grows in chains, does not form endospores, nonmotile, forms capsules and slime layers
- facultative anaerobe that ferments a variety of sugars
- does not produce catalase but does have a peroxidase system for inactivating hydrogen peroxide, which allows its survival in the presence of oxygen
causative agents for most serious cases of pharyngitis
S. pyogenes
group A streptococcus
Fusobacterium necrophorum
Scarlet Fever
as a result of complication with pharyngitis - extra toxin
result of S. pyogenes strain that is itself infected with a bacteriophage
-this lysogenic virus gives streptococcus the ability to produce ERYTHROGENIC TOXIN,
characterized by sandpaper-like rash, most often on the neck, chest, elbows, and inner surfaces of the thighs, HIGH FEVER
the deposition of antibody-antigen complexes in the body that occurs with untreated throat infections can result in
glomerulonephritis
Rheumatic Fever (as a result of a pharyngitis complication)
thought to be due to an immunologic cross-reaction between the streptococcal M protein and heart muscle.
–> means that the lymphocyte clones activated by the M protein also react with an epitope on the heart muscle
- tends to occur approx. 3 weeks after pharyngitis has subsided
- can result in PERM heart valve damage
-other sx include nodules over bony surfaces just under the skin, arthritis in multiple joints
Pharyngitis
Virulence Factors of S. pyogenes
virulence is a result of two main factors:
- ability of its surface antigens to mimic host proteins
- –> display numerous surface antigens
-possession of superantigens
- –> specialized polysaccharide on the surface of the cell wall help to protect the bacterium from being dissolved by lysozymes
- –> Lipoteichoic acid (LTA) contributes to the adherence of S. pyogenes to epithelial cells in the pharynx
- –> spiky surface projection called M. protein contributes to virulence by resisting phagocytosis
- –> capsule made of Hyaluronic Acid is formed by most S. pyogenes strains (adhesiveness)
Pharyngitis:
Extracellular Toxins
Group A streptococci owe some of their virulence to the effects of hemolysins called streptolysins (rapidly injure many cells/tissues, inc. leukocytes and liver and heart muscle)
- Streptolysin O (SLO)
- Streptolysin S (SLS)
- Key toxin in development of SCARLET FEVER is ERYTHROGENIC TOXIN
- responsible for bright red rash and fever
- -> only lysogenic strains of S. pyogenes that contain genes for temperate bacteriophage can synthesize this toxin
Transmission of pharyngitis S. pyogenes
resp. droplets or direct contact with mucus secretions
- humans are only significant reservoir
Group A streptococcal infection Culture/Dx of pharyngitis
rapid diagnostic tests (swab samples)
if culture is needed, it is usually done on sheep blood agar
–>is pharyngitis is caused by a virus: blood agar will show a variety of colony types
POC testing
Prevention of Group A streptococci of pharyngitis
no vaccine exists
good handwashing
Treatment of S. pyogenes in pharyngitis
penicillin is antibiotic of choice
-if allergy than first-generation cephalosporin, such as cephalexin is used
–SHould be treated with antibiotics when S. pyogenes infection b/c of potential sequelae
Pharyngitis: S. pyogenes
Causative Org: Streptococcus pyogenes (G+)
Trans: droplet or direct contact
Virulent Factors: LTA, M protein, HA capsule, SLS/SLO (streptolysins), superantigens, induction of autoimmunity
Culture/Dx: Beta-hemolytic on blood agar, sensitive to Bacitracin, rapid antigen tests
Prevention: hygiene practices
Tx: Penicillin, cephalexin in penicillin-allergic
D Feats: generally more severe than viral pharyngitis
Epi Feats: US: 20-30% of all cases of pharyngitis
S/S: swollen and painful pharynx/throat, potentially rheumatic fever, scarlet fever, difficulty swallowing
Pharyngitis: Fusobacterium necrophorum
Causative Org: Fusobacterium necrophorum (G-)
Trans: usually endogenous
Virulent Factors: invasiveness, endotoxin
Culture/Dx: culture anaerobically , CT scan for abscess(es)
Prevention: ?
Tx: Penicillin
D Feats: can lead to Lemierre’s syndrome
Epi Feats: causes up to 15% of acute pharyngitis in teens/young adults (can lead to septic thrombophlebitis)
S/S:
Pharyngitis: Viruses
Causative Org: viral
Trans: all forms of contact
Virulent Factors: —
Culture/Dx: goal is to rule out S. pyogenes, further diagnosis usually not performed
Prevention: hygiene
Tx: symptom relief only
D Feats: hoarseness frequently accompanies viral cases
Epi Feats: ubiquitous; responsible for 40-60% of all pharyngitis
S/S:
The Common Cold
S/S
sneezing. scratchy throat, runny nose, which usually begin 2-3 days post-infection
—> an uncomplicated cold is often not accompanied by fever, but children may experience low grade fevers
INC. PERIOD: 2-5 days