Respiratory Tract Bacteria Flashcards
The upper tract (above vocal cords) is colonized by an established and extensive microbial flora. Are there any exception? Describe the flora of the lower respiratory tract.
- middle ear spaces and sinus cavities are sterile
- lower respiratory tract is also sterile
___________ is important in physically removing aspirated particles. Therefore, damage to this process increases one’s risk of lung infection.
-mucociliary flow
When can normal upper respiratory flora become a source of infection?
-when it spreads beyond its niche in the oropharynx and nasopharynx, where it is not associated with symptoms, to normally sterile sites
Acute respiratory infection (ARI) is a leading cause of morbidity and mortality, particularly during what period of life?
-early childhood and in the elderly
What bacterium is the most common cause of community-acquired pneumonia?
-streptococcus pneumoniae (30-50%)
One of the main host defense mechanisms against bacterial infection involves the complement system, which can be bactericidal through what 2 processes?
- generation of membrane attack complex
- opsonization
2 ways successful pathogens circumvent complement
- O-antigen
2. Capsular polysaccharides (CPS)
Describe the O-antigen and what it does
-chains of covalently linked sugar residues extending from the lipopolysaccharaide prevents the membrane attack complex from acting in proximity to the cell membrane
Describe the function of capsular polysaccharides
- limit complement activation and antibody binding
- porous, noncovalently attached zones of polysaccharide that completely envelop and protect the cell
- do not activate complement efficiently in absence of specific antibody and thus serve to protect underlying bacterial cell-surface components
T/F: All CPS are comprised of the same sugar.
False; comprised of different sugar constituents or the same array of sugars linked in different ways
Both O-antigen and CPS tend to be highly immunogenic and are often the dominant antigen on the organism, Because they are the target of selective immune presence in the host, ______________.
-there is often considerable structural and thus antigenic variation
O-antigen and CPS allow extracellular bacterial survival in the non-immune host until ________.
-specific bactericidal and/or opsonic antibody to these polysaccharides is generated and the pathogen is cleared
Why is CPS expression particularly important for an organism to survive for any length in the blood stream?
- that is where complement is most abundant
- why bacteria causing meningitis which requires a sustained bactermia to cross BBB are all encapsulated
Why is a CPS made of sialic acid particularly advantageous?
-it is poorly antigenic, possibly because it is an embryonic “self antigen”
Nickname for Streptococcus pneumoniae
-pneumococcus
Physiology and structure of Streptococcus pneumoniae
- gram positive cocci
- lancet shaped diplococci
- alpha hemolytic on blood agar
- catalase negative, bile salt solube
- optochin sensitive
A discriminating characteristic used to identify the pneumococcus in the lab is its _________.
-susceptibility to optochin
3 diagnostic measures of pneumococcus
- Sputum Gram’s stain
- culture of organism outside its niche in upper respiratory tract (blood, CFS, sputum) but this is problematic for sputum due to contamination as sample passes through the colonized upper airway
- detect of antigen secreted in urine
Discuss the immunity to S. pneumoniae and why it is not always effective
- antibody to CPS is generally protective but requires many days to develop
- due to structural differences among capsules, acquisition of antibody to one type still leaves the host susceptible to other non-cross reactive types
Disease caused by S. pneumoniae is probably more of a function of its ______________________.
-ability to trigger an inflammatory response than the expression of toxins
Polysaccharide capsule allows for evasion of ______________ until….
-complement and antibody until type specific antibody develops
Pneumococcus is a common resident of the _________.
-mucosal surface of human nasopharynx
How is pneumococcus spread?
-person to person spread by colonized individuals through contact with secretions
Pneumococcus is most common in children 65 yrs and may be associated with what 5 predisposing factors?
- eustachian tube dysfunction
- aspiration of nasopharyngeal contents
- antecedent viral (especially influenza!!) disruption of the nasal mucosa
- antibody production is impaired (hypogammaglobinemia, AIDS)
- defective clearance of opsonized bacteria by neutrophils and reticuloendothelial system (splenic dysfunction)
Streptococcus pneumoniae is a prominent cause of ______________.
- lobar pneumonia in which consolidation of the entire lobe has occurred
- lobe infiltrate results from spread within airspaces until tissue barriers are reached
What is the most common pattern for pneumococcal pneumonia?
-lobar infiltrate of entire lobe
Histology of pneumococcal pneumonia
- patchy area of alveoli that are filled with acute inflammatory cells;
- at high magnification, alveolar exudate of mainly neutrophils is seen; surrounding alveolar walls have capillaries that are dilated and filled with RBCs
What does the fact that the alveolar structure is still in tact tell us about pneumococcal pneumonia?
-explains why a pneumonia often resolves with minimal residual destruction or damage to the lung
What does the exudate of penumococcal pneumonia give rise to?
-productive cough of purulent yellow or rust colored sputum
Are there any concerns with antibiotic resistance when treating pneumococcus?
-yes; penicillin and general Beta-lactam antibiotic resistance
Carriage of pneumococcus is especially common in what age period?
-early childhood
Structure and physiology of Haemophilus influenzae
- small
- nonmotile
- gram negative
- pleomorphic coccobacillus
How to identify H. influenzae in the lab?
- culture and its unique growth requirements
- aerobic growth requires 2 supplements: hemin and NAD (factor X and V, respectively)
Next to pneumococcus, _________ is the most common cause of RTI
-H. influenzae
Where is H. influenzae found?
-only resides in the human nasopharynx
Type b vs. non-typeable H. Influenzae
- type b: controlled by immunization with type b CPS
- NTHi: leading cause of acute otitis media and conjunctivitis in children and exacerbations of COPD
What causes otitis media?
- poor drainage through eustachian tube causes the accumulatioon of fluid in the middle ear space. This becomes infected with organisms residing in the upper airway that can transmit up the eustachian tube
- results in painful ear with fever and evidence of inflammation of eardrum
Immunity and Type B H. influenzae
- among capsulated strains, those with type b CPS are the most virulent
- before the vaccination era, it was a cause of life-threatening pneumonia, bacteremia, epiglottitis, and meningitis in young children between 2 months and 4 years of age
- immunity is based on antibody to CPS
Treatment of H. influenzae and resistance
-70-80% sensitive to penicillins; resistance is mediated by expression of beta-lactamase and so many cephalosporins remain effective
Infections due to type b H. influenzae vs. nontypeable strains
- type b: able to cause invasive infection
- nontypeable: unencapsulated and cause infection mostly limited to respiratory tract (pneumonia, acute otitis media)
Neisseria meningitidis structure and physiology
- the meningococcus
- gram negative
- bean-shaped dipplococcus (identical in staining and morph to N. gonorrhoeae)
- at ultrastructural level, it has prominent antiphagocytic polysaccharide capsule
Meningococcal capsular polysaccharides provide the basis for grouping the organism. 12 serogroups have identifies, but which are the most important ones associated with human disease?
-A,B, C, Y, W-135
Where does N. meningitidis colonize and what are its hosts?
- posterior nasopharynx of humans
- humans are the only known host
Carriage rates of meningococcus are highest in what age group and why?
- older children/young adults
- in conditions that promote transmission (dorms, military)
