Strep Pneumo Flashcards
Which organism causes the majority of the cases of bacterial pneumonia, leading to hospitalization?
-Strep Pneumoniae
Is strep pneumoniae gram positive or negative?
Gram + (Blurple)
What is alpha hemolysis?
-when grown on agar that contains RBC’s, a molecule called alpha-hemolysin breaks hemoglobin down to a greenish pigment
What is the outermost layer of pneumococcus?
- a polysaccharide capsule
- contains peptidoglycan
What does PMN stand for?
-polymorphonuclear Leukocytes
Why is pneumococcus not readily ingested by PMNs?
- The capsule is not recognized by receptors on PMN
- in the absence of antibodies to specific capsular polysaccharide, they won’t be eaten by PMN
- IgG to cell wall can’t be “seen” by PMN
Why are antibodies for the cell wall of pneumococcus not immune response inducing?
-The capsular polysaccharides are too long, and shield the Fc region of abs from PMNs
**Ig and complement diffuse through capsule, but capsule prevents PMN receptors from interacting with Fc of IgG.
What are the constituents of pneumococcus from the outside going in?
- Polysaccharide capsule
- Teichoic acid attached to lipid (lipoteichoic acid)
- Choline-Binding Proteins
- Peptidoglycan: Principal constiduent of cell wall
- Pneumolysin
- Autolysin
What factors cause decreased neutrophil function (chemotaxis, ingestion, killing)?
- Diabetes Mellitus
- Glucocorticosteroids
- Renal insuficiency
- Cirrhosis
- Alcohol Ingestion
- Genetic defects in PMN function
What factors can lead to defective IgG production?
- Congenital
- Acquired: myeloma, lymphoma, common variable immunodeficiency
- HIV infection
How are splenectomies related to pneumococcal pneumonia?
-doesn’t predispose to infection
***but does predispose to overwhelming sepsis and shock in pneumococcal pneumonia
What is pneumolysin?
- a major virulence factor produced by pneumococci
- activates complement (inflammation)
- Damages ciliated cells and PMN
- reproduces changes of pneumonia in animals
What is the difference between epidemiology & pathogenesis?
Epidemiology = where the organism likes to hang out
Pathogenesis = how disease comes about
How is pneumococcal pathogenesis related to viral illness?
- viral infection characterizes the major form of pneumococcal disease
- virus messes up our normal anatomy (cilia), and pneumococcus gets stuck where its not supposed to be
Describe the microbiology of pneumococcus.
- pairs or chains of elongated cocci
- gram positive
- colonies on blood agar surrounded by greenish zone (alpha-hemolysis)
- colonies collapse in center (autolysin)
- optochin susceptibility (ring of death around white thing)
- dissolve in bile salts (definitive identification)
Which TLR does Teichoic acid of pneumococcus interact with ?
TLR 2 >>4
What is important about Choline-binding proteins on pneumococcus?
- they contribute to virulence
- highly conserved between pneumococci strains
What are bacterial cell wall peptidoglycans made of?
-alternating glucosamine and muramic acid in long chains
Which TLR recognizes cell wall peptidoglycans?
TLR 2 >> 4
What is the epidemiology of pneumococcus?
- Confined to humans
- lives in nasopharynx of healthy children/adults
- contact or aerosol spread (facilitated by viral resp infection)
What must first happen for bacteria to cause disease?
- adhere to epithelial cells
- bacterial surface constituents interact with surface molecules on mammalian cells, causing adherence
What molecule on pneumococcus is responsible for adherence?
-Lipoteichoic acid
What is colonization?
-when bacteria are present in sufficient number that we can find them by culture, AND, they cause no symptoms or signs of infection
**some organisms never colonize, mere presence indicates infection (TB)
What is the pathogenesis of pneumococcus?
- carried by secretions to space from which clearance is poor (damage/obstruction)
- aspiration & inhalation = pneumonia
**organisms get where they do not belong, clearance is damaged, induce inflammation & disease results.
