Streptococcus pneumonia

Question 1

1. Describe the reservoir of S. pneumonae.

Answer 1

colonized nasopharynx or throat (highest in children in winter)

Question 2

1. How is S. pneumonae transmitted?

Answer 2

endogenous airborne spread from a colonized nasopharynx to distal sites (requires susceptible host ie. COPD, alcoholism)

Question 3

3. Discuss which groups of individuals are at risk for developing pneumococcal infections and significant risk factors.

Answer 3

young, under 2 yo; older >60 yo
splenectomy (prevents opsonization)
alcoholism (aspiration)
post influenza or viral reparatory infection
hypogammaglobulinemia
sickle cell disease
DM
COPD or HD
CSF leak
cochlear implants
crowded living conditions

Question 4

2. What are the virulence factors of S. pneumoniae?

Answer 4

capsular polysaccharide is the primary virulence factor causing inflammation and helping evade phagocytosis (unencapsulated strains are not virulent)

capsule is also the principle immunogen

other factors include adhesion, colonization, and tissue destruction

Question 5

4. Explain the laboratory tests used to identify S. pneumoniae.

Answer 5

microscopy: elliptical, gram positive diplococci, commonly with halo
culture: alpha hemolytic, optochin test inhibition means positive ID for S. pneu.

Question 6

2. Describe the diseases caused by S. penumoniae.

Answer 6

acute otitis media (#1 cause)
mastoiditis
sinusitis (#1 cause, 30% cases)
community-acquired pneumonia (#1 cause)
bacteremia
meningitis (1 of 3 leading causes)

Question 7

5. Describe how S. pneum. infections can be prevented

Answer 7

active immunization with 23-valent polysaccharide vaccine used in older adults and high risk adults
active immunization of infants and certain high risk adults with 13-valent conjugated vaccine

avoid smoking and alcohol overuse, vaccinate against flu and educate asplenics

Question 8

5. Describe how S. pneum. infections can be treated.

Answer 8

historically with penicillins; major resistance to penicillins, cephalosporins mediated through changes in penicillin binding proteins (also possible is resistance to macrocodes, clindamycin and TMP/AMX)

until susceptibility is back, often treated with vancomycin plus cetriaxone

Question 9

Describe the characteristic infection caused by aerobic Gram-positive cocci.

Answer 9

pyogenic (pus-forming) cocci cause acute, invasive infections with intense neutrophil responses, phagocytosis is the main host defense

Question 10

What are some general characteristics of streptococci?

Answer 10

gram-positive, catalase negative, us usually arranged in chains, most are facultative
main are found as part of endogenous flora (not in sterile areas)

Question 11

What are the three schemes used to classify organisms within Strep class?

Answer 11

hemolytic patterns
lancefield groups (only classify B-hemolytic strep based on serologic properties)
biochemical and physiologic properties

Question 12

Describe the three different patterns of hemolysis on sheep blood agar.

Answer 12

complete (B) hemolysis (clear zone)
incomplete (a) hemolysis (green color)
no (gama) hemolysis (no change)