Streptococcus

Question 1

Streptococci basic features

Answer 1

•gram positive
•spherical, ovoid, pairs or chains
•divide in a single plane

•non-motile
•non spore forming

•catalase negative- distinguish from staph

Question 2

Strep metabolism

Answer 2

•facultative anaerobe
•strictly fermentative, lack cytochromes for ETC
•homofermentative
•lactic acid is by-product

Question 3

Strep hemolysis

Answer 3

Alpha haemolysis
•green zone of incomplete hemolysis
•S pneumoniae

Beta hemolysis
•clear zone of complete lysis
•S pyogenes

Question 4

3 groups of Strep

Answer 4

Pyogenic strep
•pus formation
•beta hemolytic
•S pyogenes

Oral strep
•heterogenous
•mouth and upper RI tract
•S mutans: dental plaque
•S pneumoniae: alpha hemolysis

Other strep

Question 5

Typing and ID of strep

Answer 5

•serological ID, based on cell wall antigens
•20 groups A-O
•group A strep: pyogenes
•group B strep: S agalactiae
•group D strep: enterococci

Question 6

Strep pyogenes cell envelope

Answer 6

•M protein- major virulence factor of group A strep
•protein F is epithelial cell attachment factor

Question 7

Strep pharyngitis (strep throat)

Answer 7

•droplets or saliva, incubation is 2-4 days
•throat/tonsils
•inflammation
•lysis of RBCs and WBCs
•50% patients have exudate

Question 8

Post-streptococcal disease

Answer 8

Glomerulonephritis
•type III hypersensitivity
•antigen-antibody complexes deposited in glomeruli
•damage glomerulus, protein and blood leak into urine
•strep pyrogenic exotoxin B (SpeB)

Rheumatic fever
•autoimmune disease
•inflammatory lesions on heart valves, joints, subcutaneous tissue, CNS
•associates with M proteins

Question 9

Other strep infections

Answer 9

•impetigo
•ecthyma
•wound/burn infection
•necrotising fasciitis
•scarlet fever
•puerpural sepsis
•pneumonia
•meningitis
•strep toxic shock syndrome

Question 10

Pyogenes treatment

Answer 10

•penicillin is first choice
•erythromycin (macrolide)

Question 11

S pneumoniae disease process

Answer 11

•invade alveolar tissue
•inflammation
•accumulation of phagocytes and fluid reduces lung function
•30% mortality

Question 12

S pneumoniae virulence

Answer 12

•polysaccharide capsule is most important
•shields against complement and antibody binding
•prevents entrapment in mucous

•pneumococcal PCho (phosphorylcholine) binding proteins PspA and PspC
•protect against apolactoferrin
•limits deposition of opsonin C3b
•protects against complement