Streptococci

Question 1

streptococci general properties

Answer 1

gram pos

grows in chains

facultative anaerobes

catalase neg

classified by carbohydrate Ags

different patterns of hemolysis help distinguish A and B from other groups

Question 2

alpha hemolysis

Answer 2

cloudy green zone w/ intact red cells and chemically altered green heme

Question 3

beta hemolysis

Answer 3

clear zone in which all red cells are lysed

Question 4

further classification of beta hemolytic streptococci

Answer 4

get classified into groups A thru ) via an antisera precipitation test

group A streptococci are subdivided by analysis of M protein

Question 5

streptococci pyogenes epi

Answer 5

group A beta hemolytic

found on skin and in oropharynx

transmitted via respiratory droplets. requires large inoculum

5-10 % normal individuals carry group A beta hemolytic

Question 6

streptococci pyogenes pathogenesis

Answer 6

streptolysins- hemolytic enzymes that injure/lyse host cells. 2 kinds

streptolysin O- oxygen labile and functions only in reducing atmosphere- results in ASO Ab titers that are diagnostic

streptolysin S- poorly antigenic and stable in O2

streptokinase- triggers the proteolytic system of the blood that destroys fibrin clots

DNAse

Question 7

streptococci pyogenes antiphagocytic activity

Answer 7

hyaluronic acid capsule and M proteins

both help resist phagocytosis

Question 8

streptococci pyogenes proteases

Answer 8

SpeA, B, and C are proteases that cause the rash of scarlet fever and cause streptococcal toxic shock syndrome

Question 9

streptococci pyogenes clinical toxin mediated syndromes

Answer 9

scarlet fever- pharyngitis/tonsilitis w/ cutaneous rash caused by exotoxin

streptococcal toxic shock- severe hypotension, DIC, rash, necrosis, organ failure d/t exotoxins acting as superAgs

Question 10

streptococci pyogenes invasive syndromes

Answer 10

puerperal fever- infection of the uterus immediately after childbirth

acute pharyngitis- “strep throat”- headache, fever, chills, malaise

impetigo- minor superficial skin infection

erysipelas- severe cellulitis of dermis and underlying tissues

necrotizing fascitis- highly destructive

Question 11

sequelae of streptococci pyogenes infections

Answer 11

rheumatic fever- 2/3 weeks after recovery, pts experience heart and skin lesions not d/t bacterial growth. Abs to M protein cause Abs that cross react. treatment w/ penicllin is essential

acute glomerulonephritis- M proteins cause immune complexes to deposit into membrane in glomerulus. causes edema, hypertension, and hematuria

Question 12

diagnosis of streptococci pyogenes

Answer 12

look for gram pos in chains
beta hemolysis on blood agar
sensitivity to bacitracin

agglutination test w/ throat swab

titer of ASO

Question 13

streptococci pyogenes treatment

Answer 13

penicillin

Question 14

group B streptococci characteristics

Answer 14

gram pos in chains

beta hemolysin

bacitracin resitant

hydrolyze hippurate

streptococcus agalactiae

Question 15

streptococcus agalactiae epi

Answer 15

part of vaginal and colonic flora- causes neonatal septicemia, meningitis, pneumonia and death

can cause early onset disease if infected via vagina, or late onset from infant to infant spread

neonatal infections correlated w/ lack of maternal Ab, thus new infections are most dangerous

Question 16

treatment for streptococcus agalactiae

Answer 16

penicillin

Question 17

group D streptococcus

Answer 17

enterococci- enterococcus faecalis and enterococcus faecium

common inhabitants of GI

can grow in 6.5% NaCl whereas other streptococci cant

resistant to many Abs

Question 18

group D streptococcus treatment

Answer 18

resistant to many antibiotics

vancomycin is last resort

Question 19

group D streptococcus syndromes

Answer 19

cause UTIs, wound infections and sepsis

Question 20

viridans streptococci

Answer 20

alpha hemolytic

streptococcus mutans and streptococcus sanguis

normal inhabitant of mouth, nose, pharynx

cause endocarditis