streptococcus

Question 1

streptococcus characteristics

Answer 1

gram-positive cocci; typically arranged in chains or pairs

catalase negative - this trait distinguishes them from staphylococcus species, which are catalase-positive; if catalase is present, the enzymatic reaction can be witnessed as bubbles of O2 accumulate

Question 2

streptococcus classification

Answer 2

test performed on blood agar plates

Question 3

beta-hemolysis

Answer 3

bacteria that are capable of beta-hemolysis produce exotoxins that deteriorate RBCs causing complete lysis

Question 4

alpha-hemolysis

Answer 4

bacteria that are capable of alpha-hemolysis secrete hydrogen peroxide which causes oxidation of hemoglobin, turning the medium green

Question 5

gamma-hemolysis

Answer 5

describes bacteria that do not induce hemolysis of RBCs

Question 6

lancefield groups

Answer 6

serological classification scheme developed by Rebecca Lancefield for differentiationg species of Streptococcus; identifies species of Streptococcus by unique carbohydrate antigens in their cell wall; most important medically are Group A and Group B streptococci

Question 7

Streptococcus pyogenes

Answer 7

the only species of GAS; S. pyogenes is beta-hemolytic

Question 8

Streptococcus pyogenes epidemiology

Answer 8

the bacteria transiently colonize the upper respiratory tract and skin; bacteria are spread between hosts through respiratory droplets or through direct contact with breaks in the skin

Question 9

Streptococcus pyogenes virulence factors (6 factors)

Answer 9

capsule - avoids phagocytosis

M protein - prevents complement-mediated phagocytosis; adheres to host cells; allows for invasion into host epithelial cells

C5a peptidase - inactivates C5a preventing attraction of phagocytes

Streptococcal pyrogenic exotoxins (Spe family) - this family of exotoxins act as superantigens that interact with macrophages and helper T cells causing the enhanced release of proinflammatory cytokines; responsible for the clinical manifestations of severe streptococcal diseases

streptolysins - exotoxins that lyse erythrocytes, leukocyts, and platelets (reason for beta-hemolysis on blood agar)

streptokinases - cleave fibrin and fibrinogen resulting in the lysis of clots allowing the bacteria to spread

Question 10

strepotcoccus pyogenes diseases

Answer 10

pharyngitis (strep throat)

scarlet fever - a complication of pharyngitis that occurs when the infecting strain produces a pyrogenic exotoxin (Spe); diffuse rash appears; strawberry tongue

pyoderma (impetigo)

erysipelas (red skin)

cellulitis

necrotizing fasciitis (streptococcal gangrene)

bacteremia - strongly fcorrespond with necrotizing fasciitis

streptoccocal toxic shock syndrome - due to production of pyrogenic exotoxins (Spe)

rheumatic fever - complication of pharyngitis

acute glomerulonephritis

Question 11

group b streptococci (GBS)

Answer 11

streptococcus agalactiae only species of GBS; beta-hemolytic

Question 12

s. agalactiae epidemiology

Answer 12

colonize the lower gastrointestinal tract and the genitourinary tract; transient vaginal carriage is observed; primarily a pathogen of neonates

Question 13

s. agalactiae virulence factors (two)

Answer 13

capsule

streptolysins - exotoxins that lyse erythrocytes, leukocytes, and platelets (reason for beta-hemolysis on blood agar)

Question 14

s. agalactiae pathogenesis

Answer 14

the capsule prevents phagocytosis until specific antibodies develop; the lack of s. agalactiae-specific antibodies explains the preference for neonates; the calssical and alternative complement pathways are required for killing s. agalactiae during early infection; therefore there is a greater likelihood of systemic spread in premature babies who have low complement levels

Question 15

s. agalactiae disease

Answer 15

neonatal disease - bacteria are acquired in utero, at birht, or shortly after birth; disease is characterized by bacteremia, pneumonia or meningitis

infections in pregnant women - postpartum endometritis, wound infection, and urinary tract infections can occur during and immediately after pregnancy

Question 16

viridians streptococci

Answer 16

the majority of streococci in this group are alpha-hemolytic on blood agar

Question 17

s. pneumoniae

Answer 17

the most virulent member of the viridans streptococci

displays alpha-hemolysis when grown aerobically

Question 18

s. pneumoniae epidemiology

Answer 18

common inhabitant of the nasopharynx and oropharynx in healthy people

Question 19

s. pneumoniae virulence factors (three)

Answer 19

capsule - avoids phagocytosis; primary mechanism of virulence during initial infection; if a strain loses the ability to make the capsule, the strain is no longer virulent

pneumolysin - a cytotoxin that binds to cholesterol in host cell membranes and causes pores to form; this activity destroys ciliated epithelial cells and phagocytic cells

IgA protease - inactivates IgA

Question 20

s. pneumoniae pathogenesis

Answer 20

bacteria residing in the nasopharynx or oropharynx penetrate the epithelial layer and then gain access to other body areas such as the lungs, sinuses or middle ear; if the bacteria gain access to the blood, the meninges may become infected

Question 21

s. pneumoniae diseases

Answer 21

pneumonia
meningitis
bacteremia