Part 2 Clinical Bacteriology (strep)

Question 1

Streptococcus pyogenes is the leading bacterial cause of

Answer 1

pharyngitis
cellulitis

important cause of
impetigo
necrotizing fasciitis
streptococcal toxic shock syndrome

Question 2

Streptococcus pyogenes is the inciting factor of two important immunologic diseases

Answer 2

rheumatic fever and
acute glomerulonephritis.

Question 3

Streptococcus agalactiae is the leading cause of

Answer 3

neonatal sepsis and
meningitis

Question 4

Enterococcus faecalis is an important
cause of

Answer 4

hospital-acquired urinary tract infections

and endocarditis.

Question 5

Viridans group streptococci are the most common cause of

Answer 5

endocarditis

Question 6

uncommon cause of endocarditis.

Answer 6

Streptococcus bovis

Question 7

Streptococci are spherical gram-positive cocci arranged in

Answer 7

chains or pairs

Question 8

All streptococci are catalase-

Answer 8

Negative

Question 9

α-Hemolytic streptococci form

Answer 9

green zone around their colonies as a result of incomplete lysis of red blood cells
in the agar

Question 10

α-Hemolytic streptococci form a green zone around their colonies how does that occur

Answer 10

green color is formed when hydrogen peroxide produced by the bacteria

oxidizes hemoglobin (red color) to
biliverdin (green)

Question 11

β-Hemolytic streptococci form

Answer 11

clear zone around their colonies because complete lysis of the red cells occurs.

Question 12

Why does β-Hemolysis occur

Answer 12

production of enzymes (hemolysins) called streptolysin O and streptolysin S

Question 13

Some streptococci are nonhemolytic

Answer 13

γ-hemolysis

Question 14

C carbohydrate determines

Answer 14

group of β-hemolytic streptococci

Question 15

Where is C carbohydrate found

Answer 15

Cell wall

Determined by amino sugar

Question 16

most important virulence factor of Streptococcus pyogenes

Answer 16

M protein

Question 17

What does m protein do

Answer 17

protrudes from the outer surface of the cell

blocks phagocytosis

Question 18

How does M protein block phagocytosis

Answer 18

inactivates C3b,

a component of complement that opsonizes the bacteria prior to phagocytosis

Question 19

Strains of Streptococcus pyogenes that do not produce M protein are

Answer 19

nonpathogenic.

Question 20

M protein also determines

Answer 20

type of group A β-hemolytic streptococci

Question 21

Antibody to M protein provides

Answer 21

type specific immunity.

Question 22

Give 2 types of strains of streptococcus pyogenes that produce certain M protein types

Answer 22

rheumatogenic. (rheumatic fever)

nephritogenic (acute glomerulonephritis)

Question 23

Although M protein is the main antiphagocytic component of Streptococcus pyogenes, what else plays a e

Answer 23

polysaccharide capsule that plays a role in retarding phagocytosis.

Question 24

β-Hemolytic Streptococci are arranged into groups A–U known as

Answer 24

Lancefield groups

Question 25

clinical laboratory, the β-Hemolytic Streptococci group is determined by

Answer 25

precipitin tests with specific antisera or by immunofluorescence

Question 26

Which group are the most frequent bacterial cause of pharyngitis and a very common cause of skin infection

Answer 26

Group A streptococci

Question 27

Group A streptococci adhere to pharyngeal epithelium via

Answer 27

pili composed of lipoteichoic acid and M protein

Question 28

The growth of Streptococcus pyogenes on agar plates in the laboratory is inhibited by

Answer 28

antibiotic bacitracin

Question 29

Group B streptococci agalactiae colonise the…

Answer 29

genital tract of some women

Question 30

Group B streptococci agalactiae can cause

Answer 30

neonatal meningitis and sepsis

Question 31

Group B streptococci agalactiae are usually resistant to

Answer 31

bacitracin

Question 32

Group D streptococci include

Answer 32

enterococci: E. faecalis and Enterococcus faecium and nonenterococci: S. bovis

Question 33

Group D streptococci include enterococci, They are very hardy organisms because

Answer 33

they can grow in hypertonic (6.5%) saline or in bile are not killed by penicillin G

Question 34

is required to kill enterococci

Answer 34

combination of penicillin and aminoglycoside : gentamicin

Question 35

Vancomycin can also be used for Group D streptococci, but

Answer 35

vancomycin resistant enterococci (VRE) have emerged

Question 36

Nonenterococcal group D streptococci, such as S. bovis are less hardy because

Answer 36

inhibited by 6.5% NaCl and killed by penicillinG

Question 37

The principal α-hemolytic organisms are

Answer 37

Streptococci pneumoniae (pneumococci) the viridans group of streptococci: Streptococcus mitis, Streptococcus sanguinis, Streptococcus mutans

Question 38

Pneumococci and viridans streptococci are distinguished in the clinical laboratory by two main criteria:

Answer 38

1)the growth of pneumococci is inhibited by optochin, whereas the growth of viridans streptococci is not inhibited 2) colonies of pneumococci dissolve when exposed to bile, whereas colonies of viridans streptococci do not dissolve.

Question 39

Viridans streptococci are part of the normal flora of the human pharynx and intermittently reach the bloodstream to cause

Answer 39

infective endocarditis

Question 40

Streptococcus mutans synthesizes polysaccharides (dextrans), where are they found, what do they cause?

Answer 40

found in dental plaque lead to dental caries

Question 41

Streptococcus intermedius and Streptococcus anginosus (also known as the S. anginosus-milleri group) are usually α-hemolytic or nonhemolytic, but some isolates are β-hemolytic. They are found primarily in

Answer 41

mouth and colon.

Question 42

Peptostreptococci grow under what conditions

Answer 42

anaerobic or microaerophilic conditions

Question 43

Peptostreptococci are members of the normal flora of

Answer 43

gut, mouth, female genital tract participate in mixed anaerobic infections (Multiple bacterial infection)

Question 44

peptostreptococci and viridans streptococci, both members of the oral flora, are often found in

Answer 44

brain abscesses following dental surgery.

Question 45

Viridans streptococci and streptococci pneumoniae are found chiefly in

Answer 45

oropharynx

Question 46

streptococci pyogenes found on

Answer 46

skin oropharynx

Question 47

streptococcus agalactiae found in

Answer 47

vagina colon

Question 48

both the enterococci and anaerobic streptococci are located in

Answer 48

Colon

Question 49

Name the three mechanisms that Group A streptococci, streptococcus pyogenes by which cause disease

Answer 49

pyogenic inflammation exotoxin production immunologic (antibody against a component of the organism cross-reacts with normal tissue or forms immune complexes that damage normal tissue)

Question 50

The M protein of Streptococcus pyogenes is its most important

Answer 50

Anti phagocytic factor

Question 51

Group A streptococci produce Hyaluronidase , what does it do

Answer 51

degrades hyaluronic acid Hyaluronidase is known as spreading factor because it facilitates the rapid spread of S. pyogenes in skin infections like cellulitis

Question 52

What enzyme in Group A streptococci activates plasminogen to form plasmin, which dissolves fibrin in clots, thrombi, and emboli. It can be used to lyse thrombi in the coronary arteriesof heart attack patients.

Answer 52

Streptokinase

Question 53

DNase in Group A streptococci…

Answer 53

degrades DNA in exudates or necrotic tissue. Antibody to DNase B develops during pyoderma;

Question 54

IgG degrading enzyme in Group A streptococci is a

Answer 54

protease that specifically cleaves IgG heavy chains. This prevents opsonization and complement activation so enhances the virulence of theorganism.

Question 55

group A streptococci produce five important toxins and hemolysins:

Answer 55

Erythrogenic toxin causes the rash of scarlet fever. Streptolysin O is a hemolysin that is inactivated by oxidation, causes β hemolysis only when colonies grow under the surface of a blood agar plate Streptolysin S is a hemolysin that is not inactivated by oxygen not antigenic but is responsible for β-hemolysis when colonies grow on the surface of a blood agar Pyrogenic exotoxin A - most cases of streptococcal toxic shock syndrome Exotoxin B is a protease that rapidly destroys tissue- “flesh-eating” streptococci that cause necrotizing fasciitis

Question 56

Pathogenesis by group B streptococci (S. agalactiae) is based on

Answer 56

ability of the organism to induce an inflammatory response

Question 57

The main virulence factor of S. pneumoniae

Answer 57

antiphagocytic polysaccharide capsule. Many of the strains of viridans streptococci that cause endocarditis produce a glycocalyx enables the organism to adhere to the heart valve.

Question 58

Streptococcus pyogenes causes three types of diseases

Answer 58

pyogenic diseases -pharyngitis -cellulitis toxigenic -diseases such as scarlet fever -toxic shock syndrome immunologic diseases -rheumatic fever -acute glomerulonephritis

Question 59

most common bacterial cause of pharyngitis

Answer 59

Streptococcus pyogenes

Question 60

untreated, spontaneous recovery often occurs in 10 days, but rheumatic fever may occur. may extend to the middle ear (otitis media), the sinuses (sinusitis), the mastoids (mastoiditis), or the meninges (meningitis), what untreated infection can cause this

Answer 60

pharyngitis

Question 61

infecting streptococci produce erythrogenic toxin and the host lacks antitoxin, what can occur

Answer 61

scarlet fever

Question 62

characteristic lesion seen in scarlet fever.

Answer 62

Strawberry tongue

Question 63

streptococcal toxic shock syndrome is different from staphylococcal because

Answer 63

typically has a recognizable site of pyogenic inflammation and blood cultures are often positive

Question 64

Group A streptococci cause skin and soft tissue infections, such as

Answer 64

cellulitis, erysipelas necrotizing fasciitis- streptococcal gangrene impetigo

Question 65

Impetigo is formed by

Answer 65

pyoderma, is a superficial skin infection characterized by “honey-colored” crusted lesions

Question 66

serious infection of pregnant women, and sepsis can be caused by

Answer 66

Group A streptococci also cause endometritis

Question 67

What can cause neonatal sepsis and meningitis

Answer 67

Group B streptococci

Question 68

B streptococcal infections can cause what in adults

Answer 68

pneumonia, endocarditis, arthritis, cellulitis, osteomyelitis

Question 69

main predisposing factor for adult group B streptococcal infections

Answer 69

Diabetes

Question 70

Viridans streptococci are the most common cause of infective

Answer 70

endocarditis

Question 71

Viridans streptococci, especially S. anginosus, S. milleri, and S. intermedius, cause

Answer 71

Brain abscess

Question 72

especially in hospitalised patients, Enterococci cause

Answer 72

urinary tract infections

Question 73

especially in patients with carcinoma of the colon Streptococcus bovis a nonenterococcal group D Streptococcus causes

Answer 73

Endocarditis

Question 74

Peptostreptococci are one of the most common bacteria found in

Answer 74

brain, lung, abdominal, pelvic abscesses

Question 75

disorders in which a local infection with group A streptococci is followed weeks later by inflammation in an organ that was not infected by the streptococci is caused by

Answer 75

antibody response to streptococcal M proteins that cross-react with human tissues

Question 76

Acute Glomerulonephritis typically occurs how long after skin infection by certain group A streptococcal types in children

Answer 76

2-3 weeks

Question 77

most striking clinical features Acute Glomerulonephritis

Answer 77

hypertension, edema of the face (especially periorbital edema) and ankles, “smoky” urine (due to red cells in the urine)

Question 78

Acute Glomerulonephritis disease is initiated by

Answer 78

antigen–antibody complexes on the glomerular basement membrane