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Microbiology Semester 3 > Part 2 Clinical Bacteriology (strep) > Flashcards

Part 2 Clinical Bacteriology (strep) Flashcards

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1
Q

Streptococcus pyogenes is the leading bacterial cause of

A

pharyngitis
cellulitis

important cause of
impetigo
necrotizing fasciitis
streptococcal toxic shock syndrome

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2
Q

Streptococcus pyogenes is the inciting factor of two important immunologic diseases

A

rheumatic fever and
acute glomerulonephritis.

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3
Q

Streptococcus agalactiae is the leading cause of

A

neonatal sepsis and
meningitis

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4
Q

Enterococcus faecalis is an important
cause of

A

hospital-acquired urinary tract infections

and endocarditis.

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5
Q

Viridans group streptococci are the most common cause of

A

endocarditis

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6
Q

uncommon cause of endocarditis.

A

Streptococcus bovis

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7
Q

Streptococci are spherical gram-positive cocci arranged in

A

chains or pairs

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8
Q

All streptococci are catalase-

A

Negative

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9
Q

α-Hemolytic streptococci form

A

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

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10
Q

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

A

green color is formed when hydrogen peroxide produced by the bacteria

oxidizes hemoglobin (red color) to
biliverdin (green)

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11
Q

β-Hemolytic streptococci form

A

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

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12
Q

Why does β-Hemolysis occur

A

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

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13
Q

Some streptococci are nonhemolytic

A

γ-hemolysis

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14
Q

C carbohydrate determines

A

group of β-hemolytic streptococci

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15
Q

Where is C carbohydrate found

A

Cell wall

Determined by amino sugar

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16
Q

most important virulence factor of Streptococcus pyogenes

A

M protein

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17
Q

What does m protein do

A

protrudes from the outer surface of the cell

blocks phagocytosis

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18
Q

How does M protein block phagocytosis

A

inactivates C3b,

a component of complement that opsonizes the bacteria prior to phagocytosis

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19
Q

Strains of Streptococcus pyogenes that do not produce M protein are

A

nonpathogenic.

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20
Q

M protein also determines

A

type of group A β-hemolytic streptococci

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21
Q

Antibody to M protein provides

A

type specific immunity.

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22
Q

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

A

rheumatogenic. (rheumatic fever)

nephritogenic (acute glomerulonephritis)

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23
Q

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

A

polysaccharide capsule that plays a role in retarding phagocytosis.

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24
Q

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

A

Lancefield groups

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25
Q

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

A

precipitin tests with specific antisera

or by immunofluorescence

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26
Q

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

A

Group A streptococci

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27
Q

Group A streptococci adhere to pharyngeal epithelium via

A

pili composed of lipoteichoic acid and M protein

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28
Q

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

A

antibiotic bacitracin

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29
Q

Group B streptococci agalactiae colonise the…

A

genital tract of some women

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30
Q

Group B streptococci agalactiae can cause

A

neonatal meningitis

and sepsis

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31
Q

Group B streptococci agalactiae are usually resistant to

A

bacitracin

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32
Q

Group D streptococci include

A

enterococci: E. faecalis
and Enterococcus faecium

and nonenterococci: S. bovis

33
Q

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

A

they can grow in hypertonic (6.5%) saline

or in bile

are not killed by penicillin G

34
Q

is required to kill enterococci

A

combination of penicillin and aminoglycoside : gentamicin

35
Q

Vancomycin can also be used for Group D streptococci, but

A

vancomycin resistant enterococci (VRE) have emerged

36
Q

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

A

inhibited by 6.5% NaCl

and killed by penicillinG

37
Q

The principal α-hemolytic organisms are

A

Streptococci pneumoniae (pneumococci)

the viridans group of streptococci: Streptococcus mitis,
Streptococcus sanguinis,
Streptococcus mutans

38
Q

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

A

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.

39
Q

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

A

infective endocarditis

40
Q

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

A

found in dental plaque

lead to dental caries

41
Q

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

A

mouth and colon.

42
Q

Peptostreptococci grow under what conditions

A

anaerobic or

microaerophilic conditions

43
Q

Peptostreptococci are members of the normal flora of

A

gut,
mouth,
female genital tract

participate in mixed anaerobic infections
(Multiple bacterial infection)

44
Q

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

A

brain abscesses following dental surgery.

45
Q

Viridans streptococci and streptococci pneumoniae are found chiefly in

A

oropharynx

46
Q

streptococci pyogenes found on

A

skin
oropharynx

47
Q

streptococcus agalactiae found in

A

vagina
colon

48
Q

both the enterococci and anaerobic streptococci are located in

A

Colon

49
Q

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

A

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)

50
Q

The M protein of Streptococcus pyogenes is its most important

A

Anti phagocytic factor

51
Q

Group A streptococci produce Hyaluronidase , what does it do

A

degrades hyaluronic acid

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

52
Q

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.

A

Streptokinase

53
Q

DNase in Group A streptococci…

A

degrades DNA in exudates or
necrotic tissue.

Antibody to DNase B develops during pyoderma;

54
Q

IgG degrading enzyme in Group A streptococci is a

A

protease that specifically cleaves IgG heavy chains.

This prevents opsonization and complement activation so enhances the virulence of theorganism.

55
Q

group A streptococci produce five important toxins and hemolysins:

A

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

56
Q

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

A

ability of the organism to induce an inflammatory response

57
Q

The main virulence factor of S. pneumoniae

A

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.

58
Q

Streptococcus pyogenes causes three types of diseases

A

pyogenic diseases
-pharyngitis
-cellulitis

toxigenic
-diseases such as scarlet fever
-toxic shock syndrome

immunologic diseases
-rheumatic fever
-acute glomerulonephritis

59
Q

most common bacterial cause of pharyngitis

A

Streptococcus pyogenes

60
Q

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

A

pharyngitis

61
Q

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

A

scarlet fever

62
Q

characteristic lesion seen in scarlet fever.

A

Strawberry tongue

63
Q

streptococcal toxic shock syndrome is different from staphylococcal because

A

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

64
Q

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

A

cellulitis,
erysipelas
necrotizing fasciitis- streptococcal gangrene
impetigo

65
Q

Impetigo is formed by

A

pyoderma,

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

66
Q

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

A

Group A streptococci also cause endometritis

67
Q

What can cause neonatal sepsis and meningitis

A

Group B streptococci

68
Q

B streptococcal infections can cause what in adults

A

pneumonia,
endocarditis,
arthritis,
cellulitis,
osteomyelitis

69
Q

main predisposing factor for adult group B streptococcal infections

A

Diabetes

70
Q

Viridans streptococci are the most common cause of infective

A

endocarditis

71
Q

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

A

Brain abscess

72
Q

especially in hospitalised patients, Enterococci cause

A

urinary tract infections

73
Q

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

A

Endocarditis

74
Q

Peptostreptococci are one of the most common bacteria found in

A

brain,
lung,
abdominal,
pelvic abscesses

75
Q

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

A

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

76
Q

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

A

2-3 weeks

77
Q

most striking clinical features Acute Glomerulonephritis

A

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

78
Q

Acute Glomerulonephritis disease is initiated by

A

antigen–antibody complexes on
the glomerular basement membrane

Microbiology Semester 3 (7 decks)

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