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Micro Quiz 3 > 23a: streptococci - jonathan > Flashcards

23a: streptococci - jonathan Flashcards

1
Q

What is the gram status, O2 status, and Catalase status of Streptococci?

A

Gram + found in chains
Faculative anaerobe and aerotolerant
Catalase negative

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2
Q

What are the groups of streptococci and what is the basis of distinguishing them?

A

A, B, C, D, and nontypable
Carbohydrate antigens
A and B are distinguished from other groups based on their patterns of hemolysis

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3
Q

On growth mediums containing intact RBCs, explain the difference between…
Gamma hemolysis
Alpha hemolysis
Beta hemolysis

A

1) no hemolysis
2) a cloudy green zone (RBCs are intact but the heme is green)
3) a clear zone with lysed RBCs
Note: depending on the depth of hemolysis in the petri dish, the clear zone may not look completely clear

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4
Q

Describe the Lancefield classification of streptococci.

A

Carbos extracted from the bacteria are subjected to precipitation tests with antisera. This places the beta-hemolytic groups into A through O.
Note: group D is not beta-hemolytic

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5
Q

How are Group A streptococci further subdivided?

A

Analysis of their M proteins divides Group A into 90 types

There is a schema of Streptococcus pyogenes on page S-2

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6
Q

There is a diagram for classification of Streptococcus pyogenes on page S-2.
What are the three tiers of tests for Streptococcus classification?

A

1) Alpha, Beta, Gamma
2) of the Betas, Test for C carbohydrates A through O
3) of the A carbohydrates, Test for M proteins 1 through 90

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7
Q

Epidemiology of Streptococcus…
On what tissues are they found?
What is the mode of transmission?

A

Skin, oropharynx, and nose (nose-type is most infectious)

Respiratory droplets

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8
Q

General pathogenesis of Streptococcus…
What are the lysogenic compounds?
What are the antiphagocytic compounds?
What are the proteases?

A

1) Streptolysins O and S, Streptokinase, DNAase
2) Hyaluronic acid capsule and M proteins
3) SpeA, SpeB, SpeC

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9
Q

What kind of hemolysis do Streptolysin O and Streptolysis S cause (alpha, beta, or gamma)?

A

Beta

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10
Q

What are the differences between Streptolysin O and Streptolysin S in terms of oxygen stability and antigenicity.

A

O: oxygen labile and antigenic to antibody ASO
S: oxygen stable and not antigenic

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11
Q

Are acapsular streptococci pathogenic?

A

No

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12
Q

What are M proteins in streptococci?

A

M-proteins extend from the bacterial membrane through the capsule and into the extracellular membrane
They aid in adhesion and antiphagocytosis
They are antigenic and are a possible target for the immune system

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13
Q

What are SpeA, SpeB, and SpeC?

What are the two illnesses that they cause?

A

Protease pyrogenic exotoxins
SCARLET FEVER (origin oropharyngeal streptococci)
STREPTOCOCCAL TOXIC SHOCK SYNDROME

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14
Q

What are invasive syndromes associated with streptococcus (6)?

A

1) puerperal fever
2) Acute pharyngitis and tonsilitis
3) Impetigo
4) Erysipelas
5) Necrotizing fascitis
6) a bunch of other illnesses covered next year

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15
Q

What is Puerperal Fever?

A

Infection of the uterus after childbirth

Once was fatal, now is uncommon in developed countries

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16
Q

What is Acute Pharyngitis and Tonsilitis?

Why must this be Dx and Tx (ie, what is the progression of the disease if untreated)?

A

Strepthroat
Dx and Tx with penicillin
All strep strains must be treated because some strep strains can progress to RHEUMATIC FEVER

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17
Q

What is impetigo?

A

Minor superficial skin infection of streptococcus

18
Q

What is Erysipelas?

A

Severe cellulitis of the dermis and underlying tissues by streptococcus

19
Q

What is necrotizing fascitis?

A

“Flesh-eating bacteria disease”
Invasive S. pyogenes
Rapid infection
Surgery may be required

20
Q

What are two important sequelae of S. pyogenes infections?

A

Rheumatic fever

Acute glomerulonephritis

21
Q

Explain the pathogenesis of Rheumatic Fever.
On what tissue was the initial infection?
How long after initial infection?
What protein is involved?
What tissues are involved?

A 
Throat only.
2-3 weeks after strep infection
M-PROTEINS activate antigens that attack SKIN, JOINTS, AND HEART
Skin and joint problems subside.
Heart problems may be ongoing
22
Q

Why is treatment of ALL streptococcus infection important?

A

We haven’t nailed down which M-protein varieties produce Rheumatic fever, therefore we should treat all streptococcus infections with penicillin

23
Q

Explain the pathogenesis of Acute Glomerulonephritis.
On what tissue was the initial infection?
How long after initial infection?
What proteins from what subgroup of streptococci?
What are symptoms?
What is mechanism?

A 
throat or skin. Skin is more common.
1 week after infection
select M-proteins of Group A beta-hemolytic streptococci
hematuria and edema
deposition of immune complexes
24
Q

Explain the differences between
Glomerulonephritis and Rheumatic Fever…
Major symptoms?

A

Glomerulonephritis: edema, hypertension, hematuria

Rheumatic fever: carditis, polyarthritis, subcutaneous nodules, skin lesions (erythema marginatum)

25
Q 
Explain the differences between
Glomerulonephritis and Rheumatic Fever...
Major symptoms?
M-protein serotypes?
Site of infection?
Pathogenic mechanism?
A

1) G: edema, hypertension, hematuria. R: carditis, polyarthritis, subcutaneous nodules, skin lesions (erythema marginatum)
2) G: only a few types of M-protein. R: selected types of M-proteins but infection varies markedly by type
3) G: throat or skin, SKIN is more common. R: ONLY THROAT
4) G: deposition of immune complexes. R: antigenic mimicry between S. pyogenes and host tissue (heart, skin, and joints)

26
Q

Are Streptococcus pyogenes found at site of damage in Glomerulonephritis or Rheumatic Fever?

A

Nope. Infection is immunologically mediated either with immune complexes or cross reactivity of antigen vs host mimicry

27
Q

What are Dx techniques do LABORATORIES use for Streptococcus?

A

1) G + chains
2) beta-hemolysis on blood agar
3) Sensitivity to Bacitracin indicates group A
4) Titer of >160 or a four-fold increase of Streptolysin O (ASO titer)

28
Q

What Dx techniques do physicians use?

A

A bead test that demonstrates linkage by strep chains

pharyngeal swab is used

29
Q

In Dx for Streptococcus, sensitivity to Bacitracin indicates what group?

A

Group A

30
Q

What is Tx for Streptococcus?

A

PENICILLIN

Resistance has never been a problem

31
Q 
What are the qualities of Group B strepococci...
Gram stain and growth phenotype?
Hemolysin type?
Bacitracin status?
Hippurate status?
What is the most important species?
A

G+ cocci in chains
Beta hemolysin, but less hemolysis than Group A
Bacitracin resistant
Hydrolizes hippurate
Streptococcus agalactiae is the most important species

32
Q

Epidemiology of Group B streptococci…
What tissue does this group commonly inhabit?
What major infection does Group B cause?

A

Vaginal and colonic flora

1/3 of all NEONATAL INFECTIONS: septicemia, meningitis, pneumonia, and death

33
Q

Group B streptococci…
What two patterns of infection occur?
What is mode of transmission for each?
Which has more severe health risks?

A

Early onset within 1 week caused by vertical transmission from mother to newborn is more severe

Later onset is caused by infant-to-infant spread with a less fulminant course and lower mortality

Fulminant = quickly

34
Q

What is prevention of early onset/vertical transmission infection of Group B streptococci neonatal infection?

A

Culture pregnant women’s VJ and treat intrapartum parenteral penicillin or ampicillin

Intrapartum = during childbirth
Parenteral = infusion via route other than mouth
35
Q 
Bacteriology of Group D Streptococci (Enterococci)...
What are the most important species?
What are the hemolysis pattern?
Growth in Salt status?
Natural tissue habitat?
Antibiotic resistance?
Last resort antibiotic?
A

Enterococcus faecalis and Enterococcus faecium
Hemolysis varies from strain to strain
Can grow in high salt
Common in GI tract
Resistant to many antibiotics.
Vancomycin is last resort, but resistance is a problem

36
Q

What are common infections by enterococcus Group D strep?

A

UTI
Wound infections
Sepsis, especially in older patients

37
Q

Quick note: Strep Group C and D cause beta-hemolysis and are bacitracin resistant. They cause various infections.

A

.

38
Q

Viridans Streptococci…
What type of hemolysis?
What are the most common species?
What tissues do they normally inhabit?

A

Alpha hemolysis
Streptococcus mutans and Streptococcus sanguis
mouth, nose, and pharynx

39
Q

What major illness is caused by Viridans Streptococci?

A

INFECTIVE ENDOCARDITIS

40
Q

What is the pathogenesis and course of infection of infective endocarditis from Viridans Streptococci?

A

Alpha-hemolytic streptococci can infect through the mouth via oral trauma (including chewing)
Causes transient bacteremia
Bacteria can then bind to pre-existing lesion on heart valve
Vegetation on valve
Then has subacute course with intermittent bacteremia.
Possibly fatal

Micro Quiz 3 (12 decks)

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