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infectious diseases > Week 4- The Streptococci and Enterococci > Flashcards

Week 4- The Streptococci and Enterococci Flashcards

1
Q

how many genera of medical importance is there In the family of streptococcaceae

A

two:
- streptococcus
- enterococcus

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2
Q

how is gram positive cocci (GPC) often arranged

A

in chains or pairs

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3
Q

what are the characteristics of streptococci

A

non-motile, non-sporing, fastidious facultative anaerobe

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4
Q

how many species of streptococci is there

A

less than 80

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5
Q

what kind of organisms are streptococci

A

comensal organisms
(typically of the mucous membranes of upper respiratory tract, and some species in the intestines)

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6
Q

how is streptococci separated into groups

A
  1. by colony appearance on horse blood agar (BA)
  2. by lancefield grouping
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7
Q

what streptococci colonies are there

A
  • Alpha (α) haemolytic streptococci
  • Beta (β) haemolytic streptococci
  • non haemolytic streptococci
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8
Q

what are Alpha (α) haemolytic streptococci

A

S. pneumoniae and ‘viridans’ group streptococci (VGS)

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9
Q

what is Alpha (α) haemolytic streptococci

A
  • Colonies greenish appearance, approx. 1 mm diameter
    (Oxidation of haemoglobin to methaemoglobin = green)
  • No actual haemolysis
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10
Q

what do VGS tend to be

A

commensal, opportunistic pathogens of low virulence

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11
Q

what is Beta (β) haemolytic streptococci

A
  • Complete lysis of RBC
  • Zone of clearing around the colony
  • Colonies approx. 1 mm diameter, no pigmentation
  • GPC in chains
  • catalase negative reaction
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12
Q

what is non-haemolytic streptococci

A

No effect on RBC
(also known as gamma (γ) haemolysis)

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13
Q

who discovered lancefield grouping

A

Rebecca Lancefield (1895-1981)

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14
Q

what is lancefield grouping

A

Separated streptococci on their version of a major cell wall polysaccharide antigen

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15
Q

what group is lancefield group clinically applied to

A

β-haemolytic streptococci

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16
Q

how do enterococcal colonies appear on BA

A

α-haemolytic, β-haemolytic streptococci and non-haemolytic

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17
Q

what catalase is enterococcal colonies

A

catalase negative

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18
Q

what antigen is used for enterococcal colonies in lancefield grouping

A

D antigen

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19
Q

what gram is Presumptive Streptococcus species

A

Gram positive cocci

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20
Q

what catalase is Presumptive Streptococcus species

A

catalase negative

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21
Q

what should a catalase test be performed for

A

for gram positive bacteria

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22
Q

how do you perform a catalase test

A
  1. Dispense 50μl of hydrogen peroxide into a bijou
  2. Transfer one colony of the test strain to the opposite side of the bijou
  3. Cap the bijou
  4. Tip the hydrogen peroxide over the colony and observe
  5. Bubbles of oxygen indicate a positive reaction, no bubbles a negative reaction
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23
Q

what does group specific antibody conjugated to latex beads react with

A

with cell wall polysaccharide

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24
Q

what groups are of the greatest medical importance

A

A, B, C, D, F, and G

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25
Q

what is group A β - haemolytic streptococci are sensitive to

A

bacitracin

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26
Q

what’s resistant to bacitracin

A

other β - haemolytic streptococci

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27
Q

what is bacitracin often placed on

A

primary plates

28
Q

what lancefield groups are the MOST important medically

A

A, B and D

29
Q

what is group A

A

S. pyogenes
sensitive to bacitracin

30
Q

what is group B

A

S. agalactiae

31
Q

what does group D include

A

S. bovis

32
Q

what is viridans group streptococci (VGS)

A

gram positive cocci in chains or pairs

33
Q

what is the appearance of VGS on BA

A

colonies are typically greenish, smooth, circular, approx. 1 mm

34
Q

how is VGS and S. pneumoniae distinguished

A

optochin sensitivity

35
Q

what is optochin sensitivity

A
  • viridans group streptococci are resistance
  • s. pneumoniae are sensitive
36
Q

what is s. pneumoniae

A
  • gram-positive diplococcus
  • α-haemolysis on blood agar
  • polysaccharide capsule
  • quelling reaction
  • optochin sensitivity
  • bile solubility
37
Q

what is quelling reaction

A
  • Capsule – specific antibody reaction causes the capsule to appear to swell
38
Q

how can u distinguish s. pneumoniae and VGS with bile solubility

A
  • S. pneumoniae are bile soluble
  • VGS are bile insoluble
39
Q

What is the analytical profile index (API)?

A

It is used to identify based on biochemical tests

API test strips consist if wells that contain substrates to detect enzymatic activity

40
Q

What is streptococcus pyogenes aka?

A

Group A strep

41
Q

Describe what group A strep is

A

it is a commensal of the nasopharynx
Transmits via direct contact with infected skin lesions and respiratory droplets

42
Q

What are the virulence factors of group A strep - S pyogenes?

A
  1. Cell surface proteins/adhesins
  2. Toxins
  3. capsule
  4. cell envelope
  5. enzymes
43
Q

Describe the cell surface proteins/adhesins of S pyogenes (group A strep)

A

M protein - Binds to many host proteins and resists phagocytosis so can avoid immune response.

F protein -

44
Q

Describe the capsule of S pyogenes?

A

Composed of hyaluronic acid and are antiphagocytic, non immunigenic

45
Q

Describe the enzymes of S pyogenes?

A

Streptolysins - They lyse (break down) RBCS, WBCS, platelets

C5a peptidase - Cleaves human C5a (which attracts phagocytic cells) to evade phagocytosis

Streptokinase - It aids the spread of infection through tissues by binding plasminogen activating plasmin to break down fibrin.

46
Q

Describe the different toxins of S pyogenes?

A

Pyrogenic exotoxins - Thye generate fever, consists of SpeA, SpeB, SpeC

SpeA - Its antigen activity results in a huge cytokine release which results on inflammation, shock, organ failure

SpeB - associated with causing necrotising fascitis.

47
Q

What are the different types of disease caused by S pyogenes?

A

Superficial infection
Deep seated infections
Toxin mediated disease
Immune mediated disease

48
Q

Describe S pyogenes superficial infections

A

Causes infections such as Pharyngitis, Impetigo, erysipelas

49
Q

What is pharyngitis?

A

Symptoms such as inflamed pharyngeal membrane, swelling of uvula

treated with penicillin

can lead to scarlet fever.

50
Q

Describe S pyogenes deep seated infections

A

These are life threatening invasive infections such as Cellulitis, puerperal fever, necrotising fasciitis

51
Q

Describe S pyogenes toxin mediated disease aka scarlet fever?

A

This is where the toxin SpeA (causes huge cytokine release) spreads throughout the body which causes a rash spreading to most of the body

White strawberry tonguw=e which turns into a red strawberry tongue

Can lead to cellulitis, sepsis

52
Q

Describe S pyogenes immune mediated disease aka rheumatic fever?

A

This is where the antibody against the M protein of S pyogenes cross reacts with human tissue causing inflammation, rash, carditis etc

53
Q

What is streptococcus agalactiae aka?

A

Group B strep

54
Q

Describe streptococcus agalactiae (Group B strep)

A

It is a commensal of the colon and in the female genital tract

55
Q

If a pregnant woman has group B strep whilst pregnant, what can it lead to?

A

Premature labour
Neonatal sepsis, meningitis

56
Q

Describe S pneumoniae?

A

Found in the nasopharynx/upper respiratory tract.
Transmitted by direct contact, respiratory droplets

57
Q

What are the virulence factors of S pneumoniae?

A

Toxins - pneumolysin
Polysaccharide capsule

58
Q

Describe the toxin of S pneumoniae?

A

The toxin is pneumolysin - it generates pores in eukaryotic cell membranes, it activates the classical pathway leading to cytokine production and inflammation.

59
Q

Describe the polysaccharide capsule of S pneumoniae?

A

It is antiphagocytic and is essential for causing invasive infections so is used to avoid the immune response

60
Q

List the different S pneumoniae infections

A

Non invasive - Otitis media, sinusitis

Invasive Pneumococcal disease (IPD) - Pneumonia, sepsis, meningitis

61
Q

Describe pneumonia

A

This is where the alveoli in the lungs become filled with pus and fluid resulting in painful breathing and limited oxygen intake.

Symptoms consist of: Cough, purulent sputum, pyrexia, consolidation of lung.

62
Q

What is Viridans Group Streptococci (VGS)?

A

A type of bacteria that has low pathogenic potential because of very few virulence factors, has many species and is susceptible to most antibiotics

63
Q

How do VSG species enter into the body?

A

Via the oral cavity and gut, they enter into the bloodstream

64
Q

How are enterococci bacteria identified?

A

Enterococci are:
Catalase negative
Bile insoluble
Have brown/black colonies on aesculin agar
Is a lance field group D organism

65
Q

Describe an enterococcal infection

A

It is a commensal of the intestinal tract.
Can cause endocarditis, abdominal wound infections etc

Resistant to penicillin, but sensitive to amoxycillin

infectious diseases (11 decks)

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