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2.2 Microbiology > Denise - Streptococcus > Flashcards

Denise - Streptococcus Flashcards

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1
Q

How is streptococcus classified
(5)

A

Based on the haemolytic propertied of the organism e.g. Alpha haemolytic strep

Based on the presence of surface antigens determined by immunological assays

Based on biochemical reactions

Based on protein analysis

Based on genetic analysis

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2
Q

Classify step based on haemolysis

A

Alpha haemolytic strep
Beta haemolytic strep
Gamma/no haemolytic strep

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3
Q

How do we classify strep based on their serological groups, how is this done

A

Based on the Lancefield groups of streps

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4
Q

How do we group streps based on Lancefield groups?
(6)

A

C-substance polysaccharide in their cell walls

Antigenic differences

Easily extractable

Classified primarily Beta Haemolytic strep

GAS (Group A strep) and GBS (Group B strep) are the most clinically significant

S. pneumoniae and S. viridans (the alpha haemolytic streps) have no group specific antigen i.e. cannot be grouped based on lancefield groups

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5
Q

Which streps cannot be identified using lancefield groupings and why

A

S. pneumoniae and S. viridans (the alpha haemolytic streps) have no group specific antigen i.e. cannot be grouped based on lancefield groups

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6
Q

Write about S. pneumoniae

A

One of the 12 priority pathogens according to WHO

High burden of disease and rising rates of penicillin resistance

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7
Q

What type of resistance is seen in S. pneumoniae

A

Penicillin resistance

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8
Q

Why is S. pneumoniae listed as one of the 12 priority pathogens

A

High carriage rates
Genetic adaptability
Ability to shift from commensal to pathogenic interaction in its host

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9
Q

Write about the pathogenesis of S. Pneumonia
(3)

A

Colonisation is the prerequisite for both transmission to other individuals and invasive disease in the carrier

Carriers can shed S. pneumoniae in nasal secretions and thereby transmit the bacterium

Dissemination beyond its niche along the nasal epithelium, either by aspiration, bacteraemia or local spread

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10
Q

How does S. pneumonia spread from a carrier to another individual

A

Nasal secretions

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11
Q

How does S. pneumonia spread from the nasal epithelium to cause infection

A

Aspiration (bacteria into respiratory system)

Bacteraemia (bacteria in circulation)

Local spread (spread into tissues)

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12
Q

What infection is caused if there is aspiration of S. pneumonia

A

This will cause pneumonia in the lung

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13
Q

What infection is caused if there if S. pneumonia colonisation leads to bacteraemia

A

This will cause meningitis

This can occur directly from colonisation or can lead on from pneumonia

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14
Q

What does local spread of S. pneumonia from nasal epithelium lead to

A

Otitis media

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15
Q

What factors affect S. pneumonia shedding from nasal epithelium of carriers
(5)

A

Pneumolysin increases shedding

Capsule type and amount increases shedding

Viral co-infection increases shedding

Anticapsule IgG decreases shedding

Anticapsule IgA1 has no effect

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16
Q

How does pneumolysin increase shedding of S. pneumoniae?
(3)

A

Inflammation promotes secretion production by nasal epithelium

Bacteria present in mucus lining epithelium

Runny nose -> sneezing -> facilitates spread

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17
Q

How does capsule type and amount increase shedding?
(2)

A

Capsulated strains of S. pneumonia inhibit entrapment by mucin

S. pneumonia can escape the mucous produced by the S. pneumoniae

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18
Q

How can anticapsule IgG decrease Shedding?

A

IgG binds to bacteria

Agglutination blocks release

Bacteria can’t escape in mucous

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19
Q

Why does anticapsule IgA1 have no effect on S. pneumoniae

A

Bacterial protease relieves agglutination

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20
Q

Why does viral co-infection increase shedding of S. pneumoniae

A

Increases bacterial load and increases mucous production

Nasal epithelium infected with virus -> increases production of mucous

More bacteria present in mucous

Spread by runny nose etc

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21
Q

What are the two types of infections caused by S. pnuemonia

A

Non invasive
Invasive soft tissue infections

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22
Q

List the most common S. pneumonia non invasive infections

A

Acute bacterial pneumoniae
Otitis media

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23
Q

Write about acute bacterial pneumoniae caused by S. pneumoniae
(5)

A

Lower respiratory tract infection

Preceeded by viral infection

Community acquired infection Pneumonia CAP

Older adults

Seasonality - increased in winter months

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24
Q

Write about otitis media caused by S. pneumonia

A

Most common cause of middle ear infection in children

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25
Q

What indicates an S. pneumonia invasive infection

A

Isolation of S. pneumoniae from a normally sterile site e.g. blood or CSF

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26
Q

What are the main invasive infections caused by S. pneumoniae

A

Blood stream infection (SEPSIS)

Meningitis

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27
Q

What percentage of S. pneumoniae pneumonia infections will lead to BSIs i.e. SEPSIS

A

15-30% of people with pneumoniae will lead to invasive disease

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28
Q

Write about S. pneumonia caused meningitis
(2)

A

Majority of invasive pneumococcal disease (IPD) infections are caused by a subset of predominant streptococcus pneumoniae serotypes

Approximately 8-10 of 90 different serotypes cause meningitis

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29
Q

Write about S. pneumoniae epidemiology

A

Young children
Older adults
Immunocompromised
Mortality rate is now much greater in adults >65 years of age than in children <2

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30
Q

Comment on the recent trends in invasive S. pneumonia

A

IPD is a notifiable disease in Ireland

Ever increasing number

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31
Q

What does IPD include

A

Meningitis
BSI
Sterile site infection

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32
Q

Comment on incidence rate of IPD versus age of patients
(3)

A

Less common in children under 2

Increasingly common in those over 65

Very low amounts in teenagers (near zero infections)

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33
Q

What are the virulence factors of S. pneumoniae?
(5)

A

Surface structure (capsule)

Pili

Choline Binding protein A

Autolysins LytA

Pneumolysin

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34
Q

How does a capsule affect virulence of S. pneumoniae?
(6)

A

Capsule is antiphagocytic
Capsule is antigenic
Polysaccharide
Essential for colonisation -> non capsulated strains are usually avirulent
Target for Pneumococcal Conjugate Vaccines
>90 strains recognised based on capsular carbohydrates

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35
Q

How do pili affect virulence of S. pneumoniae

A

Not all pneumococci express pili
Attachment to the epithelial cells in the nasopharynx and upper respiratory tract

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36
Q

How does choline binding protein A affect?
(6)

A

Polypeptides
Number varies from 13 to 16
Anchors the protein to the choline residues present in the cell wall
Responsible for remodelling the cell wall
Responsible for adhesion
Promotes invasion

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37
Q

What are the two main enzymes responsible for virulence of S. pneumonia

A

Autolysins LytA
Pneumolysin

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38
Q

What does autolysins LytA do in S. pneumoniae

A

Cell wall degrading protease

Responsible for the release of virulence factors

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39
Q

What does pneumolysin do?
(6)

A

Cytolytic protein

Released by autolysin

Attacks cell membranes

Proinflammatory

Inhibits PMN

Activates complement

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40
Q

Describe the process behind autolysins LytA and pneumolysin in S. pneumoniae.
(5)

A

S. pneumoniae infection

Autolysin is responsible for lysis of S. pneumoniae

Lysis releases the virulence factors out of S. pneumoniae

Pneumolysin released

Pneumolysin damages mammalian cell membranes

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41
Q

What is done with S. pneumoniae on day 1 of laboratory investigation?
(2)

A

Direct gram stain

Inoculation on blood agar

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42
Q

What specimens are seen in S. pneumoniae infections
(6)

A

Sputum
Pleural fluid or lung aspirate
Pus
Aspirates
CSF
Blood

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43
Q

What investigation is done on CSF and blood for S. pneumoniae

A

Direct Molecular detection
Film array ME

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44
Q

What investigation is done on CSF?
(4)

A

White cells increased
Bacteria
Glucose decreased
protein increased

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45
Q

What investigation is carried out on day 1 for S. pneumoniae?
(2)

A

Direct microscopy gram stain

Only done on blood cultures which have flagged positive

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46
Q

How does S. pneumoniae appear on gram stain

A

Gram positive diplococci lancet shaped

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47
Q

Write about the growth requirements for S. pneumonia
(6)

A

Fastidious
Blood agar
37 degrees celsius
5% CO2
O2
Anaerobically

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48
Q

Write about the colonial morphology of S. pneumoniae

A

Alpha haemolysis
Draughtsman colonies or mucoid colonies

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49
Q

What are the basic characteristic results of S. pneumonia

A

Gram positive diplococci
KOH negative
Catalase negative
Oxidase negative

Lanceolate shaped

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50
Q

What confirmatory identification tests are done for S. pneumonia on day 2
(3)

A

Optochin susceptibility
Bile susceptible

Vitek or Maldi TOF identification

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51
Q

Why might the Vitek be used instead of Maldi for S. pneumoniae ID

A

Maldi lack of discrimination between s. pneumoniae and other closely related alpha-haemolytic streptococci

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52
Q

How is S. pneumonia treated

A

B lactams -> penicillin (if not resistant)
Macrolide -> Erythromycin
Cephalosporin -> Cefotaxime

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53
Q

Write about S. pneumoniae resistance
(3)

A

PNSP -> penicillin non-susceptible pneumococci increased gradually with age

11% isolate in younger patients but 29% in older patients over 75

Reduced susceptibility to cefotaxime and erythromycin is also observed in older patients

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54
Q

What is done with S. pneumonia which is confirmed
(3)

A

CSF sent to IMSRL (Irish Meningitis and sepsis Reference Laboratory) on Temple street

Real time PCR directly on specimen

Serogroup Capsule-PCR

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55
Q

What Pneumococcal vaccines are there currently
(3)

A

PCV7 - infants
PCV13 - infants
PPV23 - for adults over 65 and immunocompromised

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56
Q

What is the PPV23 vaccine
(5)

A

Pneumococcal polysaccharide vaccine

Purified capsular polysaccharide from 23 capsular types of S. pneumoniae

Accounts for up to 90% of IPD

Only for those >2 years old

Uptake is poor - only 30%

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57
Q

Why is the PPV23 vaccine only suitable for those over 2?

A

An adequate antibody response does not develop in those under 2 years of age

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58
Q

What are the PCV vaccines
(6)

A

Pneumococcal Conjugated Vaccines

PCV7 and PCV13

Conjugated to a protein for enhanced immunogenicity

Immunogenic from 6 weeks of age

Active against 75-90% of IPD serotypes

Uptake great with >90%

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59
Q

Comment on the outcome of S. pneumoniae vaccination
(4)

A

Clear evidence that the vaccines have reduced the burden of IPD in children

However, number of non vaccine type infections has increased

Evidence of herd protection seen

Vaccine uptake for PPV23 needs to be improved

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60
Q

Write about S. viridans
(6)

A

Commensals in the GIT, Respiratory and female genital tracts and are most prevalent in the oral cavity

Considered to be of low pathogenicity

Many species but not usually differentiated

May gain access to bloodstream through minor trauma to gums

Propensity to adhere to cardiac valves

In those with damaged heart valves can cause sub acute bacterial endocarditis

61
Q

How can S. viridans gain access to blood stream?

A

Through minor trauma to gums

62
Q

What can S. viridans cause to those with damaged heart valves

A

Sub acute bacterial endocarditis

63
Q

What is Streptococcal endocarditis
(4)

A

Patients with abnormal or damaged heart valves

Bacteria infects valves during a bacteraemia

Prophylactic penicillin may be given prior to dental treatment

Caused by oral streptococci e.g. S. mitis or S. oralis

64
Q

What species might cause streptococcal endocarditis

A

Oral streptococci e.g. S. mitis, S. oralis

65
Q

Where is S. mutans often found

A

Found in mouth/on teeth

Produces biofilm which can be involved in plaque formation and tooth decay

66
Q

What infections can S. mutans cause

A

Tooth decay

67
Q

What are the basic characteristics of S. viridans

A

Gram positive cocci in chains
Catalase negative
Oxidase negative
Fastidious
Facultative anaerobes
Alpha haemolysis

68
Q

What is done to S. viridans on day 1

A

Isolation on blood agar

69
Q

What is done to S. viridans on day 2

A

Gram stain
Investigate haemolysis
Biochemical speciation
Identification on Vitek or MALDI

70
Q

What is done on day 3 for S. viridans

A

Optochin susceptibility testing

71
Q

How does S. viridans react to optochin

A

S. viridans is resistant to optochin

72
Q

What is meant by Lancefield grouping?
(3)

A

Lancefield Groups based on differences in cell wall polysaccharides

13 Lancefield Groups

Groups A, B, C, D, F and G most commonly implicated in human infections

73
Q

What is Lancefield group A

A

Streptococcus pyogenes

74
Q

What is Lancefield group B

A

Streptococcus agalactiae

75
Q

What is Lancefield group C

A

Found in pharynx: can cause pharyngitis, sinusitis, impetigo, endocarditis

76
Q

What is Lancefield group D

A

Enterococci
Can cause wound lesions, urinary tract infections and some cases of SBE

77
Q

What is Lancefield group F

A

Streptococcus anginosus; grow better anaerobically

78
Q

What is Lancefield group G

A

Resemble group A strains

79
Q

What are the three types of infections caused by S. pyogenes

A

Non invasive

Invasive soft tissue

Non-suppurative sequelae

80
Q

List the main non invasive infections caused by S. pyogenes

A

Pharyngitis
Scarlet fever
Skin infections

81
Q

What is pharyngitis
(5)

A

Common infection
Abrupt onset
Difficult to differentiate from viral infection
5-30% of cases in children
5-10% of cases in adults

82
Q

What are the four symptoms of pharyngitis

A

Headache
Fever
Reddening
Pus

83
Q

Write about scarlet fever caused by S. pyogenes
(5)

A

Scarletina
Erythematous rash of skin and mucous membranes
Rash looks like sunburn and feels like sandpaper
Strawberry tongue
Erythrogenic toxin

84
Q

What non invasive skin infections does S. pyogenes cause

A

Impetigo
Erysipelsia

85
Q

What is impetigo

A

Honey crust lesions
Pus filled blisters

86
Q

What is erysipelsia?
(5)

A

Acute skin infection
Cellulitis
Diffuse redness
Pain
Potential spread to the bloodstream

87
Q

What invasive soft tissue infections does S. pyogenes cause

A

Necrotising facitis
Streptococcal Toxic Shock Syndrome

88
Q

Write about necrotising facitis
(7)

A

Rare infection
Tissues under the skin and muscles
Pain Redness Swelling
Fluid filled blisters/swollen tissues
Associated with wounds/breaks in the skin
Predisposition includes: cancer, diabetes, dialysis and steroids
Infected tissue has to be cut off

89
Q

What predisposes someone to necrotising facitis?
(4)

A

Cancer
Diabetes
Dialysis
Steroids

90
Q

What is streptococcal Toxic Shock Syndrome

A

Caused by superantigen
1-2 weeks after the onset of acute illness

91
Q

What are the main symptoms of toxic shock syndrome
(5)

A

High fever
Rash
Hypotension
Multiorgan failure
Desquamation typically of the palms and soles

92
Q

What are the two non suppurative sequelae infections caused by S. pyogenes

A

Rheumatic fever
Glomerular nephritis

93
Q

What is a non suppurative sequelae

A

Immune reactions 1-5 weeks after infection

94
Q

What causes rheumatic fever

A

Its seen post pharyngitis

95
Q

What causes glomerular nephritis

A

Its seen post skin infection

96
Q

What are cutaneous infections

A

Infections of upper respiratory tract and of skin and soft tissue

97
Q

What are the three main cutaneous infections caused by S. pyogenes

A

Pharyngitis
Cellulitis
Impetigo

98
Q

What is the main destructive soft tissue infection caused by S. pyogenes?

A

Necrotising faciitis

99
Q

What are the two toxin mediated infections caused by S. pyogenes

A

Scarlet fever
Toxic Shock Syndrome

100
Q

What are the non-suppurative sequelae caused by S. pyogenes?

A

Acute glomerulonephritis
Rheumatic fever

101
Q

Write about S. pyogenes epidemiology

A

Only invasive infections are notifiable iGAS (invasive group A streptococci)

Streptococcal Toxic Shock/ Necrotising Faciitis/ BSI

Increase in notified iGAS infections since october 2022

102
Q

Write about S. pyogenes virulence
(4)

A

Wide range of virulence factors
Enable bacteria to attach to host cells
Spread by penetrating host tissues
Evade the immune response

103
Q

What are the S. pyogenes virulence factors
(8)

A

Capsule
M protein
Streptolysins
Anti C5a peptidase
Streptokinase
Hyaluronidase
Exotoxins SPE A and C
DNase

104
Q

Write about M protein
(8)

A

Surface adhesin
Inhibits phagocytosis
Binds Fc portion of IgG
M types 1, 3, 12 and 28 are the most common isolates found in patients with shock and multiorgan failure
Strains lacking M protein are less virulent
Rheumatic heart disease
T-protein surface antigen
R-protein on some strains

105
Q

List the S. pyogenes Toxins and ExoEnzymes
(6)

A

Pyrogenic exotoxins
Streptolysin O and S
Streptokinase
C5a peptidase
Streptodornases
Hyaluronidase

106
Q

What does pyrogenic exotoxins do

A

Cause various effects, including the rashes seen in scarlet fever and streptococcal toxic shock disease

107
Q

What does Streptolysin O and S do

A

Damages mammalian cells, resulting in cell lysis and release of lysosomal enzymes

Lysis of RBCs, PMNs and platelets

108
Q

What does streptokinase do

A

Catalyses conversion of plasminogen to plasmin, causing lysis of clots, facilitating the rapid spread of organisms

109
Q

What does C5a peptidase do
(2)

A

Inactivates complement component C5a

Cleaves the chemoattractant C5a

110
Q

What does streptodornases do

A

DNAses degrade the viscous DNA in necrotising tissue or exudates, aiding the spread of infection

111
Q

What does hyaluronidase do

A

Disrupts the organisation of ground substance, facilitating the spread of infection

Breaks down tissue hyaluronic acid

112
Q

What does streptolysin S do

A

Oxygen stable
Not antigenic
Leucocidal action

113
Q

What does Streptolysin O do
(3)

A

Oxygen labile

Cytotoxic for red blood cells, neutrophils, platelets, cardiac tissue

Responsible for haemolysis that we see on blood agar

114
Q

What are the streptococcal exotoxins
(3)

A

SPE-A
SPE-B
SPE-C

115
Q

What does SPE stand for

A

Streptococcal pyrogenic exotoxins

116
Q

What are SPE-A and SPE-C
(3)

A

Erythrogenic toxins

Similar to staph enterotoxins

Associated with invasive infections and toxic shock syndrome

117
Q

What is SpeB

A

Cysteine protease

Associated with tissue destruction

118
Q

What are the exotoxins SPE A and C also called

A

Superantigens

119
Q

What does DNase do

A

Degrades extracellula

120
Q

What specimens is S. pyogenes found in

A

Throat swabs
Pus
Skin

121
Q

What are the growth requirements of S. pyogenes

A

Fastidious
Blood agar
Haemolysis enhanced anaerobically
37 degrees Celsius
5% CO2, O2, Anaerobically

122
Q

What confirmatory tests are done on S, pyogenes

A

Rapid latex agglutination on patient samples

123
Q

What is the colonial morphology of S. pyogenes
(5)

A

Beta haemolysis
Gram positive cocci in chains
KoH negative
Catalase negative
Oxidase negative

124
Q

What confirmatory test is done on day 2 for S. pyogenes
(4)

A

Lancefield Grouping

MacConkey

Susceptible to bacitracin

PYR

125
Q

How does S. pyogenes grow on MacConkey?

A

Fails to grow on MacConkey

126
Q

How does S. pyogenes grow with Bacitracin

A

S. pyogenes is susceptible to bacitracin

127
Q

Is S. pyogenes PYR positive or negative?

A

Its PYR positive

128
Q

What is PYR

A

Pyrrolidonyl arylamidase

129
Q

Write about S. agalactiae

A

Opportunistic pathogen
Often colonisation
Capsule may contribute to virulence

130
Q

Write about the colonisation of S. agalactiae
(5)

A

Found in the intestines of up to 30% of adults

Found in the vagina of up to 25% of women

Asymptomatic

May be intermittent

90% of adults posses no protective antibodies to Gram B Strep

131
Q

Write about the pathophysiology of group B streptococcus

A

Prenatal onset GBS
Early-onset GBS
Late-onset GBS

132
Q

Write about the prenatal-onset of group B strep

A

Occurs when a baby is infected with GBS during pregnancy

133
Q

Write about the early-onset of group B strep

A

Occurs when a baby is infected with GBS within the first week of life

134
Q

Write about the late-onset of group B strep

A

Occurs when a baby is infected with GBS after 1 week to several months of age

135
Q

Write about the epidemiology of Group B strep

A

Infections in adults: the elderly, pregnant women, others with other disease

Most common cause of life-threatening infection in newborn babies

136
Q

Write about early onset infectious GBS

A

Up to 80% of GBS infection in babies

0-6 days (usually <24 hours)

Usually septicaemia, also meningitis and pneumonia

11% mortality

137
Q

Write about late onset infectious group B septicaemia
(5)

A

Up to 20% of GBS infection in babies

7+ days (rare after 3 months)

Usually meningitis with septicaemia

5% mortality

50% of GBS meningitis survivors have neurological sequelae

138
Q

What specimens are Group B streps found in

A

Urine Sample UTI
Blood cultures BSI
CSF

139
Q

What specimens come in for surveillance in carriage of Group B strep

A

High vaginal swab
Screening for GU carriage
Carriage preceeds infection

140
Q

What are the growth requirements for Group B strep

A

Fastidious
Grown on blood agar -> haemolysis enhanced anaerobically
37 degrees celsius
5% CO2

141
Q

What is done on day 1 for Group B streps

A

Isolation on blood agar
Direct detection using geneXpert -> S. agalactiae

142
Q

What are the basic characterisation results for Group B strep, S. agalactiae

A

Lancefield group B
KOH Negative
Oxidase Negative
CAMP factor
Hydrolysis of hippurate
Does not hydrolyse aesculin
Some grow on MacConkey agar (bile)

143
Q

What is the CAMP test

A

Detects the production of extracellular protein CAMP factor

CAMP factor acts synergistically with the beta lysin produced by S. aureus

A zone of enhanced lysis of sheep or bovine blood

CAMP positive = Group B strep
CAMP negative = Not GBS

144
Q

What is the Hippurate hydrolysis test
(4)

A

Used to differentiate S. agalactiae from other Beta Haemolytic streps

Hippurate is hydrolysed by hippuricase into Benzoic acid and glycine

Ninhydrin reagent is used as an indicator to detect Glycine

Ninhydrin reacts with glycine to form a deep blue or purple colour

145
Q

What do we done when we confirm we have a Group B strep
(3)

A

CSF sent to Irish Meningitis and Sepsis Reference Lab in Temple Street

Real Time PCR directly on specimen

Serogroup capsule - PCR

146
Q

Write about Group C and G streptococcus
(4)

A

Commensal flora of the human upper airway

Asymptomatic colonisers of the skin, gastrointestinal tract and female genital tract

S. dysgalactiae subspecies S. equisimilis (SDSE)

Resembles S. pyogenes infections

147
Q

Write about the non enterococcal group D
(7)

A

Streptococcus bovis

Faecal flora

Alpha or non haemolytic

Occasionally causes UTI and Endcarditis

Bile Aesculin Positive

PYR Negative

Does not grow in 6.5% salt

148
Q

Write about beta haemolytic strep treatment

A

Penicillin
Clarithromycin (allergy)
Necrotizing fasciitis - surgery + clindamycin

2.2 Microbiology (60 decks)

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