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Infection > Session 6 > Flashcards

Session 6 Flashcards

1
Q

What is the most common congenital cardiac defect?

A

Bicuspid aortic valve

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2
Q

Bicuspid aortic valve is associated with which infection?

A

Infective endocarditis

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3
Q

Why is bicuspid aortic valve associated with infective endocarditis?

A

The structural abnormality and abnormal tissue provide a surface for bacteria to stick and form a colony

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4
Q

Other than infective endocarditis, name two consequences of bicuspid aortic valve

A

Aortic stenosis

Aortic incompetence

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5
Q

In adulthood, bicuspid aortic valve can present with…

A

Heart failure

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6
Q

Why does the endocardium normally resits bacterial seeding and infection?

A

It is non-sticky

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7
Q

Most cases of infective endocarditis relate to ___________ defects.

Give another risk factor for endocarditis

A

Structural

Injectable drug use

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8
Q

In infective endocarditis, a _____________ is formed that binds to valves or the endocardium

A

Vegetation

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9
Q

What forms the basis of the vegetation that begins infective endocarditis?

What can cause this vegetation to be more likely to form?

A

Collection of fibrin, platelets and inflammatory cells

Abnormal blood flow

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10
Q

How does infective endocarditis progress once a vegetation has been formed?

A

Microorganisms bind to the vegetation and cause local infection - further platelets, fibrin, inflammatory cells and bacteria invade resulting in an infection cascade.

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11
Q

How do microorganisms enter the heart to cause infective endocarditis? Where can these microorganisms come from?

A

Through the blood stream

Skin, mouth

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12
Q

Why is infective endocarditis difficult to eradicate?

Why is it hard to treat infective endocarditis with antibiotics?

A

Micro colonies of bacteria deep in the vegetation are dormant (hard to eradicate)

Hard for the antibiotics to penetrate the vegetation

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13
Q

What is often the treatment given for infective endocarditis?

A

Surgery to remove the valve and replace it with an artificial valve

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14
Q

Give an example of a commensal on the skin that has low virulence but can cause infection if travels in the blood and sticks to artificial surfaces

A

Staphylococcus epidermis

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15
Q

What does staphylococcus epidermis do at an artificial surface (e.g. Prosthetic joint) too cause infection?

A

Produces slime which contributes to the development of a biofilm that is hard to get rid of

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16
Q

What is a biofilm?

A

A thin but robust layer of mucilage adhering to a solid surface containing a community of microorganisms (bacteria)

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17
Q

How does the biofilm produced in the infection of prosthetic joints with staphylococcus epidermis protect the bacteria?

A

The extracellular matrix protects the bacteria from exposure to innate immune defences (opsonisation/phagocytosis) and antibiotic treatment

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18
Q

Define a surface

A

Interface between a solid and either a liquid or gas

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19
Q

Give three examples of mucosal surfaces in the body

A

Gastrointestinal
Respiratory
Genitourinary
Conjunctival

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20
Q

Are viruses generally found as commensals on the skin?

Give two examples of viruses that affect the skin

A

No - usually all cause infection

HPV
Herpes Simplex

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21
Q

Is Staph aureus gram positive or gram negative?

A

Gram positive

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22
Q

Is coagulase negative staphylococci, gram positive or gram negative?

A

Gram positive

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23
Q

Is corynebacterium, gram-positive or gram-negative?

A

Gram positive

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24
Q

Is enterobacteriaceae, gram positive or gram negative?

A

Gram negative

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25
Q

Name two types of fungi that can affect the skin

Name a parasite that can affect the skin

A

Yeasts
Dermatophytes

Mites

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26
Q

Name a normal flora of the eye

A

Coagulase negative staphylococci

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27
Q

Name a normal flora of the nares (nostrils)

A

Staphylococcus aureus

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28
Q

Name two normal flora of the nasopharynx

A

Haemophilus influenzae
Neisseria meningitidis
Streptococcus pneumoniae

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29
Q

Name a normal flora of the mouth

A

Viridans streptococci

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30
Q

Name two normal flora of the stomach

A

Helicobacter bacteria
Streptococci bacteria
Lactobacilli bacteria
Staphylococci bacteria

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31
Q

Name a normal flora of the intestine

A

Lactobacillus bacteria

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32
Q

Name a normal flora of the urethra

A

Enterobacteriaceae

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33
Q

Name a normal flora of the vagina

A

Lactobacilli bacteria

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34
Q

What is another name for the microbiota?

What is the microbiota?

A

Commensals

Microorganisms that are carried on the skin and mucosal surfaces

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35
Q

Give two examples of external natural surface infections

A

Cellulitis
Conjunctivitis
UTI
Pharyngitis

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36
Q

Give two examples of internal ‘natural’ surface infections

A

Endocarditis

Septic arthritis

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37
Q

Give 4 examples of prosthetic surfaces that can be sites for infections in humans

A 
Intravascular lines
Prosthetic joints 
Cardiac valves 
Peritoneal dialysis catheters
Pacing wires
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38
Q

The causative organism for valve infective endocarditis depends on… (2)

A

Whether it is an artificial or native valve

Time since prosthetic valve surgery

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39
Q

Does a wider range of causative organisms cause valve endocarditis in native valve endocarditis or prosthetic valve endocarditis?

A

Native valve endocarditis (and post prosthetic valve surgery over a year)

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40
Q

Most bacteria/fungi can cause endocarditis in native valves

Name two microorganisms that could be the cause of endocarditis in native valves/>1 yr post prosthetic valve surgery

A

Viridans streptococci
Staph aureus
Candida albicans

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41
Q

What bacteria most commonly causes prosthetic valve endocarditis under a year post-operation?

A

Coagulase negative staphylococci

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42
Q

Name two common causative organisms for prosthetic joint infections

A

Coagulase negative staphylococci

Staph aureus

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43
Q

Name two common causative organisms for cardiac pacing wire endocarditis

A

Coagulase negative staphylococci

Staph aureus

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44
Q

Name the 4 steps involved in the pathogenesis of surface infections

A

Adherence to host cells/prosthetic surface
Biofilm formation
Invasion and multiplication
Host response

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45
Q

How do bacteria adhere to host cells/prosthetic surfaces in surface infections

A

Through pili or fimbriae to the host cell membrane/prosthetic surface

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46
Q

What is a biofilm?

A

A thin but robust layer of mucilage adhering to a solid surface containing a community of microorganisms (bacteria)

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47
Q

What is the colloquial name for a biofilm

A

Slime

48
Q

The recruitment of neutrophils in the host response of surface infections results in the production of…

A

Pus

49
Q

The recruitment of fibroblasts, lymphocytes and macrophages in the host response of surface infections results in the production of…

A

Nodular inflammatory lesions

50
Q

What is quorum sensing? How do bacteria use it?

A

A system of stimuli and response correlated to population density

To coordinate gene expression according to the density of their local population

51
Q

What molecules are produced by bacteria to control the production of biofilm in bacteria depending on the local population density?

A

Autoinducers

52
Q

What role do autoinducers play in bacteria in a surface infection?

A

Bind to cell surface/cytoplasmic receptors on the bacterial cell —> switches on gene expression —> increased biofilm/autoinducer production

53
Q

State two challenges posed in trying to identify an infecting organism and its antimicrobial susceptibilities in surface infections

A

Adherent organisms - hard to remove

Low metabolic state bacteria - hard to culture

54
Q

Name two ways of diagnosing the infecting organism and its antimicrobial susceptibilities in surface infections

A

Blood cultures

Tissue/prosthetic material sonication and culture

55
Q

What happens in tissue/prosthetic material sonication?

A

Bacteria is agitated with rapid ‘shaking’

56
Q

What is meant by bioburden?

A

The number of bacteria living on a non-sterilised surface

57
Q

Why are antibacterials not very effective in the treatment of surface infections?

A

Due to the barrier created by the biofilm

58
Q

Name three ways surface infections are measured

A

Antibacterials
Removal of prosthetic material
Surgery - removal of infected material

59
Q

What are two challenges posed by the management/treatment of surface infections

A

There is poor antibacterial penetration into the biofilm

There is low metabolic activity of biofilm microorganisms

60
Q

Describe the metabolic activity of biofilm microorganisms

A

Low metabolic activity

61
Q

Why does the low metabolic activity of bacteria pose challenges in the treatment of surface infections with antibacterials

A

Antibiotics usually only work when bacteria is metabolically active

62
Q

What protects the bacteria from host/antibacterial attack in surface infections

A

Biofilms

63
Q

What type of bacteria are Streptococci?

A

Gram positive cocci

64
Q

What colour will streptococci appear in a gram stain?

A

Purple (gram +ve)

65
Q

What is the arrangement of streptococci?

A

Cocci chain shaped

66
Q

How are Streptococci classified?

A

By haemolysis - how they affect (haemolyse) RBCs

67
Q

Name three categories of Streptococci based on haemolysis

A

Alpha haemolytic
Beta haemolytic
Gamma haemolytic

68
Q

How do alpha haemolytic Streptococci affect RBCs?

A

Partially lyse RBCs

69
Q

How do beta-haemolytic Streptococci affect RBCs?

A

Completely lyse RBCs

70
Q

How do gamma haemolytic Streptococci affect RBCs?

A

Don’t lyse RBCs

71
Q

How do alpha haemolytic Streptocci appear in a blood agar plate?

Give an example

A

Green appearance

Streptococcus pneumoniae

72
Q

How do beta haemolytic bacteria appear in a blood agar plate?

Give an example

A

Halo ‘white’ appearance

Streptococcus pyogenes

73
Q

Give an example of a gamma haemolytic Streptococci

A

Enterococcus faecalis

74
Q

The alpha haemolytic Streptococci are collectively known as the ____________ streptococci

Why?

A

Viridans

Green appearance in blood agar plate

75
Q

How can different species of Streptococci be classified apart from by haemolysis? (3)

A

Based on their cell wall antigens - Lancefield antigen classification

Sherman classification

16S ribosomal RNA sequences

76
Q

How does the Lancefield antigen classification classify Streptococci?

A

Based on their cell wall antigens

77
Q

Which groups does the Sherman classification of Streptococci divide the bacteria into?

Which of these groups is not common in humans?

A

Pyogenic
Viridans
Enterococcal
Lactic streptococci (not common in humans)

78
Q

How can the 16S ribosomal RNA sequences of Streptococci be used to classify them?

A

The sequences are species specific and can therefore be used to classify the Streptococci

79
Q

Name a type of ‘Group A Strep’ in the Lancefield antigen classification

A

Streptococcus pyogenes

80
Q

Give an example of a ‘Group B Strep’ in the Lancefield antigen classification

A

Streptococcus agalactiae

81
Q

What is S agalactiae a common cause of? In which group of the Lancefield antigen classification does it belong? In which part of the body is it found as normal flora?

A

Neonatal sepsis

Group B

Vagina

82
Q

What category of the Lancefield antigen classification does Strep pyogenes belong? What category does it belong to by haemolysis?

A

Group A

Beta-haemolytic

83
Q

Name 3 virulence factors of Strep pyogenes

A

M protein

Streptokinase

Streptococcal pyrogenic exotoxins

DNAases
Hyaluronic acid capsule 
Streptolysins 
Adhesins
Hyaluronidase
84
Q

How does the hyaluronic acid capsule of Strep pyogenes aid its survival?

A

Inhibits phagocytosis by neutrophils/macrophages

85
Q

Why is the hyaluronic acid capsule of Strep pyogenes a poor immunogen?

A

It is similar to human connective tissue hyaluronic acid

86
Q

What are M proteins in Strep pyogenes?

A

Long chain proteins sticking out from Strep pyogenes

87
Q

How do M proteins on Strep pyogenes aid in its survival?

A

Act as resistance to phagocytosis

88
Q

How do M proteins provide Strep pyogenes with resistance to phagocytosis?

A

They inhibit activation of the alternative complement pathway on bacteria cell surface

89
Q

Do all Strep pyogenes have the same M proteins?

A

No, there are many antigenically different serotypes of M proteins

90
Q

What role do Streptolysins (O and S) play in Strep pyogenes?

A

Lysis of erythrocytes, neutrophils and platelets

91
Q

What role does hyaluronidase play in Strep pyogenes?

A

Degrades hyaluronic acid in connective tissue

92
Q

What role does streptokinase play in Strep pyogenes?

A

Dissolves clots by converting plasminogen to plasmin

93
Q

What role do streptococcal pyogenic exotoxins play in Strep pyogenes?

A

Cleaves IgG bound to Strep pyogenes (group A strep)

94
Q

What is another name for Streptococcal pharyngitis?

A

Strep Sore Throat

95
Q

What is the common cause of Streptococcal pharyngitis?

A

Strep pyogenes

96
Q

Streptococcal pharyngitis is common in which group of people?

A

Children

97
Q

How is Streptococcal pharyngitis spread?

A

By droplet spread

98
Q

Name three common clinical features of Streptococcal pharyngitis

A

Abrupt, onset sore throat
Fever
Headache

99
Q

Is streptococcal pharyngitis commonly treated with antibiotics?

A

No

100
Q

Why is it common to not treat streptococcal pharyngitis with antibiotics?

A

Untreated patients develop M protein specific antibody

101
Q

Name 4 complications of streptococcal pharyngitis

A

Scarlet fever
Suppurative conditions
Acute rheumatic fever
Acute post-streptococcal glomerulonephritis

102
Q

When does scarlet fever develop from streptococcal pharyngitis?

A

When infection is by a particular strain of Strep with particular exotoxins

103
Q

Name some clinical features of scarlet fever?

A 
Rash
High fever
Sepsis
Arthritis
Jaundice
104
Q

What are suppurative complications?

A

Pus-forming complications - e.g. Abscess

105
Q

Acute rheumatic fever involves inflammation of…

A

Heart, joints and CNS

106
Q

Name 4 Streptococcus pyogenes skin infections

A

Impetigo
Erysipelas
Cellulitis
Necrotising fasciitis

107
Q

Impetigo usually affects which groups of people?

A

Children

108
Q

What is the most common cause of glomerulonephritis?

A

Impetigo

109
Q

What does impetigo involve? (What layers does it affect?)

A

Initial skin colonisation by Strep pyogenes followed by superficial intradermal infection

110
Q

What is erysipelas? (What layers does it affect?)

What is it commonly preceded by?

A

Dermis infection with lymphatic involvement

Pharyngitis

111
Q

What is cellulitis (what layers does it affect)?

A

Skin and subcutaneous tissue infection

112
Q

Give two risk factors of cellulitis

A

Injection drug use

Impaired lymphatic drainage

113
Q

What is necrotising fasciitis? (What layers does it affect?)

A

Infection of deeper subcutaneous tissues and fascia. Rapid and extensive necrosis occurs.

114
Q

Name three clinical features of necrotising fasciitis

A

High fever
Severe pain
High mortality

115
Q

Necrotising fasciitis is usually secondary to…

A

Skin break

116
Q

What is streptococcal toxic shock syndrome? What does it result in? (3)

A

When there is deep tissue infection with Strep pyogenes and entry of Strep into deeper tissues and the bloodstreams

Bacteraemia, Vascular Collapse, Organ Failure

Infection (10 decks)

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