Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Divine infection > Key Bacteria - Streptococci > Flashcards

Key Bacteria - Streptococci Flashcards

1
Q

List 7 key features of all Streptococci bacteria?

A
  • Gram positive
  • Cocci bacteria
  • in chains/strips
  • Non-motile
  • Non-spore forming
  • Catalase negative
  • Either facultative or obligate anaerobes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Classify Streptococci by Haemolysis and give examples for each?

A

Alpha-Haemolytic Strep

  • (A.K.A. Viridans streptococci)
  • partial haemolysis
  • Appear GREEN in agar
  • Can’t utilise nutrients as well as B-haemolytic Strep
  • Production of Polysaccharide capsule
  • E.g. Strep. pneumoniae

Beta-Haemolytic Strep

  • A.K.A Group A Streptococci
  • Complete haemolysis
  • Appear CLEAR in agar
  • Can utilise nutrients better than alpha- & non- haemolytic Strep
  • E.g. Strep. pyogenes

Non-Haemolytic Strep

  • A.K.A. Gamma-haemolytic strep
  • No haemolysis
  • Appears DIRTY GREY colour in agar
  • E.g. Enterococcus faecalis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe structure of Viridans Streptococci?

alpha-haemolytic Strep.

A
  • Gram positive, cocci bacteria

- in chains

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Where is Viridans Streptococci found?

A
  • Oral, gut, genital normal flora
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How does Viridans Streptococci spread?

A

Contagious spread

  • more often infection due to bacteria entering other regions of the body
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Commonly linked conditions to Viridans Streptococci infection?

A
  • Tooth decay / dental cavities
  • Bacterial Endocarditis = bacterial infection of the inner lining of the heart (if Viridans enters bloodstream).
  • Patient with abnormal heart valves. Congenital, rheumatic or sclerotic are at higher risk.
  • Patients who are Immunocompromised are at higher risk.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Virulence factors of Viridans Streptococcus?

A
  • Capsule = inc. resistance to phagocytosis

- Alpha-haemolytic = partially breaks down RBCs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Investigations for Viridans Streptococci infection?

A
  • FBC
  • CRP
  • Blood culture = appears GREEN on agar
  • Gram stain = gram +ve cocci chains
  • Catalase test = Catalase negative
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Treatment of Viridans Streptococcus infection?

A
  • surgical antibiotic prophylaxis
  • Penicillin (beta lactam)
  • Gentamicin (aminoglycoside)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Describe structure of Strep. pneumoniae?

Alpha-haemolytic Strep

A

Member of Viridans group of Strep

  • Gram +ve, cocci bacteria
  • Diplococci usually but can also be seen in short chains
  • Encapsulated
  • Lancet-shaped
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Where is Strep. pneumoniae found?

A

Normal flora

  • Skin
  • Respiratory tract
  • Also potentially Female genital tract
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How is Strep. pneumoniae spread?

A

Contagious spread

  • person to person via droplets
  • coughs and sneezes
  • also vertical spread mother to child (from mother genital tract to baby)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Commonly linked conditions to Strep. pneumoniae infection?

A
  • Pneumonia
  • Acute throat infection
  • Sinusitis
  • Neo-natal sepsis = female genital tract colonisation (vertical transmission)
  • Otitis media = Characterised by ear ache
  • Adult meningitis
  • Bacteraemia
  • sepsis = asplenic patients more susceptible to infection by encapsulated bacteria.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Virulence factors of Strep. pneumoniae?

A
  • Polysaccharide Capsule
  • Pili
  • Autolysin
  • Pneumolysin
  • Choline-binding protein A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Explain Polysaccharide capsule as a virulence factor for Strep. pneumoniae?

A
  • Chokes neutrophils trying to digest it to resist phagocytosis.
  • capsule also prevents antibody and complement attack
  • facilitates bacterial growth prior to the appearance of anti-capsular antibody.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Explain Pili as a virulence factor of Strep. pneumoniae?

A
  • Allows attachment of encapsulated pneumococci to the epithelial cells of the upper respiratory tract
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Explain Choline-binding protein A as a virulence factor of Strep. pneumoniae

A
  • Adhesion = allows the pneumococcus to attach to carbohydrates on the epithelial cells of the human nasopharynx
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Explain autolysin as a virulence factor of Step. pneumoniae?

A
  • Autolysin
  • Hydrolyse the components of biological cells in which it is produced.

Pneumolysin
- Able to attack mammalian cell membrane, causing lysis, once it’s released by autolysin from the interior of the bacterium.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Investigations for Strep. pneumoniae infection?

A
  • Full blood count
  • CRP
  • Swab then grow on blood agar = appears green
  • gram +ve, cocci (or diplococci)
  • catalase test = negative
20
Q

Treatments for Strep. pneumoniae infection?

A

Vaccine available

Antibiotics:
- Penicillin (amoxicillin) = effective against gram +ve bacteria
- Doxycycline = if patient has penicillin allergy
(However don’t give kids <12 yrs old, because can cause irreversible yellow staining to teeth and bones in young children)

21
Q

Describe the structure of Strep. pyogenes

A
  • Group A, Beta-haemolytic Strep
  • Gram +ve, cocci bacteria in chains
  • Encapsulated (Hyaluronic acid)
22
Q

Where is Strep. pyogenes found?

A

Normal flora

- skin, respiratory tract, female genital tract

23
Q

How is Strep. pyogenes infection spread?

A
  • Respiratory secretions droplet spread (coughs & sneezes)
  • Fomites = any non-living object or substance capable of carrying infectious organisms
  • Infection can be transmitted by asymptomatic carriers.
  • Spread associated with overcrowding
24
Q

List 6 Virulence factors of Strep. pyogenes?

A
  • Hyaluronic acid capsule
  • M protein
  • Adhesins
  • Streptokinase
  • Hyaluronidase
  • Streptococcal pyrogenic exotoxins
25
Q

Explain Hyaluronic acid capsule as a virulence factor of S. pyogenes?

A
  • Inhibits phagocytosis by Neutrophils & macrophages

- Poor immunogen (seem like self) because of its similarity to hyaluronate in humans (a connective tissue)

26
Q

Explain M protein as a virulence factor of S. pyogenes?

A
  • Resists phagocytosis by inhibiting activation of alternative complement pathway, on bacterial cell surface
27
Q

Explain Streptokinase as a virulence factor of Strep. pyogenes?

A

Enzyme which catalyses Dissolution (breakdown) of clots

- through conversion of plasminogen to plasmin

28
Q

Explain Hyaluronidase as a virulence factor of Strep. pyogenes?

A

An enzyme which catalyses the degradation of hyaluronic acid in host connective tissue

29
Q

Explain adhesins as a virulence factor of Strep. pyogenes?

A
  • Aid Adherence, which is the first step in colonisation/infection

Examples of adhesins:

  • M protein
  • Fibronectin-binding Protein
  • lipoteichoic acid
30
Q

Explain Streptococcal pyrogenic exotoxins as a virulence factor of S. pyogenes?

A
  • Cleaves Ig G bound to Group A strep.

- Member of superantigenic Spe family (clonal T-cell proliferation)

31
Q

Common conditions linked to Strep. pyogenes infection?

A 
It can be either non-invasive (not spread into the bloodstream)
Or 
Invasive (spread into the bloodstream and to other body sites)
  • Streptococcal pharyngitis
  • Complications of Streptococcal pharyngitis
  • Suppurative complications of Strep pharyngitis
  • Strep. pyogenes skin infections
  • Streptococcal toxic shock syndrome
32
Q

Strep. pharyngitis infection?

  • Incidence
  • Spread
  • Clinical features
  • Progression
A

Streptococcal pharyngitis — (A.k.a. Strep throat)
• Peak incidence of both resp. & skin infections = 5-15 years old

  • Person to person droplet spread (associated with overcrowding)
  • clinical features —
  • Abrupt onset soar throat
  • Malaise, fever, headache
  • Lymphoid hyperplasia
  • Tonsillopharyngeal exudates (throat pus)
  • Untreated patients develop M protein specific antibody
  • Complications —
  • Scarlet fever
  • Acute rheumatic fever
  • Acute post-streptococcal glomerulonephritis
  • Suppurative complications
33
Q

Explain Scarlet fever as a complication of Strep. pharyngitis

  • Cause
  • Spread
  • Clinical presentation
A

Due to infection with Strep. Pyrogenic exotoxins strain of S. pyogenes

Spread = can be Local or Haematogenous (carried by blood)

Clinical presentation =

  • High fever
  • sepsis
  • arthritis
  • jaundice
  • red patches on skin / in armpits
34
Q

List Suppurative (abscess-forming) complications of Strep. pharyngitis

A
  • Peritonsillar cellulitis/abscess
  • Retropharyngeal abscess
  • Mastoiditis / Sinusitis / Otitis media
  • Meningitis, Brain abscess
35
Q

Explain Acute Rheumatic fever (ARF) as a complication of Strep. pharyngitis?

  • Cause
  • features
  • mechanism
A
  • Not direct complication of infection. But as a result of the immune reaction to the infection
  • Inflammation of heart, joints & CNS
  • Follows on from pharyngitis
  • Rheumatogenic M types

Possible mechanism — ARF can arise due to:

  • Auto-immune
  • M protein binding to collagen
  • Serum sickness = hypersensitivity reaction that results from the injection of heterologous or foreign protein or serum.
36
Q

Explain Acute post-Streptococcal glomerulonephritis as a complication of Strep. pharyngitis?

  • Cause
  • mechanism
A
  • Not a direct complication of infection. But as a result of the immune reaction to the infection
  • Acute inflammation of renal glomerulus
  • Due to the formation of antigen-antibody complexes in the glomerulus
  • M types specific, but not the same as ARF M types.
37
Q

Strep. pyogenes skin infections?

A
  • Impetigo
  • Erysipelas
  • Cellulitis
  • Necrotising fasciitis
38
Q

Explain Impetigo as a Strep. pyogenes skin disease?

Define
Incidence
Cause
Progression

A

Define = Skin infection by Streptococcus pyogenes (group A beta-haemolytic streptococcus)

Incidence = Often occurs in children aged 2-5yrs

Cause = involves Initial skin colonisation, followed by intradermal innoculation

Progression =
- Impetigo = most common cause of glomerulonephritis

39
Q

Explain erysipelas as a Strep. pyogenes skin infection?

Define
Cause
Presentation

A

Define = Skin infection by Streptococcus pyogenes (group A beta-haemolytic streptococcus)

Cause = The dermis of the face and/or lower limbs is infected with lymphatic involvement

Presentation = Usually affects face or lower limb —

  • Facial lesions frequently preceded by pharyngitis
  • Lower limb infection usually secondary to invasion of skin (via trauma, skin disease or local fungal infection)
40
Q

Explain Cellulitis as a Strep. pyogenes skin infection?

Define
Risk factors
Presentation

A

Define = skin and subcutaneous tissue infection by Group A Beta-haemolytic Streptococcus (Strep. pyogenes)

Risk factors =

  • impaired lymphatic drainage
  • illicit injecting drug use

Presentation = usually on lower limb, and usually on one limb (almost never on both legs)
- occurs mainly in the elderly

41
Q

Streptococcal toxic shock syndrome

Cause
Presentation

A

Cause = Infection of deep tissue & blood by Strep pyogenes

Clinical Progression = (patient can go from healthy to dead in hrs)

—> Deep tissue infection
—> Bacteraemia
—> Vascular collapse
—> Organ failure
—> Death
42
Q

Explain Streptococcal toxic shock syndrome — mechanism —

A

Mechanism —
1) Entry of group A strep into deeper tissues and bloodstream

2) Streptococcal pyrogenic exotoxins stimulate T-cells, through binding to MHC class II antigen-presenting cells and V-β region of T-cell receptor
3) Induces monocyte cytokines (TNF-α, IL-1β, IL-6) and lymphokines (TNF-β, IL-2, IFN-γ)
4) M-protein fibrinogen complex formation

43
Q

Explain necrotising fasciitis as a Strep. pyogenes skin infection?

Define
Cause
Presentation
Test

A

Define = infection of deeper subcutaneous tissue and fascia by Strep. pyogenes

  • deep infection - even down to deep tissue and can even affect muscle
  • infection usually secondary to skin break
  • Rapid extensive necrosis
  • severe pain, even before gross changes
  • high fever, fulminant course, high mortality

Test = sweep test (using finger)

44
Q

Investigations for Strep. pyogenes infection?

A
  • Full blood count
  • CRP
  • For non-invasive Infections = Rapid Strep Test
    Throat or nose swab

Blood culture (blood agar) — sample from:

  • throat swab
  • Pus swab
  • lesion sample
  • sputum, blood or CSF

Blood agar result = appear clear
Histology = gram +ve, cocci in chains
Catalase test = catalase negative

45
Q

Treatment for S. pyogenes infection?

A

Antibiotics (Oral or IVABX - depending on severity)

  • Penicillin
  • Amoxicillin
  • Doxycycline (if Penicillin allergy)
  • Clarythromycin (if Penicillin resistant)
  • Superficial skin infections = topical antibiotic ointments
  • Where the infection has caused a lot of skin damage, for example in cases of necrotising fasciitis, damaged tissue may be removed with surgery

Divine infection (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions