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302: Scientific basis of medicine > Bacterial pathogenesis and infectious disease > Flashcards

Bacterial pathogenesis and infectious disease Flashcards

1
Q

Gram staining

A

Form of staining that identifies if bacteria has peptidoglycan in their cell wall.

Positive= Purple= has it
Negative= pink= does not have

Some bacteria do not stain well

  • Mycobateria
  • Mycoplasma
  • Chlamydia
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2
Q

Bacterial shapes

A

Cocci

  • Spherical
  • Examples: staphylococcus, streptococcus

Rods/ Bacilli
- Examples: E.coli, Neisseria

Spirals

Vibrio

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3
Q

Aerobe bacteria

A

Use O2 as a final electron acceptor (aerobic respiration)

Example:
- S.aureus

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4
Q

Anaerobe (obligate) bacteria

A

In respiration, organic molecule is final electron acceptor.

Example
- Clostridium

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5
Q

Facultative anaerobic bacteria

A

Bacteria that has the ability to switch between aerobic and anaerobic metabolism

Example
- E coli.

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6
Q

Haemolytic streptococci classification

A

Alpha haemolytic (veridans_

  • Cause partial haemolysis of blood agar
  • Greenish colour

Beta- haemolytic

  • Causes complete haemolysis
  • Translucent agar

Gamma-Haemolytic

  • No haemolysis
  • Blood agar stays brown
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7
Q

Factors that affect the pathogenicity of a bacteria

A

The immune status of the patient

The site of the infection.

The virulence of the bacteria.

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8
Q

Examples of gram positive cocci

A

S. Aureus
Coagulase negative Staphylococcus

Streptococci

  • Group A (S.pyogenes), B, C, G
  • D= enterococcus
  • S. pneumoniae
  • Viridians

Peptococus/ Peptostreptococcus

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9
Q

Exams of gram positive rods

A

B. cerus

B.anthracis

Corynebacterium

Listeria monocytogenes

Clostridium

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10
Q

Gram negative cocci

A

Neisseria

  • N. meningitidis
  • N gonorrhoea

Moraxella catarrhalis

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11
Q

Gram negative rods

A

Haemophilius influenzae

Enterobacteriaciae

  • Salmonella and Shigella
  • E.Coli
  • Klebsiella
  • Enterobacter
  • Proteus

Pseudomonas

Bacteroides

Campylobacter

Helicobacter

Vibrio cholerae

Bordetella pertussis

Legionella

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12
Q

Secretory proteins from S.aureus

A

Superantigens

  • TSST-1
  • SEA
  • SEB

Exfoliative toxins

  • Proteases
  • Target epidermal proteins

Cytolysins

  • Alpha-toxins
  • PVL
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13
Q

Surface proteins from S.aureus that increase its virulence

A

Coagulase
-Stimulates clotting allowing immune invasion

Protein A

  • Binds to Fc portion of IgG
  • immune cloaking

Adhesins: Allow tissue adherence and colonisation. Mechanism in deep infections, allows immune cloaking

  • Elastin binding protein
  • Collagen binding protein
  • Fibronectin binding protein
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14
Q

Staphylcoccal toxins

A

Cytotoxins
- Pore forming toxins

Example
- Panton-valentine leukocidin (PVL) lyses polymorphs (associated with MRSA in USA)

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15
Q

Enterotoxins

A

Superantigens
- Targets the gut
- Causes
diarrhoea

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16
Q

Scalded skin syndrome

A

Also known as Ritter’s disease

Exfoliative toxin A,B
- Serine protease for desmoglein 1

17
Q

Toxic shock syndrome

A

Caused by release of super antigen TSST

Signs and symptoms

  • Characteristic rash
  • High fever
  • Hypotension–> septic shock
  • Multiorgan failure
18
Q

S.aureus food poisoning

A

Cause by enterotoxins

Ingestion causes violent vomiting

19
Q

S. aureus bacteremia

A

Causes

  • Endocarditis
  • Osteromyelitis
  • Septic arthritis
20
Q

Coagulase negative staphylococcus

A

Less virus Staph

Commonly infects central venous line infections

  • Endocarditis
  • Orthopaedic surgical
  • Graft, implants

Example
- S.epidermis

21
Q

Examples of alpha haemolyin strep

A

S. milleri

S. mites

S. sangria

S.pneumoniae

22
Q

E.coli virulence

A

Adhesins

Siderophores

Capsule

Toxins

  • Endotoxin
  • Exotoxins (entero, vero)
23
Q

E coli adhesins

A

P fimbria

  • Binds to RBC p antigen
  • Also binds to uroepithelial antigen
  • Associated with pyelonephritis

Non fimbral GI adhesins

  • EPEC (enteropathogenic)
  • EIEC (enteroinvasive)
24
Q

Siderophores

A

Enterobactin
- Iron chelator

Allows servival in environments with low Fe3+

25
Q

E coli capsule

A

Protect E coli from complement mediated response

K1 capsular serotype associated with neonatal meningitis

26
Q

E coli toxins

A

Endotoxins

Cytolysin

Enterotoxins
- Causes fluid leak in GI tract (diarrhoea)

Verotoxins

  • Disrupts ribosomal protein synthesis= haemorrhage diarrhoea (Enterohaemorrhagic E coli)
  • Associated with haemolytic uraemia syndrome
27
Q

E coli disease

A

Commonest cause of UTI/ urosepsis

GI and biliary sepsis

Nosocomial (Hospital acquired) infection

  • Wounds
  • Devices
  • Pneumonia
28
Q

Lancefield groups

A

Classification of Strep via surface antigens
- Carbohydrate antigens

Groups A,B, C etc

29
Q

Examples of beta-haemolytic strep

A

Lancefield groups A-C, G.

S. pyogenes (Group A)
S. dysgalactidae (Group G)
S. equi (Group C)
S. agalactidae (Group B)

30
Q

S pyogenes exotoxins[4]

A

Superantigen (SpeA, SpeC)
- Causes toxic shock like syndrome.
Causes rash and fever through overstimulation of T cell response.

Hyaluronidase
- Breaks down hyaluronic acid, which facilitates spread by destroying cohesiveness of connective tissue.

Streptokinase
- Activates plasminogen into plasmin which breaks down fibrin and prevents blood clotting

Streptolysin
- Causes complete lysis of red blood cells.

31
Q

M protein

A

Endotoxin on S. pyogenes
- alpha helical coiled coil structure
Binds to serum factor H, preventing opsonization

32
Q

C5a peptidase

A

Endotoxin on S pyogenes

- Inhibits cleaving of C5a= less chemotaxis of neutrophils

33
Q

Molecular mimicry of strep infections

A

M protein is homologous with cardiac myosin/ trophomyosin and glomerular basement membrane proteins.

Strep infection can lead to cross-reactive anti-self responses

Leads to post-strep

  • Rheumatic fever
  • Glomerulonephritis
  • Guillain Barre
  • HLA B27 spondyloarthropathies.

302: Scientific basis of medicine (28 decks)

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