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302: Scientific Basis of Medicine > Infection 3: Bacterial pathogenesis and infectious disease > Flashcards

Infection 3: Bacterial pathogenesis and infectious disease Flashcards

1
Q

Gram positive bacteria

A

Thick peptidoglycans layer

Lipoteichoic and teichoic acid

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2
Q

Gram negative bateria

A

Outer membrane

  • lipopolysaccharide
  • proteins and pores

Thin peptidoglycans

Inner membrane

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3
Q

Bacterial growth- atmosphere

A

Some are aerobes e.g. S. aureus
- use O2 as final electron acceptor

Some are anaerobes e.g. clostridium Spp

  • fermentation- yields final electron acceptor is organic molecules
  • ok when substrates are plentiful
  • oxygen usually toxic to anaerobic bacteria

Many are ‘facultative anaerobes’ e.g. E.coli
- can switch between aerobic and anaerobic metabolism

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4
Q

Bacterial growth on agar

A

Morphology, requirements etc
- used in diagnostic laboratory

Some terms used clinically e.g. in classification of Streptococci

Haemolytic streptococci
- alpha, beta and gamma

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5
Q

Alpha haemolytic streptococci

A

Cause partial haemolysis of blood agar and a greensih colour

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6
Q

Beta haemolytic streptococci

A

These cause complete haemolysis making the blood agar translucent

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7
Q

Commensal

A

Something which is probably not causing disease when identified from a clinical sample

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8
Q

Pathogen

A

Something which is probably causing disease when identified from a clinical sample

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9
Q

Gram positive cocci

A

Staphylococci

  • S. aureus
  • coagulase negative staphylococci

Streptococci

  • group A (S. pyogenes)
  • group B
  • group C and G
  • group D (enterococcus)
  • S. pneumoniae
  • viridans type

Peptococcus/ peptostreptococcus

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10
Q

Gram negative cocci

A

Neisseria

  • N. meningitidis
  • N. gonorrhoea

Moraxella ctarrhalis

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11
Q

Gram positive rodes (bacilli)

A

Bacillus

  • B. cerus
  • B athracis

Corynebacterium

Propionibacterium

Listeria monocytogens

Clostridium
- C. difficile

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12
Q

Gram negative rods

A

Haemophilus influenza

Enterobacteriaciae

  • salmonella and shigella
  • Eschericia coli
  • klebsiella and enterobacter
  • proteus

Pseudomonas
- P. aruginosa

Bacterioles
- B. fragilis

Vibrio cholerae

Bordatella pertussis

Legionella

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13
Q

Staphylococcus aureus

A

Commensal of nose (60%)

G+ve cocci in clusters

  • furunculosis
  • staph abscess
  • impetigo
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14
Q

Virulence of S.aureus: coagulase

A

Stimulates clotting

Role in immune evasion

Not expressed by less virulent ‘coagulase negative’ staphs

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15
Q

Virulence of S.aureus: adhesins

A

Bind host proteins

Tissue adherence

Colonisation

Deep infections

Immune evasion ‘cloaking’’

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16
Q

Virulence of S.aureus: protein A

A

An adhesin

Binds the Fc portion of IgG

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17
Q

Staphylococcal toxins

A

Cytotoxins

Exfoliative toxins

Enterotoxins

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18
Q

Cytotoxins

A

Pore forming toxins, lyse host cells

Panton- valentine leukocidin- lyses polymorphs

19
Q

Exfoliative toxins

A

Proteases

Target epidermal structural proteins

20
Q

Enterotoxins

A

Stimulate massive T cell activation

? Immune evasion

21
Q

Scalded skin syndrome

A

Ritter’s disease

Exfoliative toxins

Outbreaks in nurseries

  • ET+ve strains
  • no immunity

Local infection e.g. umbillicus

Distant bullae

Sheet like desquamation

22
Q

Toxic shock sydrome

A

Superangtigen exotoxins

  • rash
  • renal failure
  • septic shock
  • multiorgan failure
  • skin desquamation on recovery
23
Q

S.aureus food poisoning

A

S.aureus superantigen
- enterotoxins

Ingestion –>

  • rapid brief illness
  • vomiting
  • minimal diarrhoea
24
Q

S.aureus pneumonia

A

Rare except with influenza

  • impaired ciliary function
  • lost mucosal integrity
  • specific immunocompromise

Associated with panton valentine leukocidin

25
Q

S.aureus infections

A

Normal commensal

Pathogen in skin/ soft tissue infections

Vascular line related

Bactaraemia (endocarditis, osteoylelitis, septic arthritis)

Surgical site indections

Toxic mediated

26
Q

Coagulsae negative staphyloccocus

A

Gram positive cocci in clusters

Don’t make coagulase

  • less virulent
  • differentiated in the lab

Includes several species
- S. epidermidis most commonly

27
Q

S. epidermidis

A

Lives on the skin

Frequently contaminates blood culture

Central venous line sepsis

  • endocarditis (prosthetic valves)
  • orthopaedic surgical infections
  • foreign material in ‘sterile’ place
28
Q

Three ways to classify streptococci

A

Appearance on blood agar

Lancefield groups
- surface carbohydrate antigens

True species names

29
Q

Classification of streptococci by haemolysis

A

Alpha- partial (green colour)
- common commensals of the mouth

Beta- complete

Gamma- none

30
Q

Necrotising fasciitis

A

Caused by S.pyogenes of deep tissues

Production of tissue- destructive enzymes by organisms in stationary phase

  • pain out of proportion to physical signs
  • bruising and blistering
  • generalised toxaemia
  • renal impairment
  • very high inflammatory response
  • raised creatine kinase
31
Q

Superficial S.pyogenes infections

A

Pharyngitis

Cellulitis

32
Q

Deep S.pyogenes infections

A

Severe soft tissue infection

Myositis

Necrotising fasciitis

33
Q

Autoimmune sequelae of S.pyogenes infections

A

Rheumatic fever- a major cause of heart disease

Glomerulonephritis

34
Q

S.pyogenes exotoxins

A

Superantigens

Streptococcal inhibitor of complement

Haemolysins

DNAses

Hylauronidase

Streptokinase

35
Q

Streptococcal M protein

A

A major antigenic determinant of S.pyogenes
- immunity is type specific

A major virulence factor

  • binds serum factor H- regulator of complement activation
  • prevents opsonisation

Involved in pathogenicity

  • has an alpha helical ‘coiled coil’ protein
  • molecular mimicry
36
Q

Molecular mimicry and autoimmune sequelae

A

M protein- alpha helical coiled coil structure

Homology with

  • cardiac myosin
  • glomerular basement membrane

Recurrent childhood infection associated with cross reactive anti-self responses

Rheumatic fever

Post streptococcal glomerulonephritis

37
Q

Enterobacteriaciae

A

Commensals of the gut

Not enterococcus

GNRs including

  • klebsiella
  • enterobacter
  • citrobacter

Opportunistic infections where organisms gain access to sterile sites

Specific syndrome of infections associated with specific virulence mechanisms

38
Q

E.coli

A

Hugely diverse species

Hundreds of serotypes

Cell wall ‘O’ flagella ‘H’ and capsular ‘K’ antigens

Three major human diseases

  • UTI
  • enteric
  • meningitis

Four main virulence mechanisms

39
Q

E.coli adhesins

A

P fimbria

  • P= RBC P antigen
  • also binds uroepithelial antigen
  • also known as pylenonephritis associated adhesin

Non-fimral GI adhesins
- diarrhoeal diseases EPEC, EIEC

40
Q

E.coli siderophores

A

Iron chelation

41
Q

E.coli capsule

A

K1 capsular serotype

Protects from complement mediated responses

Important early in life

42
Q

E.coli exotoxins

A

Cytolysins (like gram positive streptolysins)

Enterotoxins (upper GI food poisoning) ETEC

Verotoxins

  • associated with haemolytic uraemic syndrome
  • enterohaemorrhagic E.coli (EHEC)
43
Q

E.coli disease

A

Commonest cause of urosepsis

Major contributor to GI related biliary sepsis

Major cause of nosocomial infections

  • wounds
  • devices
  • pneumonia

Commonest pathogen grown in blood

302: Scientific Basis of Medicine (18 decks)

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