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302 Scientific basis of medicine > Infection 3) Bacterial pathogenesis > Flashcards

Infection 3) Bacterial pathogenesis Flashcards

1
Q

Describe the envelope structure of gram positive bacteria

A

Thick peptidoglycan layer

Lipoteichoic and trichroic acid

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2
Q

Describe the envelope structure of gram negative bacteria

A

Outer membrane of lipopolysaccharide, proteins and pores
Thin peptidoglycans
Inner membrane

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3
Q

Give an example of bacteria that need an aerobic environment

A

Staph.aureus

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4
Q

Give an example of a bacteria that needs an anaerobic environment

A

Clostridium species

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5
Q

Give an example of a facultative anaerobe bacteria

A

E.coli

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6
Q

What is a facultative anaerobe bacteria?

A

Bacteria that can switch between aerobic and anaerobic metabolsim

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7
Q

Describe the consequence of alpha haemolytic streptococci on agar

A

Cause partial haemolytic of blood agar and produce a greenish colour

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8
Q

Describe the consequence of beta haemolytic streptococci on agar

A

Complete haemolysis so agar becomes transparent

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9
Q

What is serological typing?

A

Type of cell-surface antigens present, antibodies to expressed antigens

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10
Q

What is genotyping

A

Genes encoding those antigens

Replacing serotyping

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11
Q

What is a commensal?

A

Something which is probably not causing disease when identified from clinical sample
Living in a relationship in which one organism derives food or other benefits from another organism without hurting or helping it

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12
Q

What is a pathogen?

A

Something that causes disease

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13
Q

What 3 things determine an organism’s pathogenicity?

A

Organism’s virulence
Site
Immune state of patient

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14
Q

Describe the 2 types of site

A

Sterile - blood and urine

Unsterile - stool and throat

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15
Q

Give examples of gram positive cocci

A 
Staphylococci
 - s.aureus
 - coagulase negative staphylococci 
Streptococci
 - group A streptococcus (S.pyogenes)
 - group B, C, G
 - group D (enterococcus)
 - S.pneumoniae
 - viridans type streptococci
Peptococcus / peptostreptococcus
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16
Q

Give examples of gram positive rods (bacilli)

A 
Bacillus e.g. B.cerus and B.anthracis
Corynebacterium
Propionibacterium
Listeria monocytogenes
Clostridium e.g. C.difficle
17
Q

Give examples of gram negative cocci

A

Neisseria
- n.meningitis
- N.gonorrhoea
Moraxella (branhamella) catarrhalis

18
Q

Give examples of gram negative rods

A 
Haemphilus influenza
Enterobacteriaceae
 - salmonella and shigella
 - eschericia coli
 - klebsiella and enterobacter
 - proteus
Pseudomonoas e.g. P.aeruginosa
Bacteroides e.g. B.fragilis
Campylobacter and helicobacter
Vibrio cholera
Bordatella pertussis
Legionella
19
Q

What infections does S.aureus cause?

A

Furunculosis
Staph abscess
Impetigo
Sepsis - line, splenic abscess, lung abscess
Toxin mediated - toxic shock, scalded skin, food poisoning
Bacteraemia - endocarditis, osteomyelitis, septic arthritis

20
Q

Describe S.aureus virulence

A

Coagulase enzyme
Adhesions
Protein A
Toxins

21
Q

What toxins does S.aureus have?

A

Cytotoxins
Exfoliative toxins
Enterotoxins

22
Q

What cytotoxin does S.aureus have?

A

PVL (pantun-valentine leukocidin)

23
Q

Describe scalded skin syndrome

A 
Exfoliative toxins
Outbreaks in nurseries
Local infection
Distant bullae
Sheet-like desquamation
24
Q

Why is coagulase negative staphylococci less virulent?

A

Doesn’t make coagulase

25
Q

Give examples of alpha haemolytic streptococci

A

S.milleri
S.mitis
S.anguis
S.pneumoniae

26
Q

Give examples of beta haemolytic streptococci

A

S.pyogenes

S.equi, S.canis

27
Q

What superficial infections can streptococci cause?

A

Pharyngitis

Cellulitis

28
Q

What deep infections can streptococci cause?

A

Severe soft tissue infection
Myositis
Necrotising fasciitis

29
Q

Describe the clinical signs of necrotising fasciitis

A 
Pain out of proportion to physical signs
Bruising and blistering
Generalised toxaemia
Renal impairment
Very high inflammatory response (CRP)
Raised creatine kinase
30
Q

Describe the structure and virulence of streptococci

A 
Fibronectin-binding proteins
Collagen binding proteins
C5a peptidase
M protein
Capsule, wall, membrane
Exotoxins
31
Q

What is M protein?

A

Major antigenic determinant of S.pyogenes
Binds serum factor H to prevent opsonisation
Alpha-helical coiled coil protein

32
Q

What is molecular mimicry?

A

Structural similarity of microbial antigenic determinant and host proteins resulting in cross creativity of antibody and T-cell responses to microbial antigens with self antigens

33
Q

What exotoxins does streptococci produce?

A 
Superantigens
Streptococcal inhibitor of complement
Haemolysis
DNAses
Hyaluronidase
Streptokinase
34
Q

Give examples of non-bacterial pathogens

A

Fungal organisms
Yeasts, moulds, dimorphic fungi
Candida species
Aspergillus species

35
Q

What infections can enterobacter cause?

A 
Klebsiella
Enterobacter
Citrobacter
Wound infections, biliary infections
Hospital acquired pneumonia
Meningitis
36
Q

What are the 4 main virulence mechanisms of E.coli?

A

Adhesions
Siderophores
Capsule
Toxins

37
Q

Describe the adhesions of E.coli

A

P fimbria - binds uroepithelial antigens

Non-fimbral GI adhesions causing diarrhoeal diseases

38
Q

Describe the siderophores of E.coli

A

Enterobactin

Powerful iron chelators

39
Q

Describe the toxins produced by E.coli

A

Endotoxin
Exotoxin
Verotoxins

302 Scientific basis of medicine (28 decks)

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