Bacterial pathogenesis and infectious disease

Question 1

Gram staining

Answer 1

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

Question 2

Bacterial shapes

Answer 2

Cocci

• Spherical
• Examples: staphylococcus, streptococcus

Rods/ Bacilli
- Examples: E.coli, Neisseria

Spirals

Vibrio

Question 3

Aerobe bacteria

Answer 3

Use O2 as a final electron acceptor (aerobic respiration)

Example:
- S.aureus

Question 4

Anaerobe (obligate) bacteria

Answer 4

In respiration, organic molecule is final electron acceptor.

Example
- Clostridium

Question 5

Facultative anaerobic bacteria

Answer 5

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

Example
- E coli.

Question 6

Haemolytic streptococci classification

Answer 6

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

Question 7

Factors that affect the pathogenicity of a bacteria

Answer 7

The immune status of the patient

The site of the infection.

The virulence of the bacteria.

Question 8

Examples of gram positive cocci

Answer 8

S. Aureus
Coagulase negative Staphylococcus

Streptococci

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

Peptococus/ Peptostreptococcus

Question 9

Exams of gram positive rods

Answer 9

B. cerus

B.anthracis

Corynebacterium

Listeria monocytogenes

Clostridium

Question 10

Gram negative cocci

Answer 10

Neisseria

• N. meningitidis
• N gonorrhoea

Moraxella catarrhalis

Question 11

Gram negative rods

Answer 11

Haemophilius influenzae

Enterobacteriaciae

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

Pseudomonas

Bacteroides

Campylobacter

Helicobacter

Vibrio cholerae

Bordetella pertussis

Legionella

Question 12

Secretory proteins from S.aureus

Answer 12

Superantigens

• TSST-1
• SEA
• SEB

Exfoliative toxins

• Proteases
• Target epidermal proteins

Cytolysins

• Alpha-toxins
• PVL

Question 13

Surface proteins from S.aureus that increase its virulence

Answer 13

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

Question 14

Staphylcoccal toxins

Answer 14

Cytotoxins
- Pore forming toxins

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

Question 15

Enterotoxins

Answer 15

Superantigens
- Targets the gut
- Causes
diarrhoea

Question 16

Scalded skin syndrome

Answer 16

Also known as Ritter’s disease

Exfoliative toxin A,B
- Serine protease for desmoglein 1

Question 17

Toxic shock syndrome

Answer 17

Caused by release of super antigen TSST

Signs and symptoms

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

Question 18

S.aureus food poisoning

Answer 18

Cause by enterotoxins

Ingestion causes violent vomiting

Question 19

S. aureus bacteremia

Answer 19

Causes

• Endocarditis
• Osteromyelitis
• Septic arthritis

Question 20

Coagulase negative staphylococcus

Answer 20

Less virus Staph

Commonly infects central venous line infections

• Endocarditis
• Orthopaedic surgical
• Graft, implants

Example
- S.epidermis

Question 21

Examples of alpha haemolyin strep

Answer 21

S. milleri

S. mites

S. sangria

S.pneumoniae

Question 22

E.coli virulence

Answer 22

Adhesins

Siderophores

Capsule

Toxins

• Endotoxin
• Exotoxins (entero, vero)

Question 23

E coli adhesins

Answer 23

P fimbria

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

Non fimbral GI adhesins

• EPEC (enteropathogenic)
• EIEC (enteroinvasive)

Question 24

Siderophores

Answer 24

Enterobactin
- Iron chelator

Allows servival in environments with low Fe3+

Question 25

E coli capsule

Answer 25

Protect E coli from complement mediated response K1 capsular serotype associated with neonatal meningitis

Question 26

E coli toxins

Answer 26

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

Question 27

E coli disease

Answer 27

Commonest cause of UTI/ urosepsis GI and biliary sepsis Nosocomial (Hospital acquired) infection - Wounds - Devices - Pneumonia

Question 28

Lancefield groups

Answer 28

Classification of Strep via surface antigens - Carbohydrate antigens Groups A,B, C etc

Question 29

Examples of beta-haemolytic strep

Answer 29

Lancefield groups A-C, G. S. pyogenes (Group A) S. dysgalactidae (Group G) S. equi (Group C) S. agalactidae (Group B)

Question 30

S pyogenes exotoxins[4]

Answer 30

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.

Question 31

M protein

Answer 31

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

Question 32

C5a peptidase

Answer 32

Endotoxin on S pyogenes | - Inhibits cleaving of C5a= less chemotaxis of neutrophils

Question 33

Molecular mimicry of strep infections

Answer 33

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.