Lecture 3: Professional Pathogens

Question 1

which factors influence whether or not a pathogen will cause disease

Answer 1

• pathogenicity (virulence of the pathogen)

- immunological status of the patient

Question 2

what is staphylococcus aureus

Answer 2

• normal commensal of the nose

Question 3

is staph aureus gram positive or negative

Answer 3

gram positive and forms clusters down the microscope and golden colonies on agar

Question 4

which factors determine staph aureus’s virulence

Answer 4

• adhesins
• protein exotoxins
• coagulase
• capsule

Question 5

describe staph aureus adhesins

Answer 5

• has Protein A adhesin on surface, which binds to immunoglobin
• S. aureus coats itself in immunoglobulin, evading the immune response
• allows S. aureus to seed and spread to distant body sites eg heart valves, bones and joints

Question 6

describe staph aureus exotoxins

Answer 6

• cytotoxins eg Panton-Valentine leukocidin which lyses white blood cells
• exfoliative enzymes which act as proteases, degrading proteins in superficial skin causing it to fall off
• enterotoxins which have affect if eaten
• many encoded on mobile genetic elements so only present on a few strains

Question 7

describe staph aureus coagulase

Answer 7

• cell wall bound enzyme

- stimulates clotting, so used as a test to determine the virulent S. aureus

Question 8

describe staph aureus capsule

Answer 8

• polysaccharide microcapsule

- thinner than other bacterial capsules, helps avoid phagocytosis by neutrophils

Question 9

what does staph aureus cause

Answer 9

skin conditions
- furunculosis
- staphylococcal abscess
- impetigo
can cause food poisoning if eaten, due to enterotoxins

Question 10

which sorts of patients are susceptible to S. aureus infections

Answer 10

patients that need vascular access devices, such as for cancer treatment

Question 11

how does a Gram negative bacterial cell wall differ to a Gram positive one

Answer 11

• thinner peptidoglycan layer

- have outer lipid membrane with lipopolysaccharides

Question 12

how does the immune system respond to lipopolysaccharides

Answer 12

• LPS interacts with toll-like receptors, especially TLR 4 on macrophages and vascular endothelium
• results in activation of inflammatory pathways, coagulation pathways and makes blood vessels more leaky

Question 13

what are Gram negative bacteria predominantly found in

Answer 13

bites and contaminated wounds

Question 14

what is the cliniical manifestation of systemic immune response

Answer 14

sepsis

Question 15

which cell wall components on Gram positive bacteria activate an immune response

Answer 15

• peptidoglycan

- lipoteichoic acid

Question 16

features of meningococcus

Answer 16

• N. meningitidis causes meningococcal rash (which will not blanch when a glass is pressed over it)
• Gram negative
• has adhesins for respiratory epithelium and meninges
• very big thick capsule
• “blebs”: sheds lipopolysaccharide into surroundings

Question 17

features of streptococcus pneumonia

Answer 17

• gram positive
• has adhesins for respiratory mucosa
• produces pneumolysin
• secretes IgA protease, which prevents mucus clearance
• has a capsule so the immune system has to develop specific antibodies
• can disseminate in the blood, ends up on heart valves –> endocarditis and meninges –> meningitis

Question 18

what does pneumolysin do

Answer 18

• is cytotoxic
• binds to host cell membrane cholesterol
• forms pores and lyses in ciliated cells
• lyses host’s phagocytic cells