Theme 4 - professional pathogens

Question 1

what is the definition of infection?

Answer 1

when an organism enters the body, increases in number and damages the host in the process

Question 2

What is the definition of colonisation?

Answer 2

organism is present but doesn’t cause infection (may precede infection and amount an immune response)

Question 3

what is the definition of a pathogen?

Answer 3

an organism that evades immune defences of a normal human host to cause infection

Question 4

what step may precede infection?

Answer 4

colonisation

Question 5

what is the definition of a commensal?

Answer 5

lives on us but doesn’t cause infection

Question 6

what is symbiosis

Answer 6

mutual benefit

Question 7

what is a parasite

Answer 7

unequal benefit - advantage to the micro-organism over the host

Question 8

how often do professional pathogens cause disease?

Answer 8

almost always

Question 9

how often do opportunistic pathogens cause disease?

Answer 9

only in specific situations eg in immunocompromised patients

Question 10

what type of pathogen can commensals potentially be?

Answer 10

opportunistic

Question 11

why do some organisms cause infections and others dont?

Answer 11

because they vary in virulence

Question 12

what is virulence?

Answer 12

the fundamental property of an organism

Question 13

what sits at either end of the spectrum of pathogenicity?

Answer 13

commensal and pathogen

Question 14

name two commensal organisms

Answer 14

lactobacillus case and propionibacterium acnes

Question 15

name two organisms in between commensal and pathogen on the spectrum of pathogenicity

Answer 15

Candida albicans and staphylococcus epidermis

Question 16

name three organisms at the pathogenic end of the spectrum of pathogenicity

Answer 16

staph aureus, malaria, HIV, neisseria meningitidis and strep pneumoniae

Question 17

in what situation can organisms with low virulence be pathogens?

Answer 17

in immunocompromised patients

Question 18

what is pathogenicity?

Answer 18

the probability that an organism is causing disease when its isolated from a patient

Question 19

what determines pathogenicity?

Answer 19

the virulence of the organism and the immune state of the patient

Question 20

what three factors determine whether a pathogen from a patient is pathogenic or commensal?

Answer 20

the immune status of the patient, the site the sample was taken from (is it sterile) and the virulence of the organism

Question 21

what are four key features of staph aureus

Answer 21

commensal of the anterior nares, form golden colonies on agar, gram positive cocci they associate in clusters, very virulent

Question 22

what three features make staph aureus very virulent?

Answer 22

its surface proteins (adhesins), secreted proteins (toxins) and polysaccharide coat (capsule)

Question 23

what can allow staph aureus to be distinguished from other less virulent staphs?

Answer 23

the specific adhesins and excretions that allow the disease to manifest

Question 24

what three features make staph aureus unique?

Answer 24

adhesins that bind to host proteins, cloaking and protein A

Question 25

what do adhesins on staph aureus do?

Answer 25

bind host proteins

Question 26

what is cloaking?

Answer 26

when an organism (eg staph aureus) coats itself in host proteins to evade the immune system

Question 27

what does protein A on staph aureus cell surface do?

Answer 27

binds the fc portion of IgG (wrong way round) and therefore coats itself in the Ig to allow immune escape

Question 28

what test can be used diagnostically for staph aureus?

Answer 28

coagulase test

Question 29

how and why does the coagulase test for staph aureus work?

Answer 29

staph aureus has coagulase enzyme on its cell surface so will coagulate sheep serum

Question 30

what is the purpose of the coagulase enzyme on staph aureus cell surface?

Answer 30

is a virulence factor - stimulates blood clotting around an infection to stop WBC getting there are clearing it

Question 31

what type of staph are coagulase negative?

Answer 31

staph epidermis

Question 32

what are three key staphylococcal toxins?

Answer 32

cytotoxins, exfoliative toxins and enterotoxins

Question 33

how do staph cytotoxins cause damage?

Answer 33

form pores in the cell membrane and lyse host cells (PVL blows up macrophages)

Question 34

how do staph exfoliative toxins work?

Answer 34

degrade connective tissue in the skin - target epidermal structures so skin falls off (proteases)

Question 35

how do staph enterotoxins work?

Answer 35

aka superantigens. stimulate T cells and confuse the immune system

Question 36

where are many staph toxins encoded?

Answer 36

on mobile genetic elements - can move between strains and are only present on a proportion of strains

Question 37

what feature of staph aureus allows it to evade the immune system (opsonisation)

Answer 37

the thin polysaccharide capsule - covers surface antigens tthat antibodies normally bind to (eg peptidoglycan)

Question 38

name three staph aureus skin infections

Answer 38

furunculosis, staph abscess and impetigo

Question 39

what is the most common type of staph aureus infection?

Answer 39

line sepsis

Question 40

what type of toxins produced by staph aureus cause impetigo?

Answer 40

exfoliative toxins

Question 41

what is the most common cause of staph aureus infection?

Answer 41

bacteraemia (bacteria in the blood) - causes endocarditis, osteomyelitis and septic arthritis

Question 42

name three common sites of staph aureus infection

Answer 42

skin/soft tissue, surgical site, vascular line, blood

Question 43

is staph aureus usually commensal?

Answer 43

yes (in anterior nares)

Question 44

what happens in staph aureus food poisoning?

Answer 44

rapid brief illness, lots of vomiting and a little diarrhoea (caused by enterotoxins)

Question 45

name four ways that staph aureus demonstrates its virulence

Answer 45

adherence to nasal mucosa (adhesins), invasion of tissues (cytotoxins and enzymes), evades immune clearance (protein A and capsule), replicates and disseminates

Question 46

how does staph aureus gram stain?

Answer 46

gram positive- purple

Question 47

what additional mechanism of virulence do gram negative bacteria have?

Answer 47

lipopolysaccharide

Question 48

how sensitive is the immune system to lipopolysaccharide?

Answer 48

very - allows early detection of infection and can recognise it rapidly at very low concentrations

Question 49

what type of receptors does LPS interact with?

Answer 49

toll like receptors - especially TLR4 on monocytes and in the endothelium

Question 50

what is the result of interaction between LPS and TLRs?

Answer 50

activation of inflammatory pathways, coagulation and clotting pathways, changes in endothelial integrity

Question 51

why do people get so sick with gram negative infections?

Answer 51

due to the release of LPS (endotoxin) in the blood - causes systemic activation of immune responses

Question 52

is LPS endogenous or exogenous in bacteria?

Answer 52

endogenous

Question 53

do gram positive bacteria have LPS?

Answer 53

no - they have lipoteichoic acid and peptidoglycan that stimulate different TLRs to gram negative bacteria

Question 54

what organism causes meningococcal septicaemia?

Answer 54

neisseria meningitidis

Question 55

name two key features that contribute to the pathogenicity of neisseria meningitidis in meningococcal septicaemia

Answer 55

the pathogen has adhesins the stick to the throat, resp epithelium and meninges, it sheds LPS off the surface and into the surroundings (blebbing)

Question 56

what does blood stained sputum indicate?

Answer 56

pneumococcal pneumonia

Question 57

what type of bacteria causes pneumococcal pneumonia?

Answer 57

gram positive diplococci - pneumococcus

Question 58

what are the symptoms of pneumococcal pneumonia?

Answer 58

cough, breathlessness, consolidated lung (pus filled), haemoptysis (blood stained sputum) - can cause disseminated disease

Question 59

name four factors that contribute to streptococcus pneumoniae virulence

Answer 59

specific adhesins for the respiratory mucosa, pneumolysin, secretion of IgA protease (and other toxins), capsule, LPS, lipotechoic acid and peptidoglycan

Question 60

how does pneumolysin convey virulence in streptococcus pneumoniae

Answer 60

binds cholestrol on host cell membrane, forms pores and lyses ciliated cells, lyses phagocytic cells

Question 61

how does IgA protease convey virulence in streptococcus pneumoniae

Answer 61

breaks down secreted IgA to prevent mucosal clearance

Question 62

how does the bacterial capsule convey virulence in streptococcus pneumoniae

Answer 62

prevents complement mediated phagocytosis (need specific antibodies to target it)

Question 63

how many different types of capsule are there in strep pneumoniae?

Answer 63

>100 types

Question 64

where can strep pneumoniae disseminate to?

Answer 64

blood, heart valves (endocarditis), upper respiratory tract (sinusitis, Otis media) and meninges (meningitis)

Question 65

name four key features of clostridium difficle

Answer 65

gram postive rods, anaerobic, spore forming and cause wound/GI infections

Question 66

name three types of c difficile

Answer 66

c. tetani, c. botulinum and c welchii

Question 67

what aspect of c difficile makes it easy to spread between hospital patients?

Answer 67

it is spore forming so is resistant to drying, alcohol and antibiotics

Question 68

where are c difficile spores found?

Answer 68

in soil and in the gut of humans and animals

Question 69

what is one of the main symptoms of c difficile?

Answer 69

diarrhoea - can be mild or severe but may lead to gut perforation and death

Question 70

what infection is severe pseudomembranous colitis a symptom of?

Answer 70

clostridium difficile

Question 71

what two key things contribute to c difficile pathogenicity?

Answer 71

production of toxins that cause fluid secretion into the gut (diarrhoea and increased infectivity) and spore production (difficult to control and easy to relapse on treatment)

Question 72

what happens in some virulent strains (027) of c difficile

Answer 72

loss of regulation and hyper production of toxic genes, production of additional toxins