microbiology how bacteria cause disease

Question 1

define pathogen

Answer 1

an organism that is capable of causing the host damage or disease

Question 2

define opportunistic pathogen

Answer 2

an organism that is a member of the resident microbiota or normally inhabiting the external environment that causes infection under certain circumstances

Question 3

define symbiont

Answer 3

a member of the resident microbiota that confers benefit to the host

Question 4

define pathobiont

Answer 4

a member of the resident microbiota which confers damage to the host

Question 5

define dysbiosis

Answer 5

imbalances in the resident human microbiota or our responses to them

Question 6

describe pathogenicity

Answer 6

the degree of virulence of a microbe to cause damage in the host

Question 7

define virulence

Answer 7

relative capacity of the organism to cause damage in the host

Question 8

define virulence determinant factor

Answer 8

component of the pathogen that damages the host

Question 9

define lethal dose

Answer 9

LD50 is the number of pathogens required to kill 50% of the host

Question 10

what is the major steps of virulence mechanisms

Answer 10

• Transmission
• Adherence to host surfaces
• Invasiveness
Toxigenicity

Question 11

describe transmission

Answer 11

infections can be acquired by an internal or external sources 
eg ingestion 
inhalation 
trauma 
needle stick
sexual transmission

Question 12

what are the four portals of entry for transmission

Answer 12

skin
resp tract
GU tract
GI tract

Question 13

describe adherence to host surfaces

Answer 13

some fungi and bacteria produce substances that help with adherence
critical for colonisation

Question 14

give examples of bacteria requiring adherence to host surfaces

Answer 14

N gonorrhoea and E coli with pili

S mutans- Extracellular polysaccharide layer helps it adhere

Question 15

what is quorum sensing

Answer 15

molecules(homoserine lactone) are secreted by bacteria in biofilm
It is a cell-cell communication which allows bacteria to share information about cell density and adjust gene expression accordingly
May lead to reduction in metabolic activity or other genes being expressed

Question 16

describe invasiveness

Answer 16

It is important and depends on bacterial enzymes
Eg collagenase and hyaluronidase
Allows for the breakdown of intercellular structures and allows for bacteria to enter straight easily though tissues

Question 17

where is hyaluronidase present

Answer 17

in S aureus and S pyogenes

Question 18

where is collagenase present

Answer 18

present in clostridium perfringens

Question 19

what does a clot inhibit

Answer 19

phagocytosis and immune responsee has no access

Question 20

how do coagulase and kinase work together

Answer 20

→ The bacteria produce coagulase
→ The clot forms inhibits phagocytosis, immune response has no access, antibiotics are not effective
The bacteria later produce kinase which dissolves the clot and releases bacteria

Question 21

describe immunoglobulin protease

Answer 21

degrades IgA on mucosal surface and allows bacteria to adhere

Question 22

what are leukocidins

Answer 22

they can destroy immune host cells such as neutrophilic leukocytes and macrophages

Question 23

describe toxigenicity

Answer 23

two types of toxic
endotoxins
exotoxins

Question 24

what are endotoxins

Answer 24

are the lipid portions of the LPS that are part of the outer cell wall of the gram -ve bacteria

Question 25

what are the biological effects of endotoxins

Answer 25

→ Fever- release of IL-1 from macrophages → Hypotension, shock and perfusion of major organs- due to vasodilation → Inflammation → Tissue ischaemia → Increased phagocytic activity of macrophages Increased antibody production

Question 26

why do the biological effects of endotoxins occur

Answer 26

due to the host factors producing IL-1 and TNF from macrophages

Question 27

what can occur in +ve bacteria

Answer 27

endotoxin like effects- occur from trichroic acid or peptidoglycan which can release TNF and iL-1

Question 28

describe exotoxins

Answer 28

Produced by both gram +ve and gram -ve bacteria Mostly by gram +ve though Secreted and released into the environment via lysis

Question 29

give examples of neurotoxins

Answer 29

Tetanus, diphtheria and botulinum toxins are neurotoxins

Question 30

how do exotoxins cause disease

Answer 30

they can cause disease to a distant part of the body due to the exotoxin diffusing

Question 31

what does the tetanus toxin cause

Answer 31

locked jaw or masseter muscle spasm

Question 32

what does tentanospasmin cause muscle spasms

Answer 32

prevented the release of inhibitory neurotransmitter glycine which causes muscle spasms

Question 33

describe the botulinum toxin

Answer 33

one of the most toxic compounds

Question 34

how does the botulinum toxin work

Answer 34

The toxin blocks the release of acetylcholine at the synapse and leads to paralysis of the muscles ○ It is an obligate anaerobe and endospore former( may transform into a spore in harsh environments to protect itself)

Question 35

what are the symptoms of botulism

Answer 35

``` → 1-2 days after ingestion → Descending motor loss with flaccid paralysis → Diplopia → Dysphagia → Speech problems → Dry mouth → Resp failure → Death ```

Question 36

what is the bacterium that causes cholera and its endotoxin

Answer 36

vibrio cholerae | endotoxin is enterotoxin

Question 37

what is the bacterium that causes diphtheria

Answer 37

corynebacterium diphtheriae

Question 38

what is the bacterium that causes diarrhoea, pseudomembranous colitis

Answer 38

c difficile

Question 39

what is the bacterium that causes haemorrhage colitis and its endotoxin

Answer 39

e coli O157 | endotoxin is verotoxin

Question 40

what is the bacterium that causes whooping cough and its endotoxin

Answer 40

bordetella pertussis | pertussis toxin

Question 41

what is the bacterium that causes scarlet fever

Answer 41

strep pyogenes | exotoxins

Question 42

what is the bacterium that causes scaled skin syndrome and the endotoxin

Answer 42

s aureus | endotoxin - epidermolysin

Question 43

what are bacterial virulence factors

Answer 43

``` adhesin invasin impedin modulin aggresin ```

Question 44

what is adhesin

Answer 44

enables binding to host tissue

Question 45

what is invasin

Answer 45

enables invasion of host cell/tissue

Question 46

what is impedin

Answer 46

enables avoidance of host defence mechanism(s)

Question 47

what is aggresin

Answer 47

causes direct damage to host

Question 48

what is modulin

Answer 48

induces indirect damage by perturbing regulation of host defences