How Bacteria Cause Disease

Question 1

define pathogen

Answer 1

a microbe capable of causing host damage and disease

Question 2

what is a opportunist pathogen?

Answer 2

an organism that is a member of the resident microbiota, which can cause infection under certain circumstance

Question 3

what is a symbiont?

Answer 3

a member of the resident microbiota which benefits and receives benefit to the host

Question 4

what is dysbiosis?

Answer 4

an imbalance in the resident microbiota

Question 5

what is a pathobiont?

Answer 5

a member of the resident microbiota that causes disease when the normal balance is lost between host and microbiota

Question 6

define pathogenicity.

Answer 6

the capacity of a microbe to cause damage to a host

Question 7

define virulence.

Answer 7

the relative capacity of an organism to cause damage to a host e.g. fatality rate

Question 8

what is the virulence determinant/factor?

Answer 8

the component of the pathogen that damages the host and allows the pathogen to cause disease

Question 9

what is the Lethal Dose?

Answer 9

LD 50
= 50% Lethal Dose
= the number of pathogen required to kill 50% of healthy host cells

Question 10

What are the major mechanisms by which bacteria cause disease in humans?

Answer 10

1. Transmission
2. Adherence to Host Surface
3. Invasiveness
4. Toxigenicity

Question 11

What 5 factors do bacteria possess to be virulent?

Answer 11

1. adhesin - allows binding
2. invasion - allows invasion
3. impedin - allows avoidance of host defence
4. aggressin - cause direct damage
5. modulin - cause indirect damage by unregulating host defence

Question 12

give 6 routes of transmission.

Answer 12

• ingestion
• inhalation
• needlestick
• sexual transmission
• trauma
• arthropod bite

Question 13

how do bacteria adhere?

Answer 13

• mucus-binding membrane proteins
• receptors for host surfaces
• secrete mucinases

Question 14

give 3 bacteria which require adherence mechanisms.

Answer 14

Neisseria gonorrhoea and E.coli
- hair-like pili
- can attach to epithelium

S.mutans
- extracellular polysaccharide helps to adhere to enamel

Question 15

how does a biofilm form?

Answer 15

bacteria adheres
aggregates and builds up
strengthens

Question 16

why may organisms thrive within a biofilm?

Answer 16

• protection from the extracellular polysaccharide matrix
• high resistance to antimicrobials
• poor penetration of antimicrobials
• degradation of antimicrobials
• different pH may not lead to optimal activity of the drug

Question 17

what are the 3 bacteria’s adhesin molecules and complementary receptors on the host cells?

• streptococcus spp.
• mutans streptococci
• actinomyces naeslundii

Answer 17

streptococcus spp.
- adhesin = antigen I/II
- receptor = salivary agglutinin

mutans streptococci
- adhesion = glucan-binding protein
- receptor = glucan

actinomyces naeslundii
- adhesin = type 1 fimbriae
- receptor = proline-rich- protein (PRP)

Question 18

what is a sessile organism?

Answer 18

an immobile organism

Question 19

which 4 enzymes may be used to help bacteria invade? how do they work? which bacteria are they present in?

Answer 19

collagenase
- degrade intracellular materials
in colstridium perfringens (gangrene gas)

coagulase
- accelerates formation of fibrin clot
- inhibit phagocytosis
- s. auerus

hyaluronidase
degrade intracellular materials
- in straphlyococcus aeurus (skin infection) and streptococcus pyogenes (sore throat)

kinase
- dissolves the clot
- release bacteria into deeper tissue

Question 20

give 2 proteins that are used by bacteria involved in the invasion. what do they do and give examples.

Answer 20

Immunoglobulin A protease
- degrades IgA on mucosal surface
- allows N.gonorrhoeae, Haemophillus influenza, Streptococcus pneumonia to adhere

Leukocidins
- can destroy neutrophils, leukocytes and macrophages
- Aggregatibacter actinomycetemcomitans

Question 21

define the toxigenicity

Answer 21

refers to the toxin production

Question 22

what are the 2 types of toxins?

Answer 22

endotoxins
exotoxins

Question 23

describe the difference between gram-positive and gram-negative

Answer 23

gram positive bacteria
- lack outer membrane
- surround by layers of peptidoglycan

gram negative
- thin peptidoglycan cell wall
- surround by outer membrane

Question 24

describe endotoxins and their biological effects.

Answer 24

• lipid portion of polysaccharides
  part of the outer membrane of gram-negative bacteria
• liberated when bacteria die and break down

biological effects
- fever
- hypotension
- shock
- reduced perfusion of major organs
- activate alternative pathway
- activate coagulation system
- increase phagocytic activity of macrophage and polyclonal B activation
- increases antibody production

Question 25

describe exotoxins and their biological effects

Answer 25

• proteins produced by gram negative and mostly gram positive bacteria
• released into environment after lysis
• causes disease from diffusing throughout the body

Question 26

give 3 examples of exotoxins.

Answer 26

Tetanus
Diptheria
Botulinum

Question 27

what bacteria releases tetanus exotoxins? what does it do?

Answer 27

Clostridium tetani

• prevents the release of inhibitory neurotransmitter glycine
  = muscle spasms

Question 28

what bacteria releases Botulinum exotoxin? how does it work?

Answer 28

Clostridium botulinum

• blocks release of acetylcholine at synapses
  = muscle paralysis

Question 29

why can clostridium botulinum be hard to eradicate from sterilisation? how would you eradicate?

Answer 29

it is an anaerobe
can also transform into spores

• eradicates by autoclaving

Question 30

what are symptoms of Botulism?

Answer 30

diplopia - double vision
dysphagia - difficulty swallowing
dry mouth
speech problems
respiratory failure
death

Question 31

which exotoxin is one of the most toxic compounds on earth?

Answer 31

botulinum toxin

Question 32

give 7 diseases which are exo-toxin mediated and the bacteria they’re caused by.

Answer 32

cholera - vibrio cholerae
diptheria - corynebacterium diphtheria
diarrhoea - clostridium difficile
colitis - e.coli
whooping cough - bordetella pertussis
scarlet fever - streptococcus pyogenes
scalded-skin syndrome - S.aureus

Question 33

is e.coli gram-negative or gram-positive?

Answer 33

gram-negative