M1- How bacteria causing diseases spread

Question 1

what are commensals

Answer 1

healthy host colonised by bacteria that doesn’t cause disease

• benefit from relationship w/ another organisms but host is neither benefitted/harmed
• normal microflora

Question 2

what is a pathogen

Answer 2

infection occurs when invading micro-organisms cause ill health

Question 3

what are oppurtunistic pathogens

Answer 3

cause disease when opportunity arises - caused by disturbance in homeostasis between host + commensal
▹ immunocompromised host
▹ antibiotics
▹dietary imbalances (caries)

Question 4

what is a carriage

Answer 4

person/animal asymptomatically carries pathogenic microbe to other people

Question 5

how does normal flora help prevent infection

Answer 5

competing with pathogens for colonisation sites

▹ acts as barrier (defence mech) against colonisation + invasion by exogenous organisms

Question 6

what is virulence

Answer 6

quantitative ability of pathogen to cause disease (measure of degree of pathogenicity)

Question 7

What does pathogenicity of a microbe depend on

Answer 7

microbial + host factors

Question 8

what are the microbial factors that virulence of a microbe depends on?

Answer 8

• transmissibility
• infectivity
• invasiveness/toxicity
• ability to evade host defences

Question 9

what are the host factors that virulence of a microbe depends on?

Answer 9

• age
• genetic factors
• general + local host defences
• immunodeficiency

Question 10

what are the 2 types of infection sources

Answer 10

exogenous

endogenous

Question 11

what does exogenous infection source mean and 3 examples

Answer 11

coming from external source
▹ person-person contact
▹zoonosis = animal pathogens spread to humans
▹humans infected by microbes in env (soil/water)

Question 12

what does exogenous infection source mean

Answer 12

normal flora can invade causing endogenous infection

opportunist pathogens

Question 13

what does endemic mean

Answer 13

always present in pop at around constant level,

level can be cyclic (high in winter than summer)

Question 14

what does epidemic mean

Answer 14

high than normal level in pop, much higher than endemic + short term
(flu)

Question 15

what does outbreak mean

Answer 15

localised increase in incidence of disease

e.coli food poisoning

Question 16

what does pandemic mean

Answer 16

epidemic spread between continents

Question 17

what are the 2 general modes of transmission of infection

Answer 17

horizontal

vertical

Question 18

what does horizontal transmission infection mode mean

Answer 18

transmission of organism between individuals

Question 19

what does vertical transmission infection mode mean

Answer 19

transmission from mother to offspring in utero/ around birth via birth canal
(congenital syphilis) (Grp B streptococci)

Question 20

what are congenital infections

Answer 20

vertical transmission mode of infection
▹ via mother blood + crossing placenta (rubella)
▹ can be acquired before/after delivery
(herpes, hep B)

Question 21

what are the modes of transmission of microbes

Answer 21

▹ respiratory spread
▹ faecal-oral spread
▹ via skin or mucous membranes
▹blood
▹fomites
▹zoonoses
▹ sexual transmission

Question 22

what does fomites mean

Answer 22

inanimate object that carry microbes

Question 23

Hoe does skin to skin transfer happen

Answer 23

▹ direct contact or fomites (shared towels)

▹ transmission usually through abrasion in the epidermis (athletes foot)

Question 24

what is cellulitis

Answer 24

spread infection of soft tissues
commonly caused by streptococcus pyogenes (grp A streptococcus)
getting into small abrasion of skin

Question 25

what are signs of cellulitis

Answer 25

erythema - red, hot oedema - swelling, pain inflammation signs

Question 26

how does salivary spread happen

Answer 26

▹ contact with infected secretions (herpes) | ▹ saliva via bite breaking through victim's skin

Question 27

how does respiratory spread happen

Answer 27

▹ aerosolisation of secretions, depends on - amount of infective discharge - size of droplets - resistance of infection to drying/ inactivation by UV light ▹ fomites (tissues)

Question 28

how does faecal-oral spread happen

Answer 28

▹ poor hygiene ▹ direct hand-mouth spread (fertiliser/contamination of food) (salmonella/Hep A)

Question 29

how does blood borne transmission occur

Answer 29

▹ blood products/ dirty needles (Hep B, HIV, blood transfusion) ▹ Insect host (malaria) ▹ fleas - long distance jumps

Question 30

how does zoonotic transmission occur

Answer 30

via animals where they have natural reservoirs to humans

Question 31

what is nosocomial infections + what are most common

Answer 31

hospital acquired infections ▹ urinary tract ▹wound/skin + soft tissue ▹ resp tract

Question 32

how do spores help survival of organisms

Answer 32

bacteria make spores which can survive in env for loads of years (Bacillus anthracis) microbe can survive in host, which then acts as a reservoir of infection of new hosts

Question 33

how easily infection spreads depends on what (6)

Answer 33

- survival ability - ability to find alternative host - shedding capacity - infectivity - virulence - ability to evade immune response

Question 34

what infections are respiratory

Answer 34

influenza measles M.tuberculosis

Question 35

what infections are skin-contact

Answer 35

herpes | staphylococcus aureus

Question 36

what infections are faecal- oral

Answer 36

salmonella typhimurium | Hep A

Question 37

what infection are blood + body fluid

Answer 37

HIV Hep B syphilis

Question 38

how does attachment + invasion help spread infections

Answer 38

invading microbes must attach to host tissues by diff mechs

Question 39

how does neisseria gonorrhea spread

Answer 39

adhere to genital mucosa by fimbriae

Question 40

how does giardia laamblia spread

Answer 40

attach to jejunal mucosa by special sucking disc

Question 41

how does influenza spread

Answer 41

virus attached to host cells by its hemgluttin anitgen

Question 42

why is immune evasion important for microbes + how is it done

Answer 42

- overcome host immune defences (resp bacteria secrete IgA protease-> degrades host immunoglobulin) - avoiding destruction by host phagocytes (tuberculosis mycobacterium can survive inside host macrophages)

Question 43

what is motility of a microbe

Answer 43

ability to move which likely enhances pathogenicity | flagellae

Question 44

what are the 4 ways microbe can damage the host cells

Answer 44

▹ enzymes ▹ toxins ▹ exotoxins ▹ endotoxins

Question 45

what are 2 examples of how enzymes can damage the host

Answer 45

▹ protease (porphyromonas gingivalis - perio) | ▹ lipases, nucleases

Question 46

what are 2 examples of how toxins can damage the host

Answer 46

``` ▹ exotoxins in gram +pos bacteria - clostridium tetani - corynebacterium diphtheriae - (streptococcal erthyrogenic made by s.pyogenes -> scarlet fever( - vibrio cholerae (cholera) ▹ endotoxins in gram -neg bacteria ```

Question 47

how exotoxins can damage the host

Answer 47

- highly toxic + act at specific target sites - neutralised by antitoxin - often destroyed by heat

Question 48

how do endotoxins damage the host

Answer 48

- endotoxins from cell wall of gram -neg bacteria (liposaccharides) -> host cells to produce IL-1 + tumour necrosis factor (TNF) - > fever + shock