M4- Sources of microorganisms

Question 1

Describe how pathogenesis occurs?

Answer 1

• reservoir of pathogens
• adhere/colonize and invade
• evade host defences
• multiply/complete its life cycle
• exit host (host is damaged)

Question 2

Name some reservoirs in humans

Answer 2

• hep A and B
• influenza
• measles

Question 3

is animals source or reservoir?

Answer 3

• Zoonoses or Zoonotic diseases
• Accidental infection of man
• May involve vector, rat to tick to man

Question 4

is the environment source or reservoir?

Answer 4

• Soil & Water
• Contaminated with sewage, or naturally
contain animal excreta
• include opportunistic pathogens that can infect immuno-suppressed

Question 5

Describe a source.

Answer 5

• animate/inanimate (animal or environment )
• (human) period of infectivity
• Casual (hours), acute (days), Transient(weeks) , chronic (months +)

Question 6

what are signs of active carrier state?

Answer 6

overt clinical presentation

Question 7

what are signs of convalescent carrier state?

Answer 7

recovering but still carrier

Question 8

what are signs of a healthy carrier state?

Answer 8

no overt signs of illness

Question 9

what are signs of a incubator carrier state?

Answer 9

maintaining large numbers of pathogens prior to illness

Question 10

what is a natural way to exit a host?

Answer 10

sneezing, shedding

Question 11

what is the artificial way to exit a host?

Answer 11

blood, salvia,aerosols (drill)

Question 12

Describe the direct spread/contact of disease

Answer 12

• from one person to another
• horizontal= between each other
• vertical= mother to child

Question 13

Describe indirect spread.

Answer 13

formite - dental instruments

Question 14

Describe air-borne spread.

Answer 14

droplets/aerosols

Question 15

Describe vector-borne spread.

Answer 15

insects i.e flea

Question 16

How do microbes escape from the body?

Answer 16

• tears
• salvia
• nasal secretions
• semen
• urine

Question 17

what can vary during the course of a disease?

Answer 17

reservoirs

Question 18

what is exogenous?

Answer 18

Infective material derived from outside patients body

Question 19

Describe an endogenous infection?

Answer 19

– Bacteria/Fungi part of natural microbiota (commensal)

– Misplaced, transfer from non-sterile to normally sterile site : S. sanguinis mouth to blood to heart & endocarditis

– Change in natural flora
: e.g. antibiotic therapy
C.albicans or C.difficile

Question 20

Name some infections by exogenous bacteria.

Answer 20

• tuberculosis (humans)
• pneumoniA (soil/water)
• tetanus (soil)

Question 21

how does it go from commensal(mutualistic) to pathogen?

Answer 21

• damage to epithelium (burns or wounds)
• presence of forge in body (prosthesis, catheters, absence of shedding surface and formation of biofilms)
• transfer of bacteria to incorrect site (mouth to lower respiratory tract)
• suppression of immune system (cancer therapy)
• infection by exogenous pathogen
• disruption of microflora by antibiotics

Question 22

Describe biofilms.

Answer 22

• Organism behaving as part of multi-cellular community.
• 3 dimensional structure
• Contains interfaces
• Spatial heterogeneity
• Permeated by water channels
• Organisms resistant to antimicrobial agents & host defenses

Question 23

Describe an oral biofilm.

Answer 23

• dental plaque
• multi species biofilm (no single biofilm)
• can be tightly or loosely packed on the top of the tooth
• complicated

Question 24

How do you establish disease?

Answer 24

• dose of infective agent
• virulence of organisms
• susceptibility/resistance of host

Question 25

Describe the stages of development of infectious disease (pathogenesis).

Answer 25

• source of the microbe
• escape from the source
• spread to a new host
• entry into the host
• infection of the host
• damage to the host

Question 26

what is good dental practise?

Answer 26

• primary sources- secretions, salvia , blood :gloves, mask,gown, aspiration
• secondary source- surgery equipment e.g. drill :cleaning disinfection sterilisation

Question 27

what challenges faced by pathogenic bacteria in water?

Answer 27

• low temperature
• low nutrient and osmotic strength
• pH near neutral
• O2 available• respiratory metabolism
• free iron available
• adhesins to stick to rocks

Question 28

what challenges faced by pathogenic bacteria in human?

Answer 28

• higher temperature (37oC)
• higher osmotic strength, C and energy sources abundant
• low pH then higher pH
• low or no O2
• fermentative metabolism
• iron bound to haem
• adhesins to stick to cells
• exposure to bile salts

Question 29

what microbes are more likely to poise a threat?

Answer 29

endogenous microbe adapted to host and adhere

Question 30

what does infection control requires knowledge of?

Answer 30

–  Source of infection 
–  Transmission
–  Exogenous
–  Endogenous
–  Commensal/Microflora threat