Topic 1-6/7 (Lec 6/7)

Question 1

What is the role of a clinical microbiologist?

Answer 1

To isolate and identify the causative agent of an infectious disease within 48 hrs of receiving the specimen

Question 2

Why is rapid identification important?

Answer 2

1) can minimize severity and duration if treatment starts rapidly
2) can ID the most suitable antibiotic for treatment
3) Identify the causative agent for the outbreak of disease (ex. contaminated supplies)

Question 3

What is the advantage of using microscopy in identification?

Answer 3

Good for preliminary diagnosis

Can be used on bacterium that cannot be grown outside the body

Question 4

What is the disadvantage of microsopy?

Answer 4

Sample may contain multiple different microorganisms, and thus identification of the causative agent is difficult

Question 5

How does growth-dependent identification methods work?

Answer 5

Collect sample of bacteria, then grow it on general purpose media (or enriched media if required). Identify using growth-dependent assays

Question 6

How do specialized media work?

Answer 6

Culture suspected pathogen in special growth media. Metabolic activities resulting from growth cause colour change in indicator dye, suggesting identity of the pathogen

Question 7

What is selective media?

Answer 7

Media which compounds are used to inhibit the growth of certain bacteria but not others (hence “selective”)

Question 8

What is differential media?

Answer 8

Media in which bacteria are identified by their appearance on the growth media

Question 9

What test is used to to identify antibiotic sensitivity?

Answer 9

Disk diffusion antibiotic susceptibility test

Question 10

How would one perform the disk diffusion antibiotic susceptibility test?

Answer 10

1) Spread bacteria on agar plate such that a confluent lawn will form
2) Place paper disks impregnated with antibiotics on surface (antibiotics will diffuse onto the agar)
3) Observe the “zone of inhibition” that appears around the plate and compare to standard
4) If zone of inhibition greater than or equal to standard, bacteria is sensitive. If zone of inhibition is smaller than standard, organisms is resistant.

Question 11

What factors influence the size of the zone of inhibition?

Answer 11

Diffusion rate of antibiotic
Degree of sensitivity to antibiotic
Growth rate of bacteria

Question 12

What are examples of growth-independent identification methods?

Answer 12

Agglutination assays - have beads with antibodies (agglutination/clumping indicates presence of bacteria)

Fluorescently-labelled antibodies - florescence under microscopy of the serum after addition of antibodies indicate presence of bacteria

*Antibodies recognize surface antigens

Question 13

What is the usual procedure to identify bacterial pathogens?

Answer 13

Isolation of bacteria, identification using growth-dependent methods, then confirmation using serolgical assays (growth-Independent methods)

Question 14

What is a postulate?

Answer 14

(From Google) “a thing suggested or assumed as true as the basis for reasoning, discussion, or belief.”

Question 15

What is Koch’s posulates?

Answer 15

1) Suspected pathogenic organisms is present in all cases of disease and absent in health animals
2) Pathogenic organisms should be isolated and cultivated in pure culture
3) Cells from pure culture must cause disease in healthy animal
4) Pathogen should be re-isolated from experimentally infected animals & shown to be the same as the original isolated pathogen

Question 16

What are the big 2 problems with Koch’s postulates?

Answer 16

1) some pathogens cannote be cultivated in vitro

2) Sometimes there are no animal models for a specific disease

Question 17

What are Koch’s postulates used for?

Answer 17

Used to prove a causative relationship between bacterial pathogens and their respective diseases

Question 18

Who came up with a molecular version of Koch’s postulates?

Answer 18

Stan Falkow

Question 19

What is the molecular version of Koch’s postulates that Falkow came up with?

Answer 19

1) Gene/factor should be present in pathogenic strains of an organisms and absent from non-pathogenic strains
2) Deletion of the virulent gene/factor should reduce the virulence of the strain, whereas introduction of the gene to an avirulent strain will cause virulence
3) Gene must be expressed during the infectious process in experimentally infected animals
4) Antibody against virulence factor should offer (some) protection against infection

Question 20

What is epidemiology?

Answer 20

The study of when and where disease occur and how they are spread

Question 21

What is the incidence of disease?

Answer 21

The fraction of a population that CONTRACTS (i.e. newly acquired) the disease during a specific time period

Question 22

What is the prevalence of diesease?

Answer 22

The fraction of a population having SYMPTOMS of the disease during a specific time period (include current AND newly squired cases during the time period)

Question 23

What is a sporadic disease?

Answer 23

A disease that occurs occasionally (often in geographically separated areas; i.e. separate, unrelated cases

Question 24

What is an endemic disease?

Answer 24

A disease that occurs CONTINOUSLY at a relatively low level (not very virulent disease, ex. cholera)

Question 25

What is an epidemic?

Answer 25

A disease that sporadically (i.e. irregularly) occurs at elevated levels and occurs continuously at low levels between sporadic periods

In other words, sometimes spiking, but relative constant basal rate every other time

Question 26

What is a pandemic?

Answer 26

An epidemic, but widely distributed (increase in geographical scale)

Question 27

What is a disease outbreak?

Answer 27

An increase in the number of disease cases in an area which initially had only sporadic cases

Question 28

What is a disease reservoir?

Answer 28

A site in which viable infectious agents remain and from which infection of individuals may occur

Question 29

What are possible reservoirs of disease?

Answer 29

Humans
animals (zoonoses - transfer of disese to humans, may occur)
insects (ex. fleas, l ice, flies)
inanimate/non-living reservoirs (ex. from water or soil

Question 30

What is a symptomatic human reservoir?

Answer 30

A human reservoir for a disease that currently has the disease

Question 31

What is a convalescent human reservoir?

Answer 31

A human reservoir for disease that is recovering from the disease, but still has the infectious agent

Question 32

What are the types of human disease carriers, and what is the difference?

Answer 32

Acute carriers - individuals that have the pathogen, but show no symptoms (transient carrier state, on the way to symptomatic)

Chronic carrier - individuals who have recovered from the disease but still have the pathogen, or one that carries the pathogen as part of their microbiota

Question 33

What are the possible modes of transmission of disease?

Answer 33

Contact transmission (transmit via contact)

Common vehicle transmission (transmission by fomites, or inanimate objects, food, water, blood, drugs)

Airborne transmission (transmission via droplets or dust)

Vector transmission (transmission via living agents, ex. insects, rodents)

*ex of fomites - skin cells, hair, clothing)

Question 34

What is virulence?

Answer 34

The relative ability of a pathogen to cause disease

Question 35

What is the infectious dose?

Answer 35

The number of bacteria required to produce disease

Question 36

What is the lethal dose?

Answer 36

The number of bacteria required to kill (usually determined in laboratory animals and expressed by number of bacteria required to kill 50% of the population ; LD50)

Question 37

What does lethal dose depend on?

Answer 37

Route of entry (ex. intravenously, orally, etc)

Question 38

What is a nosocomial infection?

Answer 38

An infection acquired by patients as a consequence of hospitalization

Question 39

What are some examples influencing nosocomial infections?

Answer 39

1) hosptials treat people with infectious diseases, and those patients could be reservoirs of disease
2) Patients are exposed to pathogens in a hospital setting
3) Patients with weakened immune systems are more susceptible to infection
4) Pathogens can be transferred from patient to patient by hospital staff or visitors

Question 40

What is the difference between endogenous, exogenous, and iatrogenic nosocomial infections?

Answer 40

Endogenous - coming from microbiota (found WITHIN)

Exogenous - coming from other individuals (ex-)

Iatrogenic - coming from doctors (lit. “Doctor induced”), so from surgeries, invasive procedures, etc.

Question 41

How can nosocomial infections be minimized?

Answer 41

Isolating infectious patients, having good housekeeping measures, good hand-washing practices, and having barrier protection (ex. gloves, caps, gowns)