L1 Intro to Microbial World

Question 1

Infection

Answer 1

when microorganisms invade host tissue and multiply

Question 2

Subclinical infections

Answer 2

asymptomatic (no symptoms apparent) but immune response is induced

Question 3

Localised infections

Answer 3

confined to one area of the body. e.g. ear infection

Question 4

Systemic infections

Answer 4

infection spreads to other organ systems

Question 5

Disease

Answer 5

Harmful alteration to the host

Question 6

Pathogen

Answer 6

A microorganism capable of causing disease

Question 7

Pathogenesis

Answer 7

a process by which disease arises (not unique to infectious disease)

Question 8

Pathogenicity

Answer 8

the measure of the ability of a pathogen to cause disease

Question 9

Pathogenic determinant/virulence factor

Answer 9

a feature of a pathogen that influences how well it can 
cause disease (pathogenicity/virulence)

Question 10

Endemic

Answer 10

disease that is always present in a given population. There is a permanent reservoir (human or
other animals)

Question 11

Epidemic and Pandemic

Answer 11

Epi- a sudden rapid rise in the incidence of a disease in a particular population

Pan- Global epidemic

Question 12

Outbreak

Answer 12

a relatively high number of infections are observed where no cases or only sporadic cases
occurred in the past

Question 13

Epidemiology

Answer 13

‘Father’: John Snow

Study of occurrence, spread and control of disease

Question 14

Koch’s Postulate

Answer 14

4 postulates that must be satisfied to prove a link

between a particular microbe and a disease.

Question 15

Describe the 4 Koch’s postulates

Answer 15

1. assumption: suspected pathogen is present in ALL cases of the disease but is absent from healthy animals (e.g. rat)
2. sus. pathogen must be grown in pure culture.
3. cells from a pure culture of sus. pathogen must cause disease in a healthy animal.
4. sus. pathogen must be reisolated & shown to be the same as original.

Question 16

Describe/explain the progression of infectious disease

Answer 16

6 steps.

1. attachment and/or entry into body
2. local or general spread in the body
3. multiplication
4. evasion of host defences
5. shedding
6. cause damage in host (can occur at any step)

Question 17

Infectious disease

Answer 17

• caused by an infectious agent

- infected person can be transmitted to others

Question 18

Difference between Gram-positive (G+) and Gram-negative (G-) in bacteria

Answer 18

G+ : thick cell walls, can retain purple stain

G- : no cell wall, cannot retain purple stain, is stained red/pink

Question 19

Why it is important to know about the bacterial characteristics, particular to health care setting?

Answer 19

To accurately ID bacteria and do rapid tests to choose treatment.
Gram status, morphology and functional
characteristics are sufficient information for choosing appropriate
treatment for patient.

Question 20

Binary Fission in bacterial reproduction

Answer 20

Bacterial cells undergo Binary Fission to reproduce a cell into two parts which involves:

1. DNA replication to get two copies
2. Moving of the DNA strands to opposite ends of the cell
3. Splitting of the cell in the middle into two separate bacteria that has the same genetic material

Generation Time is time taken for one cell to reproduce itself. E.g. every 20 mins, each bacteria multiply into 2.

Question 21

Name the 4 growth phases in bacterial reproduction.

Answer 21

1. Lag Phase: Initial adaptation to conditions
2. Logarithmic Phase: Exponential increase in cells
3. Stationary Phase (limiting nutrients): Rate of cell division equals cell death
   4: Death Phase (nutrients run out): Decrease in cell numbers

Question 22

Ways to measure bacterial growth.

Answer 22

Turbidity is a direct indication of growth that can be measured using a spectrophotometer (light source): the cloudier the fluid = more bacterial cells.

Optical density (OD): More cells = more scatter = higher OD