Isolation and identification (L3)

Question 1

what is medical microbiology

Answer 1

Differentiate between viral and bacterial infection

Question 2

what is epidemiology

Answer 2

Track the spread of disease

Question 3

what is transport medium

Answer 3

medium is for temporary storage of specimens being transported from a location after collection to the laboratory for processing.

Question 4

what is the hazard group 3 factors

Answer 4

the likelihood that it will cause disease by infection or toxicity in humans;

■ how likely it is that the infection would spread to the community;

■ the availability of any prophylaxis or treatment

Question 5

what are the 2 types of culture media

Answer 5

Natural/complex (undefined) media
Defined media

Question 6

what is selective media

Answer 6

Contain one or more agents that are inhibitory to all organsims except the those selected for by the growth condition or chemical – Colistin/naladixic acid agar

Question 7

what is differential media

Answer 7

Contains factor that allows colonies of one bacterial species to demonstrate metabolic or culture characteristics that distinguish it from other bacteria growing on same plate –

Question 8

what is enriching media

Answer 8

Contains specific nutrients required for growth of a particular organism
- chocolate agar

Question 9

why is selective media used

Answer 9

used for the growth of only selected microorganisms while inhibiting others.

Question 10

MacConkey agar Selective

Answer 10

contains bile salts that inhibit the growth of some bacteria but allows the growth of enteric organisms such as E. coli.

Question 11

MacConkey agar Differential

Answer 11

lactose helps to differentiate organisms which ferment the sugar to produce lactic acid (reduces pH). The colonies of bacteria that ferment lactose appear pink due to action of the indicator dye.

Question 12

what is enriched media

Answer 12

have additional nutrients to enhance the growth of fastidious microbes but are non-selective.

Question 13

Cultivation advantages

Answer 13

Relatively cheap
Removes non-pathogenic strains & allows growth of pathogen
Ability to grow on medium helps identification

Question 14

Cultivation disadvantages

Answer 14

Microbial growth can be slow (esp for bacteria
such as mycobacteria) – too late for patient

Some microbes difficult to culture

Many viruses difficult to grow in culture

Question 15

Microscopy can be coupled with staining:

Answer 15

Gram stain

Acid fast

Endospore

Question 16

what is the acid fast stain

Answer 16

The acid-fast stain is a differential stain used to identify acid-fast organisms

Question 17

why do bacteria create endospores

Answer 17

bacteria can survive in hostile conditions.

Question 18

Endospores can form within different areas of the vegetative cell:

Answer 18

Central
Subterminal
Terminal

Question 19

why is Thioglycolate Broth

Answer 19

used in microbiology to determine oxygen requirements.

Question 20

what do they require Microaerophiles

Answer 20

require lower level of oxygen and carbon dioxide (candle jar)

Question 21

what does identification of microrganism depends on

Answer 21

depends on the assessment and comparison of constant phenotypic characteristics

Question 22

give me 3 Chemical Tests

Answer 22

Catalase test
DNase test
Oxidase test

Question 23

what is the purpose of oxidase test

Answer 23

When the reagent is oxidized by cytochromec, it changes from colourless to a dark blue or purple compound, indophenol blue

Used to differentiate between Gram negative bacteria

Question 24

Methyl Red (MR) test

Answer 24

Detect ability of an organism to produce and maintain acid from glucose fermentation

Question 25

what is the point of citrate test

Answer 25

Determines an organisms ability to utilize citrate as a carbon source.

Positive results due to increase in pH which is detected by pH indicator

Blue indicates a Positive result