SH2: Microbiology history, methods and ideas

Question 1

Describe how the common belief that living organisms spontaneously arose were disproved.

Answer 1

This was disproved for the replication of macro organisms, by an experiment were meat was left out in the open, and maggots could lay their eggs and multiply, and then meat was left out but covered and the maggots could not reproduce. However, it was still believed that the generation of micro-organisms was spontaneous, until the modified Schwann experiment was carried out. Heated up meat (sterilise) broth in a flask with a tube with two half bends in, and allowed it too cool, microorganisms would be trapped in first bend, broth would stay clean. Then shows that if the broth came into contact with the trapped contents in the neck of the tube, the broth would go back, disproving spontaneous formation of microorganisms.
Shape of the neck prevented dust and microorganisms entering flask.

Question 2

What helped people in hospitals survive child birth, operations etc in the past

Answer 2

Sterilisation

Question 3

What is Koch’s postulates (set of criteria) to determine if the aetiology (specific cause) is an infectious disease

Answer 3

• The agent must be present in every case of the disease
• The agent must be isolated and cultured in vitro – can be hard to do
• The disease must be reproduced when a pure culture of the agent is inoculated into a susceptible host
• The agent must be recoverable from the experimentally-infected

Question 4

What is modern microbiology is largely dependent

Answer 4

microscopes and (gram) staining, sterility

Question 5

How to make a culture:

Answer 5

• Sterilise work service, equipment, media
• Inoculate your media with the desired microorganism and there are many ways to do this
1. Micromanipulation is technically difficult and expensive
2. Extinction dilution is based upon statistics and is difficult to carry out
3. Streaking on agar plates and pick the one colony that contains the one organisms wanted, them culture this pure species

Question 6

Different ways of inoculation

Answer 6

1. Micromanipulation is technically difficult and expensive
2. Extinction dilution is based upon statistics and is difficult to carry out
3. Streaking on agar plates and pick the one colony that contains the one organisms wanted, them culture this pure species

Question 7

Why is maintaining stock cultures important

Answer 7

To send them to other scientists, or keep them for years so you can keep working on the species.

Question 8

Plating is important for

Answer 8

• Purifying microorganisms
• Dilution cultures to determine viable counts
• Determine requirements/conditions for growth
• Enrichment/ selective cultures, adding substance to aid/stop grown of certain species

Question 9

What conditions must be mimicked in order to allow a culture to grow

Answer 9

temperature, pH, osmotic pressure, atmospheric composition

This about Thermophiles (heat), psychrophiles (cold), Alkaliphiles, acidiphiles, halophiles (salt high) barophiles/ piezophiles (high pressure), xerophiles (dry), aerobes (oxygen), anaerobes (no oxygen).

Question 10

When looking at classification you can look at metabolic activity, so how the organism gets:

Answer 10

• Energy – phototrophs (light), chemotrophs (organics), chemolithotrophs/ lithotrophs (inorganic compounds)
• Carbon- autotrophs (carbon dioxide), heterotrophs (organic)

Question 11

Microbial growth phases

Answer 11

• Lag phase- preparation for active growth
• Exponential phase- maximal metabolism and growth
• Stationary phase- nutrients depletions/ limited and accumulation of toxic compounds
• Death- death of cells

Question 12

Describe Synchronous and non-Synchronous

Answer 12

Synchronous (experimental infection, where everything is at the same phases of growth), non-synchronous (normal, where they are at different phases of growth).