Lecture 1: Introduction to microbes

Question 1

Learning Objectives

Answer 1

To understand and be able to describe:

• the importance of microbial life
• the history of microbiology as a discipline
• Koch’s postulates
• the properties of some bacterial pathogens

Question 2

What are micro-organisms?

Answer 2

Viruses, bacteria, archaea, algae, fungi, protozoa

Macro-organisms include animals and plants

Question 3

Why study microbiology?

Answer 3

• Knowledge: much of our knowledge initially comes from studying bacteria, esp. E. coli (most studied micro-organism on the planet and we still don’t know what 80% of its genes do)
• Importance:
• digestion, agriculture
• Medicine, food, alcoholic drinks, biotechnology.

Question 4

What is the ratio of bacterial to human cells in the human body?

Answer 4

10:1

Question 5

Which important products do micro-organisms produce?

Answer 5

• Antibiotics, e.g. Penicillin, tetracycline
• Enzymes, e.g. glucose isomerase, laundry proteases and lipases
• Food additives, e.g. Vitamins, amino acids
• Chemicals, e.g. Bio-fuels, citric acid
• Alcoholic beverages, e.g. beer, wine, distilled spirits

Question 6

What was Woese’s important discovery in the 1970s?

Answer 6

In the 1970s Woese discovered that archaea and eukaryotes are more genetically similar to each other than to bacteria.

Question 7

When a) were bacteria discovered, b) was spontaneous generation disproved, c) were Koch’s postulates formed, d) was penicillin discovered, e) was HIV discovered, f) was the first entire genome synthesised?

Answer 7

a) 1684
b) 1864
c) 1884
d) 1929
e) 1983
f) 2012

Question 8

Who disproved spontaneous generation?

Answer 8

Louis Pasteur in 1864

Question 9

What is the theory of spontaneous generation?

Answer 9

The idea that a sterile medium will spontaneously grow life/micro-organisms.

Question 10

How did Louis Pasteur disprove spontaneous generation in 1864?

Answer 10

He poured non-sterile liquid into a flask, then heated the neck of the flask so that it became a swan neck. Then the liquid was sterilised by heating, forcing air out of the open end of the swan neck. The liquid was then cooled slowly, with the dust and micro-organisms being trapped in the bend of the swan neck.
The flask was then left for a long time and spontaneous generation did not occur.
Then the flask was tipped so the micro-organism-laden dust come in contact with the sterile liquid. The flask was then left and the micro-organisms grew in the liquid.

Question 11

What were Koch’s postulates related to?

Answer 11

The fact that a specific micro-organism causes a specific disease.

Question 12

Which micro-organism did Koch work with?

Answer 12

Bacillus anthracis, which causes anthrax in cattle (and humans).

Question 13

How did Koch study the pathogens?

Answer 13

In the blood of infected animals under the microscope.

Question 14

What was Koch’s first postulate?

Answer 14

The suspected pathogenic micro-organism should be present in all cases of the disease and absent in all healthy animals.

Question 15

What was Koch’s second postulate?

Answer 15

The suspected organism should be grown in a pure culture.

Question 16

What was Koch’s third postulate?

Answer 16

Cells from a pure culture of the suspected organism should cause disease in a healthy animal. The newly infected animal should suffer in the same way as the original animal.

Question 17

What was Koch’s fourth postulate?

Answer 17

The organism should be re-isolated and shown to be the same as the organism.

Question 18

What is the exception to Koch’s postulates?

Answer 18

Mycobacterium leprae (causes leprosy). This is an exception because it can’t be grow in culture (lab).

Question 19

Discuss the change in death rate from infections from 1900 to 1960 and its reason.

Answer 19

Infections are reduced from a major killer in 1900 down to 5-10% of what it was by 1960. Possible reasons for this dramatic reduction include:

• Vaccines
• Antibiotics
• Public health education

Question 20

Give examples of infectious diseases which are still a problem today.

Answer 20

• HIV, malaria and Tuberculosis (esp in Africa)
• Emerging diseases: Ebola, bird/swine flu
• Antibiotic resistant bacteria, e.g. MRSA

Question 21

What can be done about the problem of antibiotic-resistant bacteria?

Answer 21

• Discover and develop new and novel antibiotics which bacteria are not yet resistant to
• Educate doctors to not just prescribe antibiotics all the time
• Educate people on the importance of finishing their course of antibiotics.

Question 22

Give some of the characteristics of bacteria.

Answer 22

• Each bacterial colony is derived from a single cell (this is a pure culture)
• all the cells in a single colony are genetically identical (except for mutations)
• there are 100,000s of bacteria in each colony

Question 23

Why do some bacterial colonies look shiny on an agar plate?

Answer 23

The bacteria are secreting polysaccharides.

Question 24

What are the three domains of life?

Answer 24

Eukaryotes
Bacteria (prokaryote)
Archaea (prokaryote)

Question 25

How do you spell the genus of E. coli?

Answer 25

Escherichia

Question 26

Give some of the classification within the domain bacteria.

Answer 26

- The domain bacteria contains over 40 phyla, e.g. Proteobacteria is one phylum. - Each phylum contains several genera, e.g. Pseudomonas, Escherichia are genera - Each genus contains many species, e.g. Pseudomonas aeruginosa (pathogen of man and animals, common in cystic fibrosis sufferers), Pseudomonas syringae (plant pathogen), Pseudomonas putida

Question 27

What are the rules for naming prokaryotes?

Answer 27

- Write the genus then species. - Once the genus has been written out in full once, it can be abbreviated, provided it in unambiguous - Leave a space between the genus and species names - Put the names in italics (on computer) or underline (handwritten) - Capitalise genus, but not species E. coli is correct

Question 28

Give the five bacterial shapes, with examples of bacteria which are that shape.

Answer 28

Bacillus - rod shaped, e.g. Escherichia coli Coccus - circular, e.g. Staphylococcus aureus Spirillum - spiralling, e.g. Vibrio cholera Spirochetes - tightly coiled, e.g. Treponema pallidum (syphilis) Filamentous - filamentous, e.g. Steptomyces sp. (antibiotics)

Question 29

Give the common arrangements of bacteria and the reason for these arrangements.

Answer 29

Clusters, chains (esp cocci), sheets or randomly distributed These arrangements are formed because bacteria don't always completely separate during division until later on in the division.

Question 30

Describe Streptococcus pyogenes.

Answer 30

Steptococcus pyogenes is a medically important Gram-positive cocci. - It forms chains - 1 to 2 micrometres long - Produces many virulence factors, including toxins and enzymes: Steptolysins O and S are toxins that lyse host cells, Streptokinase dissolves fibrin clots, Hydaluronidase dissolves hyaluronic acid in connective tissue, Erythrogenic toxin causes scarlet fever rash. - The main symptoms of the disease caused by Streptococcus pyogenes are scarlet fever, septic sore throat and rheumatic fever.

Question 31

Describe Staphylococcus aureus.

Answer 31

Staphylococcus aureus is another medically important Gram-positive cocci. - Found in the nose and vagina - Forms 'clusters of grapes' - 0.5-1 micrometres long - Causes skin infections, boils, respiratory infections, toxic shock syndrome (tampons can increase the risk of this) and scalded skin syndrome. - Can cause serious infections after operations - MRSA is Methicilin Resistant Staphylcoccus aureus. - Many virulence factors are produced, including toxins and enzymes (these are species specific): a-toxin: secreted protein, lyses host cells, entertoxin: induces vomiting and diarrhoea, Toxic shock toxin: systemic shock, organ failure

Question 32

Give two examples of Gram-positive Bacillus bacteria.

Answer 32

- Bacillus subtilis (non-pathogenic soli bacteria, model gram-positive bacteria, intensively studied) - Bacillus anthracis (causes anthrax, studied by Koch, pathogenic because it acquired a gene for the anthrax toxin)

Question 33

Give an example of a Gram-negative cocci.

Answer 33

Neisseria gonorrhoea. - Causes gonorrhea (STD) - diplococcus (occurs in pairs)

Question 34

Give an example of a Gram-negative bacillus.

Answer 34

Escherichia coli (E. coli). - can be pathogenic or non-pathogenic - non-pathogenic strains live in the human gut - has a large genome - pathogenic strains can cause diarrhoea - pathogenic cells adhere closely to gut cells and induce the formation of pedestals by reconfiguring the cytoskeleton. Protein effectors are transferred into the gut cell which changes the physiology of the whole cell.