Categorisation

Question 1

Microbial culture

Answer 1

A collection of cells that have been grown in or on a nutrient medium

Question 2

Medium

Answer 2

Plural = media

A liquid or solid nutrient mix that contains all of the nutrients required for a microorganism to grow

Question 3

Growth

Answer 3

In microbiology the word growth is used to refer to the increase in cell number as a result of cell division - a single microorganism can grow into millions and billions of cells to form a visible colony

Question 4

Microbes live in communities cooperatively and in conflict

Answer 4

• typically live in complex microbial communities and their activities are regulated by interactions with each other, with their environments and with other organisms
• Microorganisms were on the land and in the seas for billions of years before plants and animals appeared - they are very diverse
• microorganisms are a major part of the earth’s biomass and are essential in sustaining life
• for example, oxygen we breathe is the result of microbial activities
• evolution of plants and animals are heavily influenced by by microbial and symbioses and by pathogens
• there are many ways to study microorganisms

Question 5

cylindrical

Answer 5

A cylindrically shaped cell is called a rod or a bacillus (plural, bacilli).

Question 6

Spiral

Answer 6

A spiral-shaped cell is called a spirillum (plural, spirilla).

Question 7

Curved

Answer 7

A cell that is slightly curved and comma-shaped is called a vibrio.

Question 8

spirochete

Answer 8

A spirochete is a special kind of organism that has a spiral shape but which differs from spirilla because the cells of spirochetes are flexible, whereas cells of spirilla are rigid.

Question 9

Irregular shape

Answer 9

Some bacteria are irregular in shape. Appendages, such as stalks and hyphae, are used by some cells for attachment or to increase surface area. In addition, asymmetrical cell division such as budding can result in irregular and asymmetrical cell shapes.

Question 10

Cell division and morphology

Answer 10

Cell division impacts morphology because cells that remain attached together can form distinctive shapes, eg. Some cocci occur in pairs (diplodocus) and some form long chains (streptococci)

Question 11

Filamentous bacteria

Answer 11

Filamentous bacteria are long thin rod shaped bacteria that divide terminally and then form long filaments composed of many cells attached end to end

Question 12

Size

Answer 12

• the bigger it gets the more it is limited by the nutrients
• small cells have more surface area to volume ratio than larger cells
• as the cell size increases the S/V ratio decreases
• S/V ratio controls many processes in the cells, including its growth rate and shape
• cellular growth rate depends in part on the rate at which cells exchange nutrients and waste products with their environment
• as cell size decreases, the S/V ratio of the cell increases, and this means that small cells can exchange nutrients and wastes more rapidly (per unit cell volume)than can large cells
• free living cells that are smaller therefore tend to be more efficient than those larger and any given mass of nutrients will support the synthesis of more small cells than large cells.
• Cell morphology is often predicated on the effect of cell shape on S/V ratio.
• Eg. Cell shapes that increase the overall membrane are of the cell, such as those having thin appendages or invaginations, allow bacteria to increase their S/V ratio for any given mass of cytoplasm

Question 13

Gram staining

Answer 13

1. Flood the heat fixed smear with crystal violet for 1 min (all cells remain purple)
2. Add iodine solution for 1 min (all cells remain purple)
3. Decolorize with alcohol for 20 sec (gram positive cells are purple and gram negative are colourless)
4. Counterstains with safranin in for 1-2 min (gram positive cells are purple and negative are pink to red

Question 14

Example tests

Answer 14

morphology
physiology - what conditions are required for the growth of the microorganism?
biochemistry
serology
bacteriophage
pathogenicity
DNA analysis

Question 15

Physiology:

Answer 15

• At either too hot or too cold a temperature microorganisms will not be able to grow and may even die.
• As temperature rises the rate of enzymatic reactions increases and growth becomes faster
• However, above a certain temp, proteins and other critical cell components may become denatured or otherwise irrevocably damaged.

Question 16

Cardinal temperatures

Answer 16

• for every microorganism there is also a minimum temperature below which the organism cannot grow. Optimum temp - where growth is the most rapid, max temp - growth is not possible above this
• These three temperatures are called the cardinal temperatures
• they can differ largely between species

Question 17

psychrophiles

Answer 17

low temperature optima

Question 18

mesophiles

Answer 18

midrange temperature optima

Question 19

thermophiles

Answer 19

high temperature optima

Question 20

hyperthermophiles

Answer 20

very high temperature optima

Question 21

Tolerance to chemical inhibitors

Answer 21

• respiratory inhibitors
  - Gram -ve bacteria are sensitive to sodium azide (NaN3) as it inhibits cytochrome c oxidase. Whereas Enterococcus (e.g. E.faecalis) and other Gram +ve bacteria are resistant
• chaotropic agents - mess up water which can lead to protein desaturation
  - Pseudomonas resistant to phenol
• Antibiotics
  - Mycoplasma lack a cell wall therefore resistant to penicillin
• we can characterise bacterial isolates by scoring the ‘minimal inhibitory concentration’ (MIC) for range of antibiotics
• alternatively, antibiotic impregnated discs

Question 22

Biochemical tests can be used to distinguish specific enzymes or metabolic pathways

Answer 22

E.g sugar metabolism

Question 23

Fermentation

Answer 23

anaerobic breakdown of the sugar into smaller molecules with the release of waste products (sometimes ethanol), sometimes organic acids, sometimes gases). Different waste products characteristic of different species

Oxidation: breakdown of sugar to CO2 and water. An aerobic process:

Check notes for result colours

Question 25

Catalase test

Answer 25

Bubbles of oxygen = catalase + e.g. staphylococci No bubbles = catalase - e.g streptococci

Question 26

Urease test

Answer 26

Urea —-> NH3 (pH rises —-> colour change) - these and numerous other biochemical tests can be miniaturised and automated - test strips contain dehydrated substrates + indicators in microtubes - just add the bacterial suspension and incubte - different strains give characteristic colour patterns

Question 27

Serology

Answer 27

- detection of bacteria antigens using specific antibodies 1. Expose to specific antibodies (e.g from blood serum) 2. Test in vitro for recognition of the cell- surface antigens (with ELISA, agglutination, precipitation, complement-fixation and fluorescent antibodies and chemiluminescence - serology tests can be similarly miniturised e.g in 96 well microlitre plates (look at notes for diagram)

Question 28

Bacteriophage type

Answer 28

Bacteriophages - bacterial viruses. Most have a specific host range Check notes for diagram

Question 29

Pathogenicity

Answer 29

Pathogens: - Specific symptoms - definite host range sometimes symptoms alone are enough to indicate identity. for example - 1. Dipheria - formation of pseudomembrane in the throat - corynebacterium diptheriae 2. Leprosy - loss of fingers and toes - Mycobacterium leprae 3. Plague - buboes, skin darkening - Yersinia pestis

Question 30

i. Genome sequencing

Answer 30

- Numerous bacterial species now completely sequenced - sequences do not give the complete answer to how a bacterium functions but do provide a huge amount of comparative information on biochemistry, physiology, phylogenetic relationships and evolution - note* - determining the sequence and gene content of a bacterial genome is still a major undertaking - not what you would do initially to characterise a new isolate. However complete genome sequences can be used as refernce points when characterising new isolates

Question 31

ii. Polymerase chain reaction (PCR)

Answer 31

- simple in vitro technique to amplify short, specific DNA sequences. Now used regularly to diagnose bacterial/viral infections - PCR is incredibly sensitive - can be used to detect single bacterial cells - With DNA based tests, we can identify bacteria without culturing them first - makes clinical diagnosis much faster - many of these test are used in a clinical context Check notes for diagram

Question 32

(Meta)genomics

Answer 32

- most of our knowledge of bacteria comes from pure strains in culture - but >99% of species are thought to be uncultivatable