Microbiology And Disease

Front 1

Describe bacteria?

How can bacteria be identified?

Back 1

Bacteria Prokaryotes, has cell wall, cell membrane, cell wall, no nucleus no nuclear membrane.

Cocci ( singular coccus); spherical

Bacilli (singular bacillus) rod shaped

Spirilla (singular spirillum) spiral shaped

Vibrio: curved shape

Front 2

1. Gram negatives

2. Gram positive

Back 2

1. Gram negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. They show the colour red.

Gram negative bacteria has tin layer of peptidoglycan (glycoproteins), they have a layer of outer membrane (similar to cell membrane but has highly branded fatty sugar called lipopolysacharide these walls do not retain stains) for protection.

2. Gram positive bacteria appear a purple/ blue colour when stained by crystal violet.

Gram positive bacteria’s has thick cell wall (peptidoglycan= glycoprotein peptidoglycan has no lipopolysaccharides) this makes cell wall absorbent and so it retains stain. Cell wall also contain teichoic acid maintains cell structure and gives cell surface an acidic charge (-)

Front 3

1. What is binary fission

2. How dose binary fission occur

3. What is generation time

4. What is Exponential increase

Back 3

1. Binary fission is a process where bacteria reproduce asexually.

2. In binary fission one cell is divided into to two cells, then 4 then 8 and so on

- cell elongates, circular DNA replicates and attaches to mesosome

- septum (wall) is synthesised to separate cell

- septum grows across cell deviding the genetic material and forming two daughter cells.

- two new daughter cells separate and begin a new cell cycle.

3. It’s the time taken for a bacterial population to double in number

4. Continuous doubling of numbers

Front 4

The population descended from one cell after a number of generations of growth in favourable conditions can be estimated by the equation

Back 4

Population in the nth generation =2^n

Front 5

Growth of bacteria ( state the growth phase) lag phase, log exponential phase, stationery phase, death phase.

Back 5

1. Lag phase- no or little cell division occurs, cell increases in size. RNA, proteins and enzyme synthesis occurs.

2. Log/ exponential phase- maximum cell division. Conditions are at optimum eg nutrient levels, temperature and PH, no factors are limiting growth

3. Stationary phase- no increase in population number of cells being produced is equal to the number of cells dying.

4. Death phase- unfavourable conditions eg temp/ ph/ toxins/ increases death rate above reproduction rate. Many cells undergo autolysis self digestion.

Hint 5

Curve pic gro

Front 6

Growth of bacteria ( state the growth phase) lag phase, log exponential phase, stationery phase, death phase.

Back 6

1. Lag phase- no or little cell division occurs, cell increases in size. RNA, proteins and enzyme synthesis occurs.

2. Log/ exponential phase- maximum cell division. Conditions are at optimum eg nutrient levels, temperature and PH, no factors are limiting growth

3. Stationary phase- no increase in population number of cells being produced is equal to the number of cells dying.

4. Death phase- unfavourable conditions eg temp/ ph/ toxins/ increases death rate above reproduction rate. Many cells undergo autolysis self digestion.

Hint 6

Curve pic gro

Front 7

State the 4 factors which affects the microbial growth

Back 7

Bacteria only grows when external conditions are suitable.

- Temperature : low slow growth, because low kinetic energy reduces enzyme activity. Depp freeze prevents bacteria growth but dose not kill bacteria. However high temperatures destroy most bacteria by denaturing enzyme ( autoclaving or incineration is used to ensure sterilisation)

- Ph: higher or lower than optimum ph causes denaturation of enzymes necessary for cell metabolism and growth ( that’s why buffers are used)

- Oxygen: some bacteria require it some dose not. Yeast can respite both aerobically producing CO2 and H2O or anaerobically (during brewing) producing alcohol and CO2

- Nutrient: different microbes require different minerals, vitamins. And all need nitrogen source (usually nitrate) to produce amino acids for protein synthesis which produces enzyme required for growth

Front 8

1. What is heamocytometry

2. Define heamocytometer

3. What are the methods for measuring growth of bacteria

Back 8

1. Process which used to measure total cell count

2. Heamocytometer is a counting chamber. Most has a volume of 0.004mm^2

3. Well mixed sample diluted , seen under microscope, number of microorganisms in several square is counted, an average is found and using the dilution factor the number of microorganisms in the original sample is estimated. (Rule- only count cells which overlap the line on the top and left of the square; those at the bottom and right is not counted) this is only total cell count it dose not tell us if the cell are alive or dead

Front 9

Turbidimetry is another type of method in which total cell number is counted explain how?

Back 9

In this technique a colorimeter is used. Sample revived aseptically and mixed throughly before placing in cuvette and put into calorimeter, optical density is measured (recorded as percentage absorbance) if more cells present = grater turbidity = higher percentage absorption.

(Note: living cells cannot be distinguished from dead, particles and cells cannot be distinguished either. So to over come this the calorimeter is set to zero before use by using a blank containing the culture medium alone. 🌚

Front 10

There are two forms of estimate of cell number in a microbial population state them

Back 10

1. A total cell count = the total number of cells present, living dead. Includes two methods heamocytometry and turbidimetry

2. A viable count = only living cells eg only the cells capable of dividing. Dilution platting/ serial dilution

Front 11

There are two forms of estimate of cell number in a microbial population state them

Back 11

1. A total cell count = the total number of cells present, living dead. Includes two methods heamocytometry and turbidimetry

2. A viable count = only living cells eg only the cells capable of dividing. Dilution platting/ serial dilution

Front 12

Explain dilution plating/ serial dilutions (viable counts) number of living cells

Back 12

- samples of standard volume is removed aseptically at a set time period

- large number of cells can be diluted by serial dilution using water (10^-1,10^-2,10^-3,10^-4 etc)

- measured sample from each dilution is aseptically transferred by a sterile syringe to a sterile agar plate and incubated under optimum conditions.

Because colony produced has arisen from single microorganism the number of microorganisms in the original sample can be calculated.

Note: usually 3 samples are taken from each dilution and the average number of colonies is used from these 3 plates ( random chance)

Note : plates which has too many bacterial colonies are not used as there are too many to count, plates with few cannot be used as using this could result in sampling error. So medium plates are used.

Hint 12

Calculation

1. Count cell

2. Calculate number of cells in a given volume (normally/cm3)

3. Correct for any dilution factor

4. Convert to the correct volume units