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Bacteria (single celled, prokaryotic)
Only small number are pathogens
Asexually reproduction by binary fission / 2 identical daughter cells
Grow best at optimum conditions (human body)Constant temperature
Neutral pH
Constant supply of food, H2O, O2
Mechanism removing waste
Most bacteria are aerobic / obligated aerobes
Aerobic bacteria growing with absent oxygen / facultative anaerobes
Bacteria which find oxygen toxic / obligate anaerobes
Sigmoid growth curve shows the number of bacteria plotted against time
Bacteria MUST grow in closed system and nutrient medium → BACTERIAL CULTURE1) Population grows slowly - LAG PHASE
2) Rapid increase of population growth - LOG PHASE
3) Reaches equilibrium when number remains constant - STATIONARY PHASE
Lag Phase → initial phaseLow number of reproducing organisms
Bacteria increase in size before division
This requires nutrients which need to be digested
Digestion requires enzymes, proteins → activation of genes → time consuming process
Log Phase → exponential phase; max growth rate; steep curveOptimum conditions: no limiting factors, waste does not accumulate to a toxic level
Bacteria most susceptible due to production of new cellsAntibiotics inhibit cell wall formation
Antibiotics inhibit DNA replication
Antibiotics inhibit protein synthesis
Stationary Phase → reduced growth rateNew cell production balanced by death of cells
Limiting factors, declining nutrients, accumulating waste influence population size
Decline Phase → bacteria stop dividingDeath rate increases; numbers may fall to zero
Lack of nutrients, build up of toxic waste products
Aseptic conditionsSterilise equipment, instruments, thus, to prevent contamination with the culture.
Use high temp and disinfectants
Total cell count
Number of cells whether living or dead
Count cells with haemocytometer
Stop bacteria entering the flask with a stopper. Important as bacteria would have been caused reduced growth rate of yeast/killed yeast and competed for space/nutrients
Culture is shaken to achieve a uniform distribution of yeast cells/spread out yeast
Larger number is taken to avoid anomalies/produce an average
Measurement of growth
Generation time: time taken for a bacterial population to double
Rate of population= increase in number of yeast cells/time
 = number larger - number less/(time larger - time less)
Suppose the number of cells in one square are 6 8 9 5 7
The sum of the cells in 5 squares is 35
The mean for one type B square is 7
Therefore 25 squares have 25 x 7 = 175 in 0.1mm3
In 1mm3 there will be 1750 cells or 1,8 x 103
Viable cell count
Only living cells since these are the only ones capable of dividing
1cm3 original sample is diluted in 9cm3 distilled H2O
Mix 1cm3 from last dilution with 9cm3 distilled H2O - serial dilution
1cm3 of each dilution is put on an agar plate and counted. Number is multiplied by the dilution factor
Measurement of growth
Number of colonies on the 10-3 dilution plate = 35
Number of viable colonies in 1cm3 of 10-4 dilution of milk
35 x 1/0.1 = 350
Sample was diluted by 10-3
Number of bacteria in 1cm3 of


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