Isolation

isolated colonies

made of one type of microorganism

colony

millions of identical microorganisms arises from division and growth of a single organism

purity of food is determined by

concentration of bacteria present

purpose of streaking plate

separate bacterial species in a mixed culture, pattern results in isolated colonie, will show macroscopic morphology

quadrant streak plate method

streak 1st quadrant, rotate plate 90^o and streak plate in 2nd quadrant overlapping with the first a few times. repeat for 3rd and 4th quadrant. do not obtain additional samples for 2nd, 3rd, and 4th quadrants since it is suppose to be organism of quadrant 1 spread out, flame between streaks so that all the samples come only from the streak before

isolated colonies in streak plate method

in 3rd or 4th quadrant

advantages and disadvantages of isolation

requires one sterile plate and inoculating tool, more skill, quickly conducted to obtain good results

what is a pure culture and why is it important

one type of microorganism, study morphological, physiological, and growth characteristics of a single organism

single colony

started as single cell, cells in colonies are the same, can be used to inoculate media to start pure culture

cfu

colony forming unit

for a plate count how many colonies are too few to give a statistically reliable result

<30

for a plate count how many colonies are too many to give a statistically reliable result

>300

formula used to calculate bacterial density for a standard plate count

cfu/ml = (# of colonies x dilution factor) / volume added to plate (ml)

spectrophotometer

As the number of cells in a culture increase with time, the turbidity (cloudiness) of the culture will also increase. turbidity is measured using this. light passes through a culture tube, it will be absorbed or scattered by the bacterial cell, which prevents the light from reaching the light detector. This amount of light lost is referred to as the absorbance or optical density (OD). The larger the number of cells in the culture, the more light will be absorbed/scattered, and the higher the absorbance/optical density of the culture

lag phase

A. pop has small growth, adjustment to new environment, cells are metabolically active as they synthesize macromolecules needed to division

log (exponential) phase

cells dividing at max rate and growth curve shows a steep increase

stationary phase

cell multiplication often offset by cell death, so pop. numbers stay consistent

death phase

pop. begins to occur at rapid rate and curve shows steep decrease in numbers