Lab 8: serial dilutions and plate counts

what can microbes do in favorable growth?

reproduce exponentially and reach extremely high population densities in a short time

generation time is?

amount of time it takes a population of microbial to double in numbers

E. coli generation time in the right conditions can take?

As little as 25 minutes

E. coli can grow approximately:

10^6 in 8 hours

Evaluating the Effectiveness of Antimicrobial

-Pasteurization
-Food preservation methods
-Disinfectants/Antiseptics
-Antibiotics

Sanitation reasons to monitor microbial growth in lab settings

-Drinking water quality
-Wastewater quality

Ways to count microorganisms in laboratory settings: microscopically

HEMOCYTOMETER

PROBLEMS with the hemocytometer

• CAN'T DISTINGUISH LIVE/DEAD MICROBES
• DIRT IN SAMPLES CAN BE MISTAKEN FOR MICROBES

viable organisms can be estimated using what?

plate count assays

plate count assays include

pour plate method and spread plate method

pour plate method can what?

estimates the number of facultative anaerobes

facultative anaerobes are:

microorganisms that are capable of growth in either the presence or absence of oxygen

spread plate method can what?

estimate the number of obligate aerobes

Obligate aerobes are:

microorganisms that require oxygen for growth

when preparing agar we use what?

autoclaves

for an autoclave we use what to make sure the temperature is correct?

autoclave tape and autoclave ampoules

Plates with __________ will be used to determine CFUs:

30-300

aliquots are what?

subsamples

CFU stands for what?

colony-forming unit

CFU/mL formula

(# of colonies / volume plated [mL] ) x (dilution factor)

dilution formula

volume of sample/ (volume of sample + volume of diluent)

dilution factor formula

you invert the dilution number