Bacterial GrowthBacterial Growth

I. Determine in terms of population size.I. Determine in terms of population size.

Nature there is a of Nature there is a of organisms living together. organisms living together.

How can we get a certain type of How can we get a certain type of bacteria?bacteria?

- separating the progeny - separating the progeny of a single bacterium from all of a single bacterium from all others.others.

- interested in disease causing - interested in disease causing bacteria (major contributor to pure culture bacteria (major contributor to pure culture techniques).techniques).

Initially grew bacteria on potato surface but had Initially grew bacteria on potato surface but had problem:problem:

Not enough for bacterial Not enough for bacterial growth.growth.

Added gelatin as a solidifying agent. Added gelatin as a solidifying agent. (Warm - (Warm - pour, cool - solid)pour, cool - solid)

- simplest & most - simplest & most common method to isolate a single common method to isolate a single

bacterium.bacterium.

Hesse (Koch’s assistant) Hesse (Koch’s assistant) (polysaccharide (polysaccharide extract from marine algae) extract from marine algae) - easier to work - easier to work with then gelatin (solid with then gelatin (solid over a wider range over a wider range then gelatin). then gelatin).

Julius Petri - Julius Petri -

Streak-Plate MethodStreak-Plate Method

II. Bacterial growthII. Bacterial growth

formula to determine formula to determine population size:population size:

b = B2b = B2nn

= Number of = Number of cells at cells at time zero time zero (beginning).(beginning).

= number a cells = number a cells at at any later time.any later time.

= number of cell = number of cell generations.generations.

ReviewReview Why is agar used instead of gelatin or potato?Why is agar used instead of gelatin or potato?

Why is the petri dish unique to prevent Why is the petri dish unique to prevent contamination?contamination?

What is the advantage of bacterial growing by What is the advantage of bacterial growing by binary fission? What is the disadvantage?binary fission? What is the disadvantage?

How many bacteria will there be after 10 hours How many bacteria will there be after 10 hours if the bacteria double every 30 m inutes?if the bacteria double every 30 m inutes?

A. Growth can be A. Growth can be measured as an increase measured as an increase in (weight) of the in (weight) of the population.population.

B. Growth can be B. Growth can be measured as an increase measured as an increase in .in .

1. 1. - - count the count the number of number of colonies colonies on the medium.on the medium.

2. 2. - - counting the counting the number of bacterium in number of bacterium in an known volume of an known volume of liquid.liquid.

III. Factors that influence III. Factors that influence microbial growth.microbial growth.

A. TemperatureA. Temperature

1. Most bacteria grow 1. Most bacteria grow within within or near .or near .

2. groups of 2. groups of bacteria bacteria based upon based upon their optimum their optimum growth growth temperatures.temperatures.

a. 5C a. 5C - 20C- 20C

b. b. 20C - 50C20C - 50C

c. c. 50C - 50C - 80C80C

d. d. +80C+80C

ReviewReview

Describe the difference between Describe the difference between direct count and plate count method.direct count and plate count method.

What are the three temperate What are the three temperate ranges that bacteria tend live in?ranges that bacteria tend live in?

3. Food Preservation

Refrigerators food spoilage because most of the microorganism that cause spoilage are .

4. Temperature & Human diseases.Human body

37C ( ).

20C - 25C ( ).

Ex - leprosy (Mycobacterium leprae)- involves the

regions of the body.

ReviewReview

Why do we store our food in Why do we store our food in refrigerators?refrigerators?

Why do you not want to keep heating Why do you not want to keep heating and cooling the same leftover and cooling the same leftover throughout the week?throughout the week?

Which temperature range to most Which temperature range to most tend to live in and why?tend to live in and why?

B. Oxygen Requirements1. - require free oxygen to grow.2. - will not grow in the presence of free oxygen, may even be killed.3. -prefers the presence of low oxygen (2% - 10% Oxygen).4. - lives in the presence of both:

Growth occurs more rapidly in the presence of oxygen.5. - will grow in the presence of oxygen but do not posse an oxidative metabolism:

Derive no benefit from the presence of oxygen.

Why can some bacteria thrive in the presence of oxygen but others are killed by it?

Oxygen can be converted into a toxic form like (H2O2) & (O2-).

Cells that do not die in the presence of oxygen produce enzymes (

) into a form (H20 & O2).

C. pH

Most bacteria grow best in an medium with a pH of (neutral).Can live in a wider range

Ex. Helicobacter pylori - live in very environments ( ) & may cause ulcers.

Bacteria produce metabolic products that may acidic or basic.

Need a ( ) to grow bacteria.

4. - pressure that is required to prevent the net flow of water across the cell membrane.

effect water movement.

Use salt as an

factor in food preservation.

IV Cell multiplication requires a source of energy & raw material for synthesis of cell components.

A. Bacterial NutrientsRaw Materials

Carbon, Nitrogen, Oxygen, Hydrogen.

all other compounds including ions.

Two Purposes of nutrition1. (Synthesize)

protoplasm.2. Supply energy to

.

B. C. D.

Small organic molecules other than carbon that bacteria must provide in order to grow (amino acids & vitamins).

V. Dynamics of population growth.