Microbiology Chapter 5.txt

• Binary fission
• The cell doubles in mass
• DNA replicates and the two strands separate
• The cell wall and cell membrane begin to invaginate
• A cross wall forms
• The cell separates

Is an inward pinching of the cell membrane and cell wall to separate the cell into two genetically identical cells

• The generation (or doubling) time is the interval of time between successive binary fissions
• In pathogens, a shorter doubling time means a shorter incubation period of disease

• Lag phase - Getting used to new environment
• Log phase - Exponential growth
• Stationary phase - Birth rate = death rate
• Death phase - Waste (typically acid) contaminates the environment and causes death

• During the lag phase, no cell division occurs while bacteria adapt to their new environment
• When reproductive and death rates equalize, the population enters the stationary phase
• The accumulation of waste products and scarcity of resources causes the population to enter the decline (exponential death) phase
• Exponential growth of the population occurs during the logarithmic (log) phase
• Human disease symptoms usually develop during the log phase
• When reproductive and death rates equalize, the population enters the stationary phase
• The accumulation of waste products and scarcity of resources causes the population to enter the decline (exponential death) phase

• Highly resistant structure formed by Bacillus and Clostridium when nutrient supplies are low
• A stress cell undergoes asymmetrical cell division creating a small prespore and a larger mother cell separated by the transverse septum.

• Cytoplasm
• DNA
• Dipicolinic acid which stabilizes DNA and proteins

Matures the prespore into and endospore then disintegrates, freeing the spore

• Resistant to heat and desiccation
• Undergo very few chemical reactions

• Cell membrane
• Cortex
• Spore coat - thick peptidoglycan
• DNA
• Protein stabilizer - EDTA, similar to Dipicholinic acid

• Mostly G+
• Bacillus anthracis - anthrax
• Clostridium botulinum - botulism
• Clostridium tetanii - tetanus
• Clostridium perfringens - gas gangrene

2 hours boiling

When environmental conditions are again favorable, protective layers break down and the spore germinates into a vegetative cell

• Temperature
• Oxygen
• pH
• Pressure

Each prokaryotic species has an optimal temperature for growth and about a 30� range of acceptable temperatures

Grow optimally below 15�C, and make up the largest portion of all prokaryotes on Earth

Multiply best around 60�C, living in compost heaps and hot springs

Are Archaea that grow optimally above 80�C, found in seafloor hot-water vents

Thrive at the medium temperature range of 10� to 45�C, including pathogens that thrive in the human body

• Many prokaryotes are obligate aerobes, which require oxygen to grow.
• Streptococcus

• Clostridium
• Do not or cannot use oxygen;

Are inhibited or killed by oxygen

Grow either with oxygen, or in reduced oxygen environments

Can be used to test an organism�s oxygen sensitivity

Require an atmosphere low in oxygen and rich in carbon dioxide

Likes a small amount of oxygen

The majority of species grow optimally at neutral (~7.0) pH

• Acid-tolerant prokaryotes
• For example, those used to turn milk into buttermilk, sour cream, and yogurt

• Barophiles can withstand incredibly high hydrostatic pressure
• For example, psychrophiles living at the bottom of the ocean

• Are salt-tolerant prokaryotes
• They can maintain optimal osmotic pressure without suffering from plasmolysis

• Broth
• Living Tissue
• Agar

• General Purpose
• Enriched
• Selective
• Differential
• Synthetic

A complex medium is a chemical unidentified medium such as a nutrient broth or nutrient agar

Primarily for growing rickettsia

• In a synthetic medium, the chemical composition of the medium is known
• Each amino acid is added individually
• Primarily for genetic research

• Contains ingredients to inhibit growth of certain species and allow the growth of others
• SS agar = Salmonella & Shigella

• Will only grow staphylococcus.
• Contains phenol red dye.
• Staph aureus produces acid and turns dye yellow
• Staph epidermidis does produce acid, so the dye turns redder.

Contains specific chemical to indicate species that possess or lack a biochemical process

• Some "fastidious" organisms require an enriched medium containing specific nutrients
• Blood
• Cooked blood (chocolate)

Many prokaryotes cannot be cultured in a laboratory

A pure culture is a population consisting of only one species of prokaryote

• The pour-plate isolation method allows separation of species through dilution of a sample
• Molten agar is poured over a culture in a culture dish

• Method for isolating colonies
• The streak-plate isolation method spreads out individual cells to form discrete colonies of species

• Turbidity - cloudiness
• Direct measurements - actually count
• Indirect methods - measure dry weight of the cell population to get an indication of the mass. Oxygen uptake in metabolism can also be measured as an indication of metabolic activity.

• In the standard plate count procedure, colonies grow on a plate containing a sample of diluted broth
• The number of colonies indicates the original number of viable (living) cells in the broth