Micr 22 Ch.9 Flashcards

How do bacteria reproduce?

By binary fission

What happens to a bacterium before binary fission?

It grows and approximately doubles in size

What structure forms in the center during binary fission?

Fission ring

What forms as the fission ring contracts?

Cross-plate

What are the four phases of the bacterial growth curve?

Lag, log (exponential), stationary, and death phase

What does the bacterial growth curve measure?

Viable cells over time

Why is bacterial growth usually plotted on a logarithmic scale?

Because bacteria grow exponentially

What is generation time?

Time it takes for one cell to divide or for a population to double

What are the units for generation time?

Hours per generation

What is growth rate?

Number of generations per hour

What is the relationship between generation time and growth rate?

They are reciprocals

What formula is used to determine number of generations?

(log P2 − log P1) / log 2

What is the value of log 2 used in bacterial growth calculations?

0.301

How can future bacterial population size be predicted?

P1 × 2ⁿ

What does P1 represent in bacterial growth equations?

Starting population size

What does n represent in bacterial growth equations?

Number of generations

What is one of the most important factors affecting bacterial growth?

Temperature

What is an optimum temperature?

The temperature at which bacteria grow best

What are psychrophiles?

Bacteria that grow best in cold temperatures

What are psychrotrophs?

Bacteria that grow in cold temperatures but prefer moderate temperatures

What are mesophiles?

Bacteria that grow best at moderate temperatures

What are thermophiles?

Bacteria that grow best at high temperatures

What are hyperthermophiles?

Bacteria that grow best at extremely high temperatures

What are aerobic bacteria?

Bacteria that use oxygen for life processes

What are obligate aerobes?

Bacteria that require oxygen

What are microaerophiles?

Bacteria that require small amounts of oxygen

What are anaerobic bacteria?

Bacteria that do not use oxygen for life processes

What are obligate anaerobes?

Bacteria that cannot survive in oxygen

What are aerotolerant bacteria?

Bacteria that tolerate oxygen but do not use it

What are facultative anaerobes?

Bacteria that grow with or without oxygen

Why can oxygen be harmful to bacteria?

It forms reactive oxygen species

What enzyme breaks down superoxide radicals?

Superoxide dismutase (SOD)

What enzyme breaks down hydrogen peroxide?

Catalase

What is singlet oxygen?

A reactive form of oxygen that strips electrons from molecules

What is the optimal pH for most bacterial growth?

pH 7

What pH range is tolerable for many bacteria?

About ±1.5 from optimum

What are acidophiles?

Bacteria that grow in acidic environments

What is an example of an acidophile?

Lactobacillus

What foods commonly involve acidophiles?

Yogurt and sour cream

What are halophiles?

Bacteria that grow best in high salt concentrations

What are halotolerant bacteria?

Bacteria that grow best without salt but tolerate it

What does hypertonicity cause in bacterial cells?

Plasmolysis

What is plasmolysis?

Shrinking of the cytoplasm due to water loss

How do extreme halophiles resist plasmolysis?

By keeping high solute concentrations inside the cell

What solutes may extreme halophiles use to resist plasmolysis?

KCl or organic solutes

What are endospores?

Resistant resting cells formed by some bacteria

Which genera commonly form endospores?

Clostridium and Bacillus

Why do bacteria form endospores?

When deprived of key nutrients

Are endospores metabolically active or inactive?

Inactive

What conditions can endospores survive?

Heat, drying, radiation, and toxic chemicals

What is sporogenesis?

The process of endospore formation

What type of division occurs during sporogenesis?

Asymmetric division

What happens to DNA during sporogenesis?

It becomes compacted

What forms around the developing spore?

A thick peptidoglycan spore coat

What happens to the original parent cell during sporogenesis?

It dies

Why can honey be dangerous for infants?

It may contain Clostridium botulinum endospores

What disease can Clostridium botulinum cause in infants?

Botulism

What toxin is produced by Clostridium botulinum?

Botulinum neurotoxin

What effect does botulinum toxin have?

Flaccid paralysis

Why are adults less affected by botulism from honey?

Their normal microbiota prevent bacterial growth

What is the goal of bacterial isolation techniques?

To separate bacteria from a mixture

What is the purpose of a streak plate?

To isolate bacterial colonies

What is the purpose of a pour plate?

To isolate bacterial colonies in agar

What are indirect methods of measuring bacterial growth?

Methods that measure the population as a whole

What is turbidity?

Cloudiness caused by bacterial growth

What instrument measures turbidity?

Spectrophotometer

What units may a spectrophotometer use?

Absorbance, transmittance, or optical density (OD)

Does turbidity measure live cells only?

No, it measures live and dead cells

What is a direct microscopic count?

A method counting cells under a microscope

Does microscopic count measure live cells only?

No, it counts live and dead cells

What are the units for microscopic count?

Cells/mL

What does MPN stand for?

Most probable number

What does the MPN method estimate?

Viable bacterial cells

What units are used in MPN results?

Bacteria/100 mL

What is the standard plate count method?

A method counting viable bacteria as colonies

What does CFU stand for?

Colony-forming units

What assumption is made in standard plate counts?

Each colony came from one live bacterial cell

What dilution range is commonly used in serial dilutions?

Factors of 10

What colony range is considered countable on a plate?

30-300 colonies

What is the formula for standard plate count calculations?

# colonies / (dilution × volume plated)

What are the units for standard plate count results?

CFU/mL

Why are serial dilutions used?

To obtain countable numbers of colonies

What happens during the lag phase?

Bacteria adjust to the environment

What happens during the log phase?

Bacteria divide rapidly

What happens during the stationary phase?

Growth rate equals death rate

What happens during the death phase?

Cells die faster than they divide