Unit 3 Flashcards by Emily Ulrich

What are the 2 levels of bacterial growth

Cellular growth

Replication

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Cellular growth of bacteria

Increasing mass at the cellular level (in preparation to divide)

Makes new cell components (proteins, cytoplasm, cell wall, DNA)

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Replication in bacterial growth

Increasing mass at the population level

The number is cells increase exponentially due to binary fission

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Binary fission

How bacteria replicate: one bacteria divides into 2 identical daughter cells

2 stages:
Replication of cellular components

Separation into two equal and identical halves by forming a septum in the middle of the cell

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Generation time (AKA doubling time)

Time required for one round of binary fission (amount of time to double the number of bacteria)

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What does the generation time depend on

Environment: growth factors, temp, oxygen, nutrients etc

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Exponential (log) growth

The number of bacteria or population size doubles every generation

Equation:

N(total)=(Ni) 2^n

N= population 
n= generation

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Bacterial growth curve is observed when

Microorganisms are grown in a culture in a closed system (limited space and nutrients)

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What are the 4 phases of the bacterial growth curve

Lag phase

Exponential/log phase

Stationary phase

Senescence/death phase

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What is the lag phase

Period of adjustments after cells are inoculated into fresh media

Very slow growth

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What happens during the lag phase

Cells adapt to new conditions
Cells repair, and replenish spent materials
Increase in size due to synthesis of DNA and proteins
Minimal cell division

Varies in length (short, long or absent)

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What is the exponential phase?

AKA log or logarithmic phase

Bacteria have acclimated and conditions are now optimal for growth (excess nutrients, space, lack of toxins)

Rapid growth (consistently doubles)

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Why is the log phase clinically significant? (2)

Population is most uniform (chemical and physical properties): best time to identify bacteria

Bacteria in this phase are MOST susceptible to antibiotics

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Why are bacteria most susceptible to antibiotics during the log phase

Because antibiotics often target a stage in binary fission

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What is the stationary phase

Rate of replication equals rate of death

Overall number of bacteria stays constant

Occurs when growing conditions are no longer ideal

Less susceptible to antibiotics here

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What is the senescence/death phase

Rate of cell death exceed rate of growth

Rapid decline in numbers of viable bacteria

Majority of cells die by autolysis

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Autolysis

Expression of specific self-digestion Genes

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Dormancy (metabolically inactive) bacteria is a response to what

Potential or actual change in environment, when it becomes unfavourable

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What makes an environment unfavourable

Lack of nutrients 
Lack of spaces
Increased waste 
Change in oxygen 
Change in temp
Presence of antibiotics

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Examples of dormant states of bacteria

Persister cells

Endospores

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What are persister cells

Small number of cells in a population that are slow or non growing

When environmental conditions improve, they reestablish population/reinfect

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Persister cells are more ____ to kill with antibiotics

Difficult

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Persister cells hide out in macrophages, and can survive through antibiotic treatment, to

Re infect

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What are endospores

A dormant, tough, non reproductive structure in bacteria (gram positive)

Production Triggered by lack of nutrients (starvation)

Resistant to dry conditions/heat

Difficult to eliminate

Bacillus and clostridium produce these

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Why is it important to know which phase of growth bacteria are in?

Bacteria can be identified best in the log phase Bacteria are most vulnerable to harm in the log phase Cells are more difficult to treat and identify in stationary phase Stages of growth correspond to stages of infection

Physical and chemical requirements for growth

``` Temperature Oxygen levels PH Moisture Osmotic pressure Space ```

Temperate affects

Rate and amount of growth

Minimum temperature

Lowest temperature that growth will occurs | Less than minimum will inhibit growth

Optimal temperature

Growth is maximal Ex. Incubator temperatures

Maximum temperature

Highest temperature at which growth will occur If exceeded, denaturation will occur

Most clinically relevant species are mesophiles, their range of temperature is

20-45 degrees Celsius

Fever

A Mechanism the body uses to decrease microbial growth during infection

The ability to withstand low and high temperatures would be considered a

Pathogenic factor

Ideal temperatures for: psychrophile

0-20 degrees Celsius

Ideal temperatures for: psychrotrophs

0-30 degrees Celsius 15 degrees is optimal

Ideal temperatures for: mesophile

20-45 degrees Celsius

Ideal temperatures for: thermophiles

45-85 degrees Celsius

Ideal temperatures for: thermoduric

Able to withstand high temp but do not grow at them, can survive pasteurization, including spores

Bacteria require certain amounts of oxygen for growth depending on

The type of metabolic enzymes they express

Bacteria that produce energy via oxidative phosphorylation and the electron transport chain

Require oxygen

Bacteria that produce energy via fermentation

Do not require oxygen

Aerobes

Grown in 21% oxygen

Obligate aerobes

Can’t grow without oxygen

Facultative anaerobe

Grown best in aerobic conditions but can grow in absence of oxygen (Intestinal bacteria)

Obligate anaerobe

Cannot grow if exposed to oxygen

Microaerophile

Grow in 2-10% oxygen

Some bacteria can alter their environments pH, how does E. Coli do this

Frequent cause of UTIs Produces urease: an enzyme that converts urea to ammonia and CO2 to bring urine closer to ideal pH Urine is slightly acidic, E.Coli has an optimal growth at pH of 7

Optimal pH range for: acidophils

pH 4 (0-5.5)

Optimal pH range for: neutrophils

pH 7.2 (5.5-8.5)

Optimal pH range for: alkaliphils

pH 9 (8.5-11.5)

Bacteria are made up of 70% water | So moisture is

Necessary for growth

Osmotic pressure is

Difference in solute concentration between the inside of the bacteria cell and external environment

Isotonic

No water movement

Hypotonic

Less solutes outside the cell, more solutes inside the cell Water moves into the cell, cell swells and bursts (lysis due to osmotic pressure) Cell wall protects from osmotic lysis

Hypertonic

Water moves out of the cell causing shrinkage (dehydration) (plasmolysis) More solutes outside the cell

Why do bacteria need room to grow?

Space allows toxic metabolic waste to diffuse out

Normal intestinal flora are important in maintaining health by

Occupying space and preventing pathogenic bacteria from finding space to grow

Metabolism: catabolism

Process of energy production | Energy is released by breaking down large molecules into smaller ones

Metabolism: anabolism

Energy requiring processes Energy is used to build molecules for growth and repair

Heterotrophs

An organism that eats other plants or organisms for energy Require pre-formed organic matter for energy and carbon needs (must be supplied)

Why are bacteria more versatile than mammals in terms of nutrition?

Bacteria can utilize a wider range of nutrients including inorganic sources of carbon and other elements

Macronutrients

Nutritional elements required in relatively large amounts by all living organisms

Main macronutrients

Carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus

True or false | Some bacteria can obtain carbon, nitrogen and sulfur from inorganic sources

True

Other macronutrients need in lesser amounts

Potassium, calcium, sodium, magnesium, iron Needed for proper function of enzymes and to maintain osmolarity

Micronutrients | AKA trace elements

Only very small amounts required Involved as co-factors in enzyme function and protein structure

Examples of micronutrients

Manganese, zinc, Cobalt, Molybdenum, nickel, copper

Essential nutrients are

Any nutritional component that has to be provided to the cell/organism because it is unable to produce it on its own Usually taken from the host

Bacteria have Different nutritional requirements based on the

Metabolic enzymes they have genes for

Why must you know nutritional differences when growing bacteria in vitro

Can use to differentiate between different species

Unit 3 Flashcards

(70 cards)