Microbial GrowthMicrobial Growth

Requirements for GrowthRequirements for Growth

Temperature pH Osmotic pressure Oxygen Nutrients

Temperature pH Osmotic pressure Oxygen Nutrients

TemperatureTemperature

Psychrophiles – cold loving Mesophiles – moderate Thermophiles – heat loving

Most important human pathogens are mesophiles

Optimum growth temperature is 37°C

Psychrophiles – cold loving Mesophiles – moderate Thermophiles – heat loving

Most important human pathogens are mesophiles

Optimum growth temperature is 37°C

Growth Rates and Temperature

Growth Rates and Temperature

Food SpoilageFood Spoilage

pH and GrowthpH and Growth

Most bacteria and especially the important human pathogens grow best at a pH near neutral, 6.5 – 7.5

Neutrophiles Acidophiles – bacteria that can

survive and grow at low pH Alkalinophiles – bacteria that can

survive and grow at high pH

Most bacteria and especially the important human pathogens grow best at a pH near neutral, 6.5 – 7.5

Neutrophiles Acidophiles – bacteria that can

survive and grow at low pH Alkalinophiles – bacteria that can

survive and grow at high pH

Osmotic PressureOsmotic Pressure

Bacteria are 80-90% water If the cells are placed in a high salt

or sugar solution the cells lose water and cannot grow

PLASMOLYSIS Few bacteria survive high salt HALOPHILES

Bacteria are 80-90% water If the cells are placed in a high salt

or sugar solution the cells lose water and cannot grow

PLASMOLYSIS Few bacteria survive high salt HALOPHILES

PLASMOLYSISPLASMOLYSIS

How about some nice salt pork?

How about some nice salt pork?

Because high salt or sugar prevents bacterial growth such foods as salted meats, honey, jellies, etc will usually not spoil if kept at room temperature

Salt preserved meats were used for long ocean trips

Molds can grow however in high sugar, so be careful!

Always refrigerate when in doubt

Because high salt or sugar prevents bacterial growth such foods as salted meats, honey, jellies, etc will usually not spoil if kept at room temperature

Salt preserved meats were used for long ocean trips

Molds can grow however in high sugar, so be careful!

Always refrigerate when in doubt

Chemical RequirementsChemical Requirements

Carbon source – needed to make all organic compounds

Nitrogen, sulfur, phosphorus – synthesis of proteins, nucleic acids, and ATP

Trace elements – iron, zinc, copper

Carbon source – needed to make all organic compounds

Nitrogen, sulfur, phosphorus – synthesis of proteins, nucleic acids, and ATP

Trace elements – iron, zinc, copper

Oxygen RequirementsOxygen Requirements

Strict aerobe – requires oxygen Facultative anaerobe – grows in the

presence of oxygen but can without oxygen

Obligate anaerobes – cannot use oxygen for growth

Aerotolerant anaerobes – do not use oxygen for growth but can tolerate it

Strict aerobe – requires oxygen Facultative anaerobe – grows in the

presence of oxygen but can without oxygen

Obligate anaerobes – cannot use oxygen for growth

Aerotolerant anaerobes – do not use oxygen for growth but can tolerate it

Anaerobe jarAnaerobe jar

What’s the problem with oxygen?

What’s the problem with oxygen?

During normal respiration bacteria produce oxygen free radicals O2- which combine with 2H+ to produce hydrogen peroxide H2O2 which is toxic

The enzyme that makes this reaction happen is SUPER OXIDE DISMUTASE (SOD)

Another enzyme CATALASE breaks down the H2O2 into H2O and O2

Obligate anaerobes usually have neither SOD or catalase and are killed by oxygen and toxic by-products

During normal respiration bacteria produce oxygen free radicals O2- which combine with 2H+ to produce hydrogen peroxide H2O2 which is toxic

The enzyme that makes this reaction happen is SUPER OXIDE DISMUTASE (SOD)

Another enzyme CATALASE breaks down the H2O2 into H2O and O2

Obligate anaerobes usually have neither SOD or catalase and are killed by oxygen and toxic by-products

High CO2 - CapnophilesHigh CO2 - Capnophiles

Growth of Bacterial Cultures

Growth of Bacterial Cultures

Bacteria reproduce by BINARY FISSION

Time required for a cell to divide is the generation time

Generation time is highly variable Generally 1-3 hours but can be as

short as 30 min

Bacteria reproduce by BINARY FISSION

Time required for a cell to divide is the generation time

Generation time is highly variable Generally 1-3 hours but can be as

short as 30 min

Growth curveGrowth curve

Stages of Growth CurveStages of Growth Curve

Lag – little increase in number, cells are “getting ready” to grow

Log – rapid, exponential growth, cells most metabolically active, most rapid generation time

Stationary – growth rate slows, equilibrium

Death – decline, cell death exceeds cells formed

Lag – little increase in number, cells are “getting ready” to grow

Log – rapid, exponential growth, cells most metabolically active, most rapid generation time

Stationary – growth rate slows, equilibrium

Death – decline, cell death exceeds cells formed

Measuring Bacterial Populations

Measuring Bacterial Populations

Plate counts Most common way to measure

bacterial number Make a series of dilutions, plate

selected dilutions, count colonies Multiply number of colonies by

dilution factor to get COLONY FORMING UNITS

Plate counts Most common way to measure

bacterial number Make a series of dilutions, plate

selected dilutions, count colonies Multiply number of colonies by

dilution factor to get COLONY FORMING UNITS

On what do you grow bacteria?

On what do you grow bacteria?

Culture media Culture media can either be solid or

liquid and contains all the nutrients the microbe needs to grow

Adding bacteria to sterile media is called INOCULATION

The growth is called a CULTURE Visible growth on solid media is called a

colony

Culture media Culture media can either be solid or

liquid and contains all the nutrients the microbe needs to grow

Adding bacteria to sterile media is called INOCULATION

The growth is called a CULTURE Visible growth on solid media is called a

colony

What is agar?What is agar?

Agar is the solid agent on which bacteria grow

Agar is made from seaweed Bacteria cannot break down the

agar so it is the perfect solid media on which to observe bacterial growth

Agar is the solid agent on which bacteria grow

Agar is made from seaweed Bacteria cannot break down the

agar so it is the perfect solid media on which to observe bacterial growth

Types of mediaTypes of media

Chemically defined media

Exact chemical composition is known

Chemically defined media

Exact chemical composition is known

Complex media Exact chemical

composition if media is not known

Most common type of lab media

Complex media Exact chemical

composition if media is not known

Most common type of lab media

Chemically defined mediaChemically defined media

Complex mediaComplex media

Selective and Differential Media

Selective and Differential Media

Selective media Special media

that inhibits growth of unwanted bacteria and encourages the growth of desired bacteria

Selective media Special media

that inhibits growth of unwanted bacteria and encourages the growth of desired bacteria

Differential media Media that allows

you to distinguish different types of bacteria growing on a plate usually by color of colonies or growth patterns

Many media are BOTH selective and differential

Differential media Media that allows

you to distinguish different types of bacteria growing on a plate usually by color of colonies or growth patterns

Many media are BOTH selective and differential