Microbiology – Alcamo Growth and Growth Phases. Growth Human Terms: Growth = Larger Microorganism Terms: Growth = More.

Microbiology – AlcamoGrowth and Growth Phases

Growth

• Human Terms:

Growth = Larger

• Microorganism Terms:

Growth = More

Growth

• Binary Fission – bacteria reproduce asexually:– Chromosome duplicates– Cell elongates– Plasma membrane pinches in at center– Nuclear material distributes evenly– Cell wall thickens to separate dividing

cells

Growth

• Binary fission – gives immortality to bacteria

• The first bacterium never dies

• It reproduces and becomes a new, young cell again

• The original bacterium (billions of years old) is still among us

Binary Fission United Streaming

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Growth

Reproduction

Binary Fission

20 Generation

21 Generation

22 Generation

23 Generation

Generation Time

• Time between cell divisions when bacteria grows and develops its unique features

• Also called “Doubling Time”

• A determining factor in the amount of time that passes between entry of an organism into our bodies and the appearance of disease symptoms

Growth

• Each microorganism has it’s own characteristic generation time

• Range: – Usually 1 to 3 hours– Minimum 20 minutes (E. coli)– Maximum 33 hours (T. pallidum -

syphilis)

BACTERIAL GROWTH IS LOGARITHMIC

Growth

Growth Rates

• If after 48 hours of incubation, a colony is pinpoint size, long GT is indicated.

• If after 48 hours, the colony is ¼” wide, short GT is indicated.

Growth Example

E. coli has a 20 minute generation time under ideal conditions:

Time # of Bacteria

0 1

1 hour 8

2 hours 64

3 hours 512

10 hours > 1 billion

36 hours Cover face of the earth

Growth

Growth Rates

• Exponential growth signifies ideal conditions and maximum reproduction

• But the reproductive potential of bacteria is never fully realized due to environmental limitations

Growth Phases

• Many dynamics affect the population of bacteria over the course of time

• A certain population’s history may begin when:– Several bacteria enter the human

respiratory tract– Several bacteria are transferred to a tube

of growth medium in a lab

Growth Phases

Lag Phase:

• First few hours of growth curve

• Period of adjustment to new environment

• If an infection, WBC’s can be engulfing some cells

• If in a lab, some cells may die from transfer shock

Growth Phases

• The activity of the remaining cells is intense as they:– Store nutrients– Synthesize enzymes– Prepare for binary fission

• But the curve remains at a plateau, where the number of cells reproducing equals the number of cells dying

Growth Phases

Log Phase:

• Also called “exponential” phase

• The mass of each cell increases rapidly and reproduction follows

• As each generation time passes, the number of bacteria doubles and the graph rises quickly

Bacterial Growth

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Growth Phases

• In humans, disease symptoms arise during the log phase– Bacterial population is high enough to

cause damage– Fever, coughing, tissue damage arise

• In a lab, visible signs of growth will be seen: – colonies will appear on solid media– broth media will become cloudy

Growth Phases

• Research experiments are usually done during the log phase because the population of bacteria is at its maximum potential

Growth Phases

Stationary Phase:

• Period of even population numbers

• Reproduction rate = death rate

• No change in total number of bacteria

Growth Phases

• Stationary Phase:

• In humans: – the immune system may be destroying the

bacteria – antibiotics have been administered

• In the lab:– nutrients are becoming scarce– waste products are building up– oxygen or water could be in short supply

Growth Phases

Decline Phase:

• Environment becomes progressively worse and exerts its limiting powers

– pH is changing

– oxygen and nutrients are scarce

– accumulation of toxins

Growth Phases

• Decline Phase:

• Number of cells dying exceeds the number of new cells formed

– Spore forming species will start to produce spores

– Flagellated species will try to move to a new location

– For other species, culture death is eminent

Things That Affect GrowthTemperature

• Different species grow at different temperatures– Psychrophiles – grow best between 0oC

and 20oC– Mesophiles – grow best between 20oC and

40oC– Thermophiles – grow best between 40oC

and 90oC

Things That Affect Growth Temperature

• Most bacteria are Mesophiles, especially pathogenic bacteria that grow in the human body (37oC)

• When the body’s temperature rises to 40oC (104oF) there is a slightly negative affect on bacterial growth

• The lab incubator is set at 37oC to encourage bacterial growth

Things That Affect Growth Temperature

• Some mesophiles can grow at refrigerator temperatures and cause food spoilage

• Staphylococci can grow in the refrigerator and deposit their toxins on cold cuts, salads and leftovers

• If these foods are eaten without further cooking, food poisoning can result

Things That Affect Growth Temperature

• Salmonella outbreak in a restaurant in 1991

• Restaurant employee prepared Caesar salad dressing which contains raw egg

• It may have remained at room temperature too long before being served

• Within 3 days, 15 people were ill with diarrhea, fever, cramps and vomiting

Things That Affect Growth Oxygen

• Aerobic bacteria – require oxygen to grow

• Anaerobic bacteria – require an oxygen-free environment to grow– Includes Clostridium species that cause

tetanus and botulism

• Facultative bacteria – grow in either the presence or absence of oxygen– includes many staphylococci, streptococci

and bacilli

Things That Affect Growth pH

• Bacteria have a neutral internal environment

• Will tolerate a pH range of 6.5 – 7.5

• Human blood and tissues have a pH of ~7.2 – 7.4

• Provides a suitable environment for disease causing bacteria to grow

Things That Affect Growth pH

• Certain bacteria are acid-tolerant

• Useful in the food and dairy business

• Lactobacillus and Streptococcus produce the acid that converts:– milk to buttermilk– cream to sour cream– milk curds to cheese

• These bacteria pose no threat to good health even when eaten in large quantities

Things That Affect Growth pH

• Most bacteria do not grow well under acidic conditions

• Stomach’s acidic environment prevents disease

• Certain acidic foods are hardly ever contaminated with bacteria– Citrus fruits– Cabbage– Tomatoes

Things That Affect Growth Pattern of Nutrition

• Bacteria (like us) need:

–water

–foods to serve as energy sources and as raw materials for synthesis of cell components

Things That Affect Growth Pattern of Nutrition

• Two patterns for obtaining nutrition:– Autotrophy – can make their own food

using inorganic carbon, water and sun’s energy

– Heterotrophy – obtain preformed organic molecules from the environment for structural components and energy

• Saprobes – feed exclusively on dead organic matter such as rotting wood

• Parasites – feed on living organic matter such as human tissues

Things That Affect Growth Bacterial Cultivation

• In the lab, bacteria are grown in:– nutrient broth containing water, beef

extract and peptone (protein supplement)– nutrient agar – contains the same, plus

agar, a polysaccharide derived from marine algae

*Most bacteria grow well in these

Things That Affect Growth Bacterial Cultivation

• Some bacteria require enriched or specialty media

• The streptococci that cause strep throat and scarlet fever grow well when whole blood is added to the media

• Blood agar – heated before solidification to disrupt the red blood cells and release hemoglobin

• Sometimes called chocolate agar

Things That Affect Growth Bacterial Cultivation

• Selective media – contain ingredients to inhibit the growth of certain bacteria in a mixture while promoting the growth of others– Mannitol salt agar – high salt content

inhibits the growth of most bacteria, but allows for staphylococci to grow

– Eosin methylene blue agar – contain dyes that inhibit Gram-positive bacteria, but allow growth of Gram-negative

Things That Affect Growth Bacterial Cultivation

• Differential Media – makes it easy to distinguish colonies of one organism from colonies of another on the same plate

• MacConkey’s agar contains red dyes as well as lactose– Colonies of bacteria that ferment lactose

are red– Colonies of bacteria that don’t ferment

lactose are colorless

Things That Affect Growth Bacterial Cultivation

• Natural Media – not chemically defined– Exact components and quantities are not

known– Some bacteria will only grow on natural

media

• Synthetic Media - chemically defined– The nature and amount of each component

is known

Things That Affect Growth Intermicrobial Relationships

• Symbiosis – situation in which two populations of organisms interact in a close and permanent association

• Benefits obtained may involve:– food– protection– support

Things That Affect Growth Intermicrobial Relationships

• Mutualism – symbiosis that benefits both populations

• Bacteria living on roots of plants:– Bacteria trap nitrogen for plants to

synthesize amino acids– Plants provide a stable environment and

growth factors for bacteria

Things That Affect Growth Intermicrobial Relationships

• Commensalism – one population receives benefit from the relationship while the other is not helped or harmed

• Bacteria that inhabit human skin:– Bacteria has a place to live and food– We are not helped or harmed in any way

Things That Affect Growth Intermicrobial Relationships

• Synergism – two populations live together and accomplish what neither could alone

• Trench mouth – two populations of bacteria (usually rods and spirochetes) must be present for infection of the oral cavity to occur

Things That Affect Growth Intermicrobial Relationships

• Parasitism – symbiosis is beneficial to one population (parasite) but harmful to the other (host)

• The bacteria of all human diseases are parasites

Applications

• Industrial: Recover growth products Penicillin Vinegar Wine Pickles Beer Cheese Alcohol

• Medical: Phases of disease parallel growth phases of pathogen