Chapter 10: Bacterial Growth

Why is bacterial growth important (2)?

1. An increase in numbers is one of the requirements for infection

2. Understanding the requirements for growth will help in understanding the infectious process and how to prevent/inhibit infection

_____________________ vary between bacterial species; time interval between cell divisions

Generation times

What are generation times heavily influenced by?

Environmental pH, osmotic pressure, oxygen level, availability of nutrients, and temperature

What are examples of organisms that have the shortest generation (doubling) times?

E. coli, Salmonella, S. aureus (20 minutes)

What is an example of an organism that has the longest generation (doubling) times?

Mycobacterium (around 30 days); one month to go from one cell to two

What are usual bacterial generation times?

1-3 hours

doubling in bacteria

Binary Fission

How many generations (doublings) would it take for one cell to become a population of more than a million cells?

20 generations yield 1,048,576 bacteria (over a million)

If the bacteria has a generation time of 30 minutes, how long for one cell undergoing doubling to become a visible colony? (Rule of thumb: a visible colony of bacteria has a million or more bacteria in it)

Ten hours (20 generations of 30 minutes each); why streaking for isolation grows colonies in the plate overnight

what happens when you take loop with bacteria then put it in broth

Standard Growth Curve

What are the 5 phases on the Standard Growth Curve for bacteria?

1. Lag phase

2. Exponential log phase

3. Stationary phase

4. Death phase

5. Prolong/decline

bacteria are adjusting to their environment and may have to synthesize enzymes to utilize the nutrients available in the environment

Lag phase

Lag phase: What does how long this phase lasts vary depending on?

The organisms/bacterial species and the environment/culture conditions

Lag phase: How much binary fission occurs?

Little if any

What is the lag phase like for the cell?

No change in numbers, but an intense time

phase where the number of bacteria doubles exponentially

Exponential log phase

Log phase: There is a constant minimum __________________

generation time

How long does the log phase last/is sustained?

Only as long as suitable levels of nutrients is available and when environmental conditions remain favorable

Log phase: Conditions for this phase can be what?

Artificially maintained

device that permits the replacement of depleted medium with fresh, nutrient rich medium

Chemostat

Log phase: What are bacteria like during this phase?

Most metabolically active and therefore most sensitive to antibiotics (as well as radiation and and adverse environmental changes)

Log phase: Why are antibiotics that target peptidoglycan extremely effective during this period?

When bacteria divide, cell wall production is at its peak

Log phase: Why are treatments targeting the bacterial ribosome also highly effective?

Translation is also maximal during this phase

phase caused by a decreasing availability of nutrients; waste levels begin to rise

Stationary phase

Stationary phase: What is the number of cells dying equal to?

The number of cells being produced during cell division

Why is the stationary phase relatively short?

Since it depends on the availability of nutrients, which continue to disappear throughout this phase

phase in which there is a continuous decline in the number of dividing cells that is caused by the exhaustion of the nutrient supply and the collapse of the environment due to the build-up of toxic waste products

Death phase

What is the death phase AKA?

Logarithmic decline phase

E. coli was incubated with aeration (shaking) in a nutrient medium containing 2 carbon sources, and the growth curve below was made from this culture.

a. Explain what happened at the time near the 2nd line

b. Which substrate provided better growth conditions for the bacteria? How can you tell?

a. Transition from log to stationary

b. Glucose: substrate (glucose) is used at first because it is a better carbon substrate as rise in log number of cells is faster than with lactose

Why did it switch from log to stationary the first time?

Glucose was exhausted

multiple log phases, medium contains more than one carbon source

Diauxic growth

What are the 2 major categories for bacterial growth?

Physical and chemical

What are the physical requirements for bacterial growth?

Temperature, pH, osmotic pressure

What are the chemical requirements for bacterial growth?

Sources of carbon, nitrogen, sulfur, phosphorus, organic growth factors, and trace elements

What is there an especially notable and diverse relationship among bacteria?

To oxygen (O2)- ranging from absolute requirement to lethal, toxic gas

temperature at which the highest rate of growth occurs

Optimum growth temperature

What are the 2 types of cold-loving bacteria?

Psychrophiles and psychotrophs

grow at cold temperatures; can grow at a few degrees below 0 if they are in the presence of salts of sugars that prevent ice

Psychrophiles

grow best between 20-30 C; can grow from 0 to 35

Psychotrophs

most human pathogens are this, most common types of bacteria; bacteria that grow best at moderate temperatures; 25-40 C

Mesophiles

heat-loving bacteria (2); only grow at temps above 40 C

Thermophiles and hyperthermophiles

grows best between 40 to 80 C

Thermophiles

those that grow above 70-80C; none of these bacteria are pathogenic to humans, the human body would be like a refrigerator to them

Extreme thermophiles AKA hyperthermophiles

Listeria grows in the fridge, why is this that significant?

Fridge works to keep food pathogens from growing as they are mostly mesophilic. Listeria is psychrophilic, so even properly stored food may support the growth of Listeria (cause of stillbirth pregnancy and life-threatening for AIDS, cancer, and transplant patients)

Who is at highest risk for Listeria?

Pregnant, 65 or older, or a weakened immune system

What foods are mostly contaminated with Listeria?

- Soft cheese

- Raw milk

- Deli meats

- Sprouts

lowest temperature at which the organism grows

Minimum growth temperature

highest temperature at which growth occurs

Maximum growth temperature

Why is temperature so important to the function of bacteria?

Importance of protein structure and function, once again; temperature denatures protein, destroying its ability to function

What are some examples of bacteria that prefer certain temps and show that in how they reside there?

Syphilis preferring the lips, tongue, etc; leprosy preferring the extremities of the body

Many human pathogens have optimal growth temperatures at 37 degrees Celsius. So what might one of your body's responses to an infection (fever) do for you?

Fever may raise body temperature above the optimum temperature for the pathogen, bumps organism off optimum growth rate

Why are Mycobacterium leprae infections limited to body surfaces and extremities?

Optimum growth temperature is less than 37 C; cannot grow at our body temperature of 37 C, so it grows on body surfaces and extremities that are cooler

Why are 9-banded armadillos used to culture M. leprae?

Zoonotic reservoir that has a body temperature less than ours, so it supports the growth of M. leprae

bacteria that grow in extremely low pH values

Acidophiles

Some bacteria, such as ____________, produce chemical buffers to protect against the pH changes in their environment

H. pylori

What can changes in pH do that can be lethal for bacteria?

Denature proteins

pressure exerted on a bacteria by the water inside and outside the cells; can affect bacterial growth and can be used to inhibit bacterial growth

Osmotic pressure

What is an example of how osmotic pressure can be used to inhibit bacterial growth?

Food being preserved in high salt concentrations creates a hypertonic environment and causes organisms that might spoil the food to undergo plasmolysis

bacteria that prefer to be in a high-salt (high-solute) environment

Halophiles

require high salt concentration for growth

Obligate halophiles

live with or without high salt concentrations

Facultative halophiles

can grow in the presence of very high levels of salt

Extreme halophiles

Chemical requirements for bacterial growth what?

Vary widely

Bacteria use growth factors such as what?

Vitamin B1, B2, and B6

What must bacteria do because they cannot synthesize growth factors?

Be obtained from the environment

What do bacteria also require as enzyme co-factors?

Potassium, magnesium, and calcium

Some bacteria also require trace elements such as what?

Iron, copper, and molybdenum

all living things require these atoms for the construction of biological molecules; required for cell structures

Carbon

required for making bacterial amino acids and nucleic acids; integral part of the structure of amino acids, involved in protein synthesis

Nitrogen

What is nitrogen a part of?

The structure of DNA and RNA molecules

How can nitrogen be obtained?

Through decomposition of existing proteins and from ammonium ions found in organic material or from atmospheric nitrogen through nitrogen fixation

required to make some bacterial amino acids (and vitamins)

Sulfur

How is sulfur primarily acquired?

By decomposing existing proteins in which one or more of the component amino acids contain sulfur

In what form is sulfur procured?

Sulfate ion form (SO4^2-)

required for making bacterial nucleic acids, membrane phospholipid bilayer, and ATP (as well as AMP and ADP)

Phosphorus

How is phosphorus obtained?

By cleaving ATP to ADP plus inorganic phosphate

In what form is phosphorus procured?

Ion form PO4^-3

required for functioning of certain bacterial enzymes

Potassium, magnesium, calcium

required for bacterial metabolism

Iron

certain vitamins; some cannot be synthesized and must be obtained from the environment; elements potassium magnesium, calcium to function as enzyme cofactors; trace elements such as iron, copper, molybdenum, and zinc

Organic growth factors

components of bacterial proteins

Amino acids

functions in electron transport in bacteria

Heme

electron carrier

NADH

precursor of bacterial NAD+ and NADP+

Niacin (nicotinic acid)

component of bacterial coenzyme A

Pantothenic acid

precursor of folic acid, which is involved in the bacterial metabolism of carbon compounds and in nucleic acid synthesis

para-Aminonezoic acid

components of bacterial nucleic acids

Purines, pyrimidines

used in the synthesis of bacterial amino acids

Pyroxidine (vitamin B6)

precursor of bacterial FAD

Riboflavin (vitamin B2)

used in some bacterial decarboxylation reactions

Thiamine (vitamin B1)

any bacterium that requires not 1 or 2, but a large number of growth factors; usually slow growing, in a lab, growth medium provides all essential growth factors

Fastidious bacteria

What is an example fastidious bacteria?

Heamophilus influenzae requires rich, complex media containing amino acids, sugars and cofactors, but also NADPH+ and heme (supplied in chocolate agar, containing cooked blood), elevated CO2 levels, and careful temp regulation

What is an example of a non-fastidious bacteria?

E. coli requires only glucose, NaCl, Ammonium phosphate, Mg-phosphate, and K-phosphate

Wild-type E. coli has no what?

Growth factor requirements, and metabolically it can transform glucose into all of the macromolecular components that make up the cell

Where does E. coli get essential trace elements such as iron, copper, molybdenum, and zinc?

E. coli is a very fastidious scavenger. It is difficult to prepare glassware, water, and purified chemicals without tiny amounts of essential trace elements it requires. Can use these trace elements

Heamophilus influenzae is what?

Not the cause of influenza (flu), causes otitis media

Many bacteria do not require ____________ for growth, but die in its presence

oxygen

What is the dark side during normal bacteria respiration?

Form free radicals that are unstable and steal electrons from other molecules, leading to the death of the bacterial cell

What are the 2 aspects to consider when thinking about a bacteria's relationship to oxygen?

Use and toxicity

bacteria are obligated to grow in the absence of O2; cannot survive in the presence of oxygen

Obligate anaerobe