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Medical Microbiology > Chapter 6 - Growth > Flashcards

Chapter 6 - Growth Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

What are the 3 main groups that classify microbes based on their preferred growth temperatures?

A

Psychrophile

Mesophile

Thermophile

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2
Q

What are psychrophiles, their temperature range, and peak?

A

Microbes that grow in cold environments

Range: -10 - 20℃

Peak: 10℃

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3
Q

What are mesophiles, their temperature range, and peak?

A

Microbes that live in mid-temperature environments (human body and most environments)

Range: 10 - 50℃

Peak: 37℃

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4
Q

What are thermophiles, their temperature range, and peak?

A

Microbes that grow in hot environments

Range: 40 - 70℃

Peak: 60℃

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4
Q

What are hyperthermophiles?

A

A subset of thermophiles that live in even higher temperatures, ranging from 65 - 100℃

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5
Q

How are microbes classified based on preferred pH?

A

Alkaliphile

Neutrophile

Acidophile

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6
Q

What are alkaliphiles?

A

Microbes that live in high pH (basic)

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7
Q

What are neutrophiles?

A

Microbes that live in middle/neutral pH

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8
Q

What are acidophiles?

A

Microbes that live in low pH (acidic)

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9
Q

How does osmotic pressure effect the growth and survival of microbes?

A

In high solute concentrations, water exists the cell through the plasma membrane

Causes plasmolysis - Shrinkage of the cell’s cytoplasm

Growth is inhibited as the plasma membrane pulls away from the cell wall

High salt or sugar draws water out of cells to prevent their growth

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10
Q

What are the 2 classifications for microbes that can survive high-salt environments?

A

Extreme/obligate halophiles

Facultative halophiles

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11
Q

What are extreme halophiles?

A

Microbes that have adapted so well to high salt concentrations that they require them for growth

AKA - Obligate halophiles

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12
Q

What are facultative halophiles?

A

Microbes that do not require high salt concentrations but are able to grow at salt concentrations up to 2% - concentration that inhibits growth of many other organisms

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13
Q

What is carbon used for in microbes, and why is it needed in large amounts for growth?

A

Carbon is the structural backbone of living matter and is needed for all the organic compounds that make up a living cell

Microbial cells need a lot of carbon so they can copy their organic material that will be used in the daughter cells when it dividies
- Without enough carbon, the cell would not be able to synthesize the necessary components, preventing it from growing/dividing

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14
Q

What is nitrogen used for in microbes, and why is it needed in large amounts for growth?

A

Nitrogen is used to form the amino group of the amino acids of proteins

They need nitrogen because proteins are vital to life and microbes require proteins to perform biochemical reactions and express their DNA

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15
Q

What is phosphorus used for in microbes, and why is it needed in large amounts for growth?

A

Phosphorus is used in the synthesis of nucleic acids and phospholipids of cell membranes

Microbes need nucleic acids to survive because they make up the DNA that encodes for proteins, which are necessary for function; also need phospholipids for the cell membrane so they can have selective permeability and bring in/out the necessary substances

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16
Q

What is sulfur used for in microbes, and why is it needed in large amounts for growth?

A

Sulfur is used to synthesize methionine and cysteine (sulfur-containing amino acids) as well as certain vitamins

Without sulfur, microbes could not synthesize these necessary amino acids in order to make the proteins they need to function; particularly methionine as it is the amino acid produced by the start codon AUG - without it, no amino acids would be recruited and formed into proteins

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17
Q

What determines if oxygen is toxic to a microbe?

A

Enzymes that can help detoxify the environment - Catalase and Superoxide dismutase (SOD)

Organisms with these can live in oxygenated environments

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18
Q

How are microbes classified based on their oxygen needs?

A

Obligate aerobe

Facultative anaerobe

Obligate anaerobe

Aerotolerant anaerobe

Microaerophile

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19
Q

What does catalase do?

A

Destroys hydrogen peroxide by converting it into water and oxygen

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20
Q

What does superoxide dismutase do?

A

Neutralizes oxygen radicals and hydrogen peroxide

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21
Q

What are obligate aerobes, their growth pattern, and oxygen’s effects?

A

Microbes that require oxygen to live

Growth only occurs where high concentrations of oxygen have diffused into the medium (growth only at the top of a tube)

Presence of enzymes catalase and superoxide dismutase allows toxic forms of oxygen to be neutralized so they can use oxygen

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22
Q

What are facultative anaerobes, their growth pattern, and oxygen’s effects?

A

Both aerobic and anaerobic growth - greater growth in the presence of oxygen
- Most used in lab

Growth is best where most oxygen is present (top of tube), but occurs throughout tube

Presence of enzymes catalase and SOD allows toxic forms of oxygen to be neutralized so it can use oxygen

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23
Q

What are obligate anaerobes, their growth pattern, and oxygen’s effects?

A

Only aerobic growth, ceases in presence of oxygen

Growth occurs only where there is no oxygen (bottom of tube)

Lacks enzymes to neutralize harmful forms of oxygen, so it cannot tolerate oxygen

24
Q

What are aerotolerant anaerobes, their growth pattern, and oxygen’s effects?

A

Only anaerobic growth, but continues in presence of oxygen

Growth occurs evenly, oxygen has no effect (throughout tube)

Presence of one enzyme, SOD, allows harmful forms of oxygen to be partially neutralized, so it can tolerate oxygen

25
Q

What are microaerophiles, their growth pattern, and oxygen’s effects?

A

Only aerobic growth, oxygen required in low concentration

Growth occurs only where a low concentration of oxygen has diffused into medium (middle of tube)

Produce lethal amounts of toxic forms of oxygen if exposed to normal atmospheric oxygen

26
Q

What are planktonic bacteria?

A

Free-floating bacteria

27
Q

What is a biofilm?

A

Mass of bacteria stick to and multiply on a solid surface

Ex: dental plaques, gunk in drains, stream or river slime on rocks, medical catheters or tubing

Held together with sugary extracellular polymeric substances (EPS) - polysaccharides, proteins, extracellular DNA

Complex 3D, resilient, attached communities

28
Q

What is quorum sensing and what is its function?

A

Cell-to-cell chemical communication

Allows bacteria to coordinate activity and group together into beneficial communities

29
Q

How does a biofilm form?

A

Planktonic bacterium attaches to a surface

Uses quorum sensing to produce a signling inducer that diffuses into the medium and recruits other bacteria, which also begin producing inducer

Form pillar-like structures with water channels so that all bacteria can get proper nutrients and expel waste

Individual microbes and some slime occasionally leave to form a new biofilm

30
Q

How do planktonic bacteria differ from those living in a biofilm?

A

Bacteria within biofilms are often more tolerant to environmental changes than planktonic bacteria because of the added protection from a biofilm
- Also more resistant to bacteria than planktonic

Biofilm bacteria can lose their flagella or other motile instruments because they are no longer moving, while planktonic still have them

Planktonic bacteria can move freely, whereas biofilm bacteria are trapped within the biofilm unless they break off

31
Q

What is a chemically defined media?

A

Media whose exact chemical composition is known

Used for most autotrophic bacteria

32
Q

What advantage is there to chemically defined media?

A

You can ensure that the bacteria you are trying to grow will actually grow because you can be sure that it has the correct sources of carbon and energy for its metabolic needs - particularly useful in lab

Also useful in growing fastidious organisms because they need multiple growth factors in the media, so you can use a chemically defined to ensure that all growth factors are included

33
Q

What is complex media?

A

Media whose ingredients are not all known

Made up of nutrient extracts from yeasts, meat, or plants

Used for most heterotrophic bacteria

34
Q

What is selective media?

A

Media that suppresses the growth of unwanted bacteria and encourages the growth of the desired microbes

35
Q

What is differential media?

A

Media that allows you to distinguish colonies of the desired organism from other colonies growing on the same plate

Based on metabolic characteristics

36
Q

How are selective and differential media used in the lab?

A

Identify and isolate microorganisms

If you’re trying to see if a particular bacteria is present in a sample, you can tailor the media to select for the type of bacteria and differentiate based on metabolic characteristics

Also allows you to identify microbes present in an unknown sample based on what grows (selective) and how it presents from its metabolic characteristics (differential)

37
Q

What is anaerobic media?

A

AKA: reducing media

Media that contains chemicals that combine with oxygen to remove it from the media

Allows for anaerobic bacteria to be grown

38
Q

What are fastidious bacteria?

A

A microbe that has complex or particular nutritional requirements

Difficult to grow in lab

39
Q

What is enrichment media?

A

Media that has added nutrients or environmental conditions that favor the growth of a particular microbe but not others

Often for fastidious organisms

Used to increase the number of a desired microbe that is present in small quantities to a detectable amount

40
Q

What is mannitol salt media?

A

Media that contains a high concentration of salt
- Selective for Gram-positive bacteria since this level of salt is inhibitory in most other bacteria

Also differential for mannitol-fermenting staphylococci
- Contains carbohydrate mannitol and indicator phenol red, a pH indicator for detecting acid produced by mannitol-fermenting staphylococci
- If organism can ferment mannitol, an acidic byproduct is formed that causes the phenol red in the agar to turn yellow

41
Q

What is phenylethyl alcohol media?

A

Selective for Gram-positive

Isolate staph and strep

Inhibits most Gram-negative
- Interferes with DNA synthesis in Gram-negative

42
Q

What is blood agar?

A

Enriched and differential media
- Used to isolate fastidious organisms and detect hemolytic activity
- Accelerate the growth of medically-important fastidious bacteria

Made of nutrients and a little bit of sheep blood

43
Q

What is endo agar?

A

Used as coliform medium

Selective for Gram-negative

Coliform organisms ferment the lactose in media, producing a green metallic sheen
- Non-lactose-fermenting organisms produce clear, colorless, colonies

Colorless, beige, or not pink - lactose not utilized and is probably a Gram-negative non-coliform

Good growth that is pink/red - lactose utilized and bacteria is probably a Gram-negative coliform

Good growth (pink/red) with a bright metallic sheen - lactose highly utilized and bacteria is probably a Gram-negative coliform

44
Q

What is phenol red glucose media?

A

Differential broth that indicates gas production through color

45
Q

What is generation time?

A

Time required for a cell to divide (and its population to double)

46
Q

How is growth defined?

A

Increase in bacterial number

47
Q

Why is bacterial growth considered an increase in number not size?

A

Bacteria reproduce through binary fission, where a single cell divides into two identical daughter cells - exponential growth

While individual cells increase in size before division, the overall growth is measured by an increse in number of the size increase of minimal cells is minimal compared to the exponential increase in cell numbers

48
Q

What are the 4 phases of growth?

A

Lag phase

Log phase

Stationary phase

Death phase

49
Q

What occurs during the lag phase?

A

Number of cells does not change - little or no cell division

Cells are not dormant - undergoing DNA synthesis, enzymes/proteins are made, etc/

Also getting used to the media

50
Q

What occurs during the log phase?

A

Period of rapid growth

Cellular reproduction is most active

Generation time reaches a constant minimum
- Gen. time determined from log phase

Most sensitive to adverse conditions

51
Q

What occurs during the stationary phase?

A

Number of cell deaths balances the number of new cells - population stabilizes

Exponential grwoth stops because bacteria approach carrying capacity - number of organisms the environment can support
- Controlled by available nutrients. accumulation of wastes, and space

52
Q

What occurs during the death phase?

A

Number of deaths exceeds number of new cells formed

Continues until population is diminished to a tiny fraction of the number of cells in the previous phase or until population dies out entirely

53
Q

What is the difference between direct and indirect measures of growth?

A

Direct - measure cell number or total mass (directly proportional to cell numbers)

Indirect - estimates microbial numbers and activity without directly counting cells

54
Q

What are 4 examples of direct measurements of growth?

A

Plate count - measures number of viable cells; perform serial dilutions of bacterial sample and then spread inoculum on agar surface

Filtration - counts small quantity of bacteria, such as those present in lakes or pure streams; sample run through a filter and filter is transferred to a nutrient agar so colonies can arise

Most probable number - measure number of bacteria for those that don’t grow on solid media and when growth of bacteria in a liquid differential medium is used to identify the microbes; based on fact that the greater the number of bacteria in a sample, the more dilution needed to reduce density to the point in which no bacteria are left to grow

Direct microscopic count - often counts bacteria in milk; a measured volume of a bacterial suspension is placed within a confined area on a microscope slide, number is counted in several different fields, and average number of bacteria per viewing is calculated

55
Q

What is a serial dilution?

A

Original inoculum is diluted several times to ensure that some colony counts are in the 30 to 300 countable range

56
Q

What is a colony forming unit?

A

A measure of viable cells in a colony derived from a single progenitor cell

57
Q

What are 3 examples of indirect measurement of growth?

A

Turbidity - as bacteria multiply in liquid media, it becomes more turbid/cloudy; absorbance read with a spectrophotometer; not useful for small numbers of bacteria because a large quantity is needed to visualize turbidity

Metabolic activity - assumes metabolic products (acid, CO2, ATP, or DNA) is present proportionally to number of bacteria present

Dry weight - often used for filamentous bacteria and molds; microbe is removed from medium, filtered to remove excess, dried in a desiccator, and weighed

Medical Microbiology (4 decks)

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