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Clinical Bacteriology (Laboratory) > Bacterial Quantification by Culture (Labster Lab Manual | M) > Flashcards

Bacterial Quantification by Culture (Labster Lab Manual | M) Flashcards

1
Q

Can a bacterial population expand at an exponential rate in ideal conditions?

A

Yes

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2
Q

If a single E.coli can spawn a population over 1 B strong in a 10 hr timeframe, what is the optimal generation time (roughly) for this to happen?

A

Roughly 20 mins

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3
Q

Can a single E. coli spawn a population over 1 B strong in a 10 hr timeframe?

A

Yes

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4
Q

What is the result of the rapid growth of E. coli (in a 10 hrs timeframe)?

A

It can transform a tube w/ clear growth medium into a hazy solution in the course of a day

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5
Q

How to express the exponential progression of E. coli?

A

2^n

*a simple expression

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6
Q

What does ‘n’ from 2^n represents?

A

It represents the # of generations

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7
Q

At the start, the initial bacteria (in exponential form) is equal to what?

A

2^0

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8
Q

After 3 generations, the population will expand to what?

A

2^3 or 2 X 2 X 2

so it is equivalent to 8 cells

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9
Q

How to calculate the generation time of the bacterial population?

A

Execute the simple mathematics of the exponential growth of bacteria

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10
Q

Is the bacterial growth (exponentially) spontaneous nor constant and follows distinct growth curves?

A

Yes

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11
Q

What is CFU?

A

It is a measurement to estimate the # of viable bacteria or fungal cells in a sx

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12
Q

When is a cell only considered viable?

A

If it is able to multiply via binary fission under controlled conditions

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13
Q

How to calculate CFUs?

A

These can be calculated by spreading a sp volume of the microbial culture onto an agar plate

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14
Q

What happens after incubating the agar plate?

A

The # of colonies is proportional to the # of viable colonies in the tube

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15
Q

Explain how to compute the CFU per mL of a bacterial culture

A

Ex.
If 0.1 mL of a bacterial culture results in 25 colonies. The CFUs per mL can be calculated as follows:

cfu / mL = colonies / volume spread 25 colonies / 0.1 mL = 250 cfu / mL

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16
Q

Can a bacterial culture containing many viable cells be counted directly?

A

No

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17
Q

What should be done if there are many viable cells present in a bacterial culture?

A

In this case, you need to perform a serial dilution

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18
Q

Why should serial dilution be done?

A

In order to decrease the # of cells that you use for spreading

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19
Q

How to calculate the cfu / mL of a diluted sx?

A

Multiply the # of colonies w/ the dilution factor

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20
Q

What are the other techniques that can be used to quantify the # of bacteria in a sx?

A

Examination w/ a microscope

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21
Q

What is required (or criteria) if the # of bacteria in a sx is quantified via examination w/ microscope?

A

These alternative methods require significant growth and also don’t exclude dead or non-viable cells

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22
Q

What is the importance of serial dilutions?

A

These are useful when we want to obtain a very diluted solution from very concentrated stock solutions

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23
Q

If we want to obtain 10 mL of 1 mM (M?) solution from a 1 M stock solution, compute the value (volume) for direct dilution

A

M1V1 = M2V2
V1 = M2V2/M1
= (10 mL X 1/1000M) /1M
= 0.01 mL

Water to add: 10 mL - 0.01 mL = 9.99 mL

In these cases, direct dilution is not very helpful because it would be difficult to pipette exactly 9.99 mL

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24
Q

For serial dilution, what is done?

A

We first look at the final volume and concentrations needed, then determine the dilution factor

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25
Q

If we need 10 mL of a 1mM solution, what is the dilution factor?

A

Dilution factor = 1/ (final concentration/ initial concentration) = 1/ (0.001 M/ 1 M) = 1000X

We can split up 1000X into multiple factors: 10 X 10 X 10
This means we can set up 3 tubes to perform the serial dilution. When it is a 10X dilution, it means that it is 1 part of the solution, 9 parts of the diluent (usually it is water). Similarly, for a 15X dilution, it will be 1 part of the solution, 14 parts of the diluent

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26
Q

What is usually used as a diluent?

A

H2O

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27
Q

How is the process (or principle) of serial dilution done?

A

10 mL stock solution (1 M) + 1 mL to 9 mL diluent (0.1 M) + 1 mL to 9 mL diluent (0.01 M) + 1 mL to 9 mL diluent (0.001 M)

1 mL of stock is transferred to the 2nd tube that contains 9 mL of diluent (ex. H2O). Then 1 mL (aliquot) of the 2nd tube is taken and transferred to the 3rd tube. The process of transferring aliquot is repeated until the desired dilution concentration is achieved

28
Q

True or False.

Although serial dilution requires more preparation, it will give more accurate dilutions, provided that your technique is precise

A

True

29
Q

What is ensured via the application of sterile technique?

A

It is used to ensure a “clean” lab environment

30
Q

What is the importance of application of sterile technique?

A

It is essential to ensure the reliability of experimental results

31
Q

When are sterile practices especially important?

A

When working w/ microorganisms

32
Q

Can a single spore or tiny bacterium overgrow the whole medium and destroy the exp?

A

Yes

33
Q

What are the steps used to keep lab work sterile?

A

1) Lab doors and windows are kept closed to prevent air currents, preventing surface microorganisms becoming airborne
2) The wire loop and glass spreader are sterilized before and after use w/ a Bunsen burner to prevent the introduction of unwanted microorganisms
3) Lids from bottles and tubes are held when removed, and not placed on the bench during mat transfer from one bottle or tube to another
4) The neck of a bottle or tube must be immediately heated using the Bunsen burner so that any air movement is outward
5) The bottle or tube are opened for the minimum time possible, and while open, all work is performed close to the Bunsen burner flame
6) Media and equipment are sterilized to prevent the growth of unwanted microorganisms

34
Q

What should be done to prevent surface microorganisms becoming airborne?

A

Lab doors and windows are kept closed to prevent air currents, hence, preventing surface microorganisms becoming airborne

35
Q

What should be done to the wire loop and glass spreader before and after use?

A

These should be sterilized

36
Q

What should be done to lids from bottles and tubes when removed?

A

The lids from bottles and tubes are held when removed, and not placed on the bench during mat transfer from one bottle to another

37
Q

What is the purpose of heating the neck of the bottle immediately using the Bunsen burner?

A

So that any air movement is outward

38
Q

Can the bottle or tube opened all the time during the lab procedure?

A

No, the bottle or tube are opened for the minimum time possible

39
Q

What should be done to the media and equipment to prevent the growth of unwanted microorganisms?

A

These should be sterilized

40
Q

What is antibiotic resistance?

A

It is the general process in w/c bacteria (usually infectious) becomes insensitive to a sp drug or a sp class of drugs

41
Q

When do antibiotic resistance usually appear?

A

When a microbe is exposed to sub-lethal concentrations of a sp antibiotic: due to selective pressure, the surviving microbes might develop resistance mechanisms across several generations through mutations in their DNA

42
Q

How are the surviving microbes (in antibiotic resistance) might develop resistance mechanisms across several generations through mutations in their DNA?

A

Due to selective pressure

43
Q

The resistance mechanisms can be sorted into how many categories?

A

4

44
Q

What are the categories of the resistance mechanisms?

A

1) The modification of the primary target of the antibiotic, such as the transpeptidase for ampicillin resistance
2) The inactivation of the antibiotic compound itself, such as the production of B-lactamase enzymes to degrade penicillin G inside the cell
3) Preventing the antibiotic from reaching the target, by reducing the permeability of the membrane or using efflux pumps to keep the drug outside the cell, as observed against ciprofloxacin for example
4) Using alternative metabolic pathways to compensate for the action of the antibiotic and ensure the survival of the organism

45
Q

What is the modified primary target for ampicillin resistance?

A

Transpeptidase

46
Q

What is the action of B-lactamase enzymes?

A

To degrade the penicillin G inside the cell

47
Q

How is the antibiotic prevented from reaching the target?

A

By reducing the permeability of the membrane or using efflux pumps to keep the drug outside the cell, as observed against ciprofloxacin for example

48
Q

What is the action of a drug-resistant bacterial strain?

A

It can transfer the resistance gene to other strains of the same spp - or to individuals of a diff spp altogether - that have never been exposed to the drug in the first place

49
Q

How can antibiotic resistance spread widely and compromise the whole antibiotic therapies?

A

Via the transfer of the resistance gene by a drug-resistant bacterial strain to other strains of same spp or to individuals of a diff spp altogether that are not exposed to the drug in the first place

50
Q

What is the result of the accumulation of antibiotic resistance genes?

A

It leads to the creation of “superbugs”

51
Q

What are superbugs?

A

These are bacterial strains that are immune to all but the most drastic treatments

52
Q

What are the current strategies to overcome antibiotic resistance?

A

To discover new antibiotics w/ novel modes of actions or to use diff antibiotics in “cocktails” - presuming that a bacteria might survive facing 1, but not 2 or 3 antibiotics simultaneously

53
Q

What is the importance of antibiotic resistance genes in the lab?

A

These are an important tool for genetic engineering to select for transformed cells

54
Q

What are the characteristics of E. coli?

A

1) Rod-shaped bacterium
2) Commonly found in the lower intestine of warm-blooded organisms
addition: they are gram (-), anaerobic, and coliform bacteria of genus Escherichia

55
Q

Can most E. coli strains cause harm?

A

No, most E. coli strains are harmless

56
Q

Can some serotypes of E. coli cause serious food poisoning in their hosts, and are occasionally responsible for product recalls due to food contamination?

A

Yes

Serotypes are:

1) Enterohemorrhagic (EHEC)
2) Enteroinvasive (EIEC)
3) Enteropathogenic (EPEC)
4) Enterotoxigenic (ETEC)
5) Enteroaggregative (EAEC)

57
Q

What are the actions of some serotypes of E. coli strains?

A

1) It can cause serious food poisoning in their hosts

2) They are occasionally responsible for product recalls due to food contamination

58
Q

Are the harmless strains of E. coli part of the normal flora of the gut?

A

Yes

59
Q

Can the harmless strains of E. coli produce vitamin K2 for their hosts? If yes, what is its effect? If not, what is its effect?

A

Yes, these strains produce vitamin K2 w/c can produce benefits to their hosts

60
Q

What are the actions of the harmless E. coli strains?

A

1) To produce vitamin K2

2) To prevent colonization of the intestine w/ pathogenic bacteria

61
Q

Can E. coli be grown and cultured easily and inexpensively in a lab setting?

A

Yes

62
Q

Is E. coli considered as one of the best-studied model organisms? If yes, why? If no, why not?

A

Yes, because E. coli can be grown and cultured easily and inexpensively in a lab setting

63
Q

What are the important spp of bacteria in the fields of biotechnology and microbiology?

A

E. coli

64
Q

What is the purpose of E. coli in the fields of biotechnology and microbiology?

A

E. coli serves as the host organism for the majority of work w/ recombinant DNA

65
Q

What is the generation time of E. coli under favorable conditions?

A

Only 20 mins

Clinical Bacteriology (Laboratory) (24 decks)

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