Lab Practical 2

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UV is used to kill bacteria in

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Biology

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1

UV is used to kill bacteria in

food processing, hospitals, sewage treatment, labs

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2

____ range is effective for killing bacteria, but ____ is the opitmal wavelength for killing bacteria by damaging the bacterial DNA

240-300 nm, 260 nm

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3

Two mutanagenic effects of UV light on DNA

deamination of cytosine, formation of thymine dimers

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4

Deamination of cytosine

reaction converts cytosine to uracil and induces a mutation, structural change destabilizes the DNA molecule

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5

Formation of thymine dimers

Formation of dimes between adjacent thymine on the same strand (covalent bond), DNA cannot be replicated or transcribed (DNA polymerase does not recognize)

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6

Can DNA be repaired from UV damage?

yes

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7

2 Methods of repairing thymine dimer repair

photoreactivation, biochemical excision repair

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8

Biochemical Excision Repair

excision of damaged bases; reconstruction of a functional DNA from undamaged fragments; hydrolysis of ATP for energy

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9

Photoreactivation is only for

thymine dimers

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10

Photoreactivation

photolyase breaks apart thymine dimers, visible light powers photolyase

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11

Spore forming bacteria can survive adverse conditions by

making spores

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12

Spores have a thicker

outer core wall

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13

Spores are resistant to

heat, chemicals, radiation

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14

Spores can germinate and

develop into functional vegetative cells

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15

Under conditions of nutrient starvation, a metabolically active vegetative cell starts developing an endospore through a process called

sporogenesis

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16

Endospore structure

central core, PG cortex, two protein layers

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17

Central core contains

outer core wall, cell membrane, nuclear region, and other cell components

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18

Two protein layers endospore

spore coat and exosporium

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19

An easy way to select for a sample containing endospore is to heat at ____ for 15-20 minute

70-80 degrees C

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20

UV light wavelengths are between

100-400 nm

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21

Germicidal

having the ability to kill germs or other microorganisms

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22

The enzyme ____ can bypass the stalled DNA polymerase caused by thymine dimers, but this results in ______

translesion polymerase, high frequency of mutations

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23

Antimicrobial drugs are used to treat infectious diseases by

killing microorganisms, inhibiting growth

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24

Bacteriocidal

kills bacteria

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25

Bacteriostatic

inhibits bacterial growth

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26

Antimicrobial drugs include

antibacterials, antiviral, and antifungal drugs

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27

Another name for disc diffusion test

Kirby Bauer

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28

Disc diffusion test does not determine

if agent is bacteriostatic or bacteriocidal

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29

Efficacy of Kirby Bauer is indicated by

diameter zone of inhibition

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30

Factors affecting size of inhibition zone

sensitivity of organism, molecular size and concentration of agent, density of culture, diffusion rate of agent, size of inoculum, time and temperature of incubation, interactions between antibiotic and medium

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31

Using disc diffusion, we don't get an ________ of an antibiotic that is most effective

accurate measure of concentration

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32

Minimum inhibitory concentration (MIC)

the smallest concentration (highest dilution) of drug that visibly inhibits growth

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33

Standard for MIC

.5 McFarland standard

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34

First step of MIC lab

dilute bacterial culture to same turbidity as mcfarland standard

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35

How do you incubate antibiotic plate

right side up

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36

What agar is used for antibiotic disc diffusion

Mueller Hinton agar

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37

What organism forms spores in the UV lab

Bacillus

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38

Depending on the zone of inhibition, an organism is classified as ___, ____ or _____

resistant, intermediate, sensitive to the antimicrobial

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39

Therapeutic concentration

high enough to inhibit bacterial growth but low enough to avoid tissue damage

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40

Standard incubation time and temp for antibiotic disc diffusion

16-18 h, 33-37

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41

MBC stands for

minimum bactericidal concentration

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42

MBC is defined as

the minimum concentration that inhibits growth and induces cell death

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43

If MBC is close to MIC

the agent is bactericidal

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44

If MBC is much greater than MIC

the agent is considered bacteriostatic

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45

Antiseptic

a chemical agent that can be safely used externally on living tissues to destroy microorganisms or inhibit growth

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46

Antibiotics have to be used at a _____

therapeutic concentration

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47

Disinfectant

a chemical agent used on inanimate objects to destroy microbes or inhibit their growth

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48

Biofilms are made of _____ secreted by bacterial cells

exopolysaccharides

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49

Exopolysaccharides act as a protective mechanism against

nutrient/water loss

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50

Biofilms are commonly foun

on teeth, on catheters, on drains, on contacts

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51

Some organisms form biofilms at _____ interface when inoculated in a test tube

air-liquid

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52

What is in the tube in the biofilm experiment

glucose and Lb

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53

What organisms do we use for the biofilm former

P. aeruginosa or S. aureus

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54

Four stages of biofilm formation

reversible attachment, non-reversible attachment, maturation, active dispersal

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55

What happens during reversible attachment

motile bacteria bump into a surface and then swim away

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56

Nonreversible attachment is due to an increase in production of

cell strucutres (pili, glycocalyx_ and surface proteins

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57

What happens during maturation stage

actively growing cells produce polysaccharide and typically lose flagella

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58

Active dispersal occurs when

the surrounding environment becomes. more favorable and flagella are produced so motile cells can escape the biofilm

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59

Cells in the biofilm community may differentiate to express or silence genes, producing an antibiotic tolerant subpopulation of

persister cells

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60

What are used as disinfectants

aldehydes, chlorine, and derivatives

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61

Disinfectants typically work by

destroying the cell membrane of microorganisms or interfering with their metabolism

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62

bacterial replication is ____, meaning that a single organism will divide into two, maintaining _____ gene transfer

binary, vertical

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63

bacteria can aquire new genetic information from ______

horizontal gene transfer

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64

conjugation

direct cell to cell contact that mediates transfer DNA

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65

transduction

genetic information carried by bacterial virus from one bacterium to another

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66

transformation

acquire DNA from surrounding environments

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67

Ways for bacteria to aquire new genetic information

conjugation, transduction, transformation

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68

plasmid

small circular DNA molecule that can replicate independently of the chromosome

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69

extra genetic info from plasmid could be responsible for

antibiotic resistance, virulence factors, nutrient utilization, among other benefits

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70

The contact during conjugation is formed by a

sexual pilus (f pilus)

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71

F pilus is produced by a plasmid called

fertility factor, or F factor

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72

A cell that has F factor is called a ____ cell

F+ cell

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73

During conjugation, a copy of F factor is _________

nicked, unwound, and a single strand is transferred to the recipient cell

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74

What is the recepient cell called during conjugation

F- cell

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75

once a recepient cell obtains F factor it replicates the _____ to make a _____ molecule

single stranded DNA, double stranded DNA

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76

Transconjugate

recipient cell that has received a copy of F factor

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77

The F factor is a type of ____ that contains specific genes within the _____

plasmid, tra-operon

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78

Tra-operon contains genes responsible for

transferring the plasmid from donor to recipient cell

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79

R plasmid

F plasmids that carry more than one gene for antibiotic resistance

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80

Which F factor do we use

F'128 factor

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81

F'128 factor also contains the ____ operon, and a gene ____

lac, cat that codes for resistance to chloramphenicol

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82

The F factor is present in ____ in the donor cell

multiple copies

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83

The chromosome of the donor cell does not have genes responsible for ______

lactose utilization

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84

Only one cell among _____ donor or recpient cells is transconjugate

10^5 or 10^6

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85

What gene does the recepient cell contains

kan, that codes for resistance to kanamycin

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86

The recipient cell is naturally _____ negative

lac

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87

Occasionally, the F factor transfer will be interrupted before the transfer is complete, meaning ____ will be transferred but not ____

cat, lacZ

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88

The interrupted mating process can be used to determine the _____ between the cat gene and the lacZ gene on the F factor

genetic distance

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89

MacConkey+chloramphenicol

F+: cells grow, lac+ F-: no growth trans: majority donor cells, very few transconjugate, both lac +

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90

MacConkey + kanamycin

F+: no growth F-: cells grow, lac- Trans: mixture of lac- recipient and lac+ trans (very few)

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91

MacConkey+chloramphenicol+kanamycin

F+: no growth F-: no growth Trans: trans cells only, most lac+

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92

Bacteriophage

virus that bacteria is susceptible to

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93

In some estimates, there as many as ___ times as many phages as there are bacteria on earth

10

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94

Phages contain their own ____

genetic material that is transcribed and translated within the host cell

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95

PHages exist _____ in an infective but nonliving state called

extracellularly, virion

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96

Viral reproduction occurs exclusively inside a host cell, and can occur in one of two cycles

lytic cycle, lysogenic cycle

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97

Basic structure of a virion

capsid (protein shell) that encloses nucleic acid (either DNA or RNA)

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98

Examples of virion shapes

helical, polyhedral, binal

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99

With the binal phage, all of the viral nucleic acid is located in the ____

head, and the tail is used for attachment

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100

Stages of lytic infection

attachment/absorption, penetration, biosynthesis, maturation, release

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