microbiology test 2

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1

what effect does UV radiation have on DNA?

it creates covalent bonds between pyrimidine bases, preventing proper replication/transcription

2

psychrophiles

cold-loving microbes (approx -5-20 C)

3

mesophiles

moderate-temp-loving microbes (approx 10-50 C)

4

thermophiles

heat-loving microbes (approx 40-70 C)

5

minimum growth temperature

lowest temp at which species will grow

6

optimum growth temperature

temp at which species grows best

7

maximum growth temperature

highest temp at which species will grow

8

psychrotrophs

psychrophiles that have optimum growth at 20-30 C, and therefore can cause food spoilage (even in fridge)

9

hyperthermophiles

have extremely high optimum growth temps, often found in hot springs/thermal vents

10

hypertonic solution (and effect on microbes)

solution has higher concentration of solutes than is in the cell

water leaves cell, causes plasmolysis or cytoplasm shrinkage

11

hypotonic solution (and effect on microbes)

solution has lower concentration of solutes than is in the cell

water enters cell, can cause lysis

12

most bacteria grow best in a pH around ________

neutrality (6.5-7.5)

13

toxic forms of oxygen

- singlet oxygen

- superoxide radicals

- peroxide anions

- hydroxyl radicals

14

how can superoxide radicals be neutralized?

superoxide dismutase

15

how can peroxide anions be neutralized?

catalase or peroxidase

16

obligate aerobes

require oxygen to live

17

facultative aerobes

will use oxygen when present but can still grow without it

18

obligate anaerobes

can't grow in presence of oxygen

19

aerotolerant anaerobes

unable to use oxygen but can tolerate it

20

where are obligate aerobes found in tube of growth medium?

why?

clustered near the surface

highest concentration of oxygen

21

where are obligate anaerobes found in tube of growth medium?

why?

furthest from surface

no oxygen

22

where are facultative anaerobes found in tube of growth medium?

why?

mostly near surface but still throughout entire tube

best growth occurs with oxygen but it's not needed

23

where are aerotolerant anaerobes found in tube of growth medium?

why?

event throughout tube

oxygen level has no effect

24

how do obligate aerobes avoid toxic forms of oxygen?

use enzymes (SOD and catalase) to neutralize it

25

how do facultative anaerobes avoid toxic forms of oxygen?

use enzymes (SOD and catalase) to neutralize it

26

why can't obligate anaerobes utilize oxygen?

lack the enzymes needed to neutralize toxic oxygen

27

why can aerotolerant anaerobes tolerate oxygen?

have one enzyme (SOD) to partially neutralize toxic forms

28

quorum sensing

chemical communication used between cells within biofilm

29

chemically defined media

have exact known chemical composition

30

complex media

have unknown exact chemical composition

31

how to culture anaerobic microbes?

use reducing media or keep them in a special chamber that lacks oxygen

32

reducing media

media containing ingredients that chemically deplete oxygen levels

33

differential media

makes it easier to distinguish colonies of desired organism from others on plate

34

selective media

designed to suppress growth of unwanted organisms and encourage growth of desired ones

35

blood agar

differential media that contains RBCs, used to identify microbes that destroy RBCs

36

mannitol salt agar

media that differentiates between bacteria that can ferment mannitol and those that can't

also selects for bacteria that can grow in high salt content

37

enrichment media

used for preliminary isolation that favors growth of desired organisms, or to boost colonial growth

38

two methods of culture preservation

- deep freezing

- lyophilization (freeze drying)

39

how do bacteria reproduce?

binary fission (DNA is replicated and thing splits in two)

40

generation time

time required or cell population to double in number

41

four phases of bacterial growth

1. lag phase

2. log phase

3. stationary phase

4. death phase

42

lag phase

bacteria are adjusting to media and preparing to grow but do not yet

43

log phase

bacterial population grows exponentially

44

stationary phase

period of bacterial population equilibrium (births = deaths)

45

death phase

bacterial population decreases exponentially

46

population number = ?

# of cells / mL of liquid (or gram of solid)

47

sepsis

bacterial contamination

48

asepsis

absence of bacteria

49

antisepsis

destroying harmful bacteria from living tissue

50

sterilization

removal/destruction of all microbial life

51

commercial sterilization

killing Clostridium botulinum endospores from canned food

52

disinfection

destroying harmful microorganisms, but not all life

53

degerming

mechanical removal of microbes from limited area

54

sanitization

lowering microbial counts to safe public health levels (e.g. on eating utensils)

55

biocidal

describes treatments that kill microbes

56

bacteriostatic

describes treatments that inhibit microbial growth, but don't kill them

57

effectiveness of microbial control treatment depends on _______ (4)

- number of microbes

- environment

- time of exposure

- microbial characteristics

58

D-value

decimal reduction time

time in minutes to kill 90% of bacteria at a given temperature

59

if there is a population of 1014 bacteria, what D treatment would be useful for eliminating most of them?

14D treatment

60

how does moist heat kill microorganisms?

denatures proteins by breaking H-bonds

61

pasteurization

kills spoilage microorganisms without seriously affecting a food's taste

62

filtration

substance passes through filter with pores small enough to retain microbes

method of heat-sensitive sterilization

63

effect of low temperature treatments on bacteria

decrease metabolic reactions, induce bacteriostasis

64

how is high pressure used to control microbial levels?

what is an advantage?

alters the structure of proteins and carbohydrates, inactivating cells

preserves flavors, colors, nutrients in products

65

physical methods of food preservation (5)

- low temperatures

- high pressure

- desiccation (lyophilization)

- osmotic pressure

- ionizing radiation

66

how is ionizing radiation used to control microbial levels?

gamma rays, X rays, electron beams are used to ionize water and form hydroxyl radicals -> damage DNA

67

how is non-ionizing radiation used to control microbial levels?

UV light is used to create extra bonds in DNA, prevents proper replication

68

effective chemical disinfection can be influenced by _______ (4)

- concentration of disinfectant

- presence of organic matter

- pH

- time

69

use-dilution test

method of evaluating effectiveness of disinfectants via serial dilution

70

disk-diffusion method

test to determine microbial susceptibility to chemotherapeutic agents

71

zone of inhibition

area of no bacterial growth

forms when a disk containing effective chemical agent is placed on bacterial culture

72

phenolics

1. MOA

2. best for

1. disrupt lipid-containing plasma membranes

2. mycobacteria

73

bisphenols

1. MOA

2. best for

1. disrupt lipid-containing plasma membranes

2. gram-positive staphylococci and streptococci

74

biguanides

1. MOA

2. best for

1. disrupt plasma membranes

2. skin and mucous membranes

75

iodine

1. MOA

2. best for

1. impairs protein synthesis

2. skin and wound treatment

76

chlorine

1. MOA

2. best for

1. forms HOCl and alters cell

2. disinfecting sources of water, food-related equipment

77

alcohols

1. MOA

2. best for

1. denatures proteins, dissolves lipids

2. degerming skin before injections, enhancing effectiveness of other chemical agents

78

heavy metals

1. MOA

2. best for

1. oligodynamic action to denature proteins

2. biocidal or antiseptic effects

79

surfactants

decrease surface tension among molecules of a liquid

includes soaps/detergents, acid-anionics, and quats

80

soaps/detergents

1. MOA

2. best for

1. mechanical removal of dirt and microbes

2. gently removing contaminants

81

acid-anionics

1. MOA

2. best for

1. disrupt plasma membranes

2. cleaning food processing equipment

82

quats

1. MOA

2. best for

1. affect cell's permeability

2. strong biocidal effect against gram positive bacteria

83

chemical methods of food preservation (2)

- organic acids

- nitrates/nitrites

84

aldehydes

1. MOA

2. best for

1. inactivate proteins

2. preservation of specimens, disinfection of hospital equipment

85

common chemical sterilants (2)

- ethylene oxide gas

- hydrogen peroxide gas

86

plasma sterilization

excited gas particles emit free radicals that destroy microbes

87

peroxygens

1. MOA

2. best for

1. oxidation

2. disinfection of inanimate objects/surfaces

88

why are biocides usually less effective against gram-negative bacteria?

presence of external lipopolysaccharide layer in cell wall

89

which two gram-negative genera are especially hard to kill?

why?

Pseudomonas and Burkholderia

they have specially structured porins that resists entry of particles into cell

90

why are mycobacteria so resistant to biocides?

cell walls contain lipids

91

tuberculocidal

describes treatments that are effective against mycobacteria

92

what is the difference between enveloped and non-enveloped viruses that influences how easy they are to kill?

enveloped viruses have lipid coat that is susceptible to wider range of antimicrobials (easier to kill)

non-enveloped viruses have protein coat that is more resistant to biocides (harder to kill)

93

chemotherapy

treatment of disease with chemical substances

94

selective toxicity

ability of antimicrobial agent to target pathogens without damaging the host

95

term for totally synthetic drugs meant to inhibit microbes?

antimicrobial drug

96

term for natural substance produced by microbes to inhibit other microbes?

antibiotic

97

more than half of antibiotics are produced by what?

Streptomyces species

98

broad spectrum

describes antibiotic drug that affects a large range of organisms

99

narrow spectrum

describes antibiotic drug that affects a small range of organisms

100

5 main actions of antimicrobial drugs

- inhibition of cell wall synthesis

- inhibition of protein synthesis

- inhibition of nucleic acid replication

- inhibition of metabolite synthesis

- injury to plasma membrane

101

antibiotics that interfere with protein synthesis (4)

- chloramphenicol

- erythromycin

- tetracycline

- streptomycin

102

antibiotics that interfere with cell wall synthesis (4)

- penicillins

- cephalosporins

- bacitracin

- vasomysin

103

antibiotics that interfere with metabolite synthesis (2)

- sulfanilamide

- trimethoprim

104

antibiotic that causes injury to plasma membrane

polymyxin B

105

chloramphenicol MOA

binds to 50S portion of ribosome, inhibits formation of peptide bond

106

tetracycline MOA

interfere with attachment of tRNA to mRNA-ribosome complex

107

how do antibiotics inhibit metabolite synthesis?

antimetabolites resemble the normal substrate for an enzyme (e.g. PABA), allowing them to competitively inhibit that enzyme's action (e.g. folic acid production)

108

common structure found in all penicillins

nucleus containing beta-lactam ring

109

penicillinase

enzymes produced by many bacteria that inhibit activity of beta-lactam ring

110

penicillin MOA

beta-lactam ring prevents successful cross-linking of peptidoglycans (and therefore inhibits cell wall synthesis)

111

2 broad spectrum penicillins

- ampicillin

- amoxicillin

112

vancomycin

polypeptide antibiotic that was considered last line of defense against MRSA (but not so much anymore)

113

2 major anti-mycobacterial antibiotics and what they do

- isoniazid, inhibits synthesis of mycolic acids

- ethambutol, prevents integration of mycolic acids into cell wall

114

lipopeptides

antibiotics that cause damage to plasma membrane (e.g. polymyxin B)

115

E test

modified disk diffusion test

involves placing a stick containing increasing concentrations of an antibiotic into bacteria, determining the minimal inhibitory concentration

116

broth dilution test

determines if antibiotic is bactericidal or bacteriostatic

involves multiple wells containing bacteria + increasing concentrations of antibiotic, seeing at which concentration bacteria are killed (minimal bactericidal concentration)

117

antibiogram

reports that record susceptibility of organisms encountered clinically

118

4 major mechanisms of antibiotic resistance in cells

- prevention of drug's entry into cell

- enzymatic deactivation of drug

- alteration of drug's target site

- efflux of drug out of cell

119

therapeutic index

assessment of a drug's risk/benefit ratio, contraindications, side effects

120

synergism

when the combined effect of multiple antibiotics is greater than that of either one alone

121

antagonism

when the combination of multiple antibiotics is less effective than just one of them alone

122

gene

DNA segment that codes for a functional product

123

central dogma of molecular bio

DNA > transcription > RNA > translation > protein

124

gene expression

production of functional product through transcription and translation

125

base substitution

mutation where a single bp at one point in DNA sequence is replaced by another

126

frameshift mutation

mutation where one or more bps are deleted or inserted into the DNA sequence

127

missense mutation

base substitution that leads to insertion of incorrect amino acid

128

nonsense mutation

base substitution that leads to premature insertion of STOP codon

129

vertical gene transfer

aka replication

flow of genetic information from one generation to the next

130

horizontal gene transfer

aka recombination

flow of genetic information between cells of same generation

131

bacterial transformation

genes transferred from one organism to another as "naked" DNA in solution

132

competence

ability of recipient cell to take up donor DNA

133

conjugation

transfer of genes via direct cell to cell contact

134

F factor

fertility factor

plasmid that permits its own transfer from one (F+) bacterium to another via formation of sex pili

135

what must be true of two cells engaged in conjugation?

they are of opposite mating type (donor cell contains plasmid, recipient cell does not)

136

Hfr cell

cell that receives F factor via conjugation and integrates it into its chromosome

137

what results from conjugation between F+ and F- cells?

both will end up F+

138

what results from conjugation between Hfr and F- cells?

F- cell integrates Hfr cell's DNA into its own chromosome, becomes recombinant F- cell

139

transduction

transfer of genes between cells via bacteriophage

140

generalized transduction

random chromosome fragments are packaged within phage and transferred to donor cell

141

specialized transduction

only certain chromosome fragments are packaged within phage and transferred to donor cell

142

what kind of operon is the lac operon?

inducible (and catabolic)

143

inducible operon

transcription is turned off unless molecule of interest is present

144

repressible operon

transcription is turned on unless molecule of interest is present

145

nucleotide

sugar + base + phosphate

146

nucleoside

sugar + base

147

how many H bonds between base pairs?

two between A and T

three between C and G

148

replica plating

method of negative indirect selection (identifies a mutant that cannot perform a specific function)

149

Ames reverse gene mutation test

determines if a given substance is a mutagen

done by applying the substance to cells and seeing how many colonies are revertant

150

revertant bacteria

mutant bacteria that, after being re-exposed to a mutagen, revert back to original state

151

DNA gyrase

topoisomerase - relaxes supercoiling ahead of replication fork

152

DNA ligase

makes covalent bonds to join DNA strands

153

topoisomerase

relaxes supercoiling ahead of replication fork (e.g. DNA gyrase)

154

helicase

unwinds double-stranded DNA

155

primase

RNA polymerase that makes RNA primers from a DNA template

156

DNA polymerase

synthesize DNA, proofread and facilitate repair of DNA

157

which end of a nucleotide is the 3' end?

where -OH attaches to 3' carbon

158

which end of a nucleotide is the 5' end?

where phosphate attaches to 5' carbon

159

to which end do polymerases add new nucleotides?

3' end

160

how often is a mistake made in DNA replication?

once in every 10 billion bases

161

where does the energy needed for DNA replication come from?

new nucleotides being added have 3 phosphates - two are hydrolyzed and release energy while the other is attached to -OH

162

two components needed for transcription (apart from DNA)

- RNA polymerase

- RNA nucleotides

163

codon

group of three nucleotides that correspond to an amino acid

164

tRNA

transfer RNA

contains anticodon that complements a codon in mRNA and transports required amino acid

165

operon

group of genes that are transcribed together and controlled by one promoter

166

promoter

location on operon where RNA polymerase initiates transcription

167

operator

part of operon where repressor protein binds

168

repressor protein

protein that interacts with operator to allow or inhibit transcription

169

corepressor

in repressible operon, a molecule that binds to repressor and enables it to bind to operator

170

formula for counting cells

N = N0 x 2n

N = final # of cells

N0 = initial # of cells

n = # of generations

171

formula for finding number of cell generations

n = T / TG

T = time of growth

TG = generation time

172

the addition of salts preserves food because it ________

lowers osmotic pressure

173

process by which some microbes use gaseous nitrogen directly from the atmosphere

nitrogen fixation

174

heat-resistant bacteria that survive pasteurization are ________

thermoduric

175

what is the optimum concentration of ethanol to be used as a biocide?

why?

70%

some concentration of water is required for denaturation

176

superbugs

bacteria that are resistant to large numbers of antibiotics

177

which biosafety level allows work on open bench surfaces but requires gloves, lab coats, face and eye protection?

BSL-2

178

which biosafety level requires that the lab be negatively pressurized and equipped with air filters?

BSL-3

179

which biosafety level requires the lab to be sealed, negatively pressurized, and its air filtered twice?

BSL-4

180

a microbiology classroom is typically at which biosafety level?

BSL-1

181

what chemical agent is effective against endospores?

chlorine

182

microorganisms from easiest to hardest to kill (9)

1. lipid-enveloped viruses

2. gram positive bacteria

3. large non-enveloped viruses

4. gram negative bacteria

5. fungi

6. small non-enveloped viruses

7. mycobacteria

8. spores

9. prions