Exam III Flashcards Preview

Microbiology Lab > Exam III > Flashcards

Flashcards in Exam III Deck (360)
Loading flashcards...
1

Describe a coliform

Gram negative rod
Ferment lactose with production of gas within 48 hrs at 37C
Generally associated with fecal material
Most common coliform is E.coli

2

The presence of coliforms are used to indicate what?

Whether a water sample has become contaminated with fecal material and therefor with potential bacterial pathogens

3

What method is used to determine if a water sample is contaminated with coliforms?

Most Probable Number (MPN) also known as the multiple tube fermentation method

4

The MPN procedure allows you to calculate what?

Total coliform counts in a water sample

The E.coli counts in a water sample

5

What is the first step of determining the MPN

Making a 1:10 serial dilution of the water

6

What is the second step of MPN

1 mL of dilution tubes is added to Lauryl Tryptose Broth (LTB)

7

What are the contents of LTB?

Lauryl sulfate

Lactose

Durham tube

8

What is the purpose of Lauryl sulfate in the LTB?

Inhibits the growth of organisms other than coliforms

9

What is the function of lactose in LTB?

Coliforms can ferment this sugar

10

What is the purpose of the Durham tube in LTB?

Will indicate if gas has been produced from the fermentation of lactose

11

LTB is a media that is what for coliforms?

Selective

12

LTB gives a presumptive determination of what?

The presence of coliforms

13

What is the third step of MPN?

After 48 hours, broths are examined for
1. Growth
2. Presence of gas

14

The presence of growth is considered what for LTB tubes?

Positive for coliforms

15

Transfer how many loops of culture from every LTB tube that shows what into one of each what?

2; growth; one tube Brilliant Green Lactose Bile broth (BGLB) one tube of E.coli broth

16

At what temperature do you incubate the BGLB?

37 C

17

At what temperature do you incubate the E.coli broth (EC) at?

45 C

18

What are the contents of BGLB?

Lactose
Durham tube
2% bile

19

What is the function of Lactose in BGLB?

Coliforms can ferment this sugar

20

What is the function of a Durham tube in BGLB?

Will indicate if a gas has been produced from the fermentation of lactose

21

What is the function of the 2% bile for BGLB

Inhibits non-coliforms

22

BGLB is a selective media that does what?

Confirms the presence of coliforms

23

After 48 hours, GBLB broths are examined for the presence of what?

Gas

24

BGLB tube with gas are considered what?

Positive

25

The presence of gas in BGLB tubes is used to determine what?

The total coliform counts

26

What are the contents of EC broth?

Lactose

Durham tube

Bile salts

27

EC broth is a media that is selective for what when grown at what temperature?

E.coli; 45 C

28

After 48 hours, EC broth is examined for the presence of what?

GAS

29

EC tubes containing gas are considered what?

Positive for E. coli

30

Positive EC broth results are used to determine what?

E.coli counts

31

What is the MPN formula?

MPN/100 ml = 100P / sqrt(VnVa)
Where P is the total number of positive results either (BGLB or EC)
Vn is the combined volume of sample in LTB tubes that produced negative results in BGLB or EC
Va is the combined volume of sample in all LTB tubes

32

What contains one or more specific compounds that can prevent the growth of certain bacteria?

Selective Media

33

To achieve selectivity what does the media contain?

Inhibitors

34

What do inhibitors adversely effect?

DNA synthesis
Gene expression
Enzymatic activity
Membrane permeability

35

What contains one or more specific compounds that can distinguish between different bacterial species?

Differential media

36

What are the two important components of differential media?

Substrate

Indicator

37

What does the substrate provide for differential media?

An energy source such as a carbohydrate that only certain bacterial species can utilize in a specific chemical reaction or set of chemical reactions

38

What does an indicator provide for differential media?

A visible means of showing that a specific chemical reaction has occurred (color change in media)

39

Selective and differential media provides what?

A simple way to screen out certain bacterial species

Some biochemical information on the organisms present in the culture (presumptive identification)

40

Can coliforms form endospores?

No

41

What kind of respiration do coliforms perform?

Aerobic or facultative anaerobic

42

What can coliforms ferment?

Lactose

43

What kind of media is MacConkey Agar?

Selective and differential

44

What is MacConkey Agar used to identify?

The presence of coliforms

45

What are the important components in MacConkey Agar?

Bile salts (selective)

Crystal Violet Dye (selective)

Neutral Red Dye (colorless > pH 6.8; red < pH 6.8)(differential)

Lactose (differential)

46

What role do the bile salts and crystal violet dye play in MacConkey Agar?

They inhibit the growth of Gram positive bacteria
(Only Gram negative bacteria will grow on MacConkey Agar)

47

How is MacConkey Agar differential?

Not all Gram negative bacteria can ferment lactose to produce acidic compounds

48

If acidic compounds are produced on a MacConkey agar what will happen?

The pH of the media will drop and the Neutral Red Dye (pH indicator) will cause the media to turn reddish/pink

49

If lactose cannot be fermented on the MacConkey agar what happens?

No acidic products are formed so there is no drop in pH which means no change in color happens

50

If the organism can grow on MacConkey agar and the media turns reddish/pink, what is the organism presumed to be?

Coliform

51

If there is growth on the MacConkey agar but the media remains colorless what can be presumed about the organism?

That it is Gram negative

52

What type of agar is Eosin Methylene Blue (EMB) Agar?

Selective and differential

53

What is EMB agar used to identify?

The presence of coliforms

54

What are the important components in EMB agar?

Eosin Y Dye (selective and differential)

Methylene Blue Dye (selective and differential)

Lactose (differential)

55

What do both Eosin Y and Methylene Blue dyes inhibit?

The growth of Gram positive bacteria

56

Why is EMB agar differential?

Not all Gram negative bacteria can ferment lactose to produce acidic compounds

Not all Gram negative bacteria produce the same amount of acidic compounds if they can ferment lactose

57

If there is poor to no growth on an EMB agar what does it mean?

The bacteria is Gram positive

58

What does it mean if there is colorless growth on an EMB agar?

Gram negative but can not ferment lactose (not a coliform)

59

What does it mean if the growth on EMB agar is pink and mucoidy

Small amount of acidic compounds were made by the slow fermentation of lactose (possible coliform)

60

What does it mean if the growth is dark purple to black with a green metallic sheen?

Large amounts of acidic compounds were made due to the vigorous fermentation of lactose (probable coliform)

61

What kind of agar is Hektoen Enteric Agar?

Selective and differential

62

What is Hektoen Enteric Agar used for?

To isolate and distinguish between Salmonella and Shigella species

63

Can Salmonella and Shigella break down lactose, sucrose, or salicin sugars?

No

64

Can Salmonella or Shigella reduce sulfur?

Shigella can but Salmonella cannot

65

What are the key components of Hektoen Enteric Agar?

Bile salts (selective)
Sucrose (differential)
Salicin(differential)
Lactose(differential)
Sodium thiosulfate (sulfur source)(differential)
Ferric ammonium citrate (differential)
Bromthymol blue dye (differential)
Acid fuchsin dye (differential)

66

Bile salts in the media inhibits what?

The growth of Gram positive bacteria

67

What does it mean if there is poor to no growth on Hektoen Enteric Agar?

Gram positive bacteria

68

What does it mean if the colonies are orange/yellow on Hektoen Enteric Agar?

Large amounts of acidic products made which means fermentation of the sugars happened and the bacteria is neither Salmonella or Shiegella

69

what does it mean if the growth is bluish/green on Hektoen Enteric Agar?

A rise in the pH indicating no fermentation but a breakdown of proteins producing alkaline products (possibly salmonella or shigella)

70

What does it mean if the growth is bluish green with black precipitate on Hektoen Enteric agar?

Rise in pH due to break down of proteins and thiosulfate is reduced to H2S which reacts with ferric ammonium citrate to produce an insoluble black metallic compound. (Sulfur reduction)
Possibly Salmonella

71

What is a single media that can be used to determine an organism’s ability to ferment three different sugars as well as the ability of an organism to reduce sulfur?

Triple Sugar Iron Agar (TSIA)

72

What is TSIA used for?

To differentiate between enteric bacteria such as Salmonella, Shigella, and E.coli

73

What are three important points to remember about the fermentation pathway?

Glucose is not the only carbohydrate that can be used to glycolysis

The end products of fermentation include acidic compounds

Gas can also be an end product

74

Most enteric bacteria use what kind of metabolism?

Facultative anaerobic respiration

75

In the absence of oxygen certain enteric species can use sulfur as what?

The terminal electron acceptor to produce energy

76

One specific biochemical pathway for sulfur reduction uses Thiosulfate as a what?

Electron acceptor

77

Under acidic conditions what is reduced by the enzyme thiosulfate reductase to produce sulfite and hydrogen sulfide (H2S) which is expelled from the bacterium

Thiosulfate

78

What can H2S be considered as which can react with metal ions to form metal sulfides?

A reducing agent

79

In the presence of H2S ferrous sulfate (FeSO4) is converted to what?

Ferrous sulfide (FeS)

80

What is a insolvable black metallic compound?

Ferric sulfide

81

Thiosolfate is reduced to sulfite and H2S
H2S and Ferrous sulfate react to produce what?

Ferrous sulfide

82

What are the important ingredients in TSI Agar?

Low concentration of glucose .1%
High concentration of Lactose 1%
High concentration of Sucrose 1%
Sodium Thiosulfate (sulfur source)
Ferrous Sulfate (H2S indicator)
Phenol Red (pH indicator, which is red at neutral pH)

83

TSI agar is always prepared as a what?

Slant

84

The slant portion of the TSIA provides what kind of conditions?

Aerobic

85

The butt portion of the TSIA provides what kind of conditions?

Anaerobic

86

If TSIA has a yellow bottom and a pink top what does it mean?

Glucose only fermentation

87

The glucose in TSIA is used up in how long?

~12 hours then bacteria break down amino acid in the media

88

If the butt is yellow and the slant is yellow in a TSIA what does it mean?

Glucose and lactose and/or sucrose fermentation

89

If TSIA is pink on top and bottom what does it mean?

No fermentation

90

Cracks and bubbles in TSIA indicates what?

Gas production

91

If the bottom is yellow (acidic) and the top is pink either pink or yellow(alkaline) and there is the presence of the color black for a TSIA what does it mean?

Sulfur can be reduced under acidic conditions by thiosulfate reductase, therefore the bacteria can ferment at least one of the three sugars and can reduce sulfur

92

If fermentation by glucose only and the organism can reduce sulfur what color will the top be?

Pink

93

What kind of media is Columbia CNA with 5% Sheep Blood agar?

Selective and differential

94

What is CNA with 5% sheep blood used for?

To specifically grow Gram positive organisms

95

What is in Columbia CNA Blood Agar?

Digested casein
Digested animal tissue
Beef extract
Yeast extract
Corn starch
Sheep blood

96

The extremely nutrient rich content of Columbia CNA Blood agar allows for a wide variety of organisms to grow except what?

Gram negative organisms

97

What is in Columbia CNA Blood agar that selects against gram negative organisms?

Colistin and nalidixic acid which are antibiotics

CNA is short for Colistin Nalidixic Acid

98

Colistin contains many polycationic regions that can insert into what?

The outer membrane of the Gram negative bacterial cell wall

99

What does the insertion of colistin do?

Disrupts the integrity of the outer membrane which can lead to bacterial lysis

100

What does naldixic acid inhibit?

DNA gyrase/topoisomerase

101

What is the function of DNA gyrase/topiosomerase?

Allows supercoiled DNA to be relaxed and reformed and is necessary for DNA replication

102

Nalidixic acid inhibits what in the cell?

DNA synthesis

103

Gram negative bacteria are more sensitive to what than Gram positive bacteria?

Nalidixic acid

104

Different bacteria will show what when grown on agar that contains sheep’s blood?

Red blood cell hemolysis patterns

105

A large clearing on CNA blood agar indicates what?

Complete lysis of RBCs (red blood cells)
Beta hemolysis

106

Partial lysis of RBCs is indicated how?

Greening of the media which is the partial lysis of RBCs
Alpha hemolysis

107

If there is no media color change or clearing on CNA blood agar what does it mean?

No lysis of RBCs
Gamma hemolysis

108

What is mannitol salt agar used for?

To identify pathogenic staphylococcus species from non pathogenic staphylococcus species

109

What are the three important components in MSA (mannitol salt agar)

7.5% salt (selective)
Mannitol (differential carbon source)
Phenol red (pH indicator red at neutral pH)(differential)

110

The high salt concentration of MSA only allows what to grow?

Staphylococcus

111

Only some Staphylococcus species can ferment mannitol making the media what?

Differential

112

If acidic products are formed in MSA the pH will drop and the media will turn what color?

Yellow

113

Non pathogenic Staphylococcus cannot ferment what?

Mannitol (the media will remain red)

114

What is in regular Blood Agar?

TSA and 5% sheep blood

115

Many types of bacteria can produce secreted protein toxins called what?

Hemolysins

116

What are able to hemolysis RBCs and destroy hemoglobin?

Hemolysins

117

What are the three major types of hemolysis?

Beta
Alpha
Gamma

118

Which type of hemolysis is the complete destruction of RBCs and hemoglobin?

Beta

119

Which type of hemolysis is the partial destruction of RBCs and hemoglobin that produces a green coloring around a bacterial colony?

Alpha

120

What produces the green color in alpha hemolysis?

The partial break down of hemoglobin to methemoglobin

121

Methemoglobin is what type of hemoglobin?

Oxidized

122

What type of hemolysis produces no destruction of RBCs?

Gamma

123

What is DNA composed of?

Nitrogenous bases, deoxyribose sugar, and phosphates

124

What are linked by covalent bonds and together make up the sugar/phosphate backbone of the DNA molecule?

Ribose sugars and phosphates

125

What enzyme is segregated by certain bacterial species that breaks the covalent bonds between phosphate and ribose sugar molecules?

DNase

126

Is the presence of DNase considered a virulence factor?

Yes

127

The breaking of covalent bonds in the DNA backbone causes what?

Depolymerization

128

One type of DNase breaks the bond between the 5’ carbon atom of the ribose sugar and the what?

Phosphate

129

A second type of DNase cleaves the bond between the phosphate and the what?

3’ carbon atom of the ribose sugar

130

What are the two important media components in DNase agar?

DNA

Methyl Green Dye

131

Because the dye binds to polymerized, uncleared DNA, the media is what color?

Blue/green

132

If there is no zone of clearing is DNase present?

No

133

If a bacteria has DNase present, what happens?

A zone of clearing is produced because the dye cannot bind to cleaved DNA

134

What is a medically important alpha hemolytic Streptococcus species?

Streptococcus pneumonia

Streptococcus mutants (causes dental plaque)

135

Beta hemolytic Streptococcus can be classified into how many groups based on the different types of carbohydrates/sugars on their surface?

7

136

Of these groups which is the most medically important beta hemolytic Streptococcus species?

Group A and Group B

137

Newborns with Group B Streptococcus can have what?

Pneumonia and/or meningitis

138

What percentage of newborns with a GBS infection die?

20%

139

What percentage of newborns with GBS will suffer permanent brain damage?

30-50%

140

Group A Streptococcus (GAS) can cause what common infection?

Strep throat

141

Occationally GAS can become invasive and cause what life threatening illness?

Necrotizing fasciitis

142

How can you quickly tell if the organism is a Group A Streptococcus rather than GBS or another type of non-pathogenic Streptococcus species?

PYR test

143

What are Gram positive diplococci that generally grow/appear in short chains and show gamma hemolysis?

Enterococcus (Enterococcus faecalis)

144

What is a member of the normal human intestinal flora and generally considered to be an opportunistic pathogen which causes nosocomial infections (hospital required)

Enterococcus faecalis

145

What can cause urinary tract infections via catheters, bacterial endocarditis via Hearst and pacemakers, and meningitis via intravenous lines?

Enterococcus faecalis

146

Enterococcus faecalis has natural antibiotic what?

Resistance

147

What are Enterococci that are resistant to vancomycin?

Vancomycin Resistant Enterococci (VRE)

148

What percentage of GAS and Enterococcus species produce the enzyme L-pyrrolindonyl arylamidase (PYRase)?

98% of Group A
96% Enterococcus

149

What is a peptidase involved in the degradation of proteins?

PYRase

150

Specifically what does PYRase do?

Removes the N-terminal pyroglutamic acid residues from polypeptides

151

If PYRase is present, the beta naphthylamine plus a PYR reagent will produce a Schiff base that produces what?

A red precipitate

152

What are substances that are produced by the natural metabolic processes of some bacteria or fungi that can inhibit or destroy other microorganisms?

Antibiotics

153

What is a Gram positive rod that is commonly found in the soil that is capable of secreting the antibiotic Bacitracin?

Bacillus licheniformis

154

Bacitracin in an antibiotic that is commonly found in what?

Over the counter topical first aid ointments

155

What does Bacitracin target?

The bacterial cell wall, specifically the incorporation of peptidoglycan in the cell wall

156

Bacitracin interferes with what?

The transport of peptidoglycan components across the cell membrane

157

Is Bacitracin effective against both Gram positive and Gram negative organisms?

Yes

158

Is the activity of Bacitracin bactericidal?

Yes (kills bacteria)

159

Which antibiotic is orally toxic to humans but very effective topically?

Bacitracin

160

Normally which lipid is used to transport NAM and NAG sugars across the cell membrane during the synthesis of peptidoglycan?

Bactoprenol

161

Bacitracin blocks bactoprenol from transporting what?

NAM and NAG sugars

162

Since not all bacterial species are bacitracin reisistant what can be used for the presumptive identification of potential pathogens?

Bacitracin susceptibility test

163

The Bacitracin susceptibility test can differentiate between what?

Beta hemolytic Streptococcus species

164

Which Streptococcus species is resistant to Bacitracin and what does it cause?

Agalactiae; neonatal sepsis in newborns

165

Which Streptoccus species can cause strep throat and in susceptible to Bacitracin?

Pyogenes

166

Bacitracin suspecptibility test can differentiate between Catalase (+/-) Gram (+/-) cocci.

(+);(+)

167

What catalase positive Gram positive cocci is Bacitracin resistant and can cause minor skin infections to life threatening diseases?

Staphylococcus species

168

What catalase positive Gram positive cocci is generally non pathogenic and part of our normal biome but are bacitracin susceptible?

Micro coccus species

169

What organism secrets Novobiocin?

Streptomycin niveus

170

What is a Gram positive filamentous rod that is commonly found in the solid that secretes Novobiocin?

Streptomycin niveus

171

What does Novobiocin inhibit?

DNA replication

172

Specifically what does Novobiocin do?

Binds to DNA gyrase, an enzyme that effects the degree of DNA supercoiling and is necessary for DNA replication

173

What is DNA gyrase?

A multi subunit enzyme that binds to and hydrolyzes ATP in order to promote DNA supercoiling

174

Novobiocin competes with what for the binding site on DNA gyrase and blocks what?

ATP; ATP hydrolysis reaction

175

Novobiocin susceptibility test can differentiate between what?

Coagulate negative Staphyloccous species

176

What is a Novobiocin resistant bacteria that is the second most likely cause of urinary tract infections?

Staphylococcus saprophyticus

177

What is a Novobiocin susceptible non pathogenic normal skin microbe?

Staphylococcus epidermidis

178

What does optochin inhibit?

ATP synthase enzyme

179

Optochin is only used for what due to severe side effects (loss of vision)?

Differentiation of S. Pneumonia from other alpha hemolytic streptococcus

180

Most alpha hemolytic streptococcus are non pathogenic and optochin resistant however this streptococcus organism is a pathogen that is optochin susceptible and can cause a number of diseases including a life threatening pneumonia

Streptococcus pneumonia

181

To determine if an organism is resistant to an antibiotic, what must you do?

Measure the diameter of the zone of clearing and compare it to a zone diameter interpretative chart.

182

Who publishes the interpretative charts?

National Committee for Clinical Laboratory Standards

183

For bacitacin an organism is resistant if the zone of clearing is less than what?

10 mm

184

For Novobiocin the bacteria is resistant if the diameter of clearing is less than what?

16 mm

185

For optochin a bacteria is resistant if the zone of clearing is less than what?

14

186

S. Epidermidis is part of the normal human skin flora and is generally not considered what?

Pathogenic

187

A. aureus is considered this, and can cause minor to major skin infections, pneumonia, toxic shock syndrome etc...

Opportunistic pathogen

188

Name an organism that is associated with hospital acquired infections?

Methicillin-resistant S. Aureus

189

What two tests can be used to differentiate S. Aureus from S. Epidermidis?

Mannitol fermentation
Presence of coagulase

190

Coagulase is only present in which of the two staphylococcus?

A. Aureus

191

What is a protein which binds to prothrombin?

Coagulase

192

What is involved in blood coagulation and the generation of fibrin clots?

Prothrombin

193

Prothrombin is inactive and must be cleaved in order for it to be converted to what active enzyme?

Thrombin

194

Thrombin is the final portion of what?

The blood coagulation cascade

195

When coagulase binds with prothrombin II it produces what active enzyme?

Staphylothrombin

196

Staphylothrombin can bind to and act on what?

Fibrinogen acting like thrombin to produce a cross-linked fibrin clot

197

In S. Aureus coagulase can be present in what two forms?

Bound
Free

198

Bound coagulase is attached to what?

The bacterial cell wall

199

Bound coagulase binds to and activate prothrombin in what?

Blood plasma

200

Bound coagulase can also bind to what in blood plasma?

Fibrinogen

201

Bound fibrinogen cleaved by coagulase activated prothrombin produces what?

Fibrin clots

202

What is secreted by the bacteria into the surrounding environment?

Free coagulase

203

Free coagulase binds to and activates what in blood plasma?

Prothrombin

204

Name the two types of coagulase test

Slide
Tube

205

Both types of coagulase tests require the use of what?

Plasma

206

What is the yellow colored liquid portion of blood that the red blood cells are suspended in?

Plasma

207

Plasma is composed of what?

90% water plus compounds such as clotting factors

208

Coagulase slide/clumping factor test only detects what?

Bound coagulase

209

Which coagulase test involves mixing bacteria with a small amount of rabbit plasma on a glass slide?

Slide

210

Bacteria associated with fibrin will do what on a slide?

Clump together

211

The coagulase tube test detects what?

Both bound and fee coagulase

212

Which test mixes bacteria with rabbit plasma in a test tube?

Tube

213

In a tube test fibrin in the plasma will link together causing what to form?

A clot

214

What is the possible role of Coagulase as a virulence factor?

Allows the bacteria to evade the host immune response

215

Production of a fibrin clot around the bacteria may protect it from what?

Phagocytosis my macrophages

216

What term is more applicable today when referring to antibiotics?

Antimicrobials

217

List mechanisms of antimicrobial agents

Disruption of the bacterial cell wall
Inhibition of protein synthesis
Inhibition of nucleic acid replication
Disruption of folic acid metabolism
Disruption of the bacterial cell membrane

218

Bacteria may not be adversely affected by what?

All the mechanisms used by antimicrobial agents

219

Bacteria have different patterns of what kind of susceptibility?

Antimicrobial

220

What factors influence the antimicrobial susceptibility of a bacterium?

Type of bacterial cell wall
Difference in metabolic pathways and/or enzymes
The environment the bacterium resides in (aerobic vs anaerobic)
The acquisition of drug resistance

221

What method allows for the simultaneous establishment of the susceptibility of a bacterium to several antimicrobial drugs?

Disk Diffusion (Kirby-Bauer) method

222

What is the term used to describe growth over the entire surface of a plate?

Bacterial lawn

223

Immediately after the plate has been inoculated, paper disks that have been impregnated with what at a specific what are placed on the plate at a fair distance apart?

A specific antimicrobial drug; concentration

224

What is used in a clinical laboratory for consistency and to reduce the amount of time required for a Kirby-Bauer test?

Disk dispenser

225

At what temperature and time is a plate undergoing a Kirby-Bauer test subjected to for incubation?

37 C, 24 hours

226

During incubation, the antimicrobial drug on the paper disk does what?

Diffuses out of the disk and through the agar

227

Diffusion of the drug generates what?

A concentration gradient of the antimicrobial drug around the disk

228

Also during the incubation of a Kirby-Bauer plate, what begins to grow?

Bacteria

229

How many possible outcomes from the diffusion of antimicrobial drugs and the growth of bacteria are there?

2

230

What is it called if the bacterial lawn is around the disk

Resistance to the drug

231

If there is no growth around the disk we say that the bacteria is what?

Sensitive or susceptible to the antimicrobial drug

232

What is complete reisistance?

Growth directly around the disk

233

What is the area around the disk without bacteria growth called?

Zone of clearing or zone of inhibition

234

Moving away from the disk the antimicrobial drug concentration does what?

Decreases

235

The periphery of the zone of inhibition is also called what?

The minimal inhibitory concentration

236

What do you measure in a Kirby-Bauer Test?

The diameter of the zone of clearing

237

After taking the diameter measurement what do you compare the diameter to?

Results on a zone diameter interpretive chart

238

Who develops the standards for accurate antimicrobial susceptibility tests and generates numerous charts for interpretation of these zones for many different pathogenic organisms and many different antimicrobial drugs?

The Clinical and Laboratories Standards Institute (CLSI)

239

What is the result if the Kirby-Bauer test is not done according to CLSI guidelines?

Improper treatment

240

What is the rigorous monitoring of all components and reagents used in tests?

Quality control

241

What are some components that are tightly monitored for quality?

The agar plates used
The concentration of bacteria used to inoculate the plates

242

Agar plates must be prepared at a specific what in the Kirby-Bauer test because if it fluctuates it can change the growth of the bacteria and/or the activity of the antimicrobial drug?

PH

243

Agar plates used in the Kirby Bauer test must be what?

Of a specific thickness

244

what results if the agar plate is too thick for a Kirby Bauer test?

The diameter of the concentration gradient will be too small
A smaller zone of clearing

245

What results if the agar plate is too thin during a Kirby Bauer test?

The concentration gradient will be large laterally
The zone of clearing will be too big

246

Why must a specific concentration of bacteria be used to inoculate plates in a Kirby Bauer test?

The turbidity of the bacterial culture is compared to the turbidity of a specific McFarland standard

247

What are McFarland standards?

A set of reference samples of different turbidity that can be used to estimate the number of bacterial cells in a sample

248

As the standard number increases what increases?

The cell concentration

249

The turbidity of the bacterial culture used in a Kirby Bauer test is prepared so that it is equivalent to the turbidity of what McFarland standard?

.5

250

If the bacterial concentration is higher than the approved McFarland standard what happens?

The drug is not as effective since it must act on a much greater number of bacteria which results in a higher concentration of drug required to kill the bacteria. The zone of clearing will be small which will produce an incorrect interpretation of results

251

When looking for the best antibacterial drug to use, what is desirable?

To find a drug that can kill the disease causing bacteria without killing the normal bacterial flora which can be beneficial

252

Besides finding a drug that does not kill beneficial bacteria what is another goal in drug choice?

Find the therapeutic dose that limits the toxicity and causes fewer side effects

253

What are three ways to determine susceptibility to antimicrobial drugs?

Kirby-Bauer Method
E-Test
Tube dilution test

254

What are the advantages of the Kirby Bauer Test?

Quick and easy
Many different antimicrobial drugs can be tested simultaneously

255

What is the disadvantage of the Kirby Bauer test?

Does not provide any information on a therapeutic dose

256

What are a the advantages of the E-test (combination of disk diffusion and tube dilution)

Quick and easy
Different antimicrobial drugs can be tested simultaneously
Can give an approximate MIC

257

What is a disadvantage of the E-test

Cannot provide a definitive MIC

258

What are the advantages of the Tube dilution test?

Precise MIC
Test can be automated

259

What are disadvantages of the tube dilution test?

Prior to automation it was complicated and time consuming
Prior to automation it could only test a single drug at a time

260

What broth was used in the laboratory during the Tube dilution test?

Mueller-Hinton

261

The first dilution tube that shows no growth during a tube dilution test is the what?

MIC

262

What ratio of dilutions is prepared for a MIC determination?

1:2

263

Each tube divides the concentration of the drug in the tube prior to it in by what?

2

264

How many results can an automated microbiology system report for MIC testing?

100 antimicrobial susceptibility plates/panels in a total of 18 hours

265

Who discovered penicillin?

Sir Alexander Fleming in 1928

266

All members of the penicillin group of drugs share the same what?

Basic structure

267

The R group is different for each penicillin group member but they all have what?

A beta lactam ring

268

Cephalosporins were discovered in what year?

1948

269

The cephalosporin structure contains a beta lactam ring that as a different ring compound than what?

Penicillin group members

270

All beta lactam antibiotics target what?

The bacterial cell wall

271

Specifically what do beta lactam drugs affect within the cell wall?

Peptidoglycan

272

What does peptidoglycan do for the cell?

Gives it strength which helps prevent the cell from lysis

273

What is the structure of petidoglycan?

A polysaccharide chain made up of two sugars NAG and NAM linked through glycosidic bonds and then cross-linked by peptide bridges

274

What enzyme allows for the formation of the peptide bridges?

Transpeptidase

275

Beta lactam drugs bind to what?

Covalently to transpeptidase

276

What does the binding of transpeptidase do?

Results in the inactivation of the enzyme

277

In 1943 what happened

Penicillin became widely available

278

By 1950 what percentage of S. Aureus were resistant to penicillin?

40%

279

List mechanisms by which bacteria can acquire drug resistance

Natural selection/spontaneous mutations
Transfer of plasmids with resistance factors
Use of alternative metabolic pathways
Changes to drug binding sites
Activation of drug pump
Decreased bacterial cell permeability
Drug inactivation

280

What is a common target in beta lactam antibiotics?

The beta lactam ring for drug inactivation

281

Bacteria can acquire plasmids that carry what?

Antibiotic resistance genes

282

What do certain resistance genes encode for?

Enzymes that can specifically inactivate beta lactam antibiotics

283

What are enzymes that can inactive beta lactam called?

Beta lactamases

284

What does beta lactamase destroy?

The beta lactam ring which inactivated the antibiotic

285

What is nitrocefin?

A chromogenic cephalosporin that contains a beta lactam ring

286

Beta lactamase cleaves nitrocefin to form cephalosporanic acid resulting in a color change to what?

Pink/red

287

All electromagnetic energy travels how?

In waves

288

The shorter the wavelength the greater the what?

The energy it carries

289

Gamma rays have extremely short wavelengths as so are what?

Highly energetic

290

Radio waves are longer and have considerably less what?

Energy

291

What includes high energy gamma and x rays?

Ionizing radiation

292

What is the best example of nonionizing radiation?

UV light

293

What are highly penetrable with the exception of lead and cause the direct and complete breakage of DNA?

Gamma rays

294

What are gamma rays used for?

Sterilize medical equipment and for food preservation

295

What is very poor at penetrating substances so bacteria must be directly exposed to be killed?

UV light

296

What three groups can UV be divided into?

UVA, UVB, and UVC

297

What is the average wavelength of UVA?

315-400 nm

298

UVA includes the UV in what?

Sunlight

299

What is the average wavelength for UVB?

280-315 nm

300

UVB can be used for what?

Tanning

301

What is the average wavelength for UVC?

100-280

302

What is UVC used for

To kill bacteria (it is bactericidal)

303

How does UVC cause DNA damage?

By thymine dimer formation

304

What is a covalent bond that forms between 2 adjacent thymine bases?

Thymine dimer

305

Diners distort DNA helix making what difficult?

Replication and transcription

306

Formation of many thymine dimers results in what?

Bacterial death

307

What are two mechanisms of thymine dimer repair?

Photoreactivation (light repair)
Excision repair (dark repair)

308

In photoreactivation what enzyme do bacteria possess?

The photo active enzyme DNA photolyase

309

DNA photolyase binds to the region of DNA that contains the dimer. Exposure to visible light activates the enzyme causing it do what?

Break the covalent bond between the thymine

310

What enzyme is used in excision repair?

Endonuclease, helicase, DNA polymerase, DNA ligase

311

What is the function of endonuclease?

Breaks bonds on either side of the DNA strand backbone that contains the dimer

312

What is the function of helicase?

Removes the damaged DNA segment

313

What is the function of DNA polymerase?

Fill in the missing nucleotides

314

What is the function of DNA ligase?

Joins the new segment to the old DNA strand

315

What is the sudden and simultaneous outbreak or increase in the number of cases of a disease in a community?

Epidemic

316

What are some examples of epidemics?

1950 polio epidemic
AIDS/HIV epidemic
H1N1 flu epidemic

317

What are some means of transmittal of infectious disease?

Ingestion
Inhalation
Sexual contact
Direct contact (handshakes)
Animal or insect bite
Blood

318

What infects many people at once?

Common source epidemic

319

What is an example of a common source epidemic?

Contaminated water after the severe flood in Pakistan

320

What is it called when a disease moves from one person to another?

Propagated transmission

321

The first person with the disease in propagated transmission is call the what?

Index case

322

In bacteria, in what three ways can gene acquisition or gene transfer occur?

Transduction
Conjugation
Transformation

323

What is the transfer of genetic material via bacteriophage?

Transduction

324

What is the acquisition of DNA via direct contact between cells?

Conjugation

325

What is the uptake of foreign DNA by bacteria?

Transformation

326

A bacterium that can take up plasmid DNA is referred to as what?

Competent

327

Bacteria can acquire competence naturally or what?

Artificially

328

What are small circular DNA molecules that can be carried by bacteria?

Plasmids

329

Plasmids are distinct and independent for the bacterial chromosomal DNA and are what?

Self replicating

330

Plasmids carry what kind of genes?

That are not essential for the growth but that are beneficial to the microorganism.

331

What is the origin of replication (ori)

The portion of the plasmid that carries the information necessary for its DNA replication within the bacterium

332

What is the beta lactamase gene (bla)

The gene that encodes for the beta lactamase enzyme which can cleave beta lactam rings of members of the penicillin group

333

What is green fluorescent protein (GFP)?

The protein first identified in the jellyfish Aequorea Victoria and under UV light glows Green

334

What does araC do?

Encodes for DNA binding transcriptional regulatory protein

335

AraC is required for what?

Arabinose utilization in bacteria

336

AraC controls what?

The arabinose operon

337

What is a cluster of functionally related genes all under the control of a single promoter?

Operon

338

What is the region of DNA where transcription intimation begins?

Promoter

339

AraC proteins bind to the DNA adjacent to the arabinose promoter doing what?

Preventing RNA polymerase to bind

340

If RNA polymerase cannot bind to the arabinose promoter what happens?

No transcription of the arabinose utilization gene

341

When arabinose is present, it binds to the AraC protein causing it to do what?

Change shape

342

To make bacteria competent requires what?

Chilling the cells in the presence of calcium

343

Chilling the cells in the presence of calcium promotes what?

The binding of the plasmid DNA to the bacterial cell surface and increases the permeability of the cell membrane

344

What form of calcium is used?

CaCl2

345

Chilling involves placing the tubes in what?

A tray of ice

346

How many microliters of pGLO was added to the + tube?

10

347

Incubate the micro tubes in the ice tray for how long?

10 minutes

348

After incubation on ice you need to initiate a what?

Heat shock

349

At what temperature do you shock the microtubes?

42 C for 1 minute

350

After heat shock the tubes are returned back to the ice tray for how long?

2 minutes

351

How many people will acquire an infection while in the hospital?

1 patient in 20

352

Infection control relies on the proper use of what?

Disinfectants and antiseptics

353

What is a chemical that can destroy most microorganisms on inanimate surfaces like a bed rail?

Disinfectant

354

What is a chemical that can destroy most microorganisms on living surfaces like your hands?

Antiseptic

355

What is it called when a disinfectant can kill a wide variety of microbes?

Broad spectrum

356

What considerations should be made when choosing a disinfectant?

Will it be compatible with the surface (rust)
Will it still work in a protein rich environment like blood or feces
Is the disinfectant safe for the user
Is the disinfectant cost effective

357

A good disinfectant should be what?

able to Destroy many different microbes
Be relatively stable
Non staining and non corrosive
Easy and safe to use

358

What are two points that are critical to know before using a disinfectant?

What is the optimal concentration of the disinfectant to use to kill most microorganisms
What is the optimal length of time that a disinfectant needs to be in contact with a microorganism before it is destroyed

359

What must a chemical pass in order to serve as a hospital disinfectant?

The American Offical Anlaytical Chemist’s Use-Dilution Test

360

The Use-dilution test examines what?

How well a disinfectant works against a high concentration of a known microorganism dried onto a non-porous object