Exam III Flashcards
(360 cards)
1
Q
Describe a coliform
A
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
Q
The presence of coliforms are used to indicate what?
A
Whether a water sample has become contaminated with fecal material and therefor with potential bacterial pathogens
3
Q
What method is used to determine if a water sample is contaminated with coliforms?
A
Most Probable Number (MPN) also known as the multiple tube fermentation method
4
Q
The MPN procedure allows you to calculate what?
A
Total coliform counts in a water sample
The E.coli counts in a water sample
5
Q
What is the first step of determining the MPN
A
Making a 1:10 serial dilution of the water
6
Q
What is the second step of MPN
A
1 mL of dilution tubes is added to Lauryl Tryptose Broth (LTB)
7
Q
What are the contents of LTB?
A
Lauryl sulfate
Lactose
Durham tube
8
Q
What is the purpose of Lauryl sulfate in the LTB?
A
Inhibits the growth of organisms other than coliforms
9
Q
What is the function of lactose in LTB?
A
Coliforms can ferment this sugar
10
Q
What is the purpose of the Durham tube in LTB?
A
Will indicate if gas has been produced from the fermentation of lactose
11
Q
LTB is a media that is what for coliforms?
A
Selective
12
Q
LTB gives a presumptive determination of what?
A
The presence of coliforms
13
Q
What is the third step of MPN?
A
After 48 hours, broths are examined for
- Growth
- Presence of gas
14
Q
The presence of growth is considered what for LTB tubes?
A
Positive for coliforms
15
Q
Transfer how many loops of culture from every LTB tube that shows what into one of each what?
A
2; growth; one tube Brilliant Green Lactose Bile broth (BGLB) one tube of E.coli broth
16
Q
At what temperature do you incubate the BGLB?
A
37 C
17
Q
At what temperature do you incubate the E.coli broth (EC) at?
A
45 C
18
Q
What are the contents of BGLB?
A
Lactose
Durham tube
2% bile
19
Q
What is the function of Lactose in BGLB?
A
Coliforms can ferment this sugar
20
Q
What is the function of a Durham tube in BGLB?
A
Will indicate if a gas has been produced from the fermentation of lactose
21
Q
What is the function of the 2% bile for BGLB
A
Inhibits non-coliforms
22
Q
BGLB is a selective media that does what?
A
Confirms the presence of coliforms
23
Q
After 48 hours, GBLB broths are examined for the presence of what?
A
Gas
24
Q
BGLB tube with gas are considered what?
A
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
