Microbiology Flashcards
(160 cards)
1
Q
What is the purpose of culture methods in microbiology?
A
To isolate bacteria in pure culture and identify them by performing various tests.
Culture methods also demonstrate biochemical, antigenic, and other phenotypic and genomic properties of the isolated colonies.
2
Q
What is required for the study of microbes?
A
Pure cultures, free of other microbes.
A clean environment must be maintained, and work should be done close to the flame.
3
Q
What are the two types of culture media?
A
- Liquid medium - diffuse growth
- Solid medium - discrete colonies
4
Q
What should be done if media does not pass quality control guidelines?
A
- Notify the supervisor
- Repeat the test using fresh isolate
- Discard the batch if test continues to fail
- Troubleshoot the reason for failure
- Do not test patient specimens until resolved
- Record all pertinent action
5
Q
What is the principle of the catalase test?
A
It demonstrates the presence of the enzyme catalase, which mediates the breakdown of hydrogen peroxide into oxygen and water.
6
Q
What is the streak culture method used for?
A
To obtain discrete colonies of bacteria by streaking on the surface of a solid media plate.
7
Q
What is the pour-plate technique?
A
The original sample is diluted, mixed with warm agar, and poured into petri dishes for isolated cells to grow into colonies.
8
Q
What is the purpose of quality control in culture media?
A
To ensure the information generated by the laboratory is accurate, reliable, and reproducible.
9
Q
Fill in the blank: The absence of catalase is indicated by a lack of _______.
A
bubble production.
10
Q
What are the expected QC results for Escherichia coli on MacConkey Agar?
A
Growth, lactose fermented, pink colonies.
11
Q
What is the lawn culture method used for?
A
To provide a uniform layer of bacterial growth on a solid medium.
12
Q
What are the two types of colonies observed in pour-plate culture?
A
- Surface colonies
- Subsurface colonies
13
Q
What should be done to test sterility in media quality control?
A
Incubate one plate at 35°C for 48 hours for every 20 plates in a lot.
14
Q
What is the expiration date for solid media containing blood or serum?
A
Up to 6 months.
15
Q
What does the presence of lactose fermenters indicate on MacConkey Agar?
A
Pink colonies.
16
Q
What is the stroke culture method?
A
Seeding slopes by lightly smearing the surface of agar with a loop in a zig-zag pattern.
17
Q
List some methods used for culturing bacteria.
A
- Streak culture
- Lawn culture
- Pour-plate culture
- Stroke culture
- Stab culture
- Liquid culture
18
Q
What is the significance of maintaining stock cultures?
A
To prepare antigens for various uses.
19
Q
What is the ideal incubation temperature for many culture media?
A
37°C.
20
Q
True or False: Antibiotic susceptibility testing is one of the uses of stroke culture.
A
True.
21
Q
What is differential media?
A
A media which has substances incorporated in it enabling it to distinguish between bacteria.
Example: Mac Conkey’s medium
22
Q
What color do lactose fermenters produce on Mac Conkey’s medium?
A
Pink colonies
23
Q
What color do non-lactose fermenters produce on Mac Conkey’s medium?
A
Colourless colonies
24
Q
What is the optimal pH for catalase action?
A
7
25
What is the function of catalase in bacteria?
Catalase helps in converting H2O2 to H2O and O2
26
What are sugar media?
Media containing any fermentable substance such as glucose, arabinose, lactose, starch, etc.
27
What is the purpose of transport media?
Media used for transporting samples to ensure delicate organisms survive the transport.
28
Give an example of transport media.
Stuart’s medium or Buffered glycerol saline
29
What is the significance of using distilled water in media preparation?
The pH and purity of tap water varies immensely; distilled water ensures consistency.
30
What is a common error in media preparation?
Not using distilled water
31
What is the purpose of the motility test?
To help differentiate species of bacteria that are motile from non-motile.
32
How is the motility test performed?
Stab motility media with inoculating needle.
33
What indicates a positive motility test?
Growth away from the stab line
34
What does the oxidation-fermentation (OF) test determine?
It determines the oxidative or fermentative metabolism of a carbohydrate.
35
What type of organisms produce an acid reaction in the open tube of the OF test?
Oxidizing organisms, e.g., Pseudomonas species
36
Fill in the blank: Indicator media change their color when _______ grows in them.
[a bacterium]
37
What is the main disadvantage of liquid cultures?
It does not provide a pure culture from mixed inocula.
38
What is the purpose of a Durham's tube in sugar media?
For the detection of gas by the bacteria.
39
What is fermentation?
An anaerobic process involving the oxidative or fermentative metabolism of a carbohydrate or its non-utilization
40
What type of bacteria are usually bacterial fermenters of carbohydrates?
Facultative anaerobes
41
What is oxidation in the context of bacterial metabolism?
An aerobic process where bacterial oxidizers are usually strict aerobes
42
What does the Hugh and Leifson test employ?
A semi-solid medium in tubes containing the carbohydrate under test (usually glucose) and a pH indicator
43
What is needed to create anaerobic conditions in the Hugh and Leifson test?
One tube is immediately sealed with paraffin oil
44
What does the citrate utilization test determine?
The ability of an organism to use citrate as its only source of carbon and ammonia as its only source of nitrogen
45
What components does the medium for the citrate utilization test contain?
* Sodium citrate
* An ammonium salt
* Bromothymol blue indicator
46
What indicates growth in the citrate utilization test medium?
Turbidity and a color change of the indicator from light green to blue
47
What is a positive result for the citrate utilization test?
Growth on the slant and a change in color to blue
48
What organism is known to produce a positive result in the citrate utilization test?
Klebsiella pneumoniae
49
What is the Voges Proskauer test used for?
To determine the ability of organisms to produce acetoin from glucose fermentation
50
What is the principle behind the Voges Proskauer test?
Detection of neutral end product acetyl methyl carbinol (acetoin)
51
What color indicates a positive result in the Voges Proskauer test?
Pinkish red color at the surface of the medium
52
What is the interpretation of a yellow color in the Voges Proskauer test?
Negative result
53
What does the Methyl Red test measure?
The ability of the organism to produce stable acid from glucose fermentation
54
What does a positive result in the Methyl Red test indicate?
Red color (indicating pH below 6)
55
What is the significance of the Lactose Fermentation test?
Tests the ability of bacteria to ferment lactose
56
What is a positive result in the Lactose Fermentation test?
Yellow color after the indicator is added
57
What does a negative result in the Lactose Fermentation test indicate?
No color change or reddish color
58
What does the Sucrose Fermentation test determine?
The bacteria’s ability to ferment sucrose and produce acid end-products
59
What indicates a positive result in the Sucrose Fermentation test?
Yellow color after the indicator is added
60
What is a negative result in the Sucrose Fermentation test?
No color change or reddish color
61
What is the media used for the Lactose Fermentation test?
Lactose broth containing beef extract, gelatin peptone, and lactose with phenol red indicator
62
What is the media used for the Sucrose Fermentation test?
Sucrose broth containing beef extract, gelatin peptone, and sucrose with phenol red indicator
63
What does Mannitol Salt Agar (MSA) test for?
The ability of bacteria to tolerate 7% salt concentration and ferment mannitol
## Footnote
MSA is selective for salt-tolerant bacteria.
64
What are the main components of Mannitol Salt Agar (MSA)?
* Nutrient agar
* Mannitol
* 7% sodium chloride
* Phenol red indicator
65
How do you perform a Mannitol Salt Agar test?
Inoculate an MSA plate using streak plate method and incubate for 24-48 hours
66
What does an alkaline slant/no change in the butt (K/NC) indicate in a Triple Sugar Iron (TSI) test?
Glucose, lactose, and sucrose non-utilizer
67
What does an alkaline slant/acid butt (K/A) indicate in a TSI test?
Glucose fermentation only
68
What does an acid slant/acid butt (A/A) with gas production indicate in a TSI test?
Glucose, sucrose, and/or lactose fermenter
69
What is indicated by black color in a TSI test?
H2S production
70
What does gas production in a TSI test indicate?
Presence of gas bubbles or cracks in the medium
71
What does a yellow slant/yellow butt (A/A) indicate in TSI results?
Lactose fermenters
72
What is the purpose of TSI agar?
To determine whether a gram-negative rod utilizes glucose and lactose or sucrose fermentatively and forms hydrogen sulfide (H2S)
73
What are the components of TSI agar?
* 10 parts lactose
* 10 parts sucrose
* 1 part glucose
* Peptone
74
What indicates the presence of acidification in TSI agar?
Phenol red indicator
75
What is the method for inoculating TSI agar?
Touch the top of a well-isolated colony, then stab through the center to the bottom and streak the surface
76
What does a positive result for acid in a glucose fermentation test look like?
Yellow after indicator is added
77
What indicates a positive result for gas production in a glucose fermentation test?
Bubble in the Durham tube
78
What does a completely negative result in a glucose fermentation test look like?
No color change or reddish color and no bubble
79
What is the procedure for the indole test?
Inoculate tryptone broth with the test organism and incubate for 18-24 hours at 37°C
80
What indicates a positive indole test?
Development of bright red color at the interface after adding Kovac's reagent
81
Which organisms are indole positive?
* E. coli
* Proteus vulgaris
* Klebsiella oxytoca
82
Which organisms are indole negative?
* Salmonella spp.
83
What does a positive indole test indicate?
Presence of E.coli, Proteus vulgaris, Klebsiella oxytoca
## Footnote
These bacteria possess tryptophanase, allowing them to hydrolyze tryptophan into indole.
84
What does a negative indole test indicate?
Presence of Salmonella spp., Proteus vulgaris, Proteus penneri, Acinetobacter baumannii, Klebsiella pneumoniae, Enterobacter aerogenes
## Footnote
These bacteria do not produce indole from tryptophan.
85
What is the principle behind the indole test?
Determining the ability of an organism to split tryptophan into indole
## Footnote
Indole is a metabolic degradation product of the amino acid tryptophan.
86
What media is used for the indole test?
Tryptone broth
## Footnote
Tryptone broth contains tryptophan necessary for the test.
87
What reagent is used in the indole test?
Kovac's reagent
## Footnote
Kovac's reagent contains hydrochloric acid, dimethylaminobenzaldehyde, and amyl alcohol.
88
What are some tests to know in microbiology?
* Indole
* Methyl Red/Voges-Proskauer
* Citrate
* H2S production in SIM
* Motility
* Lactose fermentation
* Sucrose fermentation
* Glucose fermentation & gas production
* Triple Sugar Iron Agar (TSI) test
## Footnote
These tests help differentiate various species of bacteria.
89
What are the shapes of bacteria?
* Cocci (round)
* Bacilli (rod-shaped)
* Spiral
## Footnote
These are the three basic shapes of bacteria.
90
What are some cultural characteristics used for bacterial identification?
* Shape
* Size
* Elevation
* Margin
* Surface
* Texture
* Color
## Footnote
These characteristics provide additional information for identifying bacteria.
91
What does the catalase test identify?
The presence of the enzyme catalase in bacteria
## Footnote
A positive catalase test indicates that the organism can break down hydrogen peroxide.
92
What is the purpose of selective media?
To inhibit unwanted organisms and isolate specific bacteria
## Footnote
Examples include MacConkey's medium for gram-negative bacteria and TCBS for V.cholerae.
93
What is the significance of anaerobic culture methods?
To grow anaerobic bacteria that differ in their oxygen requirements
## Footnote
Clostridium tetani is an example of a strict anaerobe.
94
What are some methods used for anaerobic culture?
* Production of vacuum
* Displacement of oxygen with other gases
* Chemical method
* Biological method
* Reduction of medium
## Footnote
These methods help create an oxygen-free environment for anaerobic bacteria.
95
What indicates a positive urease test?
The broth turns a bright pink color
## Footnote
This color change indicates the production of ammonia from urea hydrolysis.
96
What is the purpose of enrichment media?
To isolate pathogens from a mixed culture
## Footnote
Enrichment media often contain inhibitory substances to suppress unwanted organisms.
97
What are some examples of enrichment media?
* Selenite F Broth for Salmonella
* Alkaline Peptone Water for Vibrio cholerae
## Footnote
These media are designed to promote the growth of specific pathogens while inhibiting others.
98
What are the criteria for evaluating blood culture bottles?
* Degree of growth
* Presence of turbidity
* Presence of deposit
* Nature of surface growth
* Ease of disintegration and odor
## Footnote
These characteristics help assess the growth of bacteria in the culture.
99
What color change indicates a positive ammonia test?
Bright pink color
## Footnote
If ammonia is made, the broth turns a bright pink color, indicating a positive result.
100
What happens to the broth in a negative ammonia test?
No color change and no ammonia is made
## Footnote
If the test is negative, the broth has no color change.
101
What is the principle of the coagulase test?
Differentiates Staphylococcus aureus (positive) from coagulase negative Staphylococci
## Footnote
S. aureus produces two forms of coagulase: bound and free.
102
What is bound coagulase?
Bound to the bacterial cell wall and reacts directly with fibrinogen
## Footnote
Causes clumping of cells when mixed with plasma.
103
What is free coagulase?
Produced extracellularly by bacteria, causing clot formation
## Footnote
Free coagulase causes a clot when S. aureus colonies are incubated with plasma.
104
How is a positive result indicated in the slide test for coagulase?
Macroscopic clumping in 10 seconds or less in coagulated plasma
## Footnote
No clumping in saline or water drop indicates a positive result.
105
What indicates a negative result in the slide test for coagulase?
No clumping in either drop
## Footnote
All negative slide tests must be confirmed using the tube test.
106
What does a positive tube test for coagulase indicate?
Clot of any size
## Footnote
A negative result would be indicated by no clot.
107
What is the purpose of the nitrate reduction test?
Determine the ability of the organism to reduce nitrate to nitrites or free nitrogen gas
## Footnote
Reduction of nitrate to nitrite is detected by adding sulphanilic acid and alpha-naphthylamine.
108
What does a red color after adding sulphanilic acid and alpha-naphthylamine indicate?
Positive nitrate reduction test
## Footnote
Indicates that nitrite is present.
109
What indicates a negative nitrate reduction test?
No color change after adding reagents
## Footnote
If nitrate is unreduced, it remains in its original form.
110
What must be added to distinguish between nitrate reduction reactions?
Zinc dust
## Footnote
Zinc reduces nitrate to nitrite, helping to clarify results.
111
What does a red color after adding zinc indicate?
Negative nitrate reduction test
## Footnote
Indicates that nitrate was not reduced by the test organism.
112
What does the urea hydrolysis test determine?
Ability of bacteria to hydrolyze urea to ammonia
## Footnote
This is done using the enzyme urease.
113
What media is used in the urea hydrolysis test?
Stuarts Urea broth (pH 6.8) containing yeast extract, monopotassium phosphate, disodium phosphate, urea, and phenol red
## Footnote
Phenol red acts as an indicator for pH changes.
114
What does a positive urea hydrolysis test indicate?
Formation of ammonia resulting in alkalinity
## Footnote
This is due to the action of urease on urea.
115
What is the aim of the Microbiology II module?
Help students understand how two major groups of bacteria cause diseases
## Footnote
Includes understanding signs, symptoms, virulence factors, and identification techniques.
116
What indicates an organism's tolerance to salt?
Growth in saline conditions
## Footnote
If the organism is not tolerant, it will not grow.
117
What happens if an organism is tolerant to salt?
It will grow.
118
What indicates that a salt-tolerant organism can ferment mannitol?
Yellow zones around the colonies.
119
What does it mean if the media remains pink?
The salt-tolerant organism cannot ferment mannitol.
120
List the major steps in microbial analysis.
* Sample collection and identification
* Macroscopic examination
* Microscopic examination
* Culture
* Antibiotic sensitivity testing
* Reporting the results.
121
Name the main groups of Gram-positive cocci.
* Staphylococcus
* Streptococcus
* Enterococcus
* Pneumococcus
* Micrococci
122
What are the Gram-negative cocci?
* Neisseria spp.
* Moraxella
123
Identify the Gram-positive bacilli.
* Corynebacterium
* Bacillus
* Clostridium
* Non-sporing anaerobes
124
List the Gram-negative bacilli.
* Enterobacteriaceae
* Vibrio
* Shigella
* Salmonella
* Pseudomonas
* Actinobacter spp.
* Proteus spp.
* Yersinia spp.
* Pasteurella
* Francisella
* Haemophilus spp.
* Helicobacter spp.
* Campylobacter spp.
* Bordetella
* Brucella
* Legionella
* Mycobacterium
125
What is an example of an atypical mycobacterium?
Mycobacterium leprae.
126
What are the learning objectives for the module?
* Pathogenesis and epidemiology of viruses
* Common viruses in respiratory and gastrointestinal tracts
* Infections in infants and foetus
* Diagnosis, prevention, and control of RNA and DNA viruses
127
What are the basic components of simple media?
* Peptone
* Meat extract
* NaCl
128
What is complex media?
Media other than basal media with added ingredients.
129
Define synthetic or defined media.
Media prepared from pure chemical substances with known exact composition.
130
What is the purpose of the catalase test?
To determine the presence of the enzyme catalase in bacteria.
131
What does a positive oxidase test indicate?
The presence of bacterial cytochrome oxidase enzyme.
132
What are the precautions to take during sample collection?
* Apply strict aseptic techniques
* Wash hands before and after collection
* Collect specimen at appropriate disease phase
* Ensure specimen represents the infectious process
* Use sterile containers.
133
What types of biological fluids can be used as microbiology samples?
* Stools
* Sputum
* Urine
* Throat swab
* Rectal swab
134
What are the three types of culture media based on consistency?
* Solid medium
* Liquid medium
* Semi-solid medium
135
What is the principle of the oxidase test?
Oxidation of tetramethyl-p-phenylenediamine dihydrochloride to indophenol, resulting in a dark purple color.
136
Fill in the blank: The reagent used in the oxidase test is _______.
[tetramethyl-p-phenylenediamine dihydrochloride]
137
What indicates the presence of oxidase?
Development of a dark purple color
## Footnote
No color development indicates a negative test and the absence of the enzyme.
138
What are enriched media?
Substances like blood, serum, egg are added to the basal medium
## Footnote
Used to grow bacteria that are exacting in their nutritional needs.
139
Give examples of enriched media.
* Blood agar
* Chocolate agar
140
What is the purpose of labeling and dating specimen containers?
To ensure proper identification and tracking during transportation
## Footnote
Clean and uncontaminated containers are crucial.
141
What are the three basic shapes of bacteria?
* Cocci (round)
* Bacilli (rod-shaped)
* Spiral
142
What is the primary stain used in Gram staining?
Crystal violet
## Footnote
It is the first step in the Gram staining procedure.
143
What does the Gram stain differentiate?
Most clinically significant bacteria into two main groups: Gram-positive and Gram-negative.
144
What color do Gram-positive bacteria appear after staining?
Purple
145
What color do Gram-negative bacteria appear after staining?
Pink
146
What is the role of iodine in Gram staining?
Acts as a mordant by forming a crystal violet-iodine complex
147
What is used for decolorization in Gram staining?
Alcohol
## Footnote
This step removes the primary stain from Gram-negative bacteria.
148
What is the purpose of counterstaining in the Gram stain procedure?
To color the decolorized Gram-negative bacteria with safranin
149
What is a simple stain?
One dye is used to reveal shape, size, and arrangement of bacteria.
150
What are differential stains used for?
To distinguish cell types or parts using a primary stain and a counterstain
## Footnote
Examples include Gram stain and acid-fast stain.
151
What do special stains reveal?
Certain cell parts not revealed by conventional methods, such as capsules and flagella.
152
What is the significance of microscopy in diagnosing microbial infections?
To examine microorganisms for motility, morphology, and staining reactions.
153
What is a common example of a motile bacterium observed microscopically?
Vibrio cholerae in a rice water fecal specimen
154
What is the first step in the Gram staining procedure?
Make a thin smear on a clean glass slide, dry it, and fix it by passing through a flame.
155
What is the purpose of the alcohol step in Gram staining?
To decolorize the slide, allowing the counterstain to enter Gram-negative bacteria.
156
What are the characteristics of Gram-positive bacteria?
* Thick peptidoglycan layer
* Presence of teichoic acid
* Sensitive to penicillin
157
What are the characteristics of Gram-negative bacteria?
* Thin peptidoglycan layer
* Presence of lipopolysaccharides
* Less sensitive to penicillin
158
Which bacteria are oxidase positive?
* Pseudomonas spp.
* Vibrio spp.
* Neisseria spp.
* Campylobacter
* Haemophilus spp./Helicobacter spp.
159
What does the capsule stain detect?
Capsule production by organisms
## Footnote
Most capsules are composed of polysaccharides.
160
What is the composition of most bacterial capsules?
Polysaccharides
## Footnote
Some capsules are composed of polypeptides.
