Micorbiology Flashcards
1
Q
How can bacteria be distinguished from one another
A
They can be distinguished by :
Size
Shape
Metabolism - all the reaction of the body
Antigenic features
By their staining characteristics
2
Q
Waht are the three basic shapes of bacteria
A
Singular
coccus- spherical - drawn as circles
Bacillus- rod shaped
Spirillum-spiral shaped
Plural -
Coccus
Bacillus
Spirilli
3
Q
How is the shape of a bacteria maintained
A
By their cell wall
4
Q
Waht colour do gram positive bacteria stain
A
We use crytal violet to stain and their theirck petidoglycan cell wall stains purple (using a microscope)
5
Q
Waht colour do gram negative stain when they are stained using crystal violet
A
Nothing happens as ehtanol used in th decolonise the iodine after the crystal violent
Their thin peptidoglycan layer stain red using saffrin
Gram negative bacteria also have a thin lipopolysaccharide later
6
Q
Waht is gram staining used for
A
To distinguish between bacteria they can show it’s cahow and if it gram positive or gram negative
7
Q
Waht is the procedure of gram staining
A
Heat fix a smear of bacteria
Stain using crystal violet stain
Fix the stain with iodine
Decolourise with alcohol
Counterstain with safranin.
8
Q
Where can bacteria be grown
A
In a Petri dish or flask
9
Q
Waht are require by bacteria to grow
A
The right nutrients and conditions
10
Q
Waht is a common medium for culturing bacteria
A
Agar
11
Q
W hat is agar
A
Is is a common medium to grow bacteria
Jelly like substance in a Petri dish
Or a liquid in a glass
12
Q
Waht does agar look like in a Petri dish
A
Me;ly like substance
13
Q
Waht is affair like in a flask
A
Liquid
14
Q
Waht does agar contain
A
Carbon source
Nitrogen source
Water
Vitamins
Mineral salts
15
Q
Why do you add stuff to agar
A
Because some bacteria may need other substances to grow best ( eg ) blood agar , starch agar , salty agar
16
Q
Waht is another way you can distinguish bacteria
A
Through using an agar plat that is dyed .
The dye in the agar will Schengen depending on the metabolism of the of the bacteria
17
Q
Waht are some external factors that are required when culturing bacteria
A
Correct pH and temperature
18
Q
What is a recommended temperature to culture bacteria in school
A
25 degrees centigrade
19
Q
Waht is the optimum temperate when culturing pathogenic bacteria
A
37 degrees because they live in the condo and this is the temperature of the body
20
Q
Waht are the bacteria called that grow in cold temperature
A
Psychrophiles
21
Q
Waht is the recommended temperature for psychrophyles
A
1-5 degrees
22
Q
Waht are bacteria called that grow at extreme temperatures
A
Thermophiles
23
Q
Waht is the recommended natural environment for thermophiles
A
Volcanic vents
Hot springs
24
Q
Waht is a selective media
A
A media in which only certain bacteria will grow
25
What can be added to agar to prevent the growth of non-resistant bacteria
Antibiotics
26
Waht is an example of a nitrogen source that can be added to agar
Amino acids
27
Waht is an example of a carbon source that can be added to agar
Glucose
28
What are bacteria called that grow best on salty agar
Halophiles
29
Waht are bacteria called that grow best at low pH
Acidophile
30
Waht are some external factor that need to be controlled when culturing bacteria
pH
Temperature
Oxygen levels
31
Waht are the three categories different bacteria classified depending on their oxygen requirements
obligate aerobes
facultative anaerobes
obligate anaerobes
32
Waht are the require ment of obligate aerobes and why
Must have oxygen
Because to carry out :
metabolic processes
Reproduce
33
Waht is the oxygen requirement of facultative anaerobes
Oxygen can be present or absent
34
Waht doe bacteria need oxygen
To carry out metabolic processes
To reproduce and carry out metabolic processes
But reproduction is better if oxygen is present
35
Waht is the oxygen requirement for obligate anaerobes and why
They must have an oxygen free environment to reproduce and to carry out simple metabolic processes
36
37
Waht happens to bacteria if they don’t have the requirement they need
Any bacteria can survive harsh conditions by they won’t be able to reproduce and when the optimum conditions are restored they can reproduce again
38
Which area of a long tube do obligate aerobes occupy
The tops of the tube only because this is the area of most oxygen
39
How do you determine how much oxygen a microorganism needs
By culturing bacteria in a long tube filled switch special medium agar and then you pass oxygen through the tube the top of the tube has the highest oxygen the bottom of the tube has the lowest oxygen
40
Which area of the long tube doe facultative anaerobes occupy
They are seen through out the tube but mostly at the top
41
42
Which area of the a long tube do obligate anaerobes grow and why ?
At the bottom of the tube only because this is the area with the least oxygen
43
What is the most important thing to do when culturing micro-organisms
To not allow them to contaminate the atmosphere
But it is also just as important to not introduce other contaminating micro-organisms into the culture. So we carry out aseptic technique
44
Why is aseptic technique required
To prevent contamination of the atmosphere
To prevent the contamination of the bacteria culture by introducing contaminating bacteria
45
Waht is are the three stages of aseptic technique
Before starting
During transfer
After inoculation
46
How do you carry out aseptic technique before starting ?
Wash hands , sterilise table with disinfectant/ethanol in a blue flame ,wear lab coats , wear goggles
Put Bunsen on roaring flame and work very close to it
Tie back hair
Sterilise all equipment - with ethanol , inoculation loop is heated till glowing red
Some equipment is sterilised using autoclave which heats equipments to over 120.
47
Why do you not need to sterilise the Petri dish
It has already been sterilised by heat of manufacture
48
Why do you carry out aseptic technique during an transfers
Lid of agar should be held in crook of pinky finger - not placed on benches
Neck of agar bottle should be flamed on opening and before closing
Loops must be sterilised and cooled before insertion into culture and after
Label lids of Petri dishes
49
How do you carry out aseptic technique after inoculation
Seal Petri dish with cross tape - to prevent growth of human pathogen and to not allow oxygen into culture
Dish should be incubated upside down at 25 degrees for 24 hours
Don’t reopen plat e and autoclave after observations are made
50
What is a roaring Bunsen required
To make a convection current
51
The necks of agar bottle should be
Flamed
52
Inoculation equipment should be
Sterile
53
What are the different types of count of cultured bacteria
Total
Viable
54
What is a total count
This is a method where you count all the cells present but can’t distinguish between live and dad cells
55
Waht is a viable count
This is a method that only counts cell capable of reproducing (forming colonies ) and are therefore alive
56
When is a colony of bacteria formed
When a bacterium (single bacteria ) reproduces forms a colony that is visible on a plate
57
Waht should you do before starting to count be either the viable or the total count
Serial dilution should be done this dilution of the same and the. The bacteria can be calculated for the volume
58
Waht is a serial dilution
Diluting the sample of bacteria so there aren’t too many to count or so that no colonies are overlapping each other on the agar part
59
60
61
Why is ethanol used as part of gram staining ?
Most bacteria have lipopolysaccharide late and because these are lipids ethanol is used as a solvent to break them down
62
63
What is the difference between streptococcus and staphylococcus
Streptococcus-this is a chain of bacteria cells
Staphylococcus - this is a cluster of bacteria cells
64
What shape is vibrio bacteria
Comma shapes they have still stuck to a rod
65
66
How else can bacteria be distinguished
Thei mode of nutron- metabolic activity
Modes of respiration
67
What is the structure of the cell wall of the gram positive bacteria
Thicker peptidoglycan cell wall
68
What is the structure of a gram negative bacteria
Thin peptidoglycan cell wall and has a lipoprotein layer
69
What are the diffeeences in the cell wall structure of gram + and - bacteria ?
Cell wall in gram positive is thicker
Doesn’t have outer membrane gram negative does
No lipopolysaccharide layer gram negative dos
Thicker petidoglycan cell wall
70
What is the difference of gram negative and gram positive bacteria when gram staining
Gram positive bacteria retain crystal violet stain but gram negative doesn’t
71
Explain in detail the stages of gram staining
Add small amount of barrier to middle of microscope slide
Fax bacteria to slide by passing it through Bunsen
Add crystal violet to stain the peptidoglycan layer
Add iodine - bind crystal violet more strongly
Add acetone to
Remove any unbound crystal violet and polysaccharides
Gram oositive will be purple
Gram negative will be colorless- loose ther stain
Add saffrin
Gram positive remain purple
Gram negative go red - thei cell wall
72
What is the purpose of crystal violet
Binds to the peptidoglycan layer and stains it purple
73
How can the shape of a bacteria be determined by its name ?
The genus (the fist part ) indicates the shape of the bacteria
74
Waht is the job the iodine in gram staining
It’s fixes the crystal filet to the peptidoglycan more strongly
75
What is the purpose of the crystal violet
To bind to to the peptidoglycan layer
76
77
Waht is the purpose of the acetone/alcohol
To decolorise by removing an unbound crystal violet and lipopolysaccharide
Gram negative bacteria go flourless at this stage
Gram positive bacteria remain purple
78
Waht is the purpose of saffrin
It is used as a counter stain
Gram negative statin red
Gram positive remain purple
79
Waht are the three types of bacteria that will stain purple
Bacilli
Streptococcus
Staphylococcus
80
Why does gram positive bacteria stain the way that they do
Because they don’t have a lipopolysaccharide layer
This allows the crystal violet to bind more efficiently to the to the peptidoglycan layer
81
Waht are some example of gram negative bacteria
E.coli
Salmonella
82
Why does gram negative bacteria not stain with crystal violet
Their presence of a lipopolysaccharide layer doesn’t allow the crystal violet to bind to the thin peptidoglycan layer effectively and therefore the crustal violet is washed out by the acetone ‘ alcohol
83
Waht is a pathogen
An organism that causes disease in a host
84
How long do you sterilise equipment in an autoclave for
15 minutes
85
Why doe we not seat the Petri dish all the way aliens with tape
Because this would create anaerobic conditions and potentially encourage the growth of pathogenic bacteria
86
Why is the Waht is the liquid agar in a flask called
Nutrient broth
87
How can you measure the size of a population indirectly
By measuring the turbidity - this is measure in the cloudiness of the culture it is normally used in field work when you measuring the poultion of bacteria in a river for example
88
What equipment do you use to measure the turbidity of a culture
A calorimeter
89
Is turbidity a viable or a total count
A total count because it cannot distinguish between live and dead bacteria
90
Waht is a more accurate method that colony counting
Using a heamocytometer - this is a specialised microscope slide -but is can distinguish between live or fade cells so it is a total count
91
Why do bacteria have different staining characteristics
Because they have different chemical composition in their cell wall
92
Waht does serial dilution depend on
It depends in each bacteria forming a colony thefor either provide a viable count
93
Which -late do you use for counting \
The one with the largest number of distinct colonies
This helps to increase the reliability of the count
94
Waht happens if you are counting merged colines
U won’t get an accurate count
95
Waht Are the assumptions of the counts
Tha one bacteria produces one colony
But this can lead to an underestimate of the whole population size as two bacteria could have merged together to make a big colony
96
Why will Petri dish with only a small number of colonies not a good dis to use when measure the sister of the population of the bacteria
This will not give an accurate representation of the whole pollution as the number of colonies is too small to be of statistical significance
97
How can you measure growth directly
By counting colonies
98
What must you do before coming colonies
Carry out Serbia dilution
99
Waht does a serial dilution assume
That Aeschylus colonel has arisen form one bacteria
100
Waht is a limitation of serial dilution
It can give an underestimate of the whole population
101
How do you carry out a serial dilution
You add 1cm3 of the orgonal culture medium to 9cm of water and then you continue to do this the first dilation will be 10-1
But if 0.1 cm 3 of the original culture is added to 9.9 cm 3 of sterile water then the first dilation will be 10-2
Then we spre]ad ech diluted sample on an agar part incubate is at 25 for 2 days
102
Waht is the equation of calcuting population size
PS= number of colonies x dilution factor / the volume of the sample
103
Waht is a more accurate method of colony counting
Heamocytometer - total count - specialised microscope slide
104
105
