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Microbiology Flashcards

synoptic link to respiration and populations + logs practice on page 11 - very useful + serial dilutions on pages 16-17

1
Q

what is included as a microorganism?

A

bacteria
fungi
protoctists
viruses

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2
Q

describe bacteria (+fungi)

A

some bacteria and fungi decompose dead organisms, releasing and recycling nutrients

some bacteria are pathogens that cause disease in humans, crops, and domestic animals, while others are harmless or beneficial

bacteria reproduce asexually by binary fission and can do so very rapidly

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3
Q

how many bacteria in the gut and include the number of cells in humans

A

human body consists of one trillion cells, but the gut contains approx one hundred trillion bacteria from 500 - 1000 different species

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4
Q

what kingdom are bacteria in and what could they be distinguished by?

A

prokaryotae

size, shape, staining characteristics, metabolic features, antigenic features, genetic features

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5
Q

draw the structure of a bacterium

A

page 3 in booklet

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6
Q

describe the sizes of bacteria

A

size vary by species
typically ranging from 1 to 10 um in length

archaea are the smallest, with some having a diameter of 0.4 um

e.coli is 1.8 um in diameter and 7um in length

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7
Q

compare the shapes of bacteria

A

coccus (spherical) e.g. staphylococcus, streptococcus

bacillus (rod-shaped) e.g. escherichia coli

spirillum (spiral/comma/corkscrew) e.g. vibrio cholerae

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8
Q

give another way of classifying bacteria (shape has been mentioned already)

A

based on their grouping patterns

may exist individually, in pairs, in chains or in clusters

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9
Q

what two metabolic features does bacteria have?
(make sure you know the definition)

A

autotrophic
photoautotrophic

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10
Q

describe what an antigen is

A

a molecule that causes the immune system to produce antibodies against it
these may be individual molecules or those on the surface of the bacterial cells

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11
Q

how does the gram stain work and what colour does a gram positive and gram negative bacteria become at each stage of the gram stain?

A

1 - application of crystal violet (purple dye)
+: purple
-: purple

2- application of grams iodine solution
+: purple
-: purple

3- alcohol wash (decolourisation) - differential stage
+: purple
-: colourless

4- application of safranin (a counter-stain)
+: purple
-: red/pink

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12
Q

does a gram +ve or a gram -ve have a lipopolysaccharide layer in their cell wall?

A

gram -ve therefore have a more complex cell wall

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13
Q

does a gram +ve or a gram -ve cell wall retain the crystal violet stain?

A

gram +ve

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14
Q

does a gram +ve or a gram -ve have antibiotic susceptibility?

A

they both do but gram -ve bacteria are not susceptible to penicillin

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15
Q

give examples of gram +ve bacteria

A

staphylococcus
streptococcus

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16
Q

give examples of gram -ve bacteria

A

salmonella

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17
Q

overall why does a gram +ve and a gram -ve have different staining properties?

A

due to the differences in the chemical composition of their cell walls

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18
Q

describe gram +ve bacterial cell walls

(diagram on page 6)

A

thick peptidoglycan cell wall
plasma membrane

no outer lipopolysaccharide

therefore they retain the initial crystal violet stain when washed with alcohol and appear purple under a microscope

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19
Q

describe gram -ve bacterial cell walls and their susceptibility to antibiotics

A

outer lipopolysaccharide cell wall
thin peptidoglycan cell wall
plasma membrane

when washed with alcohol, they lose this outer layer with the crystal violet stain
they are then able to take up the counter stain safranin and appear red under a microscope

due to more complex cell wall, gram - ve bacteria are not susceptible to some antibiotics such as penicillin or lysozyme (tears)

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20
Q

explain why gram +ve and gram -ve bacteria look different under the microscope?

A

gram +ve: bacterial cell walls take up and retain the crystal violet dye

gram -ve: lipopolysaccharide takes up the crystal violet dye and is then removed by alcohol, allowing safranin to stain the thin layer of peptidoglycan red

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21
Q

what is the function of the peptidoglycan cell wall?

A

structural support to prevent osmoticlysis/bursting when cells are in a hypotonic solution

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22
Q

what is the function of the plasma membrane?

A

selectively permeable membrane - controls what enters and exits cell

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23
Q

describe bacterial reproduction

A

bacteria can reproduce rapidly through binary fission in suitable environment with division occurring every twenty minutes under optimal conditions

unicellular yeast may reproduce by budding

24
Q

what 4 conditions do microorganisms require for growth?

A

temperature
nutrients
pH
oxygen requirement

25
why do bacteria need temperature as a condition?
bacterial metabolism is enzyme-regulated with most bacteria thriving between 25°C and 45°C the optimum temperature for mammalian pathogens is around 37°C, the temperature of the human body
26
why do bacteria need nutrients as a condition?
in the laboratory, nutrients are supplied in nutrient media, such as nutrient agar or liquid broth the carbon source is usually glucose, while nitrogen for amino acid and nucleic acid synthesis is provided as nitrate ions
27
why do bacteria need pH as a condition?
bacteria tend to favour slightly alkaline conditions while most fungi thrive in neutral to slightly acidic environment
28
what are obligate aerobes?
they can only survive and metabolise in the presence of oxygen they cannot survive without it
29
what are obligate anaerobes?
they can only survive and metabolise in the absence of oxygen
30
what are facultative anaerobes?
they metabolise better in the presence of oxygen but can also survive and metabolise without it
31
clostridium perfringens are obligate anaerobes that grow in wounds, producing toxins that cause gas gangrene symptoms include blisters under the skin, foul-smelling fluid and jaundice treatment can involve the use of a hyperbaric oxygen chamber with air pressure 2.5 x higher than atmospheric pressure how would this treatment work to improve the patient's health?
oxygen is forced into the wound the conditions become aerobic clostridium growth is inhibited as they are obligate anaerobes white blood cells can then destroy the pathogens
32
describe population growth for microorganisms using lag, log, stationary and death phases
lag - no/little cell division intense metabolic activity such as enzyme synthesis log - rapid increase in numbers, no limiting factors to growth cell division > death rate plenty of available glucose stationary - limiting factors preventing further growth of the population e.g. competition for glucose carrying capacity has been reached death - limiting factors cause the population size to decrease death rate > cell division this could be due to the build up of toxic waste, or no glucose left in the medium
33
how would the description of population growth of microorganisms differ for rabbits?
rabbits must reach sexual maturity before they can start to reproduce birth rate not cell division stationary phase - competition for food etc death phase - disease or parasitism
34
what do aseptic techniques do and what are its two main purposes?
they keep apparatus and equipment free of microorganisms preventing contamination of pure cultures by environmental microbes (protecting microbes) preventing contamination of the environment by cultures being grown (protecting environment)
35
what to do when preventing contamination of pure cultures by environmental microbes?
sterilise all media and equipment e.g. inoculating loops before use handle cultures carefully, flaming the neck of culture bottles before opening and closing use a lit bunsen burner to create a convection current disinfect workbenches beforehand, such as with 3% Lysol
36
what to do when preventing contamination of the environment by cultures being grown?
sterilise work surfaces before and after experiments, using a disinfectant lift agar dish lid to no more than 45 degrees seal agar dishes with adhesive tape, but not all the way around flame the neck of the culture bottle without placing the cap on the work surface
37
what 7 steps to take when inoculating an agar dish?
1- pass the metal inoculating loop through a flame until red hot, then allow it to cool 2- hold the bacterial culture bottle in one hand; remove the cap with the little finger of the other hand without placing it down 3- flame the neck of the culture bottle for 2-3 seconds and dip the inoculating loop into the bacterial culture 4- lift the petri dish lid to 45 degrees, allowing entry of the inoculating loop, and streak the agar with the bacterial culture 5- secure the petri dish with adhesive tape, but do not seal it completely to avoid anaerobic conditions that could promote pathogenic growth 6- incubate at a suitable temperature (25 or 37°C) for 24-48 hours 7- sterilise all equipment after use
38
all equipment should be sterilised before and after use how to sterilise using an autoclave and with what materials do you use this with?
glassware and metal equipment (in a laboratory the preferred method of sterilisation is an autoclave) this sealed vessel sterilises equipment by: sealing it in an autoclave bag heating it to 121°C in steam (above boiling point) applying high pressure for 15 minutes
39
how to sterilise using gamma radiation and what material do you use this with?
plastic equipment before use it is often sterilised with gamma radiation after use, plastic equipment can be disposed of in a biohazard waste bin or sterilised in an autoclave
40
why is estimating bacterial population growth important?
it is vital for environmental health officers inspecting food premises, water authorities checking daily water supplies, and food manufacturers ensuring their products are safe to eat
41
how are microorganism populations in liquid culture measured?
by counting cells directly or indirectly
42
give two ways of counting cells directly
total cell count total viable count
43
what is total cell count?
living and dead cells in a bacterial sample
44
what is total viable count?
living cells in a known volume of liquid medium
45
how can the cells be counted using a microscope?
a haemocytometer is a microscopic slide with a grid engraved rectangular chamber which can be used to calculate the number of microbes in a sample the chamber has known depth, allowing the number of cells in a specific volume to be counted a coverslip is placed over the chamber and the slide is observed under a microscope to count the cells (would be known as total cell count)
46
how to calculate the number of cells per mm^3 of a culture?
count the cells in the culture
47
give a technique to count the total viable count
serial dilution
48
what does serial dilution assume?
that a single bacterial cell will reproduce asexually to form a visible colony on an agar plate after incubation the number of colonies therefore represents the number of bacteria in the original sample
49
describe how a serial dilution works (8 points)
place 9cm^3 of sterile distilled water into five sterile test tubes using a sterile pipette place 1cm^3 of the original bacterial culture into the first tube and gently mix the bacterial culture has now been diluted 10 times (i.e. it has a 10^-1 dilution) transfer 1cm^3 of this 10^-1 dilution from the 1st tube into the 2nd tube and gently mix with the 9cm^3 of sterile distilled water the bacterial culture has now been diluted 100 times (and is a 10^-2 dilution) repeat this procedure for the remaining tubes now transfer 1cm^3 of each diluted sample onto a sterile nutrient agar plate use a sterile spreader to distribute the sample evenly on each agar plate repeat twice more to give a total of 3 plates per dilution (a mean number of colonies can be calculated from the 3 plates) seal each agar plate with tape (but not all the way around) and incubate at 25°C for 24-48 hours after incubation, identify the dilution with distinct, non - merging colonies count the number of distinct colonies on each plate multiply the number of colonies by the dilution factor to give the number of bacteria in the original 1cm^3 bacterial culture sample
50
what inaccuracies may occur when carrying out a serial dilution if the original bacterial culture is under diluted?
colonies might merge (clumping) resulting in an under estimate of cell numbers
51
what inaccuracies may occur when carrying out a serial dilution if the original bacterial culture is over dilated?
there will be too few colonies to be statistically representative
52
how to indirectly count cells?
by measuring turbidity (cloudiness) of the culture which gives an indirect measure of growth
53
what does turbidimetry involve?
using a colorimeter to measure the turbidity of a culture as cell numbers increase
54
how is the colorimeter used in turbidimetry to count the cells?
bacterial population measurements are obtained by finding the suspension's absorbance value and referencing a standard graph of light absorbance plotted against the number of bacterial cells
55
is turbidimetry a total cell count or a total viable count and why?
total cell count as the colorimeter cannot differentiate between living and dead cells

biolala (32 decks)

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