Microbiology Flashcards
1
Q
What is the approximate size of a bacteria?
A
1 μm
2
Q
What are the two types of cells?
A
Eukaryote and Prokaryote cells
3
Q
What are the two kingdoms that make up Prokaryote cells?
A
Archaea
Eubacteria (bacteria)
4
Q
Do bacteria have a nuclear envelope?
A
No
5
Q
Do bacteria have membrane-enclosed organelles?
A
No
6
Q
What sort of chromosomes do bacteria have?
A
A single circular chromosome
7
Q
What are some key features of a bacterial cell? (8)
A
- chromosomes
- fimbriae/pili
- nucleoid
- ribosomes
- plasma membrane
- cell wall
- capsule
- flagella
8
Q
What is the cell wall of a bacteria made of?
A
Peptidoglycan
9
Q
Describe peptidoglycan and include its function
A
Rigid macromolecular layer that provides strength to the cell.
It protects the cell from the osmotic lysis (ie. water entering from the environment) and confers cells shape
10
Q
Bacteria without a cell wall are called
A
mycoplasmas
11
Q
Describe the structure of peptidoglycan
A
Links of alternating NAMs and NAGs attached by side-chain amino acids and cross-link amino acids
12
Q
What is the name of the enzyme that cross-links the peptidoglycan chains to form rigid cell walls?
A
Transpeptidase
13
Q
What is the role of transpeptidase?
A
It is the enzyme that catalyses the cross-link between the peptidoglycan chains to form rigid cell walls
14
Q
Describe how penicillin acts to kill bacteria
A
Penicillin bonds to transpeptidase to prevent it from catalysing the cross-link between the peptidoglycan chains to form rigid cell walls. Without the cell wall, the bacteria dies very quickly
15
Q
Describe the Gram stain procedure
A
- acquire a mixture of two different bacteria (eg. Staphylococcus aureus and Escherichia coli) and place on a slide
- apply crystal violet dye to stain the mixture
- apply iodine to set the dye
- wash with ethanol (some of the bacteria will remain purple)
- apply safranin as a counterstain (some will be purple and some will be pink)
16
Q
What type of bacteria remains purple after washed with the ethanol?
A
Gram-positive bacteria
17
Q
What type of bacteria decolourises after being washed with the ethanol?
A
Gram-negative bacteria
18
Q
Describe Gram-positive bacteria
A
- the peptidoglycan layer is very thick
- this layer encloses the plasma membrane
19
Q
Why does Gram-postive bacteria remain purple after being washed with the ethanol?
A
Because it has a very thick peptidoglycan layer which traps the crystal violet which masks the red dye
20
Q
How thick is the peptidoglycan layer in a Gram-positive bacteria?
A
20 - 80 nm
21
Q
Describe Gram-negative bacteria
A
- the peptidoglycan layer is very thin
- this layer encloses the plasma membrane but another layer of membrane encloses it (ie. there is the inner plasma membrane and then the cell wall which consists of the thin layer of peptidoglycan and an outer layer of plasma membrane)
22
Q
Why does Gram-negative bacteria decolourise after being washed with the ethanol?
A
Because the layer of peptidoglycan is so thin, the crystal violet is easily rinsed away, revealing the red safranin dye.
23
Q
How thick is the peptidoglycan layer in a Gram-negative bacteria?
A
5 - 10 nm
24
Q
What is the function of bacterial flagella?
A
to allow some bacteria movement in a liquid medium
25
What is the diameter of a flagella?
10 - 20 nm
26
How many flagella, on average, are there on a bacterial cell?
5 - 10 per cell
27
How do flagella work?
They act as a propeller (the cell rotates them to move through a liquid medium)
28
What are the three major sections of a flagella?
1. long filament
2. hook
3. basal body/basal motor
29
Describe the long filament of the flagella
- it extends into the surrounding medium
| - composed of subunits of a protein (flagellin)
30
Describe the hook of the flagella
a curved section connecting the filament to the cell surface (connect the motor)
31
Describe the basal body/basal motor of the flagella
- it anchors the flagellum into the cell membrane of the bacterium by disc-shaped structures (plates/rings)
- it sits in the cell membrane
32
What is flagella used for?
Chemotaxis
33
Describe the process of chemotaxis
the movement of bacteria along a concentration gradient towards a chemical attractant or away from a chemical repellent
34
Describe the mechanisms of chemotaxis
- bacterium can't sense the difference between the concentration at the front of the cell versus the back of the cell because they are too small
- instead it senses the changes with time (temporal gradient)
- the bacteria uses its sophisticated chemoreceptors to sense what the concentration is
- then the bacteria swims off again and remeasures the gradient
- if the concentration is going up, it keeps swimming in that direction
35
What are fimbriae?
hairlike structures on the outside of the bacteria
36
What is the purpose of fimbriae?
they have adhesive properties that cause the bacteria to stick to other surfaces
37
Fimbriae are an example of an
inherited trait (ie. not all bacteria have fimbriae)
38
What are other methods of gripping, apart from the fimbriae?
capsules and slime layers
39
Describe a capsule
Glycocalyx organised into a defined structure attached firmly to a cell wall
40
Describe a slime layer
Glycocalyx disorganised without cell shape, attached loosely to cell wall
41
What is glycocalyx?
A gelatinous polysaccharide outer covering. It forms a sticky meshwork of fibres.
- if organised into a defined structure attached firmly to a cell wall, it forms a capsule.
- if disorganised without cell shape, attached loosely to cell wall then it is a slime layer
42
What are the functions of a capsule?
- virulence factors
- adherence to cell surfaces and structures
- prevents the cell from drying out
43
What is meant by virulence factors?
Protecting the bacteria from phagocytosis and engulfment by immune cells
44
When does the bacteria form endospores?
Under unfavourable conditions (under stress such as nutrient starvation, overcrowding)
45
What are the two bacteria that make endospores?
Bacillus and Clostridium
46
Bacteria reproduce by
asexual reproduction (ie. grow and divide into two identical daughter cells)
47
What is binary fission?
Asexual reproduction by a separation of the body into two new bodies.
48
Bacterial cells that form endospores divide
asymmetrically
49
Describe asymmetric cell division
When bacteria grows, one end forms a spore and the other doesn't so a spore is growing inside the mother cell. The cells actually don't divide, it is purely altruistic behaviour of the mother (a mature spore is just formed)
50
When the conditions are favourable, the spore will
germinate into a bacteria and give rise to a vegetative cell
51
What 5 things are endospores resistant to?
heat, harsh chemicals, antibiotics, disinfectants, radiation
52
Endospores are formed during _________ and germinate under _________
unfavourable conditions
| favourable conditions
53
Why are prokaryotes so dominant?
Because they are so small and have a very fasting doubling rate which means they can evolve/adapt extremely quickly.
54
What is binary fission?
A type of asexual reproduction where once cell spilts into two
55
Describe the process of binary fission:
- the cell replicates its chromosome
- the parent cell now has two copies of the DNA
- one copy goes to each end of the cell
- the cell splits in half
- two identical daughter cells result
56
Prokaryotes reproduce ________ by cell division through the process of ______ ________
asexually
| binary fission
57
Because prokaryotes have been around for so long, they have extreme
ecological and metabolic diversity
58
What is a closed batch culture?
- a form of cell culturing
- there is limited amount of nutrients provided
- once the nutrients has been used, the cells can not proliferate
- growing in a closed system eg. no inflow or outflow
59
What is the purpose of closed batch culture?
You can see how an organism behaves under nutrient rich and nutrient poor conditions
60
What do we see in a closed batch culture?
A growth curve
61
What are the advantages and disadvantages of using closed batch culture?
Advantages:
Easy to do
Disadvantages:
Biased towards fast growing organisms like pathogens
62
What are the four stages of the growth curve?
1. lag phase
2. exponential/log phase
3. stationary phase
4. death phase
63
Describe what the lag phase is including what it looks like on a growth curve
There is a lag between adding a cell to the media and when it actually starts growing.
On the curve, this looks like a flat(ish) start to an exponential graph (positive)
64
What does the length of the lag phase depend on?
The history of the cell:
- those that have been starved previously have to turn on genes and make machinery before they can grow. The longer it takes them to make this machinery, the longer the lag phase.
- for a cell that is actively growing, the lab phase is short because it is already used to those conditions and and it knows how to take advantage of them
65
Describe what the exponential/log phase is including what it looks like on a growth curve
- there is plenty of nutrients for the cell
- they are growing and dividing at maximum capacity
- the population is doubling in a constant time interval
- seen as a steep increase in log of viable organisms
66
Describe the stationary phase including what it looks like on a growth curve
- the organisms have started running out of nutrients
- some of the cells in the culture have started to die
- cells stop growing and cryptic growth is observed
- there is a dynamic population
- the curve flattens
67
What is cryptic growth?
When organisms survive by consuming the lysed cell contents of other dead cells within the culture. When a cell dies, all its nutrients gets released into the media and all the growing cells can scavenge and grow again.
68
What is a dynamic population?
When there is an equilibrium between growing and dying cells
69
Describe the death phase including what it looks like on a growth curve
- cells die
- the viable count declines
- the equilibrium between growing and dying cells is skewed towards death
70
"No growth" actually means
death rate and growth are in balance (ie. no net growth)
71
Penicillin is an
antibtiotic
72
What are the only cells that penicillin and other inhibitors/antibiotics act on?
growing/replicating cells
73
What are persiters?
Cells that are not growing or replicating and are not dividing so they are insensitive to penicillin
74
Describe how persisters can lead to persistent infections without antibacterial resistance
- a culture can include both actively growing (sensitive) population and not growing (insensitive) bacteria.
- after an antibacterial treatment, the growing bacteria are killed but the insensitive bacteria remain
- after the antibiotic is removed, there is persistent infection as the pathogen is resuscitated
75
What do prokaryotes need in order to multiply?
- a carbon source
- an energy source
- a reducing power
76
Describe what is meant by a carbon source that prokaryotes require
a building block for macromolecular synthesis
| ie. the bulk of the cell is made up of carbon so we need a source of carbon in order to grow a cell
77
Describe what is meant by an energy source that prokaryotes require
energy in the form of electrons (electricity) to drive anabolic and catabolic reactions inside the cell
78
Describe what is meant by a reducing power that prokaryotes require
a way to carry the electrical energy/electricity
this is usually with intermediates (such as NAD+ and NADP+) that carry electricity from one side of the cell to the other side of the cell
79
Chemical energy is stored in
bonds
80
Broken bonds releases _______ that can be captured in _____ _____
energy
| new bonds
81
What is the most common energy currency?
ATP
82
Describe how microbes can access energy
Breaking bonds in glucose to release energy.
This energy has to be used to go somewhere else.
In this case, the energy is used to add a P to an ADP to form ATP.
When energy is released, you also release H which needs to be captured (by NAD+ to form NADH) and this energy can be taken to the membrane to make more energy
83
The idea of breaking and making bonds is the basis of
redox reactions
84
How do microbes harvest their energy?
- they break down substrates into products and extract energy
- this is a catabolic reaction
- energy is produced in the form of ATP
- the ATP is used to build macromolecules and other cellular constituents from monomers in a process of biosynthesis.
- this is an anabolic reaction
85
Where are the two places that microbes can get their energy from?
- light (photo)
| - chemical compounds (chemo)
86
Where are the two places that microbes can get their carbon source from?
- carbon dioxide (auto)
| - organic compounds (hetero)
87
A compound that uses light energy to fix carbon is called?
Photoautotrophs
88
What is carbon fixation?
Producing complex carbohydrates from inorganic CO2
89
A compound that uses light energy but carbon has to be provided to them from organic compounds is called?
Photoheterotrophs
90
A compound that uses chemical compounds as energy to fix carbon is called?
Chemoautotrophs
91
A compound that uses chemical compounds as energy but carbon has to be provided to them from organic compounds is called?
Chemoheterotrophs
92
Why can most organisms not be isolated in pure culture?
Most organisms depend on other members of the community and so we can't recreate the environment with pure cultures.
93
What is a population?
Groups of organisms of the same type
94
Individual microbial cells of a species proliferate and form a
population
95
What is a community?
When populations interact and communicate
96
What is the microbiome?
All organisms, and their genes, within a particular environment
97
What is enrichment culture?
Providing the temperature and chemical conditions in the laboratory that encourage the growth of specific groups of microbes.
98
Explain how an enrichment culture works
If you have a very diverse group of microorganisms living together, you want to get information about a specific subset of them, you can change the conditions in the lab so that only a portion of those start growing into higher numbers.
99
Enrichment cultures are an example of
mesocosms
100
What are mesocosms?
an experimental system that stimulates real-life conditions as closely as possible
101
What are the two outcomes from breaking bonds in a carbon based molecule?
- harvesting energy
| - harvesting building blocks
102
Energy from oxidation is shuffled through
an intermediate (NADH/NADPH)
103
Explain the process of ReDox reactions in bacteria
- H2S is oxidised to form S
- this releases energy and H
- as an opposite reaction, NADP+ is reduced to form NADPH2 (capturing the H from H2S)
- When NADPH2 is oxidised to form NADP+, H is released and energy is released
- in an opposite reaction, the energy released is used to fix carbon (reduce CO2 to CH2O)
104
ReDox in bacteria is the basis of
energy transfer in cells
105
Autotrophs are
primary producers
106
Heterotrophs are
decomposers
107
Describe autotrophs
- primary producers
- fix CO2
- self sufficient, do not require carbon
108
Describe heterotrophs
- decomposers
- need fixed carbon, cannot use CO2 directly
- dependent on primary producers
109
Where can the chemical energy come from for chemotrophs?
- carbon compounds (organic eg. glucose)
| - non-carbon compounds (inorganic eg. H2S)
110
Where does the solar energy come from for phototrophs?
energy from the sun
111
Describe how autotrophs and heterotrophs work together to access carbon
- autotrophs are primary producers which means that they can take CO2 and convert in into a complicated substrate
- heterotrophs are decomposers which means they consume this fixed carbon and break it down back into CO2 to start the process again
112
What are the two types of photosynthesis?
Cyclic and non-cyclic
113
Describe non-cyclic photosynthesis/photophosphorylation
- e- flow in one directional pathway
- e- flow from the split of H2O into PS || and then through PS | and then to NADPH
- once in the NADPH (the final acceptor), they can be transported around the cell to generate ATP or another source of energy
- generates O2, ATP, NADPH
114
Describe cyclic photosynthesis/photophosphorylation
- e- flow in a continuous cycle
- the source of e- is not from H2O and they flow straight to PS | and ATP is generated
- no oxygen is produced
115
What are some similarities between cyclic photosynthesis and non-cyclic photosynthesis?
- Both are processes that use light for energy (ATP)
- Both processes produce NADPH
- Both processes fix carbon
116
Between cyclic photosynthesis and non-cyclic photosynthesis, which one generates oxygen?
Non-cyclic photosynthesis
117
Give an example of how microorganisms exploit their environment (light)
- light is a common resource
- rather than competing for the light, microorganisms tune their antenna to different wavelengths
eg.
The light pigments of algae and cyanobacteria are absorbing light at a narrow wavelength. The other light can pass through to lower layers without being harvested
Purple bacteria have different pigment (purple chlorophyll) which is tuned to a different wavelength so they can harvest different light to the algae
The pigment of the bottom microorganism has a wide spectrum so it is mopping up anything that is not being absorbed in the previous layer (not a specialist, a generalist)
118
Give an example of how microorganisms exploit their environment (oxygen)
- bacteria live in anoxic environments
- they can create cables to shuttle e- from the anoxic zone to the oxic zone
- this allows them to breathe in oxygen while living in anoxic environments
119
What is the microbiota?
Individual microbial species in a biome - bacteria, fungi, archaea and viruses
120
What were the human microbiome goals?
1. To develop a _______ __________ of microbial genome ________ and to perform ___________ characterisation of the ______ ________
2. to explore the relationship between _________ and changes in the _______ ________
3. to develop new __________ and _________ for __________ _____________
4. to establish a __________ _________
5. to study the __________, __________ and ________ ___________ of the human microbiome research
1. to develop a reference set of microbial genome sequences and to perform preliminary characterisation of the human microbiome
2. to explore the relationship between diseases and changes in the human microbiome
3. to develop new technologies and tools for computational analysis
4. to establish a resource repository
5. to study the ethical, legal and social implications of human microbiome research
121
What is the phyla?
Types of organisms
122
What is meant by the metabolic pathways?
the functions of genes and enzymes in the microbiome
123
It is more important to keep the function than to keep the
specific organism
124
Every person had the same collection of
enzymes within the same site and only slight variation from site to site
125
What are the 4 bacterial groups?
- firmicutes
- bacteroidetes
- actinobacteria
- proteobacteria
126
Which part of the body has the highest density of microbes in the human body?
the gut
127
Where in our gut are there the most microbes?
the colon
128
What are functional foods?
foods claimed to have a health promoting or disease preventing property beyond the basic function of supplying nutrients
129
What are the probiotics that are often sold, and why?
Lactic acid bacteria and bifidobacteria because they can both survive in an acidic environment and so can pass through the stomach into the intestine
130
What is the difference between probiotics and prebiotics?
Probiotics are alive and are usually bacteria or yeast whereas prebiotics are an ingredient that beneficially nourishes the good bacteria already in the large intestine to stimulate the growth of probiotics
131
What is a fecal microbiota transplantation used for?
to treat Clostridium difficile infections (CDI)
132
How does a fecal matter transplant work?
- shit from a healthy donor is used to replace a patient's gut microbial flora
- the shit is blended with saline and put through a stainer and can be frozen before use
- the shit can be applied to the small intestine:
1. via a tube through the nose or mouth
2. deep into the large intestine using a colonoscopy
3. shoving the shit up your arse to reach the large intestine
133
What are some risks of a FMT?
- diseases
- complications due to procedures
- identification of correct donors
134
What are some solutions of a FMT?
- synthetic communities
| - stool banks (a collection of donors wit the best microbiome to treat the disease)
135
What are viruses?
A cellular microorganisms that cannot survive without a host because they have no metabolic abilities of their own
136
What is meant by viruses having no metabolic activity?
They cannot make DNA or proteins and cannot carry out metabolism
137
Viruses are
obligate intracellular parasites
138
What are obligate intracellular parasites?
parasitic entities that hijack the molecular resources of the host and the host can be any type of cells
139
What is the size range of a virus?
10 - 400 nm
140
What is the composition of the virus?
1. genetic material
2. capsid
3. (in some cases) an envelope of lipids
141
Describe the genetic material of a virus
could be double stranded or single stranded DNA or RNA
142
Describe the capsid of a virus
A protein coast that surrounds and protects the genetic material
143
What are capsids made out of?
Multiple units of the same protein building block known as capsomers
144
What are capsomers?
they are subunits of the capsid arranged in a precise and highly repetitive pattern around the nucleic acid
145
In how many types of symmetry can capsomers be arranged in?
3
146
What are the 3 types of symmetry that capsomers can be arranged in?
helical
icosahedral
complex
147
Describe a helical capsid
the capsomere of the capsid is wound around the RNA or DNA in a helical fashion
148
Describe an icosahedral capsid
The capsomere of the capsid is arranged in a 20 face icosahedron where each face is an equilateral triangle
149
Describe a complex capsid
The head has icosahedral symmetry and the tail is helical
150
Describe the envelope of lipids
it surrounds the protein coat of the cell
151
What is a naked virus?
One which does not have an envelope of lipids
152
The genome of viruses could be
linear
circular
segmented
153
Briefly explain how viruses affect a cell
They find a cell, infect it, replicate its genome using the cells machinery, make more virus and go on and infect more
154
What is a host organism?
An organism that a virus infects
155
Give an example of a host organism
a human
156
What is a host cell?
A cell in which a virus multiplies
157
Give an example of a host cell?
the CD4+ T cells
158
What is a bacteriophage?
a virus that infects and replicates inside a bacteria
159
Bacteriophages can cause two types of infections. What are they?
a lytic infection
| a lysogenic infection
160
What is the key difference between a lytic infection and a lysogenic infection?
In a lytic infection, the host cell dies whereas in a lysogenic infection, the host cell survives
161
Describe a lytic infection in 7 steps
1. the bacteriophage (BPH) attaches to the host cell
2. its tail fibre recognises specific receptors on the bacterial cell surface
3. the BPH injects its DNA into the host cell
4. the BPH uses the host machinery to transcribe its own DNA which encodes for proteins that degrade the bacterial protein
5. the virus takes over all the cell's machinery to replicate its own genome
6. viral particles are made and the virus is assembled
7. the bacteria bursts when 100-200 viruses have been formed
162
Describe a lysogenic infection in 6 steps
1. the bacteriophage (BPH) attaches to the host cell
2. its tail fibre recognises specific receptors on the bacterial cell surface
3. the BPH injects its DNA into the host cell
4. the viral DNA gets integrated into the host genome
5. this lysogen does not replicate the viral DNA
6. the bacteria doesn't die but the viral DNA remains in the daughter cells
163
What is prophage?
viral DNA that is part of the bacterial chromosome
164
What is a lysogen/lysogenic bacterium?
a host bacteria with a prophage
165
What can HIV lead to?
Acquired immunodeficiency syndrome (AIDS)
166
What are 6 examples of pathogens?
1. viruses
2. fungi
3. prions
4. protozoa
5. helminths
6. bacteria
167
What is the significance of the proteins on the envelope?
The proteins are how we can determine what sort of influenza virus it is.
For example, it could be H1N1 or H5N1
168
Why do we need vaccines for influenza every year?
Because if the two viral cells infects the host cell from two different areas, they can mix and match RNA and there is a constant recalibration of what proteins are on the envelope
169
Give an example of a pathogenic fungi
Trichophyton spp. causing ringworm
170
What are prions?
mis-folded proteins
171
How do prions multiply so quickly?
Because when they interact with healthy proteins, it causes a chain reaction and copies itself (like a zombie)
172
Give an example of a pathogenic bacteria
Bacillus anthracis (causing anthrax)
173
What are Koch's postulates?
Guidelines used to demonstrate that a specific pathogen causes disease symptoms
174
How did Koch determine that a specific pathogen causes disease symptoms?
He took a mouse that had died from a disease, took a colony of the pathogen and injected it into more mouse and saw that all the mouse had the same symptoms
175
What are the 4 fine prints of Koch's postulates?
- where must the pathogen be present?
- a sample of the microorganism taken from the diseased host can be grown where?
- a sample of the culture causes what when injected into a healthy host?
- the microorganism can be recovered from what?
1. the pathogen must be present in every individual with the disease
2. a sample of the microorganism taken from the diseased host can be grown in pure culture
3. a sample of the culture causes the same disease when injected into a healthy host
4. the microorganism can be recovered from the experimentally infected host
176
What are the 4 key stages of microbial pathogenesis?
1. adherence to host cells
2. invasion of host tissue
3. replication within host tissues
4. disease causing damage to host tissue
177
What are bacterial virulence factors (BVF)?
things that the bacteria have that allow it to carry out the 4 stages of microbial pathogenesis
178
What is a BVF that allow bacteria to adhere to host cells?
fimbriae
179
What are some BVFs that allow bacteria to invade host tissue?
it needs motility so it needs
- flagella
- surface proteins such as Internalin- related proteins
180
What are some BVFs that allow bacteria to replicate within host tissue?
Bacteria need to food to replicate. They get this from iron in RBC. Therefore they have Soderophores which is a protein which rips iron away from the RBC.
They also have capsules to stop the WBC phagocytosing them
181
What are some BVFs that allow bacteria to cause disease to host tissue?
Endotoxins
| exotoxins
182
What are endotoxins?
Lipopolysaccharides (LPS) that are found on the outer-membrane of Gram-negative bacteria
183
When are endotoxins released?
When the bacteria are destroyed (either by antibiotics or WBC)
184
What do endotoxins cause?
inflammation
185
What are exotoxins?
Potentially deadly toxins produced within living bacteria, and then released into the surrounding medium when the bacteria is still alive
186
What are the three types of exotoxins
1. cytotoxins
2. neurotoxins
3. enterotoxins
187
Give an example of a cytotoxin to explain its function
Streptolysin which causes the complete lysis of red blood cells
188
Give an example of a neurotoxin to explain its function
Botulinium causes paralysis by preventing the release of ACh in the synapse between the axon terminal and the skeletal muscle
189
Which is the most deadly exotoxin?
Neurotoxins
190
Give an example of a enterotoxins to explain its function
Shiga toxin causes bloody diarrhoea
191
What is meant by the term "selective toxicity"?
Drugs (ie. antibiotics) that target the microbial cell but not the host cells
192
What is penicillin?
The secondary metabolite excreted by the fungi penicillium which causes a zone of inhibition
193
What is a zone of inhibition?
the zone where the bacterial growth is inhibited
194
What are six bacterial cell components which antibiotics target?
1. inhibition of cell wall synthesis
2. inhibition of protein synthesis
3. distribution of the cytoplasmic membrane
4. inhibition of the general metabolic pathway
5. inhibition of DNA or RNA synthesis
6. inhibition of pathogen's attachment or entry into a host cell
195
How can bacteria become resistant to antibiotics?
There is diversity within the population of bacteria and if there is a mutation in a bacteria that gives it a survival advantage (eg it is resistant to antibiotics), it will survive and be able to asexually reproduce.
Overtime, all the bacteria in a population will become resistant (natural selection)
196
Why can antibiotics not kill resistant bacteria?
Antibiotic resistant bacteria produce an enzyme which destroys penicillin
197
What is the enzyme which destroys penicillin?
beta lactamase
198
What two ways can genes be transferred between bacteria?
vertical gene transfer
| horizontal gene transfer
199
What is vertical gene transfer?
Transferring genes from the parent to the offspring
200
What are four ways to reduce the development of antibiotic resistance?
1. decrease antibiotic utilisation
2. improve diagnostics
3. identify new targets
4. combination therapies
201
Explain what is meant by "decrease antibiotic utilisation"
Reduce infections and outbreaks through improved hygiene and infrastructure and restrict use in agriculture
202
Explain what is meant by "improve diagnostics"
Improve the accuracy of the diagnosis so that people can be accurately treated
203
Explain what is meant by "identify new targets"
Make new antibiotics with cellular pathways which are harder for bacteria to bypass
204
Explain what is meant by "combination therapies"
give two drugs at once ie. give traditional antibiotics that can be combined with molecules that block resistance mechanisms
205
What are three properties of a bacterial genome?
1. typically a single circular chromosome
2. there is no nuclear membrane
3. presence of plasmids
206
Instead of having a nuclear membrane, the bacterial DNA is restricted to a defined region of the bacterial cell known as the _________
nucleoid
207
What are plasmids?
Small circular self replicating DNA molecules found in the cytosol
208
What is horizontal gene transfer?
the transfer of genes directly from one organism to another (not parent to offspring)
209
What are the three strategies of horizontal gene transfer?
1. transmission
2. conjugation
3. transduction
210
Describe the process of horizontal gene transfer via transmission
When a bacteria dies (killed or naturally) and they spill their chromosomal DNA.
This naked DNA from the dead bacteria enters live bacteria and transforms it
211
Describe the process of horizontal gene transfer via conjugation
The sex pilus of one bacteria makes contact with another bacteria and the plasmids can be fed through the sex pilus into the next bacteria
212
What is a sex pilus?
A gene transfer tool used by bacteria for conjugation
213
Describe the process of horizontal gene transfer via transduction
A bacteriophage injects its DNA into a bacteria and takes over the bacteria
The bacteria DNA breaks up
The viral DNA instructs the bacteria to make more phages.
When they are being put together, instead of using their own DNA, the phages take up bacterial DNA.
When the phages leave the cells and inject DNA into another cell, they inject bacterial DNA
214
Phage virus can turn bacteria into
toxin producing bacteria through lysogenic combination
215
Give an example of a bacteria that becomes pathogenic due to lysogenic combination
Cholera
216
What is lysogenic transduction?
when a bacteria in the lysogenic cycle ejects the viral DNA and the lytic cycle can occur
217
What are the five stages of infectious disease?
1. incubation
2. the prodromal period
3. illness
4. decline
5. convalescence
218
What happens during the incubation period?
The pathogen has invaded the tissue and begins to multiply but there are no signs or symptoms
219
What happens during the prodromal period?
The pathogen has reached a certain level so there are vague signs and symptoms
220
What happens during the illness period?
There are the most severe signs and symptoms
221
What happens during the decline period?
There is a decline in the signs and symptoms and the immune system is working (often with drugs) so kill the pathogens
222
What happens during the convalescence period?
There are no signs or symptoms, even though the pathogen could still be there
223
What causes the common cold?
A virus called the rhinovirus
224
Describe the rhinovirus:
- Does it have single or double stranded RNA or DNA?
- Does it have an envelope?
- What temperature does it like to grow at?
- ssRNA
- non-encapsulated (ie. no envelope)
- grows at 32 degrees
225
The capsid of the rhinovirus has proteins which bind to the
respiratory epithelia
226
What is epidemiology?
The study of disease transmission
227
What are the six components of the "chain of infection"?
1. causative agent
2. reservoir/source
3. means of exit; way out of the body
4. mode of transmission/method of spread
5. portal of entry/way into the body
6. person at risk
228
What are the possible causative agents according to the "chain of infection"?
virus
bacteria
parasite
229
What are the possible reservoir/sources according to the "chain of infection"?
```
human
animal
fomite
food
water
```
230
What are the possible modes of means of exit; ways out of the body according to the "chain of infection"?
excretions
secretions
droplets
231
What are the possible modes of transmission/methods of spread according to the "chain of infection"?
contact
airborne
vector
232
What are the possible portal of entry/ways into the body according to the "chain of infection"?
Respiratory
Gastrointestinal system
Mucous
Skin
233
Who are the people at risk according to the "chain of infection"?
Young
Immunocompromised
Elderly
234
What are some ways to break the chain of infection in terms of the causative agent?
Rapid detection and treatment
235
What are some ways to break the chain of infection in terms of the reservoir/source?
good hygiene
sterilisation
disinfectant
236
What are some ways to break the chain of infection in terms of the means of exit; way out of the body?
waste removal
| disinfectant
237
What are some ways to break the chain of infection in terms of the mode of transmission/method of spread?
airflow control
| bed spacing
238
What are some ways to break the chain of infection in terms of the mode of the portal of entry/way into the body?
```
Aseptic technique (keeping things clean)
Wound care
```
239
What are some ways to break the chain of infection in terms of the mode of the people at risk?
Identifying those at risk and targeting them for special care, vaccination and education
240
Define mortality
the occurrence of death in a population
241
Define morbidity
the occurrence of a disease, including fatal and non-fatal diseases
242
Define incidence
the number of new cases of the disease at a given time
243
define prevalence
the total new and existing cases in a population at a given time
244
Define endemic
the amount of that particular disease that is usually present in a community
245
Define sporadic
a disease that occurs infrequently and irregularly
246
Define epidemic
a sudden increase in the number cases of a disease above what is normally expected in that area
247
Define pandemic
an epidemic that has spread over several countries or continents, usually affecting a large number of people
248
Outline the selective pressures that HIV is under
Selective pressures:
1. the immune system and changes in the receptor: viruses with the ability to bind to the CD4 receptors can survive
2. drugs: viruses with mutations that stop drugs from killing them can survive
3. the tissues: some viruses have variants that will allow the viruses to survive better in some tissue than others
249
Explain how patterns of relationships between sequences might provide evidence for evolution
HIV viruses within a patient are more similar than between patients. This, along with the pattern of the phylogenetic tree suggests a single point of entry and then diversification.
We also have all the requirements for natural selection:
1. variation
2. inheritance
3. selection
4. time
250
Explain how the HIV virus accumulates a lot of variation:
The reverse transcriptase is very error prone when turning RNA into DNA which means that there are many mutations and therefore variants formed even within one individual
251
Explain how the HIV virus is inherited
The HIV virus passes on their RNA after being inserted into the genome
252
Explain how the HIV virus can accumulate variations over. a number of generations
The HIV lifecycle is very fast (20 mins) so there is plenty of time to accumulate many variations
253
Outline the role of evolutionary change in the virulence of pathogens
HIV evolves so quickly that there could be up to 5 x 10^10 different variants of the virus in one individual. This means that it is very hard to make effective vaccines very hard.
254
Describe the importance of evolutionary thought to our understanding of disease
evolution is a key way that pathogens respond to hosts and therapy so understanding evolution can help us respond better to pathogens
255
Explain that by comparing DNA sequences, we can help understand their relationship
By sequencing DNA of HIV, we can see what is different and we can use this to see how there can be variation in patients and between patients.
