Finals: Midterm 2 Content Flashcards
(117 cards)
1
Q
toxins (2)
A
- kill cells
- alter host-cell functions without killing cells directly
2
Q
type I toxins
A
- act extracellularly
3
Q
type II toxins (3)
A
- act on the cell membrane and destroy cell membrane
- cytolytic
- can be enzymatic or non-enzymatic
4
Q
type III toxins
A
- classical A/B toxins
5
Q
cytolytic
A
- damage to membranes usually causes host cell lysis or death
6
Q
type II toxins: non-enzymatic (2)
A
- form large pores/channels in membrane
- cholesterol-dependent cytolysins
7
Q
type II toxins: how are non-enzymatic pores formed (2)
A
- toxin monomers can bind cholesterol and assemble on surface to form a pre-pore and then insert
- toxin monomer binds cholesterol and inserts into membrane, triggering monomers to bind and form a large pore
8
Q
why does cell/phagosome lysis occur after non-enzymatic pore formation
A
- water enters the cell/phagosome which causes swelling
9
Q
how does LLO function as a type II, non-enzymatic toxin (2)
A
- change in pH causes conformational change in the protein
- change allows toxin to insert into phagosome membrane
10
Q
what do type III toxins do (2)
A
- alter metabolism of the host cell
- exploit or subvert normal host cell processes
11
Q
what are A/B toxins (2)
A
- B is the Binding component of the toxin
- A is the enzymatically Active component of the toxin that binds to target inside host
12
Q
what kinds of toxins are A/B toxins (5)
A
- toxins that target protein synthesis
- toxins that alter signal transduction
- toxins that alter actin polymerization
- neurotoxins
- anthrax toxins
13
Q
A/B toxin: forms of B component (3)
A
- single unit that binds to receptor
- multi-meric structure that is preformed
- mulit-meric structure that forms on the membrane
14
Q
type II toxins: enzymatic damage (3)
A
- caused by phospholipases
- enzyme removes polar head groups from phospholipid (PlcC activity)
- causes damage to the membrane, and instability leads to lysis
15
Q
what is one way that toxins can alter signal transduction
A
- toxins can target or alter cAMP production
16
Q
what is the purpose of the techniques for studying virulence factors
A
- they are used to investigate whether something is actually a virulence factor
17
Q
Koch’s Postulate: First Postulate
A
- the microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms
18
Q
Koch’s Postulates: Second Postulate
A
- the microorganism must be isolated from a diseased organism and grown in pure culture
19
Q
Koch’s Postulate: Third Postulate
A
- the cultured microorganism should cause disease when introduced into a healthy host
20
Q
Koch’s Postulates: Fourth Postulate
A
- microorganism must be re-isolated from the inoculated diseased experimental host and identified as being identical to the specific causative agent
21
Q
Molecular Version of Koch’s Postulates: First Postulate
A
- gene for virulence should be present in the strain of bacteria that cause disease and absent in avirulent strains
22
Q
Molecular Version of Koch’s Postulates: Second Postulate
A
- (i) knocking out or disruption the gene should reduce virulence, and (ii) introduction of the cloned gene into an avirulent strain should render the avirulent strain virulent
23
Q
Molecular Version of Koch’s Postulates: Third Postulate
A
- expression of the gene should be demonstrated in human or a relevant model
24
Q
Molecular Version of Koch’s Postulates: Fourth Postulate
A
- antibodies or a cell-mediated immune response to a virulence factor should be protective
25
what are two categories of techniques used to study virulence factors (2)
- biochemical; developed first
- genetic
26
supernatant
- liquid lying above a solid residue after crystallization, precipitation, centrifugation, or other process
27
what is the basis for biochemical techniques (2)
- to purify and identify the virulence factor (toxins, adhesins, etc)
- relies on having functional assay for the virulence trait
28
what are the disadvantages of using biochemical techniques (3)
- purified molecule may be missing co-factor that was removed during purification
- molecule may not have same function in the test tube compared to the cell
- does not tell us if our purified protein is the sole contributor to disease/virulence
29
what virulence factors work well in biochemical techniques (2)
- protein-based macromolecules
- factors that can be targeted for hydrophobicity, charge, mass, ligand binding, etc
30
what are some examples of biochemical techniques (6)
- centrifugation
- ion exchange
- size exclusion
- immunoprecipitation
- ligand binding
- Ni2+ affinity/6xHis
31
biochemical techniques: centrifugation (2)
- harvest bacteria by centrifugation
- separate supernatant into fractions and test for toxicity in animal model/cultured cell assay
32
biochemical techniques: ion exchange (2)
- use of positively or negatively charged beads in a column
- proteins attracted to the beads will remain in the column, while those repelled with leaves through the bottom of the column
33
biochemical techniques: size exclusion (2)
- use of beads with small aqueous channels in a column
- large molecules pass quickly, but small molecules are slow as they spend more time in the channels
34
biochemical techniques: immunoprecipitation (4)
- use of antibodies attached to beads in a column
- proteins are loaded in pH 7 buffer; proteins recognized by antibody bond to beads and other proteins remain in solution
- column washed with pH 7 buffer to remove proteins in solution
- column washed with pH 3 buffer to disrupt protein-antibody bonds and elute proteins
35
biochemical techniques: ligand binding (4)
- use of affinity bead with ligand attached in a column
- proteins are loaded; proteins recognized by ligand bond to beads and other proteins remain in solution
- column washed with buffer to remove proteins in solution
- column washed with low pH buffer or soluble ligand to elute proteins
36
biochemical techniques: Ni2+ affinity/6xHis (4)
- use of NTA-coated agarose bead coordinate Ni2+ ions in a column
- tagged and untagged proteins are loaded; tagged proteins bind to Ni2+ and other proteins remain in solution
- column washed with buffer to remove proteins in solution
- column washed with low pH buffer or imidazole (binds Ni2+) to elute proteins
37
how would you prove that a putative virulence factor (purified protein) caused disease (3)
- isolate toxin and investigate effects in other cells
- sequence toxin and knockout toxin to see if disease occurs or investigate for its presence in avirulent strain
- identify immune response in model to show that virulence factor grants immunity
38
molecular genetic techniques (2)
- gain of function experiments
- loss of function experiments
39
gain of function techniques (2)
- look for putative virulence factors by doing gain of function in an avirulent strain
- observing for restoration of virulence
40
loss of function techniques (2)
- knock out genes and look for reduction in virulence
- can be done through directed mutants or transposon mutants
41
gene expression experiments (3)
- reporter assays - promoter traps
- hybridization-based experiments
- sequencing (RNA-seq)
42
advantages of genetic approaches (3)
- allows us to find novel genes by screening mutants
- connection with virulence is established at the beginning of the experiment
- relatively biased
43
disadvantages of genetic approaches (2)
- usefulness of the information (results) depends on the screen
- you may not be able to identify the function of the gene product
44
disadvantages of gain of function experiments (3)
- there may be other accessory factors or genes involved
- many different restriction enzymes may need to be used
- virulence may not be expressed in an avirulent strain
45
GoF Salmonella invasion experiment: what are the steps to create the library (5)
1. isolate virulent Salmonella DNA
2. cut DNA with a restriction enzyme
3. run on gel to separate DNA fragments according to size
4. DNA between 1000-3000bp are isolated from the gel
5. these DNA are cloned into plasmids
6. plasmids are transformed into avirulent E. coli to create a library
46
GoF Salmonella invasion experiment: what are the steps to test the library against an assay (6)
1. library of E. coli clones is used to infect tissue cells
2. cells are washed and incubated
3. gentamycin is added; kills extracellular bacteria, but not intracellular bacteria
4. wash to remove gentamycin
5. lyse the host cells to release the surviving bacteria
6. plate surviving bacteria on lab media
47
GoF Salmonella invasion experiment: why is DNA between 1000-3000bp isolated only
- average size of genes, so scientists are hoping to find intact genes in this region
48
GoF Salmonella invasion experiment: what is gentamycin (2)
- an antibiotic
- does not penetrate host cells
49
GoF Salmonella invasion experiment: what kind of assay is used (2)
- an invasion assay
- the gentamycin protection assay
50
GoF Salmonella invasion experiment: what are the steps to identify the possible virulence factor gene (3)
1. plasmids are isolated from each colony
2. the inserted Salmonella DNA is sequenced using Sanger's Sequencing
3. the sequence is ran through databases, such as BLAST, to identify the gene
51
Sanger Sequencing steps (3)
1. DNA sequence for chain terminator PCR
2. size separation by gel electrophoresis
3. gel analysis of determination of gene sequence
52
Illumina Sequencing steps (4)
1. sample prep
2. clustering
3. sequencing
4. data analysis
53
sanger sequencing: templates
- usually one template
54
sanger sequencing: output
- one sequence
55
sanger sequencing: typical usage (3)
- plasmids
- PCR products
- gDNA sequence
56
illumina sequencing: templates
- many barcoded templates
57
illumina sequencing: output (2)
- millions of barcoded sequencing
- cluster = one sequence
58
illumina sequencing: usage
- can multiplex (combine) experiments
59
transposon mutagenesis (3)
- mobile genetic elements
- "random" mutagenesis approach
- all contain an antibiotic resistance marker
60
loss of function experiments (4)
- uses transposon mutagenesis
- virulent bacteria is "infected" in transposon
- plates are selected with appropriate antibiotic
- collection of mutants is the library
61
what are the characteristics of the bacteria in a loss of function experiment library (2)
- mostly random mutants
- Tn is in their chromosome
62
what are some disadvantages of loss of function experiments (3)
- only generates mutants in non-essential genes
- transposons have transcriptional terminators within them
- assays can sometimes be laborious
63
loss of function experiments: how do the terminators within Tn affect the experiment (2)
- bacterial mRNA is polycistronic
- can lead to the "polar" effect
64
how can you identify a mutated gene without sequencing the entire genome (7)
1. insert Tn into bacterial chromosomes to create the random mutations
2. use restriction enzymes to randomly cut the chromosome
3. clone the fragments into E. coli
4. subject E. coli to antibiotics; the surviving E. coli contain a mutated gene
5. identify insertion site of transposon using prime from plasmid and primer from Tn
6. use Sanger's sequencing to identify gene disrupted by Tn
7. BLAST against the database
65
why do we use two primers for Sanger's Sequencing in plasmids (2)
- this method has a limit of ~800bp
- running sequencing both ways allows scientist to obtain more length of the desired DNA
66
signature tagged mutagenesis (2)
- negative selection for virulence gene identification
- involves generating strains using Tn libraries
67
how does signature tagged mutagenesis work (5)
1. mutate gene with a Tn carrying a unique tag
2. introduce Tn mutants into chosen disease model
3. harvest bacteria after certain amount of time
4. use hybridization to identify tags
5. isolate genomic material from clone and use Sanger's sequencing to find which gene the transposon was inserted into
68
signature tagged mutagenesis: what is the purpose of looking for identity tags in the last step (2)
- looking for tags that were present in initial inoculum that are absent in recovered fraction
- identifies mutants that did not grow as they were mutated for a gene that represents a potential virulence factor
69
what are the advantages of signature tagged mutagenesis (2)
- can look at many mutants at a time using a few animals
- can identify gene important for growth and survival directly in vivo
70
signature tagged mutagenesis: disadvantage (2)
- usual Tn issues
- polar effect and insertion bias
71
polar effect (2)
- when a Tn is inserted into DNA that in transcripted into a polycistronic mRNA
- describes how the insertion may remove more genes that expected
72
how can we test for the polar effect (2)
- do complementary experiments to restore function
- do targeted deletions in each gene
73
Tn Seq
- looks for genes important to survival by comparing two conditions
74
what are some required elements for Tn Seq (2)
- high coverage of the Tn insertion sites; need to create a saturating library to determine all non-important genes
- use of the Himar Mariner Tn
75
Himar Mariner Tn (3)
- contains an antibiotic resistance marker
- contain MmeI restriction enzyme recognition sites within the Tn, but cut sites occur 20bp away from site (outside of Tn)
- MmeI leaves two-bp overhang for adaptor ligation
76
Tn Seq steps (5)
1. mutanagize bacteria with Himar Mariner Tn several times to cover all possible genes
2. digest chromosomal bacteria with MmeI
3. ligate adaptors (MmeI cut site and Tn) for Illumina Sequencing
4. compare read counts for each insertion site under different conditions
5. identify loci required for growth under different conditions
77
IVET (2)
- in vivo expression technology
- promoter trap for **in vivo** expressed genes
78
IVET: reporter gene (2)
- β-Galactosidase protein
- promoter-less lacZ gene
79
how can we used IVET to identify Salmonella virulence factors: starting components (2)
- Salmonella genomic DNA
- engineered plasmid
80
how can we used IVET to identify Salmonella virulence factors: salmonella genomic DNA processes
- DNA is partially digested by Sau3AI restriction enzyme
81
how can we used IVET to identify Salmonella virulence factors: origin of replication
- it functions in E. coli, not in Salmonella
82
how can we used IVET to identify Salmonella virulence factors: experimental set-up (2)
- use a model system
- find avirulent strain that does not infect host model
83
how can we used IVET to identify Salmonella virulence factors: first 1/2 of steps (purA importance) (5)
1. ligate Sau3AI-digested Salmonella DNA and Bgl II-digested pIVET plasmid into E. coli
2. activate mob gene to transfer into LoF purA Salmonella via conjugation
3. pIVET will integrate into Salmonella purA auxotroph via homologous recombination, creating a library of Salmonella clones
4. pool library and inject into mice
5. mash up spleen and collect surviving bacteria (PurA+ phenotype) into a petri dish
84
how can we used IVET to identify Salmonella virulence factors: what are the characteristics of the surviving bacteria from the mouse spleen (2)
- fragments successfully recombined with a promoter
- gene with promoter turned on is thought to be necessary for survival in the mouse
85
how can we used IVET to identify Salmonella virulence factors: second 1/2 of steps (lacZ importance) (4)
1. plate bacteria on media containing substrate for β-galactosidase (X-gal)
2. if β-galactosidase is expressed, it will cleave X-gal and the colony will appear blue
3. collect colonies that appear white and discard colonies that appear blue
4. sequence insertion to find the gene that was expressed in white colonies
86
how can we used IVET to identify Salmonella virulence factors: importance of white colonies (3)
- β-galactosidase does not cleave X-gal; no blue appears
- these colonies are expressed in vivo, but not in vitro
- these are genes **thought** to be needed for survival specifically in the mouse model
87
how can we used IVET to identify Salmonella virulence factors: importance of blue colonies (2)
- β-galactosidase cleaves X-gal; blue appears
- these colonies are expressed in vivo and in vitro
88
how can we used IVET to identify Salmonella virulence factors: what should happen after the experiment
- LoF or biochemical experiment is needed to test the virulence/essential-ness of the gene
89
how can we used IVET to identify Salmonella virulence factors: why might genes that are only expressed in vivo have no effect on virulence (3)
- several genes may be under the same promoter
- there may be redundant factors (eg. 10 redundant adhesion factors); knocking out one does not affect the virulence as compensation by other factors will occur
- gene may be involved in house-keeping functions
90
IVET: disadvantages (2)
- genes expressed in vivo are not confirmed to be virulence factors; subsequent testing must be done
- IVET does not tell us where or when the genes were turned on
91
DFI (3)
- differential fluorescence induction
- promoter trap technology
- uses fluorescence-based selection for intracellularly-induced genes
92
DFI: reporter construct (2)
- promoterless gfp gene
- green fluorescence proteins
93
DFI steps: rough collection (6)
1. make library of random fragments of genomic DNA
2. insert upstream of the promoterless gfp gene in a plasmid
3. infect host cell (eg. macrophage) with plasmod
4. sort and collect **fluorescing macrophages**
5. lyse macrophages and plate bacteria on lab media
6. sort and collect bacteria (from lab media) with **lowest fluorescence**
94
DFI steps: refined collection/observation (5)
1. use collected bacteria to infect macrophages again
2. see enrichment of fluorescing macrophages
3. lyse macrophages and collect bacteria
4. study each bacterium in greater detail, paying attention to timing, levels and location of expression
5. sequence cloned fragments and identify the gene
95
hybridization-based techniques (3)
- used for gene expression studies
- used to compare the relatedness of 2 bacterial strains
- involves dsDNA -> ssDNA
96
subtractive hybridization
- used to identify gene sequences found in virulent strains, but not avirulent ones
97
subtractive hybridization steps (6)
1. label DNA from "avirulent" strain with biotin (after adding linkers)
2. combine all the fragments from the virulent and avirulent strain
3. denature and reanneal DNA
4. use streptavidin to remove biotinylated DNA
5. what's left (fragments without streptavidin) are fragments unique to the virulent strain
6. clone fragment into plasmid and sequence the fragment
98
subtractive hybridization: denature and reanneal steps (3)
1. mix avirulent + virulent DNA
2. avirulent + biotin strands in excess
3. complementary strands will hybridize: all virulent fragments, avirulent fragments, and shared virulent/avirulent strands will hybridize
99
gene expression experiments (2)
- exposure of virulent strains to two different conditions
- compare virulent vs avirulent strains
100
how can we use subtractive hybridization for gene expression experiments (4)
- one strain (virulent) exposed to two different conditions
- collect mRNA
- convert to cDNA; reverse transcriptase and random primers
- do subtractive hybridization experiment
101
DNA microarrays
- used for gene expression studies or strain (DNA) comparisons
102
microarray (2)
- miniaturized device containing short single-stranded DNA oligonucleotide probes attached to solid substrate
- $100 per chip
103
microarray probes (2)
- designed to have sequences complementary to segments of one or more target organism genomes
- 20,000 probes
104
microarray probe synthesis (4)
- mechanically spotted
- sprayed
- using an ink jet print head
- synthesized using photochemical reactions
105
gene expression using microarrays: steps (7)
1. expose virulent strain to 2 different conditions
2. collect mRNA from each conditions
3. convert mRNA into cDNA
4. label cDNA with fluorescent probes, using different fluorescence for each condition
5. mix and use to hybridize to an array
6. array has every gene from the organism
7. compare expression patterns (fluorescence colours)
106
microarrays to compare 2 strains (2)
- collect DNA from strain A and use it to hybridize to array from strain B
- if there are spots that don't fluoresce on array, the genes are missing from strain A
107
DNA microarray: disadvantages to comparing two strains
- won't identify any unique genes from hybridized strain
108
pangenome array
- DNA microarray with genes from many, many bacteria
109
RNA Seq (2)
- used to detect and quantify mRNA levels
- will also find small (non coding) RNA (sRNA)
110
RNA Seq: steps (7)
1. extract RNA
2. deplete rRNA and tRNA
3. fragment the RNA
4. convert to cDNA
5. add adaptors, amplify library, and do Illumina sequencing
6. align sequences to genome using bioinformatics
7. the number of sequence reads is roughly proportional to amount of mRNA for a particular gene
111
what does each cluster on an Illumina sequencing chip represent when doing RNA Seq (2)
- one mRNA transcript for gene X in the original sample
- a cluster is the bridge-amplified produce of a single transcript
112
how do we measure RNA expression using RNA seq (3)
1. count up number of identical sequences from each cluster on the chip
2. map sequences to genome
3. compare experimental conditions
113
RNA seq: advantages (3)
- can use RNA seq to compare bacteria grown under different conditions
- may discover novel genes
- small non coding RNA and antisense RNA can be found
114
dual RNA seq (2)
- can be used to find **in vivo** expressed genes
- can sequence bacterial and host cell transcripts (cDNA) at the same time
115
dual RNA seq: steps (5)
1. infect cells with fluorescently labeled bacteria
2. sort for infected cells to get a homogenous starting population
3. extract RNA, depleting rRNA and tRNA
4. convert to cDNA and sequence
5. align to host genome and the bacterial genome separately
116
protein/proteome microarrays: steps before array (5)
1. start with bacterial genome
2. amplify all open reading frames (genes)
3. clone into an expression plasmid
4. express the proteins using an **in vitro** transcription and translation system
5. do not need to purify the proteins
117
protein/proteome microarray: steps after array (4)
1. use array with nickel-NTA (Ni++) which binds 6xHis tags
2. anti-V5 tag antibody confirms expression of the construct
3. add serum from patients or from experimental model
4. if antibody binds to protein, a signal will be produced
