bacterial pathogenesis and pathology

Question 1

Can bacterial (microbial) diversity be measured? Give three examples of methodology.

Answer 1

yes by : colony morphology , cell shapes under microscopes, cell structures and staining, metabolic classification, growth classification( O2, temperature and salt), biochemical activities ultra structures analysis, cell surface antigens and genotyping

Question 2

What are the driving forces behind bacterial (microbial) diversity?

Answer 2

Competition , Attacks of the immune system ; Environnemen

Question 3

Describe briefly the culture-independent microbiome analysis.
.

Answer 3

it’s the DNA extraction of the microbiome composition. We took the DNA of a culture or a sample and we purify it for amplify it by PCR with 16 RNA genes with two primers ( F and R ). After the amplification we can create and align consensus sequence to compare it to genebank database for Blast analysis and phylogy analysis.

Question 4

Wich of the following best represent the hierarchy of Level of biological classification :

Answer 4

Kingdom , phylum, class , order, family, genus, species

Question 5

Define the following type of prokaryote and in what type of extreme environment it can 
grow. 
Thermophile : 
Acidophile : 
Alkaliphile : 
Psychrophile : 
Halophiles :

Answer 5

Thermophile : an organism with optimal growth with higher temperature
Acidophile : an organism with optimal growth at low pH value
Alkaliphile : an organism with optimal growth with high pH value
Psychrophile : an organism with optimal growth at 15C° or lower
Halophiles : an organism with optimal growth with high concentration of salt

Question 6

How do Acidophile and Alkaliphile survive during acid and alkali stresses?

Answer 6

They adjust and maintain theirs membranes by regulating ions flows using transporters :
For a shift acidity K+/H+ antiporter pumps in K+ neutralizing the pH ( and pump out protons ).
With a shift to alkaline, the Na+/H+ antiporter pumps in H + to acidify the cytoplasm (and pumps out Na + ions).

Question 7

What is hyperthermophiles? What are the factors that help hyperthermophiles can survive and grow at high temperatures?

Answer 7

Hyperthermophiles is an organism with optimal growth at 80°C or higher. To survive at these temperatures they develop different ability like :
a protein stability with a reduction of glycine content and an abundance of cystein disulfide bonds and chaperons to refold these proteins.
A DNA stability with a reverse DNA gyrase who catalyse supercoiling of closed circular DNA.
A DNA bonding proteins : like histone
A membrane phospholipid stability with monolayer of lipids

Question 8

What is the “specificity subunit” of bacterial RNA polymerase and how is it physically displayed on RNA polymerase to aid its function?

Answer 8

The specific subunit of the RNA polymerase is the sigma factor. He spread across the upstream face of the RNAP crab claw structure. He has 3 globular domains linked by flexible markers. He help the RNAP to recognize directly the bacterial promoter

Question 9

What are the primary steps in transcriptional initiation and what are the major parameters that affect their impact on promoter output?

Answer 9

Transcriptional initiation
Close complex -> open complex -> Initiation complex : promotion escape + factor released
There is different factors who can affect the output : the closer promoter sequence is to consensus, the higher is the affinity , amount of RNAP , each sigma factor are more likely to bind to a specific DNA promoter.

Question 10

Explain why many positive bacterial transcriptional activators are dual function proteins that can activate transcription from some promoters and act as repressors at other promoters.

Answer 10

Activators can bind to DNA in a specific region , upstream the -35 and -10 boxes to interact with RNAP and enhance its capacity /affinency to produce RNA. But as long as activators bind to a specific DNA if this sequence is downstream , into the forbidden region it will prevent RNAP to bind to the DNA strand and thus becoming a repressor.

Question 11

Describe the basic modes of action when acting as an activator and when acting as a repressor in terms of the important DNA motifs for RNA polymerase binding to bacterial promoters.

Answer 11

Activator :
bend DNA -> interact with RNAP a more efficient
Bind to DNA -> interact with the RNAP a more efficient
( bind before 50 nucleotides )
Repressor = same actions with opposite effects
( bind in DNA binding site or forbidden zone

Question 12

Contrast the properties of the holoenzyme using the house-hold (housekeeping) sigma70 factor with that of the holoenzyme using the alternative sigma 54-factor.

Answer 12

Sigma 70 and sigma 54 comparaison :
sigma 70 household
Sigma 54 :
Can not make RNAP working without ATP hydrolysis
Regulators (activators) are bound 100-200bp upstream of promoters they control -> name = bacterial enhancer binding protein
Regulator interacts with the front of RNAP, through sigma 54 and beta subunit
Physical interact with DNA occurs through DNA loop ( not mandatory for sigma 70 RNAP)

Question 13

What is an anti-sigma-factor? With aid of an illustration, describe one of the ways an anti-sigma-factor can work.

Answer 13

Anti-sigma-factor : factor inhibiting is a factor’s activity by binding on it, preventing its interaction with RNAP core enzyme, preventing indirectly transcription: E.g Morphological checkpoint control: FlgM = anti-sigma-factor, prevent sigma 28 , which will bind to RNAP core enzyme while the promotion of flagella is not needed.
When it is , FlgM pass through the membrane to the incomplete flagella and there release sigma28 , which will bind to RNAP so as to transcript genes who are important for teh flagella construction.

Question 14

Explain three different mechanisms by which a bacteria promoter can be made co-dependent on the activities of two different regulators. Aid your explanations with illustrations in each case.

Answer 14

1° 2 regulators on 1 promoter :
one binds to the promoter but not in the exact place so the other can replace it at the right place ( activator )
2° A repressor bind , then an activator binds near the repressor to suppress it’s activity and so allowing transcription ( or actually remove the repressor )
3° 2 activators cooperates to activate transcription

Question 15

Describe the role of CRP protein at the Plac promoter of the lactose operon.
Be sure to include in your answer how the activity of

Answer 15

CRP (= cAMP Receptor Protein) : No to glucose a cAMP level = high a bind to CRP activated , bind to :
RNAP -> activating
Forbidden zone in DNA -> repressor
Bend DNA -> Activator or repressor

Question 16

What are the principal differences between riboswitches acting at the transcription and translational level ?

Answer 16

On gram positive bacteria , riboswitch acts at the transcription level , is on RNA where is they make a formation with a metabolite resulting in a pre-mature termination on the transcript
On gram negative bacteria riboswitches acts at the translational level acts on the whole RNA ( meaning after termination ) the metabolite binding results in the ribosome not being able to bind to its ribosome binding site

Question 17

How can transcript stability be measured ?

Answer 17

We can measured the stability of the mRNA by adding rifampicin who block the function of the RNAP to measure the half-time.

Question 18

How do endo-exonucleases function ?

Answer 18

An endonuclease removes the terminals nucleotides.

Question 19

How can RNases act as regulatory devices ?

Answer 19

They can be regulatory devices by eliminates somes genes by the use of stabilizing motifs.

Question 20

The function of several small RNAs depends on the protein Hfq. How can Hfq assist small RNAs.

Answer 20

Hfq is a protein who can change the structure of several sRNAs when it binds and also increase the interaction between the sRNA and the target by changing their structure.

Question 21

What is the basic difference between riboswitches and thermosensors ?

Answer 21

Riboswitches are controlled by metabolites , thermo sensor are controlled by the temeprature resulting in differents foldings of the RNA. Thermosensors can act both on the DNA level ( causing conformational changes in promoters regions ) , the protein level ( changing conformational fold and activities ) and the RNA level ( by hiding the binding site for the ribosome).

Question 22

What is «pupylation»? With the aid of illustration describe briefly the mechanism of pupylation in bacterial physiology.

Answer 22

Pupylation is the process by which bacterial proteins are covently modified with prokaryotic ubiquitin-like protein for degradation by the proteasome
Example : in Mycobactrium tuberculosis the bacterial proteasome degrades targets conjugated to a prokaryotic ubiquitin-like protein

Question 23

List three bacterial physiological processes which is controlled by post-translational protein phosphorylation.

Answer 23

There is the two-component system , the quorum sensing and bioluminescent

Question 24

What is protein glycosylation. Describe briefly the roles of protein glycolysation in bacterial pathogenesis.

Answer 24

Protein glycosylation is an enzyme catalysed covalent attachment of glycans onto the amino-acid side in proteins.
It can be useful in adhesion or to protect the bacteria from digestion.

Question 25

Describe in words and illustration the general developmental life cycle of biofilm.
A biofilm life is divided into 3 parts :
the attachment : by motility , random contact , sticky surface , surface appendages, hydrophobicity or hydrophilicity of substratum , the electrochemical properties of the substratum.
The growth : it’s the macrocolony formation by the maturation of the biofilm. It’s also a role of the quorum sensing to coordinate many activities among the bacterial cells.
The detachment : by nutriments limitation, change in cell-cell contact or enzyme prodduction like the lysaes

Answer 25

A biofilm life is divided into 3 parts :

1) the attachment : by motility , random contact , sticky surface , surface appendages, hydrophobicity or hydrophilicity of substratum , the electrochemical properties of the substratum.
2) The growth : it’s the macrocolony formation by the maturation of the biofilm. It’s also a role of the quorum sensing to coordinate many activities among the bacterial cells.
3) The detachment : by nutriments limitation, change in cell-cell contact or enzyme prodduction like the lysaes

Question 26

Describe in words and illustration the general developmental life cycle of biofilm.
A biofilm life is divided into 3 parts :
the attachment : by motility , random contact , sticky surface , surface appendages, hydrophobicity or hydrophilicity of substratum , the electrochemical properties of the substratum.
The growth : it’s the macrocolony formation by the maturation of the biofilm. It’s also a role of the quorum sensing to coordinate many activities among the bacterial cells.
The detachment : by nutriments limitation, change in cell-cell contact or enzyme prodduction like the lysaes

Answer 26

A biofilm life is divided into 3 parts :

1) the attachment : by motility , random contact , sticky surface , surface appendages, hydrophobicity or hydrophilicity of substratum , the electrochemical properties of the substratum.
2) The growth : it’s the macrocolony formation by the maturation of the biofilm. It’s also a role of the quorum sensing to coordinate many activities among the bacterial cells.
3) The detachment : by nutriments limitation, change in cell-cell contact or enzyme prodduction like the lysaes

Question 27

Describe the protective mechanisms suggested for antimicrobial resistance in biofilms.

Answer 27

To avoid the antimicrobial activity , bacterias in the biofilm can :

• induce a general stress response
• Increase the expression of multiple drug resistance
• Activating the quorum sensing systems
• Change profiles of outer membranes proteins

Question 28

Describe the protective mechanisms suggested for antimicrobial resistance in biofilms.

Answer 28

To avoid the antimicrobial activity , bacterias in the biofilm can :

• induce a general stress response
• Increase the expression of multiple drug resistance
• Activating the quorum sensing systems
• Change profiles of outer membranes proteins

Question 29

What is mean the dimorphic cell division in Caulobacter crescendus ?

Answer 29

The dimorphic division of this Bactria is an advantage for her because she can have two differents life style : a sessile and a mobile.

Question 30

How is the initiation of sporulation by Bacillus controlled ?

Answer 30

The formation of bacillus spore’s is controlled by an asymetric division of the mother cell to form a forespore

Question 31

What aspects of the Myxococcus life demonstrate community ( cooperative ) behaviour ?

Answer 31

They can have a developmental cycle and vegetative growth. In the vegetative growth , there is a presence of nutrients cells who move in a coordinated Manner, forming swarms. And when swarms make contact with the prey, cells penetrates teh prey colony and lyse the cells
The developmental cycle : the cells are moving collectively initiate a developmental program and form aggregates and later form fruits bodies who will produce myxospores who will colonize other places

Question 32

Briefly describe the process of cellular metabolism?

Answer 32

The metabolism of the cell is all the organized chemical reaction who occurs in this cell. It’s divided into 2 majors parts :
the catabolism : to degrade compound in order to gain ATP
The anabolism : to produce compound by consuming ATP

Question 33

Bacteria generate usable energy via photosynthesis or respiration. What are the fundamental differences in these mechanisms?

Answer 33

For the bacteria who use photosynthesis , he use the photon of the solar energy to produce ATP in contrast to the respiration who use the chemical biomass to produce ATP. There is 4 types of respiration : anaerobic , aerobic , fermentation and phosphorespiration.

Question 34

What is a redox reaction and why are they central to cellular respiration?

Answer 34

A redox reaction is a reaction of oxidation-reduction. A compound donates one or more electron by the oxidation to an other compound who will accepts those electrons ( reduction ). It’s a central thing in cellular respiration because it’s will generates a proton motive force.

Question 35

What is proton motive force and how is it generated?

Answer 35

It’s the energy transferred in the ETC allows : the protons that originally from NADH and the dissociation by the water will release electrons , the pumping protons and the accumulation of OH- ions. It will generate a pH gradient and an electrochehemical gradient across the membrane. So these proton motrice force is used in active transport , the bacterial flagella rotation or the production of ATP

Question 36

In general terms, how is the molecular make-up of the electron transport chain influenced by the metabolic diversity within the bacterial kingdom?

Answer 36

There is a huge metabolic diversity, and therefore there is different molecules that can participate in the electron Transfert chain. The same bacteria species can carrying multiples forms of metabolism. Generaly speaking there is chemoautrophs , lithoautotrophs , photoautotroph , chemoheterotroph or organoheterotroph

Question 37

What is the function of an ATP synthase? How does it work?

Answer 37

The function of the ATP synthetase is to transform the proton motive force into the production of ATP. The ATP synthase is made by two parts : a cytoplasmic located headpiece and a cytoplasmic membrane spanning channel. So the proton movement through F0 drives the rotation of the C protein. And it’s this protein who will generate mechanical energy that is transmitted to F1 via the rotation. And it will be the subunit who will change the conformation allowing the bonding of an ADP with a Pi ( Phospate inorganic ).

Question 38

Aerobic bacteria perform substrate-level phosphorylation and oxidative phosphorylation. What are they doing? What are the physiological consequences of these activities?

Answer 38

Substrate level phosphorylation is the Transfert of a phosphate group from a biosynthetic intermediate to ADP yielding to ATP. This is the only way of energy for fermentation ( they only have glycolysis ) , they provide 2 ATP. Oxidative phosphorylation is the redox reaction of the electron reaction chain which give 34 ATP.

Question 39

Can anaerobic bacteria perform both substrate-level phosphorylation and oxidative phosphorylation? Explain! What about bacteria carrying out only fermentation?

Answer 39

Yes, oxidative phosphorylation just has any other terminal electrons accepting species than oxygen. Bacteria carrying out fermentation, can only perform substrate level phosphorylation.

Question 40

A lithoautotroph and an organohetotroph are growing in their preferred environments. What are energy/carbon sources for these bacteria? Which of these bacteria are likely to be growing faster? Why?

Answer 40

A litoautotroph it’s a sort of chemotroph so they take theirs energy from the energy stocked in the bonds of chemical compound harvest by the transfer of the electrons. In this specific case they take theirs energy from an inorganic compound. For the organotroph is little bit different , they are chemotroph but they took theirs energy from either organic. So I think it will be the organotroph who will grow faster because it’s more easy to destroy some molecules who are already used for energy than the mineral molecules.

Question 41

What is meant by aerobic respiration control? What happens when a aerobic respiring bacterium encounters an anoxic environment?

Answer 41

The aerobic respiration can be controlled by 2 systems : the ArcAB ( anoxic redox control ) and the FNR system a single compound system. When a aerobic bacteria sense that there is no more oxygen.

Question 42

What properties influence solute transport across the cell membrane?

Answer 42

They are 4 properties who can influence the solute transport :
the solute concentration gradient : the molecule have a tendency to diffuse down their concentration gradient
The solute charge
The solute size
The proton-motive force : the disproportional distribution of H+ across the membrane

Question 43

Compare and contrast passive and facilitated diffusion.

Answer 43

The passive diffusion it’s simple but rare because it’s unaided by any type of transporter , it’s just the movement of molecules across the membrane. It’s will be always search the equilibrium between two spaces : it can be uncharged molecules, it’ll be search the concentration equilibrium or charged molecules or ions, it’ll be search the equilibrium of concentration and the electrochemical gradient.
The facilitate diffusion is more specific because they requires a specific membrane transporter so it’s more specific than the passive. These transporter will speed up the rate of the molecule across the membrane. It exist 2 types of transporters :
the carrier protein : they interact with the solute and change conformationally to transfer it.
The channel protein : they don’t interact with the solute but these solute have small size.

Question 44

Active transport systems can be sub-divided into primary and secondary mechanisms? What defines these two mechanisms? Give specific examples of each mechanism?

Answer 44

These two mechanisms are divided into 2 because the primary mechanism requires directly an energy source while the secondary is coupled to an ionic gradient and pH gradient.

Question 45

Name the three forms of chemiosmotic transport. Describe each of their functions.

Answer 45

the uniport or facilitated diffusion : it’s unidirectional transport of one protein
The symport or co-transport : it’s the simultaneous transport of two substances in the same direction
The antiport or exchange transport : it’s the simultaneous transport of two substances in opposites direction

Question 46

Name the three forms of chemiosmotic transport. Describe each of their functions.

Answer 46

the uniport or facilitated diffusion : it’s unidirectional transport of one protein
The symport or co-transport : it’s the simultaneous transport of two substances in the same direction
The antiport or exchange transport : it’s the simultaneous transport of two substances in opposites direction

Question 47

How is chemiosmotic transport inhibited by the action of ionophores?

Answer 47

The ionophores are molecules who can neutralize the charge of the transported ion to facilitate his transport across the membrane. With that he will inhibited the action of chemiosmotic transport

Question 48

How is chemiosmotic transport inhibited by the action of ionophores?

Answer 48

The ionophores are molecules who can neutralize the charge of the transported ion to facilitate his transport across the membrane. With that he will inhibited the action of chemiosmotic transport

Question 49

What are P-type ATPases and how do they work?

Answer 49

It’s the example of one primary transport system. It’s an ubiquitous group of proteins who have :
a cytoplasmic domain with :
- A N domain who contain the ATP binding site
- A P domain who contain the site of reversible phosphorylation
- A A domain who modulates the access/ release of the cation to /from the transmembrane
binding site
- a transmembrane domain who contain multiples spanning helices and as a function as the ion channel.
Step 1 : E1 hight affinity binding of ion X+ ( from inside ) promotes ATP binding
Step 2 : E1-P Phosphorylated ( via ATP hydrolysis ) and conformational change.
Step 3 : E2-P reduces ion X+ affinity to leading to external release
Step 4 : E2 creates hight affinity binding site for ion Y+( from outside ).

Question 50

Describe the molecular composition of ABC transporters. How do they function as both importers and exporters of solutes?

Answer 50

ABC is for ATP-biding cassette it’s compound of 3 basics structures for importers :
1. two integral membranes spanning domains ( MSD1 and MSD2 ) proteins
2. Two highly conserved nucleotides bindings domains ( NBD1 and NBD2 ) peripherally associated with the membrane that bind and hydrolyze ATP.
3. One periplasmic solute-binding protein ( SBP ) with extremely high affinity for the substrate.
For exporter’s ABC there is somes keys differences :
MSD proteins are often fused to the NBD and will act as dimers
An accessory component fused to both the inner and outer membrane, termed membrane fusion proteins ( MFP )
An outer membrane proteins ( OMP ) -pore
They will exported substanced like : surface component of the bacterial cells , virulence determinants involved in bacterial pathogenesis or iron scavenging siderophores.

Question 51

ABC transporter systems are universal, with hundreds of examples known? Can you give suggestions as to why ABC transporter systems are so common?

Answer 51

It can be a transport of lipoproteins during biosynthesis , the import of maltose or iron
There are very common because they are very useful like they can do some export and import , are specific to one type of substrate. They are also part of other type of systems like the type 1 secretion system to export some proteins.

Question 51

ABC transporter systems are universal, with hundreds of examples known? Can you give suggestions as to why ABC transporter systems are so common?

Answer 51

It can be a transport of lipoproteins during biosynthesis , the import of maltose or iron
There are very common because they are very useful like they can do some export and import , are specific to one type of substrate. They are also part of other type of systems like the type 1 secretion system to export some proteins.

Question 52

Why is iron so essential for most life-forms? What mechanisms do bacteria employ to overcome iron limitation in their environment?

Answer 52

Iron are very important in life because with their structures they can catch nitrogen , do some transport , stockage and use of the oxygen. They are very important for the electron Transfert especially in the reaction chain to produce ATP So do have alway iron bacteria have develop some siderophores who are specific transporters to catch iron

Question 53

Why is iron so essential for most life-forms? What mechanisms do bacteria employ to overcome iron limitation in their environment?

Answer 53

Iron are very important in life because with their structures they can catch nitrogen , do some transport , stockage and use of the oxygen. They are very important for the electron Transfert especially in the reaction chain to produce ATP So do have alway iron bacteria have develop some siderophores who are specific transporters to catch iron

Question 54

How do bacteria overcome the lack of usable energy in the periplasm to facilitate solute import? How would you expect this to be different between Gram-negative and Gram-positive bacteria?

Answer 54

They can use the lack of usable energy in the periplasm by using a specific energizer system : the TonB-ExbB-ExbD to let enter some iron. This lack of energy is situated in the periplasm , the space bteween the inner membrane and the outer membrane. So we can find this place just in gram negative bacteria because they have these 2 membranes. To find iron gram positive bacteria have to find others ways.

Question 55

How do bacteria overcome the lack of usable energy in the periplasm to facilitate solute import? How would you expect this to be different between Gram-negative and Gram-positive bacteria?

Answer 55

They can use the lack of usable energy in the periplasm by using a specific energizer system : the TonB-ExbB-ExbD to let enter some iron. This lack of energy is situated in the periplasm , the space bteween the inner membrane and the outer membrane. So we can find this place just in gram negative bacteria because they have these 2 membranes. To find iron gram positive bacteria have to find others ways.

Question 56

What is PEP, and how does it influence the influx of certain solutes.

Answer 56

PEP is the abreviation for phosphoenol pyruvate , a molecule who are involved in group translocation system for the importation of glucose , mannose and mannitol. Faire schema

Question 57

Describe the fundamental features of various protein export mechanisms that transport substrates into and/or across the bacteria inner membrane.

Answer 57

So to export proteins there is 3 differents systems :
-1 the export of protein by the Sec-dependant-pathway :
it’s the export of unfolded proteins by using 4 differents proteins : the SecB chaperone who will unfolded the protein , SecA ATPase , the SecYEg translocon and SecDF who are an accessory proteins.
-2 the export of protein by the TAT-dependent pathway
it’s the export of folded proteins by a TaT ABC translocon with the help of a co-factor. ( faire schema )
-3 the export of proteins by the SRP-dependent pathway :
it’s for the membrane bound proteins. It’s depend of the Sec pathway and the Signal recognition particle

Question 58

Describe the fundamental features of various protein secretion mechanisms that transport substrates across the bacteria outer membrane.

Answer 58

There is 7 types of secretion systems :
- the Type 1 secretion system :
He is a member of the ABC transporter family, he can secrete inly unfolded proteins, he is Sec independent and there is no periplasmic intermediate. So it’s compound of 3 molecules : 2 cytoplasmic proteins : the ABC : the ATP binding cassette and a membrane fusion protein. The other protein is an outer membrane protein. All substrate are characterized by a non cleaved C-terminal secretion signal. And it’s these proteins who are recognized by the ABC proteins. Also chaperones are very important to keep the substrate unfolded. He belong to the family of TolC-like.
- The type 2 secretion system :
He is the main terminal branch of the General secretory Pathway. He establish periplasmic protein intermediates. He can export folded substrate. He is compound of 12-16 differents proteins.
- The type 3 secretion system :
He is a method for direct translocation of bacterial proteins into the target host cells. So the proteins can pass throught the inner membrane and the outer membrane and all the host cells barriers. Substrates don’t have any periplasmic substrates but the substrate secretion is Sec dependent. All substrates are unfolded. These type of secretion system secreted 3 types of substrates : 1 the substrate to form the needle, 2 the substrate to form the pore into the membrane of eukaryotic cells ( translocators ) and 3 the substrates who are effectors. There is 5 classes of cytoplasmic chaperones : the effectors classes, the translocator classes, the needle classes , the flagella classes.
- The type 4 secretion system :
He can transfer a variety of substrates like single stranded DNA , DNA/protein complex or simple and multicomponents systems. So he contribute to the spread of antibiotic resistance between bacterias. But he can also inject toxins into eukaryotic cells. So we can say that there is a analogy between T4SS and bacterial conjugation.
- The type 5 secretion system :
He is the type who are the most simplistic and widely distributed. There si two types : the Autotransporter ( AT ) and the Two-partners ( TP ). They don’t need a lot of specific components to work ( 1 for AT, 2 for TP ). They provides a solution to the transport of large proteins. But these system is not versatile so it’s being dedicated to the secretion of only one substrate.
- The type 6 secretion system :
He is the most recently identified it’s like the T4 bacteriophage.

Question 59

Gram positive bacteria do not possess an outer membrane. How has this influenced the mechanisms of protein export and/or secretion in these bacteria?

Answer 59

Because gram positive bacteria don’t have an outer membrane the protein secretion system is more easy for them.

Question 60

How do type IV pili resemble a T2SS?

Answer 60

There is the same components in the Type 4 pilus and on the T2SS to create the pilus : for the T2SS is for expulse the proteins out of the membrane and for the type 4 pilus is for adhesion to eukaryotic cells, to twitch motility or for DNA uptake.

Question 61

Compare and contrast T3SSs and the system for flagella biosynthesis.

Answer 61

T3SS might be analogous to the bacteria flagella because the apparatus that recognize proteins to be secreted are 100% identical

Question 62

What is the most fundamental benefit of a T5SS? What is its primary limitation?

Answer 62

The most fundamental benefit of of a T5SS it’s his simplicity , they have a low number of specific components required for the secretion process. But this strength is also a weakness because each system are dedicated to one specific type of substrate.

Question 63

What does the Tat system and the T2SS have in common?

.

Answer 63

The T2SS need a secretion of protein by Sec or TAT pathway to after push them outer of the secondary membrane by the formation of the pseudopilus. So it’s a coordination between 2 type of secretion

Question 64

What biotechnology application(s) will continue to benefit from increased knowledge about bacterial protein secretion systems?

Answer 64

It can be the production of a new vaccine by using the secretion system to deliver specific antigens for the immune system processing. It can be also the bacterial vesicles as a nanosystem for delivery of therapeutic cargo.

Question 65

The outcome ( disease versus clearance) of the interaction between bacterial pathogen and host is balance between several variables. What may influence the severity of disease following host infection by a pathogen bacterium ?
.

Answer 65

The severity of the disease can be influenced by weak host defense due to an other disease. It can be due also to the severity of the differents virulences factors like adhesins etc … the cycle of life of the bacteria can be also important

Question 66

How might a pathogenicity island contribute to the evolution of bacterial pathogen ?

Answer 66

Because they can provides some virulence genes who are controlled by regulatory genes and mobility genes. So these island can provides some genes who are important for pathogenicity of the bacterium.

Question 67

Describe the various steps in the cycle of bacterial infection.

Answer 67

They have to maintain a reservoir but after they hev to gain entry ( critical ) , attach and colonize host cells ( critical ) , invade cells ( optional ) , gain access to nutriment and multiply ( critical ) , avoid the host immune system ( critical ) , spread to others sites ( critical ) and finaly spread to an other host.

Question 68

What is the difference between exotoxin and an endotoxin ? Give examples of each category and how they might influence specific aspects of the infection process ?

Answer 68

An endotoxin is a component of all bacteria like LPS or DNA it’s PAMPs ( pathogen associated molecular pattern )
An exotoxin is secreted enzyme or toxins including cytotoxins, neurotoxins and endotoxins, the cause damage to the host by destroying cells or disrupting normal cells metabolism.
There is 4 types of exotoxins :
1 : they act from the extracellular cell surface , bind to a receptor of the cell and stimulate intracellular pathway ( E.g : superantigen and heat stable enterotoxin
2 : designed to disrupt the membrane ( E.g : channel forming toxins )
3 : intracellular toxins that must be able to gain access to the cytoplasm of target cell to exert theirs effects. ( E.g : A-B toxins like the cholerae )
4 : break the bonding between proteins that form part of the connective tissue ( E.g : hyaluronidase or collegenase )

Question 69

Discuss Koch’s postulates ! How are these now adapted to studies at the molecular level, looking to establish the role of specific genes and theirs products ?

Answer 69

These postulates can be adapted at the molecular :
the gene or its product should only be found in pathogenic bacteria causing the disease and not in the bacteria that are avirulent
Disrupting the gene should reduce the virulence of the mutant bacterial strain and/or the gene should be isolated by cloning and introduced in an avirulent bacterium increasing its virulence
The gene should be expressed during the infection of the host

Question 70

Discuss criteria for selecting the right animal model to study bacterial infection of human.

Answer 70

The animal model should develop a disease with similar symptoms , have a similar bacterial distribution and acquire the disease by the same route of infection. So these models can be rabbit , pig, mice … but also non mammalian animals

Question 71

Several options exist for identifying important virulence determinants. Describe an experimental setup, or combinaison of experiments, which you think would achieve this goal.

Answer 71

To identifying the virulence factor we can use in vitro technique or in vivo technique : 
In vitro technique : 
transposon mutagenesis 
Gene cloning 
Transcriptional gene fusion 
Deciphering genome sequence 
In vivo technique : 
in vivo expression technology ( IVET ) 
Signature-tagged Mutagenesis ( STM ) 
Real time monitoring 
RNAseq

Question 72

After a long period of decline, the infectious disease threat is on increase, due in part to multiple antibiotic resistance bacteria. What others factors are contributing to this increased threat ?

Answer 72

It’s can be the industrialization , the global warming , the increase of destruction forest , the poverty and malnutrition …

Question 73

Why study ( perform research in) bacterial pathogenicity ?

Answer 73

To understand the natural immune mechaniqm of the host , or to identifying the virulence factors of different pathogens

Question 74

Define the following terms : 
Infection: 
Disease: 
Colonization:  
Asymptomatic carrier: 
Symptoms : 
Pathogenicity : 
Pathogenesis : 
Virulence :  
Virulence factor ( mechanism ): 
Opportunist :

Answer 74

Infection: colonization of the body by a bacterium capable of causing disease
Disease: infection that cause symptoms
Colonization: bacterium occupies and multiplies in a particular area of the body
Asymptomatic carrier: an infected person who does not have symptoms
Symptoms : effects of a bacterial infection apparent to the infected person
Pathogenicity : the mechanism by which a bacterium cause a disease
Pathogenesis : the ability of an organism to cause disease
Virulence : the degree of pathology to the host that is caused by the organism
Virulence factor ( mechanism ): bacterial product or strategy that contributes to virulence/ pathogenicity
Opportunist : bacteria that normally do not cause disease in healthy people but can cause disease in people with impaired defenses

Question 75

The single most important characteristic of symptom caused by Vibrio cholerae is :

Answer 75

Profound watery diarrhea

Question 76

What animal model systems can be utilized to study the pathogenesis of Vibrio Cholerae ?

Answer 76

Suckling mouse , ligated rabbit ileal loop , caenorhabditis elegans and human volunteers

Question 77

List three virulence factors of Streptococcus pyogenes ( Group A streptococcus )

Answer 77

There is M proteins who inhibit phagocytosis ) , hyaluronic acid ( same ) , invasins and exotoxins

Question 78

Which one of the following is NOT true concerning Staphylococcus aureus ?
S.aureus is related to inflammation
S.aureus can cause pseudomonia
S.aureus can lead to acute bacterial endocarditis
S.aureus does not make coagulase

Answer 78

S.aureus is related to inflammation
S.aureus can cause pseudomonia
S.aureus can lead to acute bacterial endocarditis
S.aureus does not make coagulase

Question 79

Which is NOT correct regarding the cholera mechanism ?
adheres to and colonize small intestine mucosa
Uses virulence factors like polar flagella for motility
Uses virulence mechanisms like pili and adhesion
Produces enterotoxins which act on the stomach

Answer 79

adheres to and colonize small intestine mucosa
Uses virulence factors like polar flagella for motility
Uses virulence mechanisms like pili and adhesion
Produces enterotoxins which act on the stomach

Question 80

Name two main virulence factors utilized by V.cholerae and describe the physiological basis behind the intestinal secretion caused by this organism.

Answer 80

V.cholerae use many types of virulence factors like the cholera toxin and toxin coregulated pilus to adhere of mucosal cells.
The toxins released by the bacteria are componed of 3 types of molecules : 5 molecules B and 1 molecule A1 and 1 molecule A2. These molecules A will enter in the cell by the ganglioside receptor and will activate the adenylate cyclase who will increase the production of cAMP. And it’s this cAMP who will open gates to release nutriment from the cell.

Question 81

Describe briefly the steps in the invasion of cells and intracellular spread by L.monocytogenes.

Answer 81

The bacteria is taken up by phagocytosis. Once ingested the bacterium will produce listeriolysin( LLO ) to escape from the phagocytosis. Then the bacteria will replicate in the cytoplasm rapidly and move through the cytoplasm to invade adjacents cells by polymerizing actin to form long tails

Question 82

Describe briefly the infectious life cycle of Listeria.monocytogenesis.

Answer 82

These bacteria enter to the human body by contamined food, he will translocate him self in the liver after passed by the intestinal track. A this point these bacteria can infact the blood to contamined the brain ( cause of meningoencephalitis ) cause septicemia or infect the placenta to cause abortion. The bacteria is release into fecal shedding.

Question 83

Classify different Eschericha coli variants according to their pathotypes.

Answer 83

They are 5 intestinal species : enterotoxogenic ( ETEC ), enteropathogenic ( EPEC ), enterohaemorrhagic ( EHEC ), eneroinvasive ( EIEC ) and enteroaggregative ( EAEC ). They are also 2 types of extraintestinal species : uropathogenic ( UPEC ) and meningitis ( NMEC ).

Question 84

List three clinical diseases caused by Salmonella typhi infection.

Answer 84

Salmonella typhi can cause : gastroenteritis , septicemia and septic shock , Localized suppurative infections , enteric Fever or typhoid fever and asymptomatic colonizatio

Question 85

List five virulence factors of UPEC and describe their biological roles.

Answer 85

UPEC have many virulence factors like : siderophore receptors to catch fer , P type pilus to adhere the cell or production of toxins and adhesins to kill the cell or to catch up.

Question 86

Describe briefly the mechanism of action of botulinum toxin.

Answer 86

Botulinum toxin block the release of neurotransmitters , and thus inhibit constrictions of others muscles.

Question 87

A patient presents with severe bloody diarrhea, crampy abdominal pain, tenesmus, joint pain, and fever. Stools are a currant-like red. Initially, it appears that he may have ulcerative colitis but microbiology studies reveal the presence of bacteria. What is the most likely diagnosis ?

Answer 87

• Shigellosis

Question 88

With the aid of illustration, describe briefly the development of antibiotic resistance.

Answer 88

A plasmid with multiple antibiotic resistance gene can do 7 things to resist at the attack of antibiotic : 1 a efflux pump 2 a reduced uptake 3 an overproduction of the target enzyme 4 a metabolic bypass 5 an antibiotic degrading enzyme 6 an antibiotic altering enzyme 7 a biofilm

Question 89

What is the objective of a vaccine ?

Answer 89

It’s to stimulate the immune system to recognize the infecting agent as an foreign organism and thus destroy it

Question 90

A researcher discovers that a hyper-variable surface protein is the most immunodominant antigen produced by a clinically relevant bacterial pathogen under study. Will this make a good vaccine ?

Answer 90

No because if the protein can change rapidly the vaccine who target this protein will be not active for a long time ( cause of the rapid changing of the protein )

Question 91

What basically is the DPT vaccine? What are the component of the DPT vaccin ?

Answer 91

A DPT vaccine is a vaccine against Bordella pertussis , it’s composed by diphteria and tetanus toxoid who will killed whole cells of the bacterium.