Microbial Genetics/Drug Resistance

Question 1

What is the structure of a bacterial chromosome and how is organized? What do the contain?

Answer 1

• large, covalently closed, circular DNA molecule
• organization into loops around proteinaceous center
• essential genes

Question 2

Structure, size and location of a plasmid. Function.

Answer 2

• circular, small
• extra chromosomal or may integrate the bacterial DNA ▶️ episome
• nonessential genes for bacterial life: fertility, antibiotic resistance, exotoxins

Question 3

Where is the Bacteriophage in the bacteria and its function?

Answer 3

• integrated in bacterial chromosome as prophage

- Lysogenic conversion ▶️ make bacteria more pathogenic

Question 4

Requirements of homologous recombination

Answer 4

Homologous genes in bacterial chromosome 
Recombinase recA (enough), *recB, recC, recD (synthesized by recombination genes)

Question 5

Requirements for site-specific recombination

Answer 5

Attachment, integration or insertion site (no homologous region)
Restriction Endonucleases and RE sites on the DNA

Question 6

What is the objective of the homologous recombination? How is managed the new DNA information?

Answer 6

Exchange the new LINEAR DNA entering into the bacteria

Question 7

Objective of site-specific recombination. How is managed the DNA information?

Answer 7

Addition or integration of the new DNA entering to the bacteria with chromosomal DNA

*fertility factor, temperate phage, transposons (generally CIRCULAR DNA)

Question 8

How do you get new genetic combinations in bacteria?

Answer 8

Gene transfer ▶️ conjugation, transformation and transduction

Question 9

What is needed to make transformation by a certain bacteria?

Answer 9

To be competent ▶️ can bind, envelope and import naked environmental DNA

Question 10

What control the conjugation?

Answer 10

Fertility factors ▶️ plasmids or episomes

Question 11

What do the Fertility factors content to control and realize its conjugation?

Answer 11

• Plasmid “fertility” genes: tra region (sex pili), genes to stabilize mating pairs and direct conjugal DNA transfer
• OriT region: begin transfer
• Insertion sequence: recombination

Question 12

What type of DNA is transferred by F+ x F- cross? what is the result of that cross?

Answer 12

• Plasmid DNA (one strand of the double helix)

- a F+ cell without cromosomal DNA (no new bacterial genes)

Question 13

How is stabilized the plasmid transferred by F+ x F- cross?

Answer 13

• plasmid circularizes

- specific-site recombination (need insertion sequence)

Question 14

What type of DNA is transferred by Hfr x F- cross? what is the result of that cross?

Answer 14

• Chromosomal bacteria (bacterial genes)

- F- cell (no sex change), with New bacterial genes

Question 15

How is stabilized the plasmid transferred by Hfr x F- cross?

Answer 15

Homologous recombination

Question 16

How is call when a temperate phage is integrated into the bacterial DNA? How is it maintained inside the bacterial DNA?

Answer 16

Lysogenic conversion
Integrated by specific-site recombination
Remain repressed (prophage) by a repressor

Question 17

Principal characteristics of the generalized transduction

Answer 17

• Virulent virus or phage ▶️ just have lytic life cycle.
• Error in lytic phase ▶️ take some bacterial DNA.
• Any gene from bacterial DNA (all have the same chance).
• Transferred genes stabilized by homologous recombination.

Question 18

Principal characteristics of the specialized transduction.

Answer 18

• Lysogenic conversion ▶️ temperate phage repressed by repressor.
• Error during excision when induction occur (destroy the repressor).
• Only genes next to insertion sites can be picked up.
• Transferred genes stabilized by homologous recombination.

Question 19

Principal function that allow drug resistance mediated by plasmids

Answer 19

Enzymes that modify the drug

Question 20

Most common plasmid with B-lactamase genes

Answer 20

TEM-1

Question 21

Where come from the most common vancomycin resistant genes (vanA, vanB)?

Answer 21

From enterococcus transferred (in a transposons) to a multi drug resistant plasmid in staphylococcus aureus

Question 22

Which B-lactamase are include more microorganisms, those from gram (-) or gram (+)?

Answer 22

Gram (+) B-lactamase ▶️ little activity against cephalosporins, methicillin, oxacillin.
Gram (-) B-lactamase ▶️ act in periplasmic space, activity against penicillin and cephalosporins

Question 23

How can a multiple drug resistant plasmid be detected?

Answer 23

Identification of flanking sequences (direct and indirect repeats)

Question 24

Indication to order minimal bactericidal concentration study

Answer 24

Determine treating Immunocompromised patients