Microbial Genetics/Drug Resistance Flashcards
What is the structure of a bacterial chromosome and how is organized? What do the contain?
- large, covalently closed, circular DNA molecule
- organization into loops around proteinaceous center
- essential genes
Structure, size and location of a plasmid. Function.
- circular, small
- extra chromosomal or may integrate the bacterial DNA ▶️ episome
- nonessential genes for bacterial life: fertility, antibiotic resistance, exotoxins
Where is the Bacteriophage in the bacteria and its function?
- integrated in bacterial chromosome as prophage
- Lysogenic conversion ▶️ make bacteria more pathogenic
Requirements of homologous recombination
Homologous genes in bacterial chromosome Recombinase recA (enough), *recB, recC, recD (synthesized by recombination genes)
Requirements for site-specific recombination
Attachment, integration or insertion site (no homologous region)
Restriction Endonucleases and RE sites on the DNA
What is the objective of the homologous recombination? How is managed the new DNA information?
Exchange the new LINEAR DNA entering into the bacteria
Objective of site-specific recombination. How is managed the DNA information?
Addition or integration of the new DNA entering to the bacteria with chromosomal DNA
*fertility factor, temperate phage, transposons (generally CIRCULAR DNA)
How do you get new genetic combinations in bacteria?
Gene transfer ▶️ conjugation, transformation and transduction
What is needed to make transformation by a certain bacteria?
To be competent ▶️ can bind, envelope and import naked environmental DNA
What control the conjugation?
Fertility factors ▶️ plasmids or episomes
What do the Fertility factors content to control and realize its conjugation?
- Plasmid “fertility” genes: tra region (sex pili), genes to stabilize mating pairs and direct conjugal DNA transfer
- OriT region: begin transfer
- Insertion sequence: recombination
What type of DNA is transferred by F+ x F- cross? what is the result of that cross?
- Plasmid DNA (one strand of the double helix)
- a F+ cell without cromosomal DNA (no new bacterial genes)
How is stabilized the plasmid transferred by F+ x F- cross?
- plasmid circularizes
- specific-site recombination (need insertion sequence)
What type of DNA is transferred by Hfr x F- cross? what is the result of that cross?
- Chromosomal bacteria (bacterial genes)
- F- cell (no sex change), with New bacterial genes
How is stabilized the plasmid transferred by Hfr x F- cross?
Homologous recombination
How is call when a temperate phage is integrated into the bacterial DNA? How is it maintained inside the bacterial DNA?
Lysogenic conversion
Integrated by specific-site recombination
Remain repressed (prophage) by a repressor
Principal characteristics of the generalized transduction
- 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.
Principal characteristics of the specialized transduction.
- 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.
Principal function that allow drug resistance mediated by plasmids
Enzymes that modify the drug
Most common plasmid with B-lactamase genes
TEM-1
Where come from the most common vancomycin resistant genes (vanA, vanB)?
From enterococcus transferred (in a transposons) to a multi drug resistant plasmid in staphylococcus aureus
Which B-lactamase are include more microorganisms, those from gram (-) or gram (+)?
Gram (+) B-lactamase ▶️ little activity against cephalosporins, methicillin, oxacillin.
Gram (-) B-lactamase ▶️ act in periplasmic space, activity against penicillin and cephalosporins
How can a multiple drug resistant plasmid be detected?
Identification of flanking sequences (direct and indirect repeats)
Indication to order minimal bactericidal concentration study
Determine treating Immunocompromised patients
