Genetic transfer Flashcards
Why bacteria develop resistance to antibiotics
Competition
Self-preservation
Competition
Soil microorganism live in a complex environment with limited nutrient resources
Competition is high
Many microbes produce antibodies to kill off competitors
Self-preservation
Antibiotic producing strains must be resistant to their own antibiotics
Resistance mechanism are widespread in nature
Natural environment are reservoirs of antibiotics resistance genes
Features of antibiotic resistance
Resistance…
- arises quickly
- spreads rapidly
- spreads to other bacteria
- persistence+ cumulative (easy to get, hard to lose)
Intrinsic resistance occurs at…
Bacterial species level
Kingdom/domain level
Acquired antibiotic resistance occurs…
previously sensitive cells following
Three main mechanism of genetic information exchange
Transformation
Transduction
Conjugation
Why does intrinsic resistance occur
Due to the lack of a target – e.g. bacteria are resistant to polyene antibiotics, such as Amphotericin B, because the antibiotic target (sterols) is not present in the bacterial cell membrane.
Due to a lack of permeability – e.g. the outer envelope of Gram-negative bacteria can impede access of antibiotics to their intracellular target.
Acquired resistance occurs following…
transfer of genetic information between microbial cells
Transformation
Free DNA (e.g. fragment of chromosomal DNA) released from one cell is taken up by another.
- bacterial strains not transformable - competent
- Competent = genetically transformed gene (requires specific proteins
- Naturally competent strains
- E.coli is not competent but can when treated with high calcium con + chilled for min
Transduction
DNA is transferred from a donor cell to a recipient cell via a virus called a bacteriophage.
- DNA taken up is converted to ssDNA, one strand of chromosome will contain new gene
- when cell divides each chromosomal strand is replicated meaning 50+ of the prgeny (population) will contain resistant gene
Conjugation
Transfer of a conjugative plasmid involving cell-to-cell contact.
- donor cell must contain conjugative plasmid
- Conjugative plasmid carry genes in tra-region = regulating conjugative process
- bacteria can transfer fragments of chromosomal DNA via conjugation
Generalised transduction
any DNA fragment from the host genome can be transferred.
Specialised transduction
DNA from a specific region of the host chromosome is integrated into the virus genome (e.g. genes encoding for toxins).
Resistance plasmids
Conjugative plasmids which carry resistance genes to antibiotics or to heavy metals, or virulence factors (toxins, proteases, adhesion molecules).
