Flashcards in L3: Bacterial Genetics Deck (82)
What makes mobile genetic elements and gene transfer important to medicine? 3
1. Antibiotic resistance genes that encode drug modifying enzymes, efflux systems, alternate antibiotic targets, or metabolic enzymes are located on MGE's
2. Virulence factors are on MGE's
3. Gene transfer occurs between all bacterial species
What is a virulence factor?
genes that contribute to the ability of bacterial species to cause disease
How is gene transfer in bacteria described?
What allows for the emergence of pathogens not previously recognized and re-emergence of pathogens once thought vanquished?
transfer of antibiotic resistance genes and virulence factors
What is a core genome?
genes common to all individuals of a species
What is a pan genome?
genes sporadically present in a species but may be shared with other species
What is transformation?
A form of gene transfer involving programmed uptake of naked DNA from the environment
What does transformation require?
host homologous recombination system
What does transformation mainly transfer?
only gene fragments
What is transduction?
A form of gene transfer mediated by bacterial viruses (bacteriophage)
(Genes hitchhike on phage)
Is transduction generalized or specialized?
What is conjugation?
A form of gene transfer requiring direct cell-to-cell contact and exchange of intact genetic elements
Which of the three is the broadest host range form of gene transfer?
Does conjugation require recombination?
What is a bacteriophage?
Bacterial viruses that depend on a host cell for replication then exit the cell to infect other host cells
What is a plasmid?
Self-replicating genetic elements maintained separately from the chromosome that cannot exist independently from a host cell.
What is a transposon?
Non-replicating genetic elements capable of “hopping” or transposing from one position on the genome to another.
What is a genomic island?
Clusters of related genes variably present in strains of the same species and associated with bacteriophage-like genes and properties
What are ICE elements?
mobile genetic elements that combine features of bacteriophage, plasmids, and transposons and may include genomic islands
What are integrons?
specialized antibiotic resistance cassette accumulation system
How is it possible to detect penicillin resistant S. pneumoniae, especially high level resistance?
step-wise selection at progressively higher penicillin dosages.
Comparison of the PBP gene sequences from sensitive and resistant strains of bacteria reveal what?
What are these known as?
resistant genes contain blocks of sequence similar to oral Streptococci superimposed on a framework of S. pneumoniae sequence
S. pneumoniae is also capable of natural competence, what does this mean?
Ability to take up naked DNA from the environment
Steps of competence? (4)
1. Binding of dsDNA
2. Uptake of ssDNA
3. Recombination into chromosome
4. Gene replacement
Naturally competent bacteria are always able to do what two things?
In response to what?
1. Undergo transformation
2. Undergo a developmental program
Response to stress to form sub-population of competent cells
What is artificial competence?
Exposure of cells to various chemical treatments in a lab
Besides expressing genes required for DNA uptake, what else can competent bacteria do? (3)
1. Secrete chemicals that induce lysis of non-competent neighbors
2. Undergo periodic spontaneous lytic cycles
3. Secrete DNA through pores
What are some of the medically important competent bacteria? 4
Neisseria gonorrhoeae, Neisseria meningitides, Haemophilus influenzae, Helicobacteri pylori.
What are the advantages of transformation? (2)
1. Any DNA can be acquired using it
2. If the DNA isn't useful, you can break it down for good