LOs: 6-8 Flashcards
6 Horizontal Gene Transfer
Transfer of DNA from one bacterium to another which is not its offspring
6 Genetic Transformation
Transfer of naked DNA b/n cells
Natural Transformation occurs in bacteria such as Streptococcus, Haemophilus and Neisseria which produce a protein called the competence factor (acquired property of taking up DNA)
ss DNA is integrated into the recipient DNA by homologous recombination mediated by the RecA protein
Result: replacement of the recipient DNA by the donor DNA
Not widespread: only occurs b/n similar, but not identical, species
6 Genetic Transduction
DNA transfer mediated by a bacterial virus (bacteriophage)
A donor cell is infected by a bacterial virus (phage).
Phage replicates in the cell and degrades host DNA.
Phage particles are assembled and some of them contain small pieces of bacterial DNA.
Upon reinfection of a bacterial cell, the DNA from the original cell is integrated into the recipient chromosome by homologous recombination.
Not widespread: only occurs b/n similar, but not identical, species
6 Conjugation
DNA transfer involving direct cell to cell contact
Male cells possess extrachromosomal DNA elements termed conjugative plasmids that enable them to transfer copies of themselves to another bacterium.
Conjugative plasmids are found in both Gram-negative and Gram- positive bacteria.
Conjugation is the most common form of horizontal gene transfer in bacteria.
Widespread: can occur b/n very different types of cells
6 Transposition
The transfer of a segment of DNA from one site to another in the genome
6 Bacterial Plasmids
Ssmall extra chromosomal elements that have the ability to confer new genetic properties on the bacterial cell.
Usually circular, double-stranded DNA molecules.
Frequently contain drug resistance genes.
Main reason for the spread of antibiotic resistant bacteria in nature.
Carry genes that allow them to replicate independently of the bacterial chromosome.
Require host proteins and enzymes for replication.
6 Conjugative Plasmids
Initiate their own transfer from cell to cell
Contain tra genes that encode the sex pilus through which the DNA is transferred
Contain oriT which is nicked by a relaxase to initiate the transfer of a SS plasmid DNA
Usually contain insertion sequences & transposons
Can also promote the conjugative transfer of mobilizable plasmids containing oriT
Highly promiscuous
6 R-Plasmids (R-Factors)
Carry genes that make bacteria resistant to one or more antibiotics
Can transfer b/n different bacterial species
Contain tra genes (encoding the sex pilus), drug resistance, genes, a replication region, insertion sequences, & transposons
oriT: site where transfer of the plasmid is initiated during conjugation
6 Virulence Plasmid
Carry genes that encode toxins & other virulence factors
6 Predict the outcome of continued widespread use of medically-important antibiotics in animal feed
Farmers used to feed antibiotics to animals to protect them
Many antibiotics used are no longer effective in humans
Issue: antibiotic use in animal feed led to a spread of antibiotic-resistance genes
7 Prophylaxis
Perioperative
Endocarditis
Travel
Opportunistic
Other
use of antimicrobial agents to prevent infection
prevent surgical site infections (1 hour before incision)
prevent endocarditis
mefloquine: prevent malaria
TMP/SMX: taken by immunocompromised to prevent infections like Pneumocystis jiroveci (carinii)
- PCN: history of rheumatic fever
- levofloxacin: pts w/ ascites, prevent bacterial peritonitis
- antiretrovirals: after needlestick injury
- antibiotic: after exposure to meningococcal meningitis
7 Pre-emptive therapy
asymptomatic infection which is likely to become symptomatic
valganciclovir: transplant patient with evidence of
cytomegalovirus (CMV) reactivation by increased viral load
7 Empiric therapy
presumed infection but before the etiology of the infection is known
common infections: fever in
neutropenic patients, community-acquired pneumonia and ventilator- associated pneumonia
delaying antibiotic therapy can be detrimental in some but better in others where infeciton may resolve due to immune system
broad
7 Pathogen-directed therapy
organism is known, but antibiotic susceptibility is awaited
broader than when the susceptibility is known
7 Susceptibility-guided therapy
organism and the antibiotic susceptibility are both known
“streamlining: narrowest spectrum, most effective, least toxic, cheapest
