M8: Bacterial Genetics & Antimicrobial Resistance Flashcards
Horizontal Gene Transfer (HGT) in Bacteria:
Definition
Three main mechanisms of HGT
Different types of bacteria are resistant to a number of antibiotics because they contain _
These as well as other _ can be transferred between bacteria
the transfer of DNA from one bacterium to another which is not its offspring
transformation, transduction, and conjugation
antibiotic resistance genes
bacterial genes
Genetic Transformation:
Definition
Natural Transformation occurs in bacteria such as _, _, and _ which produce a protein called the _
_ enters the recipient cell & is integrated into the recipient DNA by _ mediated by the _ protein
This results in _
the process by which a recipient cell takes up naked DNA released by a donor cell
Streptococcus, Haemophilus and Neisseria
competence factor
a single strand (ss) of DNA
homologous recombination
RecA
the replacement of the recipient DNA by the donor DNA
Transduction:
Gene transfer from a donor cell to a recipient cell by a _
A donor cell is infected by a _. This _ in the cell and _ host DNA. These particles are assembled and some of them contain small pieces of _.
Upon reinfection of a bacterial cell, the DNA from the original cell is _ into the recipient chromosome by _
Any _ present in the donor cell can also be transferred to the recipient cell
bacterial virus (bacteriophage)
bacterial virus (phage)
replicates
degrades
bacterial DNA
integrated
homologous recombination
plasmid DNA
Conjugation:
Gene transfer between a donor and a recipient cell through _
Male cells differ from female cells by possessing _ elements termed _
Such plasmids contain genes that enable them to _
_ plasmids are found in both Gram-negative and Gram-positive bacteria, and _ is the most common form of horizontal gene transfer in bacteria
direct physical contact
extrachromosomal DNA
conjugative plasmids
transfer copies of themselves to another bacterium
Conjugative
conjugation
Bacterial Plasmids:
Plasmids are _ elements that exist in bacterial cells and have the ability to confer _ on the bacterial cell
They are usually (circular / linear), (single / double)-stranded DNA molecules, although (circular / linear) plasmids are also found in nature
Plasmids frequently contain _ genes and are the main reason for the spread of _ bacteria in nature
Plasmids are very (stable / unstable) and (rarely / often) lost from bacterial cells
All plasmids carry genes that allow them to _ independently of the bacterial chromosome
Plasmids also require _ and _ for replication
small extra chromosomal
new genetic properties
circular
doubled
linear
drug resistance
antibiotic resistant
stable
rarely
replicate
host proteins
enzymes
Replication of Bacterial Plasmids:
A plasmid replicon consists of: (3)
origin
rep gene
copy control gene (cop)
Replication of Bacterial Plasmids:
A plasmid replicon consists of:
origin - the site of _ of replication
rep gene - encodes an _ protein that is required for plasmid replication
copy control gene (cop) - involved in controlling the _ and _ of a plasmid
initiation
initiator
replication and copy number
Replication of Bacterial Plasmids:
Copy number - The number of _ per _ in a cell
The copy number for a given plasmid is (fixed / variable)
plasmid molecules
chromosome
fixed
Replication of Bacterial Plasmids:
Large plasmids, usually (conjugative / non-conjugative), have a (high / low) copy number (# per chromosome)
Small plasmids, usually (conjugative / non-conjugative), have (higher / lower) copy numbers (# per chromosome)
conjugative
low
1-2
non-conjugative
higher
more than 10
Replication of Bacterial Plasmids:
Several different plasmids can be present in the same host cell and these _ plasmids are maintained and replicated _ of each other
_ plasmids are unable to coexist stably in descendants of the same host cell
compatible
independently
Incompatible
Conjugative plasmids:
Many plasmids such as the _ plasmids (termed _ or _) initiate their own transfer by cell to cell contact
Many _ plasmids can also be mobilized by conjugative plasmids present in the same cell
R plasmids usually contain several _ genes, have a broad _, and can transfer between different _
They are found in almost all major _ and can confer resistance to almost all the _
resistance
R plasmids or R factors
non-conjugative
antibiotic resistance
host range
bacterial species
human pathogens
antibiotics
R-Plasmids (R-Factors):
R plasmids contain _ genes (encoding the sex pilus through which DNA is transferred from a donor to a recipient cell), _ genes that are usually clustered, and the _ region
_ represents the site where the transfer of the R plasmid during conjugation is initiated
This is nicked by a _ during the initiation of DNA transfer
During conjugation, a (single / double) strand of DNA is transferred to the recipient cell starting from its (3’ / 5’) end
DNA replication in both the donor and recipient cells regenerates the (single / double)-stranded plasmid DNA
R factors also contain _ sequences and _
tra
drug resistance
replication
oriT
nickase
single
5’
double
insertion
transposons
Virulence Plasmids:
Carry genes that encode _ and other _
Examples: Plasmid pXO1 of _ encodes the anthrax toxin proteins while plasmid pXO2 contains genes required for _
Plasmids also contain the tetanus toxin gene in _, and invasion genes in _
toxins
virulence factors
Bacillus anthracis
capsule biosynthesis
Clostridium tetani
Yersinia
Origin of Antibiotic Resistance Genes and Evolution of R Plasmids:
Many _ producing bacteria such as _ are the source of the antibiotic resistance genes found in other organisms
However, many “_” genes may have evolved to encode proteins and enzymes involved in drug resistance
There is a substantial pool of antibiotic resistance genes in _ and such genes (can / cannot) be transferred between different bacteria
Complex R plasmids can evolve from the insertion of _ elements and “_” (carrying antibiotic resistance genes) into plasmids
_ are mobile DNA elements encoding an _ and may carry additional genes such as those encoding antibiotic resistance
antibiotic
Streptomyces
housekeeping
nature
can
transposable
integrons
Integrons
integrase
Transposable Elements:
Definition:
A transposon (Tn) is a genetic element (a specific DNA segment) that can _
Tns generally carry one or more genes encoding _, _, etc. to the host cell
Tns are normal constituents of _ and _
Transposons (occur / do not occur) independently in a cell, and are (always / never) found as part of a genome
Insertion Sequences and transposons contain _ at their ends
repeatedly insert at many different sites in a genome
drug-resistance, toxin production
bacterial chromosomes and plasmids
do not occur
always
inverted repeats (IRs)
