L 18 and 19 antibiotic resistance Flashcards
3 was genetic information can be shared within a species
transformation
conjugation
transduction
exogenote
the DNA that was introduced from a donor cell
endogenote
the cell’s own original chromosome
transformation
the release of naked DNA into the environment by the lysis of the donor cells. The recipient cells uptake the DNA. Detergents and nucleases can interfere with transformation. Uptake is regulated/active process
competence
the ability to take up DNA from the environment. Encoded on the chromosomal genes of many species of bacteria. The genes become active under certain environmental conditions and transformation occurs readily
process of transformation in the gram+ bacterium Streptococcus pneumoiae
- donor cells release naked DNA (by death, lysis, or trauma) Donor enzymes chop the released DNA into smaller pieces. Naked DNA is highly susceptible to environmental factors
- pneumococcal cells secrete a protein competence factor that induces cells to synthesize special proteins needed for competence
- protein on the cell surface binds to double stranded DNA indiscriminately. One strand is degraded as it passes into the membrane
- the remain strain undergoes either: Degradation, circularization, or recomination
circularization
if the exogenote can replicate it will be inherited as a plasmid
Conjugation
aka mating bc it requires cell to cell contact. The donor cells contains a plasmid with the genes required for conjugation. The donor plasmid is called the conjugal plasmid.
R plasmids
conjugal plasmids containing genes for antibiotic resistance. Many carry more than one antibiotic resistance gene. can replicate itself. evolve quickly.
Process of conjugation by gram- E. coli
- genes on the R plasmid encode for a sex pilus, which captures the recipient cell and then is retracted to form a mating pair.
- conjugation bridge forms between the 2 cells and DNA is passed via transfer replication
- cells detach
transfer replication
replication initiates at the origin of transfer (oriT) and proceeds by the rolling circle mechanism. First one strand breaks and is pulled away from its complement through the conjugation bridge. The strands (one in each cell) then replicate to reform double stranded R plasmids
transduction
mediated by bacteriophages. The phage contains a protein capsid with genomic nucleic acid inside (RNA or DNA). some bacteria are avirulent unless infected by a phage with genetic material coding for a toxin such as Vibrio cholerae or Corynebacteria diphtheria
phage infections
a phage infects a cell by first aDsorbing or binding to a specific receptor on the cells surface and then injecting its genome into the interior of the cell
2 types of phages
- lytic
2. temperate
lytic phages
virulent. Cause lysis of the host cell. the phage genome replicates, proteins are synthesized and assembled into capsids, the replicated genomes are packaged within those capsids, the host cell lyses and the progeny escape into the environment to continue the process
Temperate phage
amy initiate a lytic growth process or enter a quiescent form called a prophage. The host continues to live with a latent prophage that it passes on to its dependents. AKA lysogen
the chromosome may either circularize as an autonomously replicating plasmid or by physically integrating into the host chromosome.
transduction occurs in
gram - and gram + bacteria (both kinds of transduction) but is usually limited to their own species.
clinical conditions associated with lysogenized bacteriophage
C. diphtheria B-phage and V. cholerae CTX
what characteristics of R plasmid concern the medical community
- most carry multiple genes for antibiotic resistance
- are capable of spreading between species- rapid dissemination of resistant conjugal plasmids
- mediate their own transfer through conjugation
- nonpathogenic bacteria carry R plasmids creating a reservoir for neighboring pathogenic bacteria- if a pathogen picks up a R-plasmid with multiple resistances then it becomes very difficult to treat
viron
a protein capsid enclosing a genomic nucleic acid
plasmid geneome
always double stranded DNA autonomous, self-replicating extra-chromosomal circular or linear varies in size bacteria can have more than one
usually code for virulence factors i.e. pili or toxins and proteins that confer antibiotic resistance
conjugative plasmids
usually F or R plasmids
can autonomously transfer themselves from one host to another, between individuals of the same species or in other species
non-conjugative plasmids
cannot transfer themselves, however they can be transferred by a conjugative plasmid. used for genetic engineering
bacteriophage genome
RNA or DNA
single or double stranded
linear or circular
can encode genes for virulence factors such as toxins (cholera or diptheria B- toxin)
transposable elements
genetic units that mediate their own transfer from one location in a genome to anther location within the same genome or from one genome to another.
Do not transfer DNA from one cell to another by themselves
frequently carry antibiotic resistance
Insertion sequence (IS) element
a segment of DNA about 1000 bp that only carries genes for its own transposition. These genes include: site-specific recombinase and two distinct nucleotide recognition sequences located at each terminus in inverted order.
can mediate their own transfer from one genome to another
if an IS element transposes into a gene its insertion will interrupt that gene and eliminate its function
transposition
occurs infrequently
involves recognition by the recombinase of the terminal inverted repeats and a target area into which a new copy of the IS element will be inserted. So types of IS elements leave the original copy behind while others remove the original copy
transposons
central core of genes bounded by two IS elements. Bc they contain two IS elements they carry the genes necessary for transposition. The core genes can encode for a variety of functions including resistance to antimicrobrial agents
transposable prophage
2 IS elements flank a bacteriophage. Therefore the phage genes permit lysogenic infection of a host, after infection the phage can integrate virtually anywhere in a chromosome and can then transpose itself to new locations
conjugan transposon
2 IS elements flank genes that encode antibiotic resistance and conjugal machinery
transposon can jump from location to location but can also mediate their own transfer to other cells (same or different species) Cannot replicate itself- relies on the host for replication
clinical relevance of transformation
Streptococcus pneumoniae, Haemophilus influenzae
& Neisseria gonorrhea use transformation to alter appearance of clinically important surface antigens
permits evasion of host immune system*
4 types of transposable elments
i) insertion sequence (IS) elements ; ii) transposons; transposable prophages; and iv) conjugal transposon.
