Dissemination of Antibiotic Resistance I: Genomes

Question 1

Compare/contrast eukaryotic and bacterial genomes

Answer 1

Bacterial genome one haploid chromosomes, double-stranded DNA (circular or linear)
No nuclear membrane
Like eukaryotes, histone-like proteins pack nucleoid
Average bacterial genome is about 4000 genes

Question 2

Compare/contrast structure and function of the bacterial chromosome, plasmid genome, and bacteriophage genome

Bacterial Chromosome

Answer 2

Bacterial chromosome: haploid, double-stranded DNA, circular or linear

Question 3

Compare/contrast structure and function of the bacterial chromosome, plasmid genome, and bacteriophage genome

Plasmid Genome

Answer 3

Plasmid (episome) genome: double-stranded DNA, autonomous, self-replicating, extrachromosomal, circular or linear, found in gram + and - bacteria, encode virulence factors/antibiotic resistance

Conjugative plasmids (F and R plasmids): autonomously transfer themselves from hosts and past antibiotic resistance to other species

Non-conjugative plasmids: cannot transfer themselves, though can be transferred by conjugal plasmid

Question 4

Compare/contrast structure and function of the bacterial chromosome, plasmid genome, and bacteriophage genome

Bacteriophage Genome

Answer 4

RNA or DNA, single stranded or double stranded, linear or circular. Carry genes that encode virulence factors (ie Diptheria B-toxin or cholera toxin)

Lytic: viral genome replicates and causes host cell to lyse, permitting progeny viruses to release into the environment

Lysogenic: lytic genes repressed, virus genome (prophage) becomes latent. Can circularize and be autonomous or become part of host chromosome

Question 5

Compare/contrast transposable elements

Answer 5

Genetic units the mediate their own transfer from one location to another (either same genome or another genome)
Major carriers of antibiotic resistance genes
TRANSPOSONS DO NOT TRANSFER DNA FROM ONE CELL TO ANOTHER (need genes for conjugal machinery)
Insertion sequence: carries genes for its own transposition (including a recombinanse) and flanked by recognition sequences
Transposon: Hybrid, central core bounded by TWO IS elements, can encode for resistance to antimicrobial agents

Question 6

Compare/contrast transposable elements

Transposable prophage

Answer 6

2 IS element flank a bacteriophage, permits lysogenic infection of bacterial host

Question 7

Compare/contrast transposable elements

Conjugal transposon

Answer 7

2 IS elements flank genes that encode antibiotic resistance and conjugal machinery
These can jump from locations within a cell as well as transfer to other cells and different species

Question 8

Describe why R plasmids represent the major reason for the proliferation of multiple antibiotic resistance

Answer 8

Conjugal plasmid that carries antibiotic genes, can often carry several resistance genes. Resistant to multiple antibiotics

Evolve quickly and acquire new resistances via IS elements/acquiring new transposons

Can mediate their own transfer from one cell to another through conjugation

Non-pathogenic bacteria can carry R plasmids