Dissemination of Antibiotic resistance II: Mechanisms of Bacterial Gene Exchange

Question 1

Describe clinical relevance of the bacterial gene exchange

Answer 1

Can attain multiple antibiotic resistance by acquiring DNA from other bacteria

Gram+ steptococcus pneumoniae and gram- H. influenzae and N.gonorrhea change their appearance of clinically important surface antigens to evade the host immune system

Question 2

Describe DNA transformation by bacterial cells

Answer 2

Donor cells lysed and naked DNA released into the environment, DNA is taken up the recipient cells (being able to do so is called competence)

Cells synthesize special proteins necessary for competence, ie one on the cell membrane that can bind double-stranded DNA indiscriminately

DNA enters through membrane and can be degraded, circularized, or recombined into the chromosome

Question 3

Describe conjugation and list the essential components

Answer 3

Cell-cell contact (mating)
Donor cell contain double-stranded plasmid (R plasmid) which autonomously replicates
R plasmid: carries genes for sex pilus and conjugation bridge
DNA is transferred via transfer replication (rolling circle mechanism) where the transferred strand circularizes and replicates to form a double-stranded plasmid. Donor and recipient have a complete copy of the R plasmid

Question 4

Clinical relevance of conjugal plasmids

Answer 4

Important antibiotic resistance determinants are carried on R plasmids, and many carry more than one antibiotic resistance

R plasmids can mediate conjugation between one species but also between species relatives

E. coli -> enterobacteriaceae, shigella, salmonella, proteus, serratia, enterbacter

Question 5

Describe transduction

Answer 5

Form of gene transfer mediated by bacteriophage (obligate parasites)
Can be DNA or RNA
Infects a sensitive cell by adsorbing or binding on specific cell surface receptor and injecting its genome into the cell

Question 6

Compare/contrast virulent and temperate phages and their respective infections

Answer 6

Virulent (lytic): uses host to make proteins for capsids and replicated genomes are packaged within, host cell lyses and progeny escape into the environment

Temperate (lysogenic): Enters quiescent form inside the cell called prophage, host cell harbors the latent prophage and can pass it on to it decendents. The prophage can become lytic at a later date