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Bacteria have been around for 3.5 billion years longer than we have.
They’ve gotten good at genetic engineering and they can do it
with a generation time of 20 minutes under optimum circumstances..
Bacteria can alter their genetic material in many more ways than
higher animals. Unlike higher
animals, bacteria posses both chromosomal and plasmid DNA.
Resistance can be acquired by:
Chromosomal Mutation with vertical transmission to progeny
Horizontal Transfer of Resistance Genes by plasmids, integrons,
bacteriophages and scavenging into either plasmid or chromosomal
DNA.
Resistance genes often travel in cassettes on integrons or in
clusters on plasmids, so selection driven by the presence of a
single antibiotic can simultaneously select for resistance to
multiple antibiotic classes.
Horizontal gene transfer occurs not just intra-species, but
inter-species as well.
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