Explanation: Bacteria can acquire resistance by getting a copy of a gene encoding an altered protein or an enzyme like beta lactamase from other bacteria, even from those of a different species. There are a number of ways to get a resistance gene:
1) During transformation - in this process, akin to bacterial sex, microbes can join together and transfer DNA to each other.
2) On a small, circular, extrachromosomal piece of DNA, called a plasmid - one plasmid can encode resistance to many different antibiotics.
3)Through a transposon - transposons are "jumping genes," small pieces of DNA that can hop from DNA molecule to DNA molecule. Once in a chromosome or plasmid, they can be integrated stably.
4)By scavenging DNA remnants from degraded, dead bacteria.
Unfortunately, if a bacterium gets a resistance gene stuck into its chromosomal DNA or picks one up in a free-floating plasmid, all of its progeny will inherit the gene and the resistance it confers. Why do resistance genes persist and spread throughout bacterial populations? It's basically just Darwin's idea of the survival of the fittest, reduced to a microscopic level -- bacteria with these genes survive and outgrow susceptible variants
