Mutation, HGT, and superbugs

Definitions in my own words:

• Mutation: a random change in a bacterium's DNA. Once in a while a mutation happens to make the cell able to survive an antibiotic.
• Horizontal gene transfer (HGT): when one bacterium passes a gene to another bacterium instead of to its offspring. Resistance genes can move this way, even between different species.

How one resistant cell shares its gene (conjugation): A resistant cell builds a bridge called a pilus to a neighbor, copies its resistance plasmid, and sends the copy across. Now both cells are resistant.

Why superbugs resist several drugs at once: Resistance genes often ride on the same plasmid. One transfer can hand over resistance to multiple antibiotics in a single step, so a cell can become multi-drug resistant without slowly earning each resistance on its own.

Colony-data scenario: On my plate, imagine one of my 14 colonies carried a resistance plasmid. If I added an antibiotic, that colony's descendants would survive and the others would die, so over time the resistant colony would take over the whole plate.

Linking sentence: Careful culturing lets us see resistant strains, resistance spreads through mutation and HGT, and that is exactly why stewardship (using antibiotics sparingly and correctly) matters.