The transforming principle was a puzzle about pneumonia types before it was a DNA story.
Once plasmids were visible as extra circles, hospitals could watch resistance tour the world as luggage.
Timeline
Heat-killed smooth pneumococci 'transform' live rough cells in mice.
Avery's group chemically shows the transforming substance is DNA.
Lederberg and Tatum demonstrate genetic exchange by contact in E. coli.
Zinder and Lederberg show phage can carry bacterial genes.
Joshua Lederberg popularizes 'plasmid' for extra-chromosomal elements.
Resistance plasmids become a daily hospital genetics story.
Cassette-capture systems explain stacked resistance genes.
A carbapenemase gene illustrates intercontinental plasmid travel in patients.
The timeline is discovery history, not a methods course.
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