Spatiotemporal microbial evolution on antibiotic landscapes

A group of scientists at Harvard Medical School and the Israel Institute of Technology in Haifa, Israel, studied the evolution of E. coli on an agar plate the size of a small dining table. Ciprofloxacin (or trimethoprim) at concentrations that ranged from zero to 1,000 times the concentration required to kill the test strain of E. coli had been incorporated into the agar plate. When the test strain of E. coli was inoculated onto the portion of the plate with zero ciprofloxacin, it multiplied and spread across that portion of the plate, then mutants with low level resistance to ciprofloxacin emerged and migrated across a strip of agar that contained low concentrations of ciprofloxacin. Over the course of 11 days mutant strains of E. coli evolved that could proliferate on agar that contained ciprofloxacin (or trimethoprim) at a concentration 1,000 times higher than that which would kill the inoculating strain.

An excellent video showing the evolution spread of the increasingly resistant mutant strains of E. coli is available at: www.youtube.com/watch?v=yybsSqcB7mE