MEGA-plate experiment

Bacteria reproduce asexually generating genetical identical progeny. In order to survive the harsh environment, bacteria require a genetic change that leads to a more adapted phenotype. Those genetic changes are made possible by mutation.

The scientists from Harvard Medical School and at Technion-Israel Institute of Technology have developed an experiment that models the evolution of bacteria toward antibiotic resistance. The experiment is called microbial evolution and growth arena (MEGA)–plate. The experiment involves:

A culture of non-resistant bacteria.
A giant dish (120 x 60cm) that contains sections of a growth medium with a gradual increase of antibiotic.
Lab environment that is suitable for 2-weeks incubation.

Big grey rectangle divided into five identical columns, numbered from 1 to 5. Increasing level of antibiotics is assigned to each column, starting from column number 1 on the left with 0 times antibiotic concentration, through 1 times, 10 times, 100 times, and 1000 times concentration for the fifth column on the right.

Figure 1. Layout of MEGA-plate

First, the bacteria are grown on the plate section with no antibiotic. After several hours, the bacteria colony fills all the section without antibiotic. Then the growth becomes slower before the bacteria colony is able to move to the next plate section with a 10x antibiotic concentration. The process repeats until the bacteria colony is able to reach the plate section with a 1000x antibiotic concentration. The whole experiment took approximately 2 weeks.

The experiments shows us that bacteria able to mutate and achieved resistance towards high-concentration-antibiotic in a relatively short time.