The Evolution of Bacteria on a “Mega-Plate” Petri Dish (

The development of antibacterial resistance is a modern and terrifying example of evolution by natural selection. Antibacterial resistance essentially means that a microbe has developed resistance, or can now survive, when exposed to a substance that could originally kill the organism or prevent it from reproducing. As worldwide access to antibiotics has risen, so has the incidence and spread of resistant bacteria. This is a serious health threat because scientists and doctors cannot develop new drugs as quickly as the bacteria can evolve. (The average time for a new drug to be approved for use in the United States is 12 years!!) The World Health Organization estimated in 2014 that approximately 700,000 people worldwide die annually after being infected with drug-resistant microorganisms.

1. Watch the video below where researchers demonstrate the rapid evolution of antibacterial resistance in E. coli.

2. Using your knowledge of natural selection and evolution, explain what is happening here. Outline, from a biological perspective, exactly what is taking place! A thorough and carefully thought out response will touch on all of the elements and concepts that I have been emphasizing in class.

A thorough response will hit all of the following important points:

What is happening to the individual bacteria in this population over time? (all the way from the original bacteria that started the colony to the ones that are eventually able to survive when exposed to 1000x the level of antibiotic that would have killed their ancestors)
What is happening to the population of bacteria as a whole over time?
Why did the bacterial growth pause at the boundary of each section on the plate? What is happening during that time?
What created the selective pressure in this scenario?
What ultimately allowed this population to change over time?
Did the investigators include a control? If yes, what was it? If no, what would be an appropriate control for this experiment?
FOR FULL CREDIT: Student demonstrates a strong understanding and thought critically about the experiment. Post was free of syntax, spelling, and grammatical errors.



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