Lenski’s strain used in the experiments started with a single cell. Here’s the technique microbiologists use to start colonies from a single cell.
Antibiotic resistance is not “evolution” but a “devolution” also. How so, you ask? Because despite all fears, it never spreads outside of the specific environment. It goes away by itself once favorable human intervention is removed.
That turns out to not be the case in many instances. It had been proposed by some that antibiotic resistant bacteria would tend to disappear from the local population if the antibiotic was removed from use for a period of time. However, when bacteria were surveyed after 5, 10 or more years, researchers found that resistance persisted in the populations. The key factor seemed to be the development of secondary, mutations that suppressed the negative effects of the initial resistance mutations. These further mutations allowed the bacteria to retain the resistance phenotype and compete the the ‘wild type’ non-resistant strains even when the antibiotic was not present. Here are three journal articles that people should be able to publically access (1,2,3). There are several conditions that can lead to this outcome. The emergence of secondary suppressor mutations could also be reproduced in the lab. Interestingly, in Lenski’s experiments, this sort of mutation/suppression change was found to continuously progress through the generation of cultures.