Alex is a student with Strep throat (caused by a strain of b…

Alex is a student with Strep throat (caused by a strain of bacterium) who is given a prescription for an antibiotic and is told to take the drug for two weeks. After a week, he feels better and stops taking the drug. Two months later, Alex again shows symptoms of Strep throat and decides to finish the leftover antibiotic rather than going to the doctor again. Two months after that, he develops Strep throat for a third time and returns to the doctor. This time, the antibiotic does not work. The doctor runs a test and discovers that the bacterial strain Alex is carrying is antibiotic resistant. What most likely happened?