Answer:
Bacteria adapt over time to fit their environment. This process, however, is not intentional. Bacteria are constantly mutating; sometimes some mutations have better traits that help them survive longer. As they multiply, (with the mutation) more and more "resilient" bacteria survive longer and are able to multiply more until there are a lot of resilient bacteria. This process is what drives evolution but is also what causes problems such as cancer and antibiotic-resistant bacteria.