All antibiotics are designed to reduce the bacteria causing the infection to a point where your own immune cells can then fight them off. It is always your immune system that gets rid of an infection, the antibiotics just help it get there before the infection gets out of control. However, people who are very ill, with diseases such as cancer, or AIDS, and the very old and very young, all have compromised immune systems (their own defences don’t work very well), so good antibiotics are essential for these people; without them they are likely to die.
Antibiotics have saved more lives since the early 1900’s than almost any other medication; you may have even been on antibiotics yourself, or it is likely that at some point you may be. It is essential that we prevent bacteria becoming resistant to antibiotics, because in a world without antibiotics, many, many millions of people would die of infections that we were able to cure when the antibiotic still worked.