Bacteria become resistant more quickly when antibiotics are used too often or are not used correctly (such as not taking a full course of antibiotics as prescribed by your doctor). Bacteria that are resistant to one antibiotic can sometimes be treated with other antibiotics.These other medicines may have to be given intravenously (through a vein) in a hospital. A few kinds of bacteria are resistant to all antibiotics and are now untreatable. Ear infections. 2  There are several types of ear infections. 3  Antibiotics are used for some (but not all) ear infections. 4  Sinus infections. 5  Antibiotics are often used to treat sinus infections. 6  However, a runny nose and yellow or green mucus do not necessarily mean you need an antibiotic.