Most antibiotics are not created but discovered. They are often species of fungus or other microorganisms that happen to attack certain kinds of bacteria. Take any place on earth where you might find microorganisms, grow them in a culture and then test their effects until you find one with the desired properties (kills bacteria but not human cells) and then you might be able to develop a new drug from it. The problem is we're running out of places to scoop up microorganisms from and the newest drugs are being made from fungi found deep in the most inaccessible caves underground for which bacteria above ground has not developed a resistance to. It's an evolutionary arms race which we're ultimately destined to lose which is why we need to find better ways of killing bacteria.