First, Penicillin is ‘natural’, we just found a way to remake it in the laboratory, though most modern antibiotics are artificial.
But more importantly, with the newly emergent strains of antibiotic resistant bacteria, the existing class of antitbiotics might eventually become largely useless. And you might think, “Ah! The market will just make some more!” Alas, developing a new antibiotic seems to have a rapidly diminishing risk/reward and the rate of development of new antibiotics has been shrinking to zero. The trouble is that being lower lifeforms, bacteria evolve extremely rapidly, faster than the markets produce newer drugs. This might herald an entirely different mode of treatment, just like Penicillin heralded a massive shift in treatment of bacteria-induced diseases. There are in fact ‘natural’ alternatives like Bacteriophages (look them up).
>> bacteria evolve extremely rapidly, faster than the markets produce newer drugs <<
Yeah, but I submit that new drugs would be developed much faster if we didn’t have such a stupid regulatory regime at the FDA, and if we could have reasonable reforms of the tort laws.