The serendipitous discovery and subsequent clinical success of penicillin prompted a large-scale search for other environmental microorganisms that might produce anti-infective natural products.  Soil and water samples were collected from all over the world, leading to the discovery of streptomycin (derived from Streptomyces griseus), and the realization that bacteria, not just fungi, represent an important source of pharmacologically active natural products. This, in turn, led to the development of an impressive arsenal of antibacterial and antifungal agents including amphotericin B, chloramphenicol, daptomycin and tetracycline (from Streptomyces spp.), the polymyxins (from Paenibacillus polymyxa), and the rifamycins (from Amycolatopsis rifamycinica). Antiparasitic and antiviral drugs have similarly been derived from bacterial metabolites.
Although most of the drugs derived from bacteria are employed as anti-infectives, some have found use in other fields of medicine.  Botulinum toxin (from Clostridium botulinum) and bleomycin (from Streptomyces verticillus) are two examples.  Botulinum, the neurotoxin responsible for botulism, can be injected into specific muscles (such as those controlling the eyelid) to prevent muscle spasm. Also, the glycopeptide bleomycin is used for the treatment of several cancers including Hodgkin's lymphoma, head and neck cancer, and testicular cancer. Newer trends in the field include the metabolic profiling and isolation of natural products from novel bacterial species present in underexplored environments.  Examples include symbionts or endophytes from tropical environments, subterranean bacteria found deep underground via mining/drilling, and marine bacteria.