Pharmaceutically active secondary metabolites of microorganisms

Abstract

The antibiotics have been useful in our battles against infectious bacteria and fungi for over 50 years. However, many antibiotics are used commercially, or are potentially useful, in medicine for activities other than their antibiotic action. They are used as antitumor agents, immunosuppressive agents, hypocholesterolemic agents, enzyme inhibitors, antimigraine agents, and antiparasitic agents. A number of these products were first discovered as antibiotics which failed in their development as such, or as mycotoxins. In addition to the above alternative applications, new powerful antibiotics have been discovered and commercialized in recent years and others are in clinical testing at the moment. A few successful secondary metabolites appear to have no antibiotic activity. The recently increased development of resistance to older antibacterial and antifungal drugs is being met with the use or clinical testing of older, underutilized or previously nondeveloped narrow-spectrum antibacterial products as well as powerful semisynthetic antifungal agents. 55% were produced by filamentous bacteria (= actinomycetes) of the genus Streptomyces, 11% from other actinomycetes, 12% from nonfilamentous bacteria and 22% from filamentous fungi (Berdy 1995; Strohl 1997). New bioactive products from microbes continue to be discovered at an amazing pace: 200-300 per year in the late 1970s, increasing to 500 per year by 1997. Many companies have participated in the successful discovery and application of microbial secondary metabolites (Table 2).