1.1 Natural antibiotics

Most natural antibiotics were discovered before the 1970s, using systematic non-target-based screening of soil samples. Relatively few antibiotics in use today are completely natural. Of these, about 20% are produced by fungi and 80% by a group of Gram-positive, filamentous soil bacteria called Streptomyces (Lo Grasso et al., 2016).

Two types of fungi – the Penicilliums and the Cephalosporiums – have proved good sources of antibiotics. For example, Penicillium notatum (Figure 1) was the source of the original penicillin discovered by Alexander Fleming in 1928. Cephalosporium acremonium gave rise to the first-generation cephalosporins (Clegg, 2015) .

Figure 1 Penicillium notatum – the source of penicillin

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This figure shows a scanning electron micrograph of Penicillium notatum which appears as a pink tree-like structure on a dark background.

Figure 1 Penicillium notatum – the source of penicillin

Natural antibiotics isolated from Streptomyces bacteria (Figure 2) include streptomycin, tetracycline, vancomycin, erythromycin and chloramphenicol (de Lima Procopio et al., 2012).

Figure 2 Streptomyces griseus – the source of streptomycin (Scale bar, 1 micrometre).

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This figure shows a scanning electron micrograph of Streptomyces griseus which appear as blue ‘beads-on-a-string’ on a dark background.

Figure 2 Streptomyces griseus – the source of streptomycin (Scale bar, 1 micrometre).