5. ANTIBIOSIS AND ANTIBIOTICS
257
Antibiotic is thus originally a word which defines sharply and adequately
a class of chemical substances produced by microorganisms.
Obviously, the choice of the word and the admission that it was
inspired by Vuillemin s antibiosis, implied that, initially and at first
sight at least, antibiotics were regarded, or could conceivably be regarded, as the chemical agents responsible for microbial antagonism.
Although later on their actual role in nature was much questioned (14),
it is now well known that some antibiotics are produced in the soil and
play a role in the evolution of the microflora (15).
However, Waksman's definition cannot be taken literally, and, from
the start, the notion of antibiotic was endowed with some unavoidable
vagueness. Common products of microbial metabolism, such as alcohols,
simple organic acids, and many other substances, are able, when in
sufficient concentration, to suppress the growth of, or kill, certain microorganisms. Should these common biological products be called antibiotics? To avoid the difficulty, two additional properties were tentatively
introduced into the definition of an antibiotic (16), namely, the capacity
to act at a low concentration and selectivity of action. Unfortunately,
these properties cannot be defined in a precise quantitative way and
their use introduces a subjective element of appreciation which rather
blurs the notion of antibiotic. It is therefore just as well to rely on
common sense to discard from the class of antibiotics the "common"
metabolic products, whatever this may mean, which have antimicrobial
activities.
But more serious difficulties were soon encountered when it became
obvious that substances having properties similar to those of the antibiotics, as defined by Waksman, were produced by macroscopic fungi,
higher plants, and even animals, especially when it was established that
identical antibiotics can be produced by widely different living beings,
and further when antibiotics, in the strictest sense, were produced by
chemical synthesis.
The meaning of antibiotic was therefore early stretched far beyond
Waksman s definition. The notion of microbiological origin was replaced
by the broader one of biological origin and the definition became:
chemical substances possessing antimicrobial activities that are produced by higher plants or animals as well as by microorganisms. Then,
taken literally, it includes among the antibiotics a number of agents,
for instance plant products such as many alkaloids, which are unlikely
to play any part in natural antibiosis. But this is a minor difficulty when
compared with the fact that the new definition also includes in the
class of antibiotics all the chemical armamentarium involved in the
257
Antibiotic is thus originally a word which defines sharply and adequately
a class of chemical substances produced by microorganisms.
Obviously, the choice of the word and the admission that it was
inspired by Vuillemin s antibiosis, implied that, initially and at first
sight at least, antibiotics were regarded, or could conceivably be regarded, as the chemical agents responsible for microbial antagonism.
Although later on their actual role in nature was much questioned (14),
it is now well known that some antibiotics are produced in the soil and
play a role in the evolution of the microflora (15).
However, Waksman's definition cannot be taken literally, and, from
the start, the notion of antibiotic was endowed with some unavoidable
vagueness. Common products of microbial metabolism, such as alcohols,
simple organic acids, and many other substances, are able, when in
sufficient concentration, to suppress the growth of, or kill, certain microorganisms. Should these common biological products be called antibiotics? To avoid the difficulty, two additional properties were tentatively
introduced into the definition of an antibiotic (16), namely, the capacity
to act at a low concentration and selectivity of action. Unfortunately,
these properties cannot be defined in a precise quantitative way and
their use introduces a subjective element of appreciation which rather
blurs the notion of antibiotic. It is therefore just as well to rely on
common sense to discard from the class of antibiotics the "common"
metabolic products, whatever this may mean, which have antimicrobial
activities.
But more serious difficulties were soon encountered when it became
obvious that substances having properties similar to those of the antibiotics, as defined by Waksman, were produced by macroscopic fungi,
higher plants, and even animals, especially when it was established that
identical antibiotics can be produced by widely different living beings,
and further when antibiotics, in the strictest sense, were produced by
chemical synthesis.
The meaning of antibiotic was therefore early stretched far beyond
Waksman s definition. The notion of microbiological origin was replaced
by the broader one of biological origin and the definition became:
chemical substances possessing antimicrobial activities that are produced by higher plants or animals as well as by microorganisms. Then,
taken literally, it includes among the antibiotics a number of agents,
for instance plant products such as many alkaloids, which are unlikely
to play any part in natural antibiosis. But this is a minor difficulty when
compared with the fact that the new definition also includes in the
class of antibiotics all the chemical armamentarium involved in the