IX. IDENTIFICATION OF MYCOI‘LASMAS
383
the same grouping as do these tests, but it is less specific if it gives a
broader grouping or shows more cross-reactivity between species established by these tests.
The term “sensitivity” is in fact even more ill-defined than “specificity”
and is often used in differing senses by different authors. I n the following
Sections a test is described as sensitive when a positive reaction can be
obtained with a small amount of antibody.
2. Serology as a basis for species classijication
(a) Growth inhibition. The growth inhibition (GI) test was introduced by
Nicol and Edward (1953) who observed that antiserum incorporated in
solid agar medium inhibited the growth of colonies of homologous and
closely related strains. Inhibition of growth by specific antiserum may also
occur in liquid medium and can be measured either directly, by turbidimetry or by subculturing on to solid medium, or indirectly, by the
metabolism inhibition test (see below). Direct methods of demonstrating
growth inhibition in liquid medium have gained no common usage and the
term GI test now refers only to growth inhibition carried out on solid
medium.
Although the nature of the growth inhibiting effect of specific antibody
is not fully understood two mechanisms may be operating, a blocking of the
transport systems of the cell membrane, possibly because of the lack of a
true cell wall (Edward and Fitzgerald, 1954), and a complement dependent
lysis of the mycoplasma cell. Although growth inhibition on solid medium
is generally believed to be independent of heat-labile accessory factors,
some recent reports (Roberts, 1971; Roberts and Pijoan, 1971) suggest that
such factors may be involved. It should also be remembered that some
complement is usually present in the growth medium used for the test,
being derived from unheated horse serum and/or from the antiserum if
this is used in the non-inactivated state. Further studies, including,
inter alia, electron microscopic visualisation of the interaction between
antibody and specific components of the cell membrane, are needed to
elucidate the theoretical basis of the growth inhibition phenomenon.
I n practical terms, the GI test is based on the fact that the development
of colonies is inhibited either to the extent that they do not develop at all
or that their number and/or size are significantly reduced. The original
version of the test as described by Edward and his colleagues was soon
replaced by techniques requiring smaller amounts of antiserum, viz. the
disc-, agar well- and serum-drop methods. The principles of these
modifications of the G I test will be described in Section V. B.
That the GI test shows, overall, a satisfactory degree of specificity is
attested by the experience of its use over many years. On the other hand,
383
the same grouping as do these tests, but it is less specific if it gives a
broader grouping or shows more cross-reactivity between species established by these tests.
The term “sensitivity” is in fact even more ill-defined than “specificity”
and is often used in differing senses by different authors. I n the following
Sections a test is described as sensitive when a positive reaction can be
obtained with a small amount of antibody.
2. Serology as a basis for species classijication
(a) Growth inhibition. The growth inhibition (GI) test was introduced by
Nicol and Edward (1953) who observed that antiserum incorporated in
solid agar medium inhibited the growth of colonies of homologous and
closely related strains. Inhibition of growth by specific antiserum may also
occur in liquid medium and can be measured either directly, by turbidimetry or by subculturing on to solid medium, or indirectly, by the
metabolism inhibition test (see below). Direct methods of demonstrating
growth inhibition in liquid medium have gained no common usage and the
term GI test now refers only to growth inhibition carried out on solid
medium.
Although the nature of the growth inhibiting effect of specific antibody
is not fully understood two mechanisms may be operating, a blocking of the
transport systems of the cell membrane, possibly because of the lack of a
true cell wall (Edward and Fitzgerald, 1954), and a complement dependent
lysis of the mycoplasma cell. Although growth inhibition on solid medium
is generally believed to be independent of heat-labile accessory factors,
some recent reports (Roberts, 1971; Roberts and Pijoan, 1971) suggest that
such factors may be involved. It should also be remembered that some
complement is usually present in the growth medium used for the test,
being derived from unheated horse serum and/or from the antiserum if
this is used in the non-inactivated state. Further studies, including,
inter alia, electron microscopic visualisation of the interaction between
antibody and specific components of the cell membrane, are needed to
elucidate the theoretical basis of the growth inhibition phenomenon.
I n practical terms, the GI test is based on the fact that the development
of colonies is inhibited either to the extent that they do not develop at all
or that their number and/or size are significantly reduced. The original
version of the test as described by Edward and his colleagues was soon
replaced by techniques requiring smaller amounts of antiserum, viz. the
disc-, agar well- and serum-drop methods. The principles of these
modifications of the G I test will be described in Section V. B.
That the GI test shows, overall, a satisfactory degree of specificity is
attested by the experience of its use over many years. On the other hand,