IX. IDENTIFICATION OF MYCOPLASMAS
395
examination which proceeds through a series of biochemical tests and ends
with serological testing. As a prelude to the more detailed description of
these tests in Sections IV and V a brief outline of the general principles is
presented here.
A. Biochemical screening
As a first step, the sensitivity to digitonin (1.5%) is determined (Erne,
and Stipkovits, 1973). If the strain is resistant or only slightly sensitive,
i.e. if the zone of inhibition as determined by a disc method on solid
medium is less than 2 mm, the strain can with some assurance be classified
as belonging to the genus Acholeplasma. In cases of doubt where slight
sensitivity to digitonin is observed, a similar test for susceptibility to 5%
sodium-polyanethol-sulphonate (Freundt et al., 1973a) may be useful in
confirming the genus classification, since all acholeplasmas and also some
mycoplasmas are resistant to this compound. The genera Mycoplusma,
Ureaplasma and Spiroplasma are all sensitive to digitonin. Members of the
genus Ureaplasma are distinguished by their urease activity, whereas
classification of an organism as belonging to the genus Spiroplasma depends
primarily on morphological criteria.
Species differentiation within the genus Mycoplasma is initiated by four
biochemical tests : tests for catabolism of glucose and arginine, phosphatase
activity, and digestion of coagulated horse serum. The antisera to be used
for the subsequent serological testing are usually selected according to the
results of the first two tests which provide a reliable basis for a subdivision
of the Mycoplasma species into two major biochemically defined groups:
(1) the glucose-positive/arginine-negative, and (2) the arginine-positive/
glucose-negative species. So far, the two other possible combinations:
(3) glucose-positivelarginine-positive, and (4) glucose-negative/argininenegative organisms are each represented by only a few species. A further
subdivision of these four groups may be attempted on the basis of phosphatase activity but the results should be interpreted with some caution
because of the intra-species variability sometimes experienced with
respect to this property. The serum digestion test is included as a means
of distinguishing strains of M . mycoides and M . capricolum, the only
two species so far known to be capable of liquefying coagulated horse
serum. Here again, some strain variability is known to occur within M.
mycoides.
Biochemical characterisation of members of the genus Acholeplasma
may be carried out by testing for phosphatase and for the catabolism of
aesculin and arbutin. It must be emphasised, however, that our present
knowledge about the intraspecific variability of these properties is restricted.
395
examination which proceeds through a series of biochemical tests and ends
with serological testing. As a prelude to the more detailed description of
these tests in Sections IV and V a brief outline of the general principles is
presented here.
A. Biochemical screening
As a first step, the sensitivity to digitonin (1.5%) is determined (Erne,
and Stipkovits, 1973). If the strain is resistant or only slightly sensitive,
i.e. if the zone of inhibition as determined by a disc method on solid
medium is less than 2 mm, the strain can with some assurance be classified
as belonging to the genus Acholeplasma. In cases of doubt where slight
sensitivity to digitonin is observed, a similar test for susceptibility to 5%
sodium-polyanethol-sulphonate (Freundt et al., 1973a) may be useful in
confirming the genus classification, since all acholeplasmas and also some
mycoplasmas are resistant to this compound. The genera Mycoplusma,
Ureaplasma and Spiroplasma are all sensitive to digitonin. Members of the
genus Ureaplasma are distinguished by their urease activity, whereas
classification of an organism as belonging to the genus Spiroplasma depends
primarily on morphological criteria.
Species differentiation within the genus Mycoplasma is initiated by four
biochemical tests : tests for catabolism of glucose and arginine, phosphatase
activity, and digestion of coagulated horse serum. The antisera to be used
for the subsequent serological testing are usually selected according to the
results of the first two tests which provide a reliable basis for a subdivision
of the Mycoplasma species into two major biochemically defined groups:
(1) the glucose-positive/arginine-negative, and (2) the arginine-positive/
glucose-negative species. So far, the two other possible combinations:
(3) glucose-positivelarginine-positive, and (4) glucose-negative/argininenegative organisms are each represented by only a few species. A further
subdivision of these four groups may be attempted on the basis of phosphatase activity but the results should be interpreted with some caution
because of the intra-species variability sometimes experienced with
respect to this property. The serum digestion test is included as a means
of distinguishing strains of M . mycoides and M . capricolum, the only
two species so far known to be capable of liquefying coagulated horse
serum. Here again, some strain variability is known to occur within M.
mycoides.
Biochemical characterisation of members of the genus Acholeplasma
may be carried out by testing for phosphatase and for the catabolism of
aesculin and arbutin. It must be emphasised, however, that our present
knowledge about the intraspecific variability of these properties is restricted.