IV. INVESTIGATION OF C. DIPHTHERIAE
69
toxic injury. For a thorough discussion of the matter, McLeod’s work
(1943) may be consulted.
Some strains display various characters which make it difficult to place
them in any one type; so-called minimus strains (Frobisher et al., 1945)
appear to be identical with intermedius (Johnstone and McLeod, 1949;
Freeman and Minzel, 1950).
Other atypical strains were cited by different authors, among which the
most important seem to be the atypical gravis corresponding to type IV
Wright and Christison (McLeod, 1943; Saragea et al., 1962) and variants
with “dwarf” colonies described by Maximescu (pers. camm.).
(b) Growth characteristics: media used. The following media are used for
routine microbiological diagnosis :
A liquid enrichment medium ECST (egg yolk, cystine, serum, tellurite)
(Calalb et al., 1961).
Tinsdale as a selective solid medium (Meitert and Saragea, 1967).
Cystine-tellurite-blood agar (CTBA), a medium used for differentiating
Blood agar (BA).
Loeffler slants for stock culture.
Plain or glucose broth.
the three biotypes : gravis, mitis, intermedius.
(c) Cultural aspects. In the enrichment medium a positive or suspect swab
develops black points attached to the cotton of the swab, within 10-14 h.
However, this cannot account for more than a suspicion of positivity.
On Tinsdale plates (Tinsdale, 1947; Meitert and Saragea, 1967), C.
diphtheriae develops in most cases after 24 h incubation, small circular
greyish black colonies, surrounded by a specific well-delineated brown
halo, representing the most characteristic feature on which the high
specificity of this medium is based (Fig. 2).
In a few cases, colonies develop only after 48 h incubation period during
which the brown halo becomes intensely brown. The occurrence of brown
haloed colonies is specific only for C. diphtheriae and C. ulcerans, both
high cystinase producers. Even one colony on the plate can be picked out.
None of the diphtheroids and/or of the variants of this group presents this
feature. The brown halo results from the reaction between potassium tellurite
and hydrogen sulphide (HzS) produced by cystinase, owing to the L-cystine
contained in the medium, This reaction is represented by a local tellurite
sulphur precipitate. The sodium thiosulphate provides a good reducing
agent. Welsch and Thibaut (1948), analysing the phenomenon of the
specific halo described by Tinsdale (1947), demonstrated that it represents
one of the two main biochemical properties of C. diphtheriae: cystinase
and the capacity to acidify the medium. The association of these two
69
toxic injury. For a thorough discussion of the matter, McLeod’s work
(1943) may be consulted.
Some strains display various characters which make it difficult to place
them in any one type; so-called minimus strains (Frobisher et al., 1945)
appear to be identical with intermedius (Johnstone and McLeod, 1949;
Freeman and Minzel, 1950).
Other atypical strains were cited by different authors, among which the
most important seem to be the atypical gravis corresponding to type IV
Wright and Christison (McLeod, 1943; Saragea et al., 1962) and variants
with “dwarf” colonies described by Maximescu (pers. camm.).
(b) Growth characteristics: media used. The following media are used for
routine microbiological diagnosis :
A liquid enrichment medium ECST (egg yolk, cystine, serum, tellurite)
(Calalb et al., 1961).
Tinsdale as a selective solid medium (Meitert and Saragea, 1967).
Cystine-tellurite-blood agar (CTBA), a medium used for differentiating
Blood agar (BA).
Loeffler slants for stock culture.
Plain or glucose broth.
the three biotypes : gravis, mitis, intermedius.
(c) Cultural aspects. In the enrichment medium a positive or suspect swab
develops black points attached to the cotton of the swab, within 10-14 h.
However, this cannot account for more than a suspicion of positivity.
On Tinsdale plates (Tinsdale, 1947; Meitert and Saragea, 1967), C.
diphtheriae develops in most cases after 24 h incubation, small circular
greyish black colonies, surrounded by a specific well-delineated brown
halo, representing the most characteristic feature on which the high
specificity of this medium is based (Fig. 2).
In a few cases, colonies develop only after 48 h incubation period during
which the brown halo becomes intensely brown. The occurrence of brown
haloed colonies is specific only for C. diphtheriae and C. ulcerans, both
high cystinase producers. Even one colony on the plate can be picked out.
None of the diphtheroids and/or of the variants of this group presents this
feature. The brown halo results from the reaction between potassium tellurite
and hydrogen sulphide (HzS) produced by cystinase, owing to the L-cystine
contained in the medium, This reaction is represented by a local tellurite
sulphur precipitate. The sodium thiosulphate provides a good reducing
agent. Welsch and Thibaut (1948), analysing the phenomenon of the
specific halo described by Tinsdale (1947), demonstrated that it represents
one of the two main biochemical properties of C. diphtheriae: cystinase
and the capacity to acidify the medium. The association of these two