68
A. SARAGEA ET AL.
(e) The reduction of tellurium salts is a characteristic feature of C . diphtheriae
and to a lesser extent of other members of this group. The observations of
Klett (1900) concerning the capacity of some bacteria to reduce tellurium
salts was used by Conradi and Troch (1912) to develop for C . diphtheriae a
relatively selective medium containing potassium tellurite.
Morton and Anderson (1971) found needle-like crystals in cells of
C . diphtheriae and C . xerosis grown on plates of tellurite agar. They noticed
that most of the crystals were contained wholly within cells, and suggested
that the tellurite ion is probably able to diffuse through the cell wall, where
it is reduced to tellurium metal, precipitated within the cell affording the
black colour to the colonies.
Tucker et al. (1962) by applying X-ray diffraction, supplied the first
indication that tellurite crystals accumulate in C. diphtheriae. The black
hue which corynebacteria develop on tellurite blood agar or on Tinsdale
agar facilitates the selection of corynebacteria among a mixed pharyngonasal flora.
4. Cultivation and cultural characteristics
(a) Types of C. diphtheriae. A previous section mentioned that potassium
tellurite has little effect on C . diphtheriae in contrast to most other bacteria.
By means of such media, Anderson et al. (1931) differentiated between two
colony types of C . diphtheriae. Initially, they had indications that colony
type was correlated to the severity of disease. One type, that occurred
dominantly in severe cases, was called the gravis type and another, which
came from milder cases, the mitis type. Anderson et al. (1933) differentiated
a third type-now generally known as type intermedius. The three colony
types, with their associated biochemical characters and their different
phage types (Saragea and Maximescu, 1964, 1969), are now generally
recognised as very stable, and hence still used in current practice. Today,
however, there is by no means general agreement concerning correlation
of the type with the clinical severity of the case. All three types may be
either toxigenic or non-toxigenic. As regards their epidemic behaviour,
present evidence indicates that diphtheria in its epidemic form is frequently
due to the gravis type, intermedius coming next.
I n Romania, for instance, during the last 20 years gravis was the only
type isolated in epidemics or later in sporadic cases. The same situation
occurred in the main European countries. However, in the U.S.A. in some
recently investigated outbreaks (McCloskey et al., 1972) the toxigenic
intermedius type prevailed.
Mitis is more frequent in endemic areas, and fatality with mitis strains is
believed to be due more often to tracheal or laryngeal obstruction than to
A. SARAGEA ET AL.
(e) The reduction of tellurium salts is a characteristic feature of C . diphtheriae
and to a lesser extent of other members of this group. The observations of
Klett (1900) concerning the capacity of some bacteria to reduce tellurium
salts was used by Conradi and Troch (1912) to develop for C . diphtheriae a
relatively selective medium containing potassium tellurite.
Morton and Anderson (1971) found needle-like crystals in cells of
C . diphtheriae and C . xerosis grown on plates of tellurite agar. They noticed
that most of the crystals were contained wholly within cells, and suggested
that the tellurite ion is probably able to diffuse through the cell wall, where
it is reduced to tellurium metal, precipitated within the cell affording the
black colour to the colonies.
Tucker et al. (1962) by applying X-ray diffraction, supplied the first
indication that tellurite crystals accumulate in C. diphtheriae. The black
hue which corynebacteria develop on tellurite blood agar or on Tinsdale
agar facilitates the selection of corynebacteria among a mixed pharyngonasal flora.
4. Cultivation and cultural characteristics
(a) Types of C. diphtheriae. A previous section mentioned that potassium
tellurite has little effect on C . diphtheriae in contrast to most other bacteria.
By means of such media, Anderson et al. (1931) differentiated between two
colony types of C . diphtheriae. Initially, they had indications that colony
type was correlated to the severity of disease. One type, that occurred
dominantly in severe cases, was called the gravis type and another, which
came from milder cases, the mitis type. Anderson et al. (1933) differentiated
a third type-now generally known as type intermedius. The three colony
types, with their associated biochemical characters and their different
phage types (Saragea and Maximescu, 1964, 1969), are now generally
recognised as very stable, and hence still used in current practice. Today,
however, there is by no means general agreement concerning correlation
of the type with the clinical severity of the case. All three types may be
either toxigenic or non-toxigenic. As regards their epidemic behaviour,
present evidence indicates that diphtheria in its epidemic form is frequently
due to the gravis type, intermedius coming next.
I n Romania, for instance, during the last 20 years gravis was the only
type isolated in epidemics or later in sporadic cases. The same situation
occurred in the main European countries. However, in the U.S.A. in some
recently investigated outbreaks (McCloskey et al., 1972) the toxigenic
intermedius type prevailed.
Mitis is more frequent in endemic areas, and fatality with mitis strains is
believed to be due more often to tracheal or laryngeal obstruction than to