IV. INVESTIGATION OF C . DIPHTHERIAE
65
mined by the presence of prophage (Freeman, 1951) carrying specific
determinant called toxf, and toxjgenicity is induced in non-toxigenic
strains by making them lysogenic (Holmes and Barksdale, 1969).
Within the genus Corynebacterium we shall deal especially with those
members of the group, which are common in the rhinopharynx and hence
present problems in differential microbiological diagnosis from the diphtheria bacillus, i.e. (1) C. diphtheriae as type species, the causative agent of
diphtheria, parasite of man ; (2) C. ulcerans-the second pathogenic
species with human and/or animal habitat; (3) non-pathogenic saprophytic corynebacteria.
Of the saprophytic corynebacteria, from the upper respiratory tract, the
following species will be considered : C. hofmannii, C. xerosis, atypical
corynebacteria and some variants with “dwarf” colonies.
B. Characteristics of C. diphtheriae
1. Habitat
C. diphtheriae, the causative agent of diphtheria, is usually found in the
upper respiratory tract, on the skin, conjunctiva and vagina. Its capacity
to produce toxin and the immunity state of the individual decide whether
diphtheria will evolve. At the site of entry it produces a greyish false
membrane-constituted of a fibrinoleukocytic exudate. From the false
membrane, where diphtheria bacilli are located, they produce an exotoxin, which invades the tissues by the blood stream.
In individuals with a protective level of 0.03 AU/ml (antitoxin units) the
location of C. diphtheriae on the mucosa is uneventful or results only in
mucosal erythema. The individual may become a symptomless carrier.
C. diphtheriae spreads only among human beings; there is no intermediate host. Cats, dogs and other domestic animals have rarely been incriminated. From sores on the teats of cows, virulent C. diphtheriue have been
isolated (Henry, 1920; Scott, 1934), but as a rule they have come from
sores OQ the hands of milkers who were carriers of the organism.
2. Morphology and structure
Non-motile, non-capsulated, non-flagellate club-shaped bacillus (Fig. 1).
Gram-positive. A strongly characteristic feature is the readiness with
which it decolourises. Morphologically, characteristic cell forms are obtained on smears prepared from an overnight Loeffler slant culture. With
Loeffler’s alkaline Methylene blue, Toluidine blue, or double staining (for
instance by Neisser or Del Vecchio’s method) characteristic granules
(Babes, 1886; Ernst, 1888) may be differentially stained.
By double staining, the cells have blue-black granules on a brown
65
mined by the presence of prophage (Freeman, 1951) carrying specific
determinant called toxf, and toxjgenicity is induced in non-toxigenic
strains by making them lysogenic (Holmes and Barksdale, 1969).
Within the genus Corynebacterium we shall deal especially with those
members of the group, which are common in the rhinopharynx and hence
present problems in differential microbiological diagnosis from the diphtheria bacillus, i.e. (1) C. diphtheriae as type species, the causative agent of
diphtheria, parasite of man ; (2) C. ulcerans-the second pathogenic
species with human and/or animal habitat; (3) non-pathogenic saprophytic corynebacteria.
Of the saprophytic corynebacteria, from the upper respiratory tract, the
following species will be considered : C. hofmannii, C. xerosis, atypical
corynebacteria and some variants with “dwarf” colonies.
B. Characteristics of C. diphtheriae
1. Habitat
C. diphtheriae, the causative agent of diphtheria, is usually found in the
upper respiratory tract, on the skin, conjunctiva and vagina. Its capacity
to produce toxin and the immunity state of the individual decide whether
diphtheria will evolve. At the site of entry it produces a greyish false
membrane-constituted of a fibrinoleukocytic exudate. From the false
membrane, where diphtheria bacilli are located, they produce an exotoxin, which invades the tissues by the blood stream.
In individuals with a protective level of 0.03 AU/ml (antitoxin units) the
location of C. diphtheriae on the mucosa is uneventful or results only in
mucosal erythema. The individual may become a symptomless carrier.
C. diphtheriae spreads only among human beings; there is no intermediate host. Cats, dogs and other domestic animals have rarely been incriminated. From sores on the teats of cows, virulent C. diphtheriue have been
isolated (Henry, 1920; Scott, 1934), but as a rule they have come from
sores OQ the hands of milkers who were carriers of the organism.
2. Morphology and structure
Non-motile, non-capsulated, non-flagellate club-shaped bacillus (Fig. 1).
Gram-positive. A strongly characteristic feature is the readiness with
which it decolourises. Morphologically, characteristic cell forms are obtained on smears prepared from an overnight Loeffler slant culture. With
Loeffler’s alkaline Methylene blue, Toluidine blue, or double staining (for
instance by Neisser or Del Vecchio’s method) characteristic granules
(Babes, 1886; Ernst, 1888) may be differentially stained.
By double staining, the cells have blue-black granules on a brown