74
A. SARAGEA ET AL.
(e) Nitrate-reductase is present in all corynebacteria except a variant of
the mitis type, C . belfanti, isolated from cases of ozena (Bezjack, 1958;
Oehring, 1963a, b), C . ulc&ans and C. ovis.'
(f) HaemoZysin. On sheep blood agar and still better on rabbit blood agar,
the mitis type is haemolytic, intermedius non-haemolytic, and gravis
variable in this respect.
(g) Neuraminidase (N-acetylneuraminate glycohydrolase) has been found
in some C. diphtheriae strains, both toxigenic and non-toxigenic (Morijama
and Barksdale, 1967). This enzyme has been shown to be intracellular,
possibly associated with the cytoplasmic membrane. Diphtherial toxin and
diphtherial neuraminidase have the same molecular weights, despite the
fact that neuraminidase can be produced by the PWs toxin-producing
cells grown in conditions unsuitable for toxin production (Barksdale, 1970).
According to the above authors, neuraminidase appears to be distinct
immunochemically and electrophoretically (Blumberg and Warren, 1961 ;
Heide and Haupt, 1962).
(h) Catalase is a property of all corynebacteria.
(i) Gelatin is liquefied only by C. ulcerans.
6. Resistance and sensitivity
Diphtheria bacilli may live for as long as 5 weeks in dust.
They are readily killed by heat (10 min at 58°C) and by the common
antiseptics. Corynebacterium diphtheriae has been isolated from dust
around beds in diphtheria wards (Christie, 1969). Even normal saline will
kill diphtheria bacilli within a short time, a point of importance in laboratory
practice. The organism is fully sensitive towards most antibiotics. It is
moderately sensitive to sulphonamides in vitro.
7. Pathogenicity
(a) Pathogenicity. Diphtheria is a typical tox infection, often fatal, and its
lesions are mainly produced by the action of a powerful exotoxin diffusing
rapidly throughout the body from the growing bacilli at the site of infection.
The problem of pathogenesis is mainly that of understanding the origin,
nature and mode of action of the toxic protein, elaborated by diphtheria
bacilli.
(b) Experimental models. Experimental infections have been demonstrated
in guinea pigs and rabbits which are most susceptible; dogs, cats, and
pigeons are moderately susceptible, and rats and mice very resistant.
A. SARAGEA ET AL.
(e) Nitrate-reductase is present in all corynebacteria except a variant of
the mitis type, C . belfanti, isolated from cases of ozena (Bezjack, 1958;
Oehring, 1963a, b), C . ulc&ans and C. ovis.'
(f) HaemoZysin. On sheep blood agar and still better on rabbit blood agar,
the mitis type is haemolytic, intermedius non-haemolytic, and gravis
variable in this respect.
(g) Neuraminidase (N-acetylneuraminate glycohydrolase) has been found
in some C. diphtheriae strains, both toxigenic and non-toxigenic (Morijama
and Barksdale, 1967). This enzyme has been shown to be intracellular,
possibly associated with the cytoplasmic membrane. Diphtherial toxin and
diphtherial neuraminidase have the same molecular weights, despite the
fact that neuraminidase can be produced by the PWs toxin-producing
cells grown in conditions unsuitable for toxin production (Barksdale, 1970).
According to the above authors, neuraminidase appears to be distinct
immunochemically and electrophoretically (Blumberg and Warren, 1961 ;
Heide and Haupt, 1962).
(h) Catalase is a property of all corynebacteria.
(i) Gelatin is liquefied only by C. ulcerans.
6. Resistance and sensitivity
Diphtheria bacilli may live for as long as 5 weeks in dust.
They are readily killed by heat (10 min at 58°C) and by the common
antiseptics. Corynebacterium diphtheriae has been isolated from dust
around beds in diphtheria wards (Christie, 1969). Even normal saline will
kill diphtheria bacilli within a short time, a point of importance in laboratory
practice. The organism is fully sensitive towards most antibiotics. It is
moderately sensitive to sulphonamides in vitro.
7. Pathogenicity
(a) Pathogenicity. Diphtheria is a typical tox infection, often fatal, and its
lesions are mainly produced by the action of a powerful exotoxin diffusing
rapidly throughout the body from the growing bacilli at the site of infection.
The problem of pathogenesis is mainly that of understanding the origin,
nature and mode of action of the toxic protein, elaborated by diphtheria
bacilli.
(b) Experimental models. Experimental infections have been demonstrated
in guinea pigs and rabbits which are most susceptible; dogs, cats, and
pigeons are moderately susceptible, and rats and mice very resistant.