Cultural characteristics
Biochemical characters
Phylum Actinobacteria, Class Actinobacteria, Subclass Actibacteridae, Order Actynomycetales, Suborder Corynebacterinae, Family
Corynebacteriaceae, Genus Corynebacterium,
Corynebacterium diphtheriae (Kruse 1886) Lehmann and Neumann 1896.
Type species of the genus. Four biotypes:
Corynebacterium diphtheriae biotype gravis, mitis, belfanti and intermedius.

Historical synonyms:
Microsporon diphthericum Klebs 1875, Microsporon diphtheriticum Klebs 1883, Bacillus diphtheriae Kruse in
Flugge 1886,
Pacinia loeffleri Trevisan 1889, Bacterium diphtheriae (Kruse) Migula 1900, Mycobacterium diphtheriae (Kruse)
Krasil’nikov 1941.
Gram-positive (easily decolorized, especially in old cultures) straight or slightly curved
rods with sides not parallel, frequently swollen at one or both ends (typical club
shape), 0.3-0.8/1.0-8.0 µm, arranged as single cells, in pairs, in V forms, in palisades
or in clusters with Chinese letter appearance. Usually stain unevenly and often
contain metachromatic granules (polymetaphosphate) which stain bluish purple with
methylene blue. Nonspore-forming. Nonmotile.
There are some differences between biotypes:
-C. diphtheriae biotype gravis: short, coccoid or pyriform rods, few metachromatic
-C. diphtheriae biotype intermedius: highly pleomorphic, ranging from very long to
very short rods, few metachromatic granules
-C. diphtheriae biotypes mitis and belfanti: long, curved pleomorphic, rigid
club-shaped rods, many granules.
Grow well on blood agar.
-C. diphtheriae biotype gravis colonies: ≥ 2 mm in diameter, larger and denser than biotype intermedius, slightly dry (typical for
nonlipophilic corynebacteria) : some strains produce a narrow zone of weak β-hemolysis. Broth: surface pellicle, clear fluid, coarse
-C. diphtheriae biotype intermedius colonies: < 0.5 mm in diameter, tiny, transparent (typical for lipophilic corynebacteria),
nonhemolytic. Broth: fine granular turbidity wich settles later
-C. diphtheriae biotypes mitis and belfanti colonies: ≥ 2 mm in diameter, larger and denser than biotype intermedius, slightly dry
(typical for nonlipophilic corynebacteria); most strains produce a narrow zone of weak beta-hemolysis. Broth: diffuse turbidity with

Aerobic growth. Temperature of growth: 15-40 ºC, optimum 37 ºC. Pimelic acid, nicotinic acid and beta-alanine required by almost all
strains. CAMP reaction (with a beta-hemolysin-producing strain of
Staphylococcus aureus) is negative. Tellurium salts are reduced to
tellurium (which is precipitated in the cell to color the colonies gray, brown or black on blood tellurite agar).
Isolated from the nasopharynx of healthy carriers, from skin lesions and from cases
of diphtheria or other diseases with
C. diphtheriae.
Killed by heating at 58 ºC for 10 minutes. Susceptible to the usual disinfectants.
Susceptible to erythromycin, penicillin, ampicillin, cefuroxime, chloramphenicol,
ciprofloxacin, gentamicin, tetracyclin. Relatively resistant to drying.
Specific bacteriophages. Many strains carry bacteriophages lytic for other strains, and
at least 19 lysotypes have been distinguished: conversion of non-toxigenic strains to
toxigenicity is mediated by phage. Some C. diphtheriae phages will lyse strains of
and C. ulcerans.
Pathogenic for human; the most common disease caused is diphtheria, an acute
communicable disease manifested by both local infection of the upper respiratory
tract and the systemic effects of a toxin in the heart, peripheral nerves and the kidney.
Toxigenic strains of all biotypes produce an identical toxin.
An specific exotoxin, highly lethal, 58 kDa protein, 535 aminoacid; the gene for the exotoxin (tox) is carried on a family of closely related
corynebacteriophages and has been sequenced. The crystal structure of the exotoxin whose active form consists of two polypeptide
chains linked by a disulfide bond reveals three domains, the catalytic domain, the transmembrane domain, and a receptor binding
Toxigenicity is induced in non-toxigenic strains by making them lysogenic for phages of this type.
Some clinical isolates may not possess the diphtheria
tox gene
C. diphtheriae probably has additional virulence factors, as nontoxigenic strains are also associated with significant invasive disease.
C. diphtheriae, usually nontoxigenic strains, has been associated with septicaemia, endocarditis, septic arthritis, osteomyelitis, and
cerebral abcess.
An in vitro method to measure the cytotoxicity of diphtheria toxin to
Verro cells is as sensitive and specific as the in vivo guinea pig
assay; guinea pigs and rabbits are most susceptible to experimental infection, whereas rats and mice are resistant.
Different biotypes can be present during a single epidemic and can be isolated from the same individual.
  1. Funke G., von Graevenitz A., Clarridge III J.E., and Bernard K.A., 1997. Clinical Microbiology of Coryneform Bacteria. Clinical
    Microbiology Rewiews Vol. 10, No. 1, p. 125-159.
  2. Funke G., 2006. Corynebacteria and rare coryneforms. In: Topley & Wilson’s Microbiology & Microbial Infections, 10th Edition,
    Edited by Borriello S.P., Murray P.R. and Funke G.,Edward Arnold (Publishers) Ltd., Bacteriology, volume 2.
  3. Cummins C.S., Lelliott R.A. and Rogosa M., 1975. Genus Corynebacterium Lehmann and Neumann 1896 . In: Buchanan R.E.
    and Gibbons N.E. (Editors), Bergey’s Manual of Determinative Bacteriology, Eight Edition, The Williams & Wilkins Company,
    Baltimore, 602-617.
  4. Diaconescu A. si Damian M., 2009. Identificarea corinebacteriilor. In: Buiuc D., Negut M. (Editori), Tratat de Microbiologie Clinica,
    Editia a IIIa, Editura Medicala, Bucuresti, 620-651.
  5. Holt J.G., Krieg N.R., Sneath P.H.A., Staley J.T. and Williams S.T., 1994. Bergey's Manual of Determinative Bacteriology, Ninth
    Edition, Williams & Wilkins, A Waverly Company, Baltimore, pp 571-596.
Fermentative metabolism. No oxidative metabolism. Non-partially-acid-fast.

Positive results for catalase, cistinase, H
2S on Tinsdale medium (containing L-cystine and potassium tellurite; so, also cistinase
positive), methyl red, acid production from: arabinose, fructose, galactose, glucose, maltose, mannose, rhamnose & salicin.

Negative results for alkaline phosphatase, casein hydrolysis, esculin hydrolysis, gelatinase, hippurate hydrolysis, indole, oxidase,  
pyrazinamidase, tyrosine hydrolysis, urease, acid production from: lactose, mannitol, sucrose, trehalose & xylose.

Variable results for raffinose fermentation.
Corynebacterium diphtheriae
(c) Costin Stoica
Culture media
Biochemical tests
Previous page
Differential characters of C. diphtheriae biotypes:
Legend: +  positive 90-100%, - negative 90-100%, [+] positive 75-89%, [-] negative 75-89%, d positive 25-74% of strains
Nitrate reduction
Acid from
Acid from
Acid from
C. diphtheriae biotype gravis
C. diphtheriae biotype intermedius
C. diphtheriae biotype mitis
C. diphtheriae biotype belfanti