Diphtheria bacillus and Diphtheroids: Introduction, Differences, and Keynotes

Introduction of Diphtheria bacillus and Diphtheroids

Diphtheria bacillus is also known as Klebs-Löffler bacillus and it is a Gram-positive nonmotile, club-shaped bacillus of Corynebacterium diphtheriae. C. diphtheriae is a causative agent of Diphtheria (a serious infection of the mucous membranes of the nose and throat). Diphtheroids are non-diphtherial species and they are part of normal human skin flora having property of aerobic, non-sporulating, pleomorphic Gram-positive rods which are more uniformly stained than C. diphtheriae, lack the metachromatic granules and are arranged in a palisade manner as shown in the figure.

Differences between Diphtheria bacillus and Diphtheroids
Fig. Diphtheroids colony on blood agar and their Gram staining of culture showing strongly Gram-positive, short, and thick bacilli

Differences between Diphtheria bacillus and Diphtheroids

Differences between Diphtheria bacillus and Diphtheroids are as follows-

S.No.PropertyDiphtheria bacillusDiphtheroids
1Gram ReactionWeakly Gram-positiveStrongly Gram-positive
2.Metachromatic granulesPresentAbsent
3.Arrangement of bacilliChinese letter patternPalisade arrangement
4.PleomorphismPresentVery little
5.Size and shapeLong and Chinese letter arrangement, slenderShort and thick bacilli
6.Culture on a basal medium like
peptone water and nutrient agar
No growthGrowth
7.Tellurite blood agarGenerally rough colonySmooth colony
8.Glucose and sucrose fermentationGlucose onlyBoth glucose and sucrose
10.OrganismsCorynebacterium diphtheriaeCorynebacterium pseudotuberculosis, Corynebacterium renale, C. bovis, C. striatum, C. minutissimum, C. pseudodiphtheriticum, C. haemolyticum, etc
11.PathogenicityHighly pathogenicLess pathogenic or commensals of the skin and mucous membranes
12.InfectionDiphtheriaUsually nosocomial infections
Table: Diphtheria bacillus Vs Diphtheroids

Keynotes diphtheria bacillus and Diphtheroids

  • The toxin gene is encoded by a prophage called corynephage β.
  • The common symptoms of diphtheria include pharyngitis, fever, and swelling of the neck.
  • The Elek immunodiffusion test is the most common in vitro assay for the toxigenicity of C. diphtheriae.
  • Gravis, intermedius, mitis, and belfanti are biotypes of C. diphtheriae.
  • Albert’s stain is used for diphtheria bacillus staining.

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