What is the Difference Between Corynebacterium Diphtheriae and Diphtheroids

The key difference between Corynebacterium diphtheriae and diphtheroids is that Corynebacterium diphtheriae contains metachromatic granules in polar regions while diphtheroids lack metachromatic granules but are arranged in a palisade manner.

Corynebacterium is a genus of bacteria that are gram-positive and mostly aerobic. They are rod-shaped, so they are referred to as bacilli. They widely inhabit nature in the microbiota of animals and mostly occur in commensal relationships with the host. Some are useful and non-pathogenic, while some are pathogenic and cause diseases. Corynebacterium diphtheriae is a bacterium that causes the disease diphtheria. Diphtheroids refer to a wide range of bacteria from the genera of Corynebacterium.

CONTENTS

1. Overview and Key Difference
2. What is Corynebacterium Diphtheriae 
3. What are Diphtheroids
4. Similarities – Corynebacterium Diphtheriae and Diphtheroids
5. Corynebacterium Diphtheriae vs Diphtheroids in Tabular Form
6. Summary – Corynebacterium Diphtheriae vs Diphtheroids

What is Corynebacterium Diphtheriae?

Corynebacterium diphtheriae is a gram-positive pathogenic bacterium that causes diphtheria. It is a rod-shaped, non-spore-forming, and non-motile bacterium. There are four strains of this bacterium: C. diphtheriae mitis, C. diphtheriae intermedius, C. diphtheriae gravis, and C. diphtheriae belfanti. They differ slightly by their biochemical properties and colony morphology. C. diphtheriae produces diphtheria toxin, which alters the protein function in the host by inactivating the elongation factor EF-2. As a result, this causes pharyngitis and pseudo-membrane in the throat.

Figure 01: Corynebacterium diphtheria

A bacteriophage encodes the gene responsible for diphtheria toxin and integrates it into the bacterial chromosome. The gram staining process accurately identifies the bacterium. Special staining techniques such as Albert’s stain and Ponder’s stain demonstrate metachromatic granules that form in polar regions. An enrichment medium known as Löffler’s medium acts as a favorable environment for the growth of C. diphtheriae. A differential plate known as tellurite agar allows the bacteria to reduce tellurite to metallic tellurium. This indicates brown colonies for most Corynebacterium species but forms a black halo around C. diphtheriae colonies. Elek’s plate test is an in vitro test to determine the toxigenicity or virulence of the organism. It helps to identify whether C. diphtheriae is able to produce the diphtheria toxin.

What are Diphtheroids?

Diphtheroids are aerobic, non-spore-forming, pleomorphic gram-positive bacteria included in a wide range of bacteria from genera Corynebacterium. They lack the metachromatic granules but are arranged in a palisade manner. Diphtheroids are commensals of the skin and mucous membranes. Therefore, they appear as contaminants during the isolation process from clinical samples.

Figure 02: Diphtheroids

Diphtheroids are also found on plants, in soil, in freshwater, and in saltwater. However, diphtheroids are associated with many infections such as contagious infections by pseudo-membrane of dead epithelial cells and fibrin forming around tonsils and throat, infections in the urinary tract, respiratory tract, conjunctiva and the middle ear, skin infections, and results in serious diseases such as diphtheria, caseous lymphadenitis, granulomatous lymphadenopathy, pneumonitis, pharyngitis, and endocarditis. Diphtheroids also attack immunocompromised patients. A few examples of diphtheroids are cutaneous diphtheroids and anaerobic diphtheroids, which are common in areas rich in sebaceous glands. The gram staining technique helps to determine diphtheroids.

What are the Similarities Between Corynebacterium Diphtheriae and Diphtheroids?

  • Corynebacterium diphtheriae and diphtheroid are gram-positive.
  • They are irregular, rod-shaped, non-spore-forming, aerobic and non-motile.
  • Moreover, they can be identified by Gram Staining.
  • Both occur in the upper respiratory tract.
  • They cause diphtheria.

What is the Difference Between Corynebacterium diphtheriae and Diphtheroid?

Corynebacterium diphtheriae contains metachromatic granules in polar regions, while diphtheroids lack metachromatic granules, but they are arranged in a palisade manner. Thus, this is the key difference between Corynebacterium Diphtheriae and diphtheroids. Moreover, Corynebacterium diphtheria affects the upper respiratory tract. But, diphtheroids affect the pseudo-membrane of dead epithelial cells. While Corynebacterium diphtheria mainly causes Diphtheria, diphtheroids cause diphtheria, caseous lymphadenitis, granulomatous lymphadenopathy, pneumonitis, pharyngitis and endocarditis.

The below infographic presents the differences between Corynebacterium Diphtheriae and diphtheroids in tabular form for side by side comparison.

Summary – Corynebacterium diphtheriae vs Diphtheroid

Corynebacterium is a genus of bacteria that are gram-positive, mostly aerobic, non-motile, and rod-shaped. Corynebacterium diphtheriae contains metachromatic granules in polar regions, while diphtheroids lack metachromatic granules. Corynebacterium diphtheriae is a pathogenic bacterium that causes diphtheria. Diphtheroids are bacteria included in a wide range of bacteria from genera Corynebacterium. They exist either as pathogenic or non-pathogenic bacteria. So, this summarizes the difference between Corynebacterium Diphtheriae and diphtheroids.