What is the Difference Between Spirilla and Spirochetes

The main difference between spirilla and Spirochetes is that spirilla have relatively short and rigid cells whereas spirochetes have longer and more flexible cells. Furthermore, the motility mechanisms of spirilla are based on polar flagella while the motility mechanisms of spirochetes are based on axial filaments. 

Spirilla and spirochetes are two groups of spiral bacteria that belong to a morphological category of prokaryotes with helical shape cells. 

Key Areas Covered 

1. What are Spirilla
     – Definition, Characteristics, Importance
2. What are Spirochetes
     – Definition, Characteristics, Importance
3. What are the Similarities Between Spirilla and Spirochetes
     – Outline of Common Features
4. What is the Difference Between Spirilla and Spirochetes
     – Comparison of Key Differences

Key Terms 

Cell Wall, Motility, Spiral Bacteria, Spirilla, Spirochetes

What are Spirilla 

Spirilla are spiral bacteria classified in the genus Spirillum under the family Spirillaceae. The two main characteristic features of spirilla are the presence of a rigid cell wall and the motility mechanism based on polar flagella. Additionally, spirilla are large and elongated cells. 

Figure 1: Spirilla

Furthermore, Spirilla are widespread in a number of environments. Also, they are aerobic bacteria with a helical shape. However, some species of spirilla such as Spirillum minor can cause rat bite fever in humans. Campylobacter, which is another spiral bacterial genus with comma shape bacteria, contains pathogenic species that cause campylobacteriosis, a type of intestinal infection accompanied by diarrhea. 

What are Spirochetes 

Spirochetes are the spiral bacteria characterized by the presence of a flexible cell wall and axial filaments-based motility mechanisms. Moreover, the axial filaments contain fibrils extending toward each other between two layers of the cell wall. However, spirochetes are difficult to visualize under the light microscope due to their very slender nature. Additionally, they are very difficult to cultivate and stain by Gram-staining. 

Figure 2: Spirochetes

Moreover, some spirochetes live in aquatic environments. Others are parasitic in arthropods and warm-blooded animals. Additionally, they cause diseases such as Lyme disease (by Borrelia burgdorferi) and syphilis (by Treponema pallidum). Also, Leptospira interrogans serves as an agent of leptospirosis. 

Similarities Between Spirilla and Spirochetes 

• Spirilla and Spirochetes are two groups of spiral bacteria. 
• Furthermore, they are classified based on the number of twists per cell thickness, flexibility, and motility. 
• Also, both types of bacteria can be pathogenic. 

Difference Between Spirilla and Spirochetes 

Definition 

Spirilla refer to a bacteria with a rigid, spiral structure found in stagnant water and sometimes causing disease, while spirochetes refer to a flexible, spirally twisted bacteria especially, one that causes syphilis. Thus, this is the main difference between spirilla and spirochetes.

Classification 

Moreover, there is a difference between spirilla and spirochetes in their classifications too. The spirilla is a genus while spirochetes are a phylum. 

Texture 

The spirilla are rigid while spirochetes are flexible.  

Type of Flagella 

Also, another difference between spirilla and spirochetes is that while Spirilla have external flagella, spirochetes have internal flagella. 

Gram Staining 

Gram staining is one other difference between spirilla and spirochetes. Spirilla are Gram-negative bacteria while spirochetes are difficult to Gram stain. 

Size 

Moreover, spirilla are large, 1.4 to 1.7 μm in diameter and up to 60 μm in length, while spirochetes are giants, 0.2-0.3 μm in diameter and 20-30 μm in length (Borrelia). 

Cellular Respiration 

Furthermore, Spirilla are aerobic bacteria while spirochetes are obligate or facultative anaerobes. Hence, this is another difference between spirilla and spirochetes.

Diseases 

In addition, Spirilla cause rat bite fever in humans and campylobacteriosis while spirochetes cause Lyme disease and syphilis. 

Conclusion 

Spirilla is a genus of spiral bacteria characterized by the presence of a rigid cell wall and polar flagella for motility. Also, they are gram-negative bacteria. They are aerobes. On the other hand, spirochetes are a phylum of spiral bacteria characterized by the presence of a flexible cell wall and axial filament-based motility. However, they are difficult to cultivate. Also, they are much larger than spirilla. Hence, the main difference between spirilla and spirochetes is morphology and pathogenicity.   

References:

1. Todar, Kenneth. Bacterial Pathogens of Humans, Available Here.

Image Courtesy:

1. “Spirillen” By Wolframm Adlassnig – Own work (Public Domain) via Commons Wikimedia   
2. “20100905 211652 Spirochetes” By Bob Blaylock – Own work (CC BY-SA 3.0) via Commons Wikimedia