What is the Difference Between Typical and Atypical Bacteria

The main difference between typical and atypical bacteria is that the typical bacteria contains a cell wall whereas atypical bacteria usually do not contain a cell wall. Furthermore, typical bacteria can be either Gram-positive or Gram-negative while atypical bacteria remain colorless with Gram staining. Moreover, the cells of typical bacteria are large while the cells of the atypical bacteria are comparatively small.

Typical and atypical bacteria are the two types of bacteria classified based on the presence of a cell wall. Generally, the bacterial cell is made up of peptidoglycans called murein.

Key Areas Covered

1. What are Typical Bacteria
     – Definition, Structure, Importance
2. What are Atypical Bacteria
     – Definition, Structure, Importance
3. What are the Similarities Between Typical and Atypical Bacteria
     – Outline of Common Features
4. What is the Difference Between Typical and Atypical Bacteria
     – Comparison of Key Differences

Key Terms

Atypical Bacteria, Bacterial Cell Wall, Gram Staining, Parasites, Reproduction, Typical Bacteria

What are Typical Bacteria

Typical bacteria are the common form of unicellular prokaryotes. They can live in diverse environments, and they reproduce through cell division. Since bacteria are prokaryotes, they do not contain membrane-bound organelles including the nucleus, mitochondria, chloroplasts, etc. They contain a single, circular double-stranded DNA molecule as their genetic material inside the cytoplasm. Also, they have 70S ribosomes for protein synthesis. Every cellular process occurs in their cytosol including cellular respiration, protein synthesis, DNA replication, etc.

Figure 1: Bacterial Cell Structure

Generally, bacteria have a cell wall surrounding the cell membrane. Based on the properties of the cell wall, we can classify bacteria as either Gram-positive or Gram-negative. Apart from the cell wall, some other bacteria contain a capsule surrounding the cell wall. Moreover, some of them have flagella and pili-like outer structures. On the other hand, certain genera of Gram-positive bacteria produce endospores to survive under unfavorable growth conditions. Significantly, bacteria produce energy either by photosynthesis or by the oxidation of chemical compounds.

Figure 2: Gram-Positive Streptococcus mutans

Furthermore, the main form of asexual reproduction in bacteria is binary fission. Sometimes, they undergo sexual reproduction by bacterial conjugation. Moreover, most of the bacteria are not harmful to other organisms. However, some of them are pathogenic.

What are Atypical Bacteria

Atypical bacteria are the group of bacteria that do not contain a cell wall. Therefore, they are known as incomplete bacteria. Generally, atypical bacteria are obligate parasites. Hence, they require a host for their survival. On the other hand, these bacteria can pass from animals to humans and vice versa. So, they are recognized as zoonotic. Here, the spreading can occur through the air shared by both parts. Bird flu is an example of a disease caused by such atypical bacteria.

Figure 3: Mycoplasma haemofelis

Moreover, due to the absence of a cell wall, atypical bacteria do not color by Gram staining. Therefore, they are neither Gram-positive nor Gram-negative. Some examples of atypical bacteria are Legionella, Chlamydiaceae, Mycoplasmataceae (mycoplasma and ureaplasma), and Rickettsiaceae. Here, both Chlamydiaceae and Mycoplasmataceae lack a peptidoglycan layer. On the other hand, chlamydia and mycoplasma are resistant to antibiotics. Hence, they are marked as atypical during the treatments to corresponding illnesses. In contrast, some atypical bacteria cause atypical pneumonia.

Similarities Between Typical and Atypical Bacteria

• Typical and atypical bacteria are two types of bacteria classified based on the presence of a cell wall.
• Both types of bacteria are prokaryotes that do not contain membrane-bound organelles including a nucleus.
• They are single-celled organisms.
• Their genetic material occurs in the cytoplasm.
• They have 70S ribosomes. All of their biochemical reactions, including protein synthesis and DNA replication, occur in the cytosol.
• Some of them are parasitic and can cause diseases in animals and plants.

Difference Between Typical and Atypical Bacteria

Definition

Typical bacteria refer to a member of a large group of unicellular microorganisms that have cell walls but lack organelles and an organized nucleus, including some which can cause disease while atypical bacteria refer to the bacteria that are not detectable on Gram stain and cannot be cultured using standard methods. Thus, this is the main difference between typical and atypical bacteria.

Size

The size of the typical bacteria is around 0.5-0.8 μm while the size of the atypical bacteria is 0.1-0.3 μm. Hence, this is another difference between typical and atypical bacteria.

Cell Wall

Furthermore, the typical bacteria contain a cell wall made up of peptidoglycans while in general, the atypical bacteria do not contain a cell wall.

Gram Staining

Another difference between typical and atypical bacteria is that the typical bacteria are either Gram-positive or Gram-negative while the atypical bacteria do not color with Gram staining.

Reproduction

Moreover, typical bacteria reproduce through cell division while the reproduction of atypical bacteria is complicated.

Interaction with Other Organisms

Interactions with other organisms is another difference between typical and atypical bacteria. Typical bacteria can be either mutualistic, parasitic or predators while atypical bacteria are obligate parasites.

Laboratory Cultivation

Besides, typical bacteria grow on artificial media with minimal growth factors while atypical bacteria require a living host or highly enriched media for the growth. So, this is another important difference between typical and atypical bacteria.

Conclusion

Typical bacteria are the common form of bacteria that contain a cell wall. They can be classified either as gram-positive or Gram-negative bacteria based on the structure of the cell wall. On the other hand, atypical bacteria are an incomplete form of bacteria that do not contain a cell wall. Therefore, they do not respond to Gram staining. In general, atypical bacteria are obligate parasites, and they are difficult to grow under laboratory conditions. However, the main difference between typical and atypical bacteria is the presence of a cell wall.

References:

1. “Bacteria Cell Structure.” Molecular Expressions, Available Here
2. “Atypical Pneumonia.” Community-Acquired Pneumonia – Symptoms, Diagnosis and Treatment | BMJ Best Practice, Available Here

Image Courtesy:

1. “Average prokaryote cell- en” By Mariana Ruiz Villarreal, LadyofHats – Own work (Source: Typical prokaryotic cell, Chapter 4: Mutagenicity of alkyl N-acetoxybenzohydroxamates, Concept 1: Common Features of All Cells, Cells – Structure and Function) (Public Domain) via Commons Wikimedia  
2. “Streptococcus mutans Gram” By Y tambe – Y tambe’s file (CC BY-SA 3.0) via Commons Wikimedia    
3. “M. haemofelis IP2011” By Nr387241 – Own work (CC BY-SA 3.0) via Commons Wikimedia