What is the Difference Between Salmonella Typhi O and H

The main difference between Salmonella typhi O and H is that Salmonella typhi O is the outermost portion of the bacterial surface covering whereas Salmonella typhi H is a slender thread-like structure, a part of the flagellum.

Salmonella typhi O and H are two structures on the surface of Salmonella typhi, helping the separation of Salmonella typhi into serotypes. Generally, O antigens are distinguished by their different chemical make-up. H antigens are distinguished by the protein content of the flagella.

Key Areas Covered

1. What is Salmonella
   • Definition, Characteristics, Importance
2. What is Salmonella Typhi O
   • Definition, Characteristics, Importance
3. What is Salmonella Typhi H
   • Definition, Characteristics, Importance
4. Similarities Between Salmonella Typhi O and H
   • Outline of Common Features
5. Difference Between Salmonella Typhi O and H
   • Comparison of Key Differences

Key Terms

Salmonella Typhi H, Salmonella Typhi O

What is Salmonella

Salmonella typhi is a rod-shaped, gram-negative bacteria of the family, Enterobacteriaceae. They are non-spore-forming and predominantly motile bacteria. The length of a cell is 2 to 5 μm. Salmonella contains peritrichous flagella, which allows the bacteria to move.  Salmonella is a chemotroph, obtaining its energy from oxidation and reduction reactions, using organic sources. It is also a facultative anaerobe that generates ATP in the presence of oxygen and in the absence of oxygen, Salmonella undergoes fermentation, using other electron acceptors.

Figure 1: Salmonella Typhi

Furthermore, Salmonella is an intracellular pathogen, and some serotypes of it cause illnesses. Usually, Salmonella infections are due to the ingestion of food contaminated with feces. There are two main serotypes of Salmonella: typhoidal and nontyphoidal serotypes. Nontyphoidal serotypes transmit to humans through animals. These serotypes only invade the gastrointestinal tract, causing salmonellosis. Typhoidal serotypes, however, transmit from one human to another human. It causes food-borne infections, typhoid, and paratyphoid fever. Moreover, typhoidal serotypes invade organs of the body, secreting endotoxins. In general, typhoid fever occurs when typhoidal serotypes invade the bloodstream. In addition, surface antigens are important in the determination of the serotype of Salmonella. The two remarkable antigens for the determination of serotypes are Salmonella typhi O and H antigens.

What is Salmonella Typhi O

Salmonella typhi O is the outermost portion of the Salmonella’s surface covering. Generally, the bacterial surface is covered with lipopolysaccharides (LPS) and the outermost layer of lipopolysaccharide is the antigen O. More importantly, the different chemical make-up of the Salmonella typhi O antigen is distinguishable in serotype determination. This antigen is called the O antigen.

Figure 2: Salmonella

What is Salmonella Typhi H

Moreover, Salmonella typhi H is a slender, thread-like structure and it is called the H antigen. Generally, the H antigen occurs in the flagella of Salmonella typhi. Generally, flagella are whip-like tails and bacteria use flagella for their movement. Moreover, the distinguishable feature of the H antigen is the protein content of flagella. 

Similarities Between Salmonella Typhi O and H

• Salmonella typhi O and H are two surface structures of Salmonella typhi.
• These structural components are important in the determination of serotypes.
• Moreover, they serve as antigens.

Difference Between Salmonella Typhi O and H

Definition

Salmonella typhi O refers to an antigen that makes up the outermost portion of the bacteria’s surface covering. while Salmonella typhi H refers to an antigen with a slender, thread-like structure.

Structure

Salmonella typhi O is the outermost portion of the lipopolysaccharide while Salmonella typhi H antigen is the slender, thread-like structure of the flagella.

Called as

Generally, Salmonella typhi O is called the O antigen while Salmonella typhi H antigen is called the H antigen.

Distinguish by

The chemical makeup distinguishes the Salmonella typhi O antigen while the protein content of the flagella distinguishes the Salmonella typhi H antigen.  

Conclusion

In brief, Salmonella typhi O antigen is the outermost portion of the cell surface covering the bacteria. It is also the outermost portion of the lipopolysaccharides. In contrast, Salmonella typhi H antigen is the slender, thread-like structure of the bacterial flagella. Therefore, the main difference between Salmonella typhi O and H antigen is their antigenic structure.

References:

1. Centers for Disease Control and Prevention. (2022, September 9). Serotypes and the importance of serotyping salmonella. Centers for Disease Control and Prevention. Retrieved September 27, 2022.

Image Courtesy:

1. “SalmonellaTyphiFlagellarStain” By Microbewriter – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Salmonella typhimurium” By Sun14916 – Own Work (CC BY-SA 3.0) via Commons Wikimedia