Biochemical Test of Haemophilus influenzae


Haemophilus influenzae is a type of bacteria that can cause various infections in humans, such as meningitis, pneumonia, otitis media, sinusitis, and septicemia. It is also known as H. influenzae or Hib (when referring to the serotype b strain). H. influenza was first isolated in 1892 by Richard Pfeiffer, who mistakenly thought it was the cause of influenza. Later, it was found that H. influenzae can be a secondary invader after viral infections, such as influenza.

H. influenzae is a gram-negative, pleomorphic, non-motile, and non-spore-forming bacterium. It requires certain growth factors, such as hemin (factor X) and nicotinamide adenine dinucleotide (NAD) (factor V), which are present in blood or chocolate agar. H. influenza can be classified into six serotypes (a-f) based on the presence and structure of a polysaccharide capsule. The capsule is an important virulence factor that protects the bacterium from phagocytosis and complement-mediated lysis. The most invasive and pathogenic strain is serotype b, which accounts for about 90% of invasive H. influenzae infections.

H. influenza can also be classified into biotypes (I-VIII) based on the biochemical properties of fermentation and enzymatic reactions. These properties can help to identify and differentiate H. influenzae strains from other bacteria. Some of the biochemical tests that are commonly used for H. influenzae are:

  • Indole test: detects the production of indole from tryptophan by tryptophanase enzyme
  • Urease test: detects the hydrolysis of urea by urease enzyme
  • Ornithine decarboxylase test: detects the decarboxylation of ornithine by ornithine decarboxylase enzyme
  • Catalase test: detects the breakdown of hydrogen peroxide by catalase enzyme
  • Oxidase test: detects the presence of cytochrome c oxidase enzyme

In this article, we will discuss the fermentation process and enzymatic reactions in H. influenzae in more detail and explain how they can be used for the diagnosis and identification of this bacterium.