Master Haemophilus influenzae Characteristics with Picmonic for Medicine

This organism stains Gram negative due to relatively thin peptidoglycan layer in the cell wall.

Coccobacilli are a type of rod-shaped bacteria that are short and wide, so they resemble spherical cocci.

The polyribosyl ribitol phosphate (PRP) capsule is the most important virulence factor of type B Haemophilus influenzae infections, because it plays a role in resisting phagocytosis.

A Quellung reaction is a biochemical reaction in which antibodies bind to a bacterial capsule, allowing species with a positive Quellung reaction to be visualized under a microscope. Haemophilus influenza has a positive Quellung reaction.

An IgA protease is an enzyme that cleaves certain amino acid sequences of proteins including immunoglobulin A. Haemophilus influenzae releases IgA proteases which destroy IgA, leading to increased pathogenicity. Other IgA protease producers include Neisseria gonorrhoeae and Streptococcus pneumoniae.

Haemophilus influenzae organisms require nutrient supplementation to grow in laboratory cultures. Specifically, they grow on chocolate agar, which is an enriched growth medium containing red blood cells that have been lysed, providing growth factors like NAD and hematin. The agar is named for the chocolate color of the medium and does not actually contain chocolate.

Haemophilus influenzae requires two accessory growth factors when cultured, including factor X and factor V. Factor V is NAD (nicotinamide adenine dinucleotide).

Haemophilus influenzae requires two accessory growth factors when cultured, including factor X and factor V. Factor X is hematin.

H. influenzae can grow in the hemolytic zone of Staph aureus on blood agar plates, because hemolysis of cells by Staph aureus releases factor V, which is needed for growth.