Moraxella catarrhalis

The Blood Agar is a Tryptic Soy Agar that contains sterile sheep’s blood. It is used to determine if a microbe engages in hemolysis or the breakdown of red blood cells. It is also used to distinguish normal bacteria from pathogenic bacteria. M catarrhalis uses gamma hemolysis as indicated by the lack of marked change.

The MacConkey Agar is designed to select for Gram-negative bacteria and enteric bacilli while also differentiating them based on lactose fermentation. Despite being Gram-negative M. catarrhalis does not grow on MacConkey Agar.

DNAse agar is used to differentiate organism based on their ability to produce the exoenzyme, deoxyribonuclease. M catarrhalis is positive for DNase as indicated by the formation of colorless zones around the colonies.

Gram staining is a technique used to distinguish between Gram positive bacteria; which retain have a thick layer of peptidoglycan, retain CV and appear purple, and Gram negative bacteria; which have a thin peptidoglycan layer, lose CV and retain safranin. M. catarrhalis is Gam negative indicated by the pinkish-reddish color.

Phenol red broth with glucose and Durham tubes are used to test if bacteria engage in fermentation reactions which may or may not result in gas production. M. catarrhalis does not ferment glucose as indicated by the lack of color change and absence of gas in the tube.

The SIM medium tests for the ability of an organism to reduce sulfur, produce indole, and be motile. M. catarrhalis is nonmotile and negative for indole and sulfur as evidenced by the lack of color change, absence of black precipitate, and the sharp edge of the colonies.

The Catalase Rapid enzyme tests is used to determine the presence of the enzyme catalase used to breakdown hydrogen peroxide and found in in almost all aerobic bacteria. M. catarrhalis is aerobic and positive for catalase as indicated by the formation of bubbles after adding hydrogen peroxide.

The Oxidase enzyme test is used to determine if a bacteria has oxidase, an enzyme that catalyzes the transfer of electrons in the electron transfer chain. M. catarrhalis is positive for oxidase as evidenced by the reagent turning dark blue when oxidized.