# 17 Normal Microbiota of the Throat/Skin

Streptococcus

Often found as normal Microbiota of the mouth and throat. S.mutans,S. Gordonii , and S. Salvarius (normal mouth). S.pyogenes( group A strep, normal throat flora found in 5-15% of individuals) blood agar used for hemolytic patterns

Neisseria

Fastidious organisms cultivated on chocolate agar, which contains boiled (Lysed) red blood cells that provide nutrients and growth factors needed. Chocolate is not selective so must be identified using oxidase reagent ( purple/ black coloration appears within 5 seconds)

Environmental Organisms

Many of the microbes found in the environment are fungi such as Yeasts or molds. Sabouraud's agar is an acidic medium (pH 5.5) which is used to cultivate acidophiles such as fungi from environmental specimens. Other environmental specimens which are not acidophiles can be cultivated on nutrient agar.

Transient microbiota

Members of normal Microbiota that are present for only a short time before disappearing.

Diphtheroids

Species of genus corynebacterium, non-pathogenic and part of normal skin Microbiota. Cultivated on Mueller-Hinton Tellurite plates. If present they will cultivate gray to black colonies because the Tellurite in the media is reduced to tellurium, which appears as a gray precipitate.

Staphylococcus

Staphylococcus epidermis and Staphylococcus aureus are normal Microbiota of the skin. S. Aureus tends to be found in moist environments such as nose and armpits and is known as a troublesome pathogen, whereas S. Epidermidis is found on dryer areas of the skin and is rarely pathogenic. MSA is used to select for both of these, it also differentiates between then as if it ferments mannitol and turns yellow it is S. Aureus and if not it is S. Epidermis.

Normal microbiota

The population of microbes regularly found on the body. Important part of the immune system.

Microbial antagonism

When the normal Microbiota inhibit pathogenic microbes from colonizing the host