Microbes: Other "Nerdy" Information

If you are more curious about microbes, and want to understand why Streptococcus bacteria, for example, need close contact for transmission from person to person, here are last bits of information about the microorganisms in your flora that you may encounter. Some may call this information "nerdy" or "geek-speak", but as a science person, I find it fascinating!

It’s not necessary for you to memorize any of this, because you can always come back to this page: Air Requirements, Fermentation types, Gram Staining, Spores and Laboratory-Study Lingo.

Air Requirements of Flora Microbes

Aerobic” means “with oxygen” so aerobic microorganisms need oxygen to live. “Anaerobic” means “without oxygen”, so anaerobic ones do not need oxygen to survive.

Facultative anaerobe” means that the microorganism can use oxygen if it is there or can live in environments without oxygen. “Obligate anaerobe“ means it cannot live in oxygenated places.

Aerotolerant” means that the microorganisms can survive in, but not use, small amounts of oxygen.

Lastly, “microaerophilic” means that the microorganisms needs low levels of oxygen to live, much lower than the 20% or so oxygen content of air. So you wouldn’t want to be fooled buying something like a salad dressing, for example, that contains a probiotic that is an obligate anaerobe (like some Bifidobacterium species) since the dressing is spread over the salad and exposed to air.

Fermentation Types Of Flora Microbes

Fermentation is one process of producing energy in microorganisms. It is especially important in the lactic-acid bacteria (LAB) and yeasts. Fermentation does not always have to take place in an anaerobic (no oxygen) environment, but most bacteria will use fermentation when air is absent.

Homofermentative” means that the bacteria produce mostly or only one end product, such as lactic-acid from glucose.

Heterofermentative” means that the bacteria produce different end products, such as acids, alcohols and gases, from carbohydrates such as glucose.

"Facultative heterofermentative" means that it depends on the circumstances. It may or may not produce the different end products.

Gram Staining of Flora Microbes

Bacteria is often referred to as “Gram-positive” or “Gram-negative”. The Gram method is a way of staining bacteria to determine basic cell wall properties to help identify the general type of bacteria quickly. However, not all bacteria stain either positive or negative consistently, and some don’t stain at all.

In addition to Gram staining, microorganisms were routinely cultured in a laboratory in a petri dish to identify them. Since some microbes are not able to be cultured outside of the body in a lab in a petri dish, and since Gram staining is helpful but not an absolute diagnosis, now the gold standard is to use gene sequencing to more accurately determine the genus, species and strain levels of flora.


Spores are reproductive structures that are either actively ejected from the microorganism with force, or passively distributed through contact with the environment. You have probably heard of mold spores, but may be surprised to know that some bacteria form spores, too. Microbes that produce spores are “sporulating”; those that don’t produce spores are “non-sporulating.”

Laboratory-Study Lingo

When doing experiments, scientists summarize where the study was done. “In vitro” means in isolated cells in a laboratory test tube or petri dish. “In vivo” means in the whole, living organism. “Ex vivo” means in live, isolated cells studied outside of an organism but in conditions similar to their natural conditions.

Learn about other information concerning microorganisms:

What your flora is

How probiotics are classified

What CFU means

Why CFU is important

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