The National Academies: What You Need To Know About Infectious Disease

The National Academies

What You Need To Know About Infectious Disease

Bacteria

Bacteria are 10 to 100 times larger than viruses and are more self-sufficient. These single-celled organisms, generally visible under a low-powered microscope, come in three shapes: spherical (coccus), rodlike (bacillus), and curved (vibrio, spirillum, or spirochete).
Bacteria are ancient organisms. Evidence for them exists in the fossil record from more than 3 billion years ago.
Most bacteria carry a single circular molecule of DNA, which encodes (or programs) the essential genes for reproduction and other cellular functions. Sometimes they carry accessory small rings of DNA, known as plasmids, that enable specialized functions like antibiotic resistance. Unlike more complex forms of life, bacteria carry only one set of chromosomes instead of two. They reproduce by dividing into two cells, a process called binary fission. Their offspring are identical, essentially clones with the exact same genetic material. When mistakes are made during replication and a mutation occurs, it creates variety within the population that could—under the right circumstances—lead to an enhanced ability to adapt to a changing environment. Bacteria can also acquire new genetic material from other bacteria, viruses, plants, and even yeasts. This ability means they can evolve suddenly and rapidly instead of slowly adapting.
 
Bacteria are ancient organisms. Evidence for them exists in the fossil record from more than 3 billion years ago. They have evolved many different behaviors over a wide range of habitats, learning to adhere to cells, make paralyzing poisons and other toxins, evade or suppress our bodies’ defenses, and resist drugs and the immune system’s antibodies. Bacterial infections are associated with diseases such as strep throat, tuberculosis, staph skin infections, and urinary tract and bloodstream infections.

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Disease Watchlist

What do you know about infectious disease?

Roughly how many microbes live in the human gastrointestinal tract?

  • Sorry, that’s incorrect.

    About ten trillion microbes live in the human gastrointestinal tract. They are essential for proper digestion and absorption of nutrients.

  • Sorry, that’s incorrect.

    About ten trillion microbes live in the human gastrointestinal tract. They are essential for proper digestion and absorption of nutrients.

  • Sorry, that’s incorrect.

    About ten trillion microbes live in the human gastrointestinal tract. They are essential for proper digestion and absorption of nutrients.

  • Correct!

    About ten trillion microbes live in the human gastrointestinal tract. They are essential for proper digestion and absorption of nutrients.

Infectious Disease Defined

Fungi

A taxonomic Kingdom of spore-forming organisms distinct from plants, animals, and bacteria that includes microorganisms such as yeast and molds, as well as more familiar mushrooms.

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National Academies Press

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