A S. mutans is a bacterium that causes cavities, and S. pneumonia is a bacterium that causes pneumonia.

B Fungi evolved the ability to produce anti-bacterial chemicals as they competed with bacteria over millions of years.

C The bacterium Streptococcus pyogenes causes strep throat and rheumatic heart disease.

D Species of bacteria belonging to the genus Bacteroides help the human body digest food.

A Heliobacter pylori is a bacterium that causes gastritis (irritation or inflammation of the stomach lining) and peptic ulcers, diseases which were once thought to be caused by too much acid.

B Streptococcus salivarius appears to help prevent tooth decay in the mouth but can bedangerous to people with weakened immune systems if it gets outside the mouth.

C Bacillus subtilis releases toxic chemicals to kill fungus, possibly including Trichophytoninterdigitale and other species that cause athlete’s foot.

D Skin, which is our interface with the world, supports a large number of the human body’s most diverse populations of bacteria, including Bacillus subtilis.

A Microbes first appeared over 3.5 billion years ago and have coevolved with humans over the past six million years.

B Studies suggest that rapidly increasing antibiotic use in the United States has reduced thediversity of our microbiomes.

C Bacteroides are the most numerous bacteria in the human body and help it digest food.

D The human body is an ecosystem made up of microbes that play a variety of roles in human health.

A having a lot of variety

B being harmful to others

C being helpful to others

D moving from one place to another

A lessened

B blocked

C developed

D defined