Streptococcus pyogenes: this bacteria always causes disease, which can present a wide array of manifestations in humans, ranging from mild localized infections to life-threatening invasive infections.

Lactobacillus acidophilus: this bacteria is exclusively beneficial in the human gut.

Mycobacterium tuberculosis: a bacteria that can reside in the human body for long periods of time, before producing symptoms, and is always pathogenic.

Campylobacter: people who become infected with this bacteria will get diarrhoea, cramping, abdominal pain, and fever that lasts from one to two weeks.