Streptococcus ferus is a facultatively anaerobic, gram-positive species of the Streptococcus genus.

Although uncommon, if anaerobic species are suspected (such as in cases where necrotizing enterocolitis or intestinal perforation is a concern, clindamycin is often added.

However, there is a shift at the time of weaning from predominantly facultative anaerobic species, such as Streptococci and Escherichia coli, to mostly obligate anaerobic species.

Thermoanaerobacter kivui (formerly Acetogenium kivui) is an thermophilic, anaerobic, non-sporeforming species of bacteria.

Some nematode species are microscopic,[1] as well as many loricifera, including the recently discovered anaerobic species, which spend their entire lives in an anoxic environment.

Pericoronal infection is normally caused by a mixture of bacterial species that normally are present in the mouth, such as Streptococci and particularly various anaerobic species.

The gingival crevice area (supporting structures of the teeth) provides a habitat for a variety of anaerobic species.

Cryptanaerobacter phenolicus is a gram-positive anaerobic bacterial species in the genus Cryptanaerobacter.

Among bacteria they have been found in many anaerobic species including Clostridia, Megasphaera, and Veillonella.

Propionibacterium propionicus (previously known as Arachnia propionica) is a Gram positive, aerotolerant anaerobic species of Propionibacterium, found as part of the normal human oral flora.