Bacteroides fragilis group, are the most frequently encountered anaerobes in clinical specimens.

They tend to be more virulent and drug resistant than most other anaerobes.

Therefore it is important to identify members of the B. fragilis group
Of these especially B. fragilis, B. thetaiotaomicron, and B. ovatus are highly relevant in human infections.

Taxonomy
Family: Bacteroidaceae

Natural habitats
They inhabit the mucosal surfaces of the oral cavity, gastrointestinal tract and the gut of animals and human.

Clinical significance
They are involved in a variety of infections associated with considerable morbidity and mortality.

Anaerobic bacteria can occasionally spread to the adjacent tissues and the bloodstream with serious consequences.
In cases when gram negatives anaerobes gain entrance to the bloodstream and trigger a systemic inflammatory response, this may result in a sepsis or infective endocarditis with a fatal outcome.