fragilis

Fragilis is a Latin adjective meaning fragile or easily broken, and it is commonly used in scientific naming as a species epithet to indicate delicate features of an organism. The epithet occurs across diverse taxa and does not refer to a single group or rank.

The most well-known use is Bacteroides fragilis, a Gram-negative, anaerobic bacterium that is part of the normal human gut microbiota but can act as an opportunistic pathogen. B. fragilis is a frequent cause of intra-abdominal abscesses, pelvic infections, and bacteremia, particularly when mucosal barriers are breached or in hospitalized patients. The species often produces beta-lactamases, making penicillin alone ineffective; treatment commonly involves metronidazole, carbapenems, or beta-lactamase inhibitor–containing regimens, guided by susceptibility testing. Virulence factors include a polysaccharide capsule and, in enterotoxigenic strains, the B. fragilis toxin (BFT).

Bft encodes a zinc-dependent metalloprotease that can disrupt epithelial cell junctions by cleaving E-cadherin, contributing to inflammation. Some studies have linked enterotoxigenic B. fragilis strains with colorectal inflammation and, in certain contexts, with carcinogenic processes, though causal relationships remain an area of ongoing research.

Beyond Bacteroides fragilis, fragilis serves as a Latin epithet in other species' names to denote fragile characteristics, reflecting its descriptive origin in taxonomy. The term thus appears in miscellaneous scientific names rather than indicating a single, unified taxonomic group.