ABSTRACT
Species of Bacteroides, including Bacteroides fragilis, in an unbalanced gastrointestinal ecosystem, can produce several infections of endogenous nature, and recently have been linked to colon cancer. This chapter summarizes the key phenotypic characteristics of the species of the Bacteroides fragilis group. The genus Bacteroides has undergone major taxonomic revisions in the past few years, and most species suffer changes frequently. Virulence factors produced by B. fragilis can be divided into three categories: adherence to epithelial tissues, protection from the host immune response, and destruction of tissues. By using electron microscopy, three capsule variants within an individual strain of B. fragilis might be observed: large and small capsules, and noncapsulate strain. The ability to evade the host's immune response contributes to the bacterial virulence. Laboratories studying anaerobic bacteria use some principles for isolating and identifying Bacteroides species. The antimicrobial resistance can be due to altered target binding affinity, decreased penetration due to permeability or by the presence of inactivating enzymes.
