1. Cartoon depiction of the salient features of a theoretical composite of Bacteroides fragilis and Bacteroides thetaiotaomicron that underscores the extent of its interaction with its environment.
Cartoon depiction of the salient features of a theoretical composite of Bacteroides fragilis and Bacteroides thetaiotaomicron that underscores the extent of its interaction with its environment. (A) Tetracycline has a stimulatory effect on expression of the RteA-RteB two-component regulatory system and induces expression and transfer of tetracycline resistance. The RteA-RteB two-component system controls the expression of a third regulatory gene, rteC, which, in turn controls excision and transfer of CTnDot, a conjugative transposon carrying the tetracycline resistance gene (tetQ). CTnDot can then transfer tetQ to other bacteria. (B and C) ECF-type σ-factor and its membrane-tethered cognate anti-σ-factor. These factors are frequently associated with operons for starch utilization and may be involved in the adaptive ability of B. thetaiotomicron to express different enzymes according to specific nutrient availability. (D) ETBF can excrete an endotoxin implicated in GI illness and possibly IBD. (E) B. fragilis may resist antimicrobial action in a number of ways. Two of these mechanisms are periplasmic β-lactamase enzymes that digest β-lactamases (and, depending on the enzyme, carbapenems). Another mechanism is the RND-type efflux pumps, which can expel the antibiotic and may contribute to multiple antimicrobial resistance. (F) A hybrid two-component signal system interprets the nutrient environment and may also be involved in sensing the neighboring polysaccharide landscape and modulating “mimicry” so that the surface polysaccharide structure of the bacterium can be altered to match the surrounding landscape. This may allow the bacterium to avoid eliciting a host immune response. (G) The capsule of B. fragilis can induce abscesses in the host. Somewhat ironically, the zwitterionic nature of the capsule allows it to “dock” on a groove on the APC and be presented to the CD4+ T cell, which then produces a number of cytokines, including IL-10, which can inhibit abscess formation in the host. (H) Expression of the bmeB RND pumps in B. fragilis can be induced by a variety of agents, including bile, antimicrobial agents, cleansers, and autoinducers important in quorum sensing among bacteria.
Hannah M. Wexler Clin. Microbiol. Rev. 2007; doi: /CMR