CTnDOT is a 65-kb conjugative transposon that is found in Bacteroides spp., which are one of the more abundant members within the lower human gastrointestinal tract. CTnDOT encodes resistance to the antibiotics erythromycin and tetracycline (Tc). An interesting feature of CTnDOT is that exposure to low levels of Tc induces a cascade of events that ultimately results in CTnDOT conjugative transfer. However, Tc is apparently not a switch that activates transfer but rather a signal that appears to override a series of negative regulators that inhibit premature excision and transfer of CTnDOT. In this minireview, we summarize over 20 years of research that focused on elucidating the highly coordinated regulation of excision, mobilization, and transfer of CTnDOT.
Importance: Bacteroides spp. are abundant commensals in the human colon, but they are also considered opportunistic pathogens, as they can cause life-threatening infections if they should escape the colon. Bacteroides spp. are the most common cause of anaerobic infections and are rather difficult to treat due to the prevalence of antibiotic resistance within this genus. Today over 80% of Bacteroides are resistant to tetracycline (Tc), and a study looking at both clinical and community isolates demonstrated that this resistance was specifically due to the conjugative transposon CTnDOT.