(653b) The Antibiotic Resistance Game: The Genetic Regulation of Antibiotic Resistance Transfer In Enterococcus Faecalis

One of the main factors driving the rise of drug resistant microbes is the transfer of antibiotic resistance genes present on mobile plasmids between donor and recipient cells via the mechanism of conjugation. In order to combat microbial drug resistance, novel strategies need to be developed to block such transmission of antibiotic resistance. In this work, we study the gene regulatory components involved in transfer of tetracycline resistance conferring plasmid pCF10 between plasmid-carrying donor cells and plasmid-deficient recipient cells in bacterium Enterococcus faecalis. The onset of conjugation is tightly regulated via multi-layered regulation offered by two-key genes prgQ-prgX present on pCF10 in response to a signaling molecule secreted by recipient cells. Using mathematical modeling and experimentation, we describe a novel mechanism of gene-regulation due to transcriptional interference and interaction between sense-antisense transcripts in the prgX/prgQ operon, which causes the system to demonstrate a bistable genetic switch (Chatterjee et al., 2011). Once the genetic-switch is ON, expression of approximately 30 genes downstream of prgQ gene, encoding various proteins involved in transfer of the plasmid, are induced. Induction also results in production of an inhibitor of conjugation, giving rise to negative feedback loop. Mathematical model and experiments indicate that such a negative feed-back loop causes downstream genes to demonstrate a “pulse” of expression, with nearly 2-3 orders of magnitude increase and decrease in expression within a short duration post-induction. Furthermore, proteomic analysis also shows dynamic expression of proteins encoded by the downstream genes. An interplay of positive and negative feedback loops allows the system to quickly transition between ON and OFF states and is critical both for the transfer of plasmid and survival of the donor cell. Studying both the turning-ON and turning-OFF mechanisms of the switch allows identification of potential drug targets for blocking transmission of antibiotic resistance for use in future therapy.

Chatterjee, A., Johnson, C.M., Shu, C.-C., Kaznessis, Y.N., Dunny, G.M., and Hu, W.-S. (2011) Convergent transcription confers a Bistable switch in Enterococcus faecalis conjugation. Proc Natl Acad Sci U S A (in press).