This result demonstrates that in E. coli RamA can mediate an MDR phenotype independently of a functionally intact marA , likely by direct activation of MarA-controlled genes .
The expression of MarA is further activated when MarA binds marbox in the operator of marRAB .7 MarA not only regulates its own expression , but also the expression of many genes involved in adaptation to stress conditions , such as oxidative-stress , heavy metals or antimicrobials .10 A well-known example of an adaptive phenotype controlled by MarA is increased tolerance to antibiotics such as tetracycline , chloramphenicol and fluoroquinolones ,11,12 and to other anti-microbial compounds such as triclosan13 and pine oil .14 This is achieved mainly due to control of efflux by up-regulation of 15 the AcrAB-TolC efflux pump and control of influx by the induction of micF ,13,16 which encodes an antisense RNA involved in the regulation of outer membrane protein F ( OmpF ) , through which hydrophilic substances enter the cell .