Comparative Target Analysis of Chlorinated Biphenyl Antimicrobials Highlights MenG as Molecular Target of Triclocarban.

Triclocarban (TCC), a formerly used disinfectant, kills bacteria via an unknown mechanism of action. A structural hallmark is its N,N′-diaryl urea motif which is also present in other antibiotics including the recently reported small molecule PK150. We here show that, like PK150, TCC exhibits an inhibitory effect on Staphylococcus aureus menaquinone metabolism via inhibition of the biosynthesis protein MenG. However, the activity spectrum (MIC90) of TCC across a broad range of multi-drug resistant staphylococci and enterococci strains was much narrower compared to PK150. Accordingly, TCC did not cause an over-activation of signal peptidase SpsB, a hallmark of the PK150 mode of action. Furthermore, we were able to rule out inhibition of FabI, a confirmed target of the diaryl ether antibiotic triclosan (TCS). Differences in the target profile of TCC and TCS were further investigated by proteomic analysis, showing complex, but rather distinct changes in the protein expression profile of S. aureus. Downregulation of the arginine deiminase pathway provided additional evidence for an effect on bacterial energy metabolism by TCC. Importance TCC9s widespread use as an antimicrobial agent has made it a ubiquitous environmental pollutant despite its withdrawal due to ecological and toxicological concerns. With its antibacterial mechanism of action still being unknown, we undertook a comparative target analysis between TCC, PK150, a recently discovered antibacterial compound with structural reminiscence to TCC, and TCS, another widely employed chlorinated biphenyl antimicrobial, in the bacterium Staphylococcus aureus. We show that there are distinct differences in each compound9s mode of action, but also identify a shared target between TCC and PK150, which is interference with menaquinone metabolism by inhibition of MenG. The prevailing differences, however, which also manifest in a remarkably better broad spectrum activity of PK150, suggest that even high levels of TCC or TCS resistance observed by continuous environmental exposure may not affect the potential of PK150 or related N,N′-diaryl urea compounds as new antibiotic drug candidates against multi-drug resistant infections.