OVERALL ASSESSMENT:
STRENGTHS: The authors showed that several metabolites fromC. sativa had MIC values that warranted further investigation as candidate antibiotics. They not only assessed killing of free-living MRSA, but they extended the study to examine biofilm disruption and killing of persister cells, increasing the clinical relevance of the study. Furthermore, the authors investigated how readily MRSA can acquire resistance to CBG, one of the seven metabolites they identified in their screen. They could not identify a single resistant mutant through a variety of different screening approaches, indicating that resistance could be difficult to develop. Finally, the authors determined that CBG works by disrupting the cell membrane of Gram-positive bacteria. They found that CBG alone could not kill Gram-negative bacteria but disrupting the outer membrane with polymyxin B allowed CBG to work on the inner membrane and restore its antibacterial effects. Overall, the study has clear potential for impact and provides a foundation for future studies.
WEAKNESSES: While the experimental design was generally good, we identified some weaknesses in data presentation. The methods section was lacking in detail required for others to reproduce experiments. There were inconsistencies in figure labels and legends that must be addressed. While the authors showed that CBG is an effective antibiotic, it was not clear whether this molecule has any toxicity in animals or humans that would limit its utility. This could be addressed by discussing previous CBG studies that established these parameters, or through in vivo experiments. Finally, the in vivo aspect of this study was underdeveloped; we believe that this study could have benefited from evaluating the effectiveness of polymyxin B and CBG in a skin infection model, as polymyxin B is known to be toxic if ingested (there was some debate in the group as to whether this skin model was beyond the scope of the current manuscript). Without more in vivodata or information about CBG toxicity it remains difficult to properly evaluate the manuscript.