Biofilm and planktonic Staphylococcus aureus exhibit distinct gene expression patterns in response to cinnamaldehyde

Staphylococcus aureus forms biofilms in the context many infections, including endocarditis, lung infection, and the colonization of implants. How antimicrobials specifically affect S. aureus biofilms as opposed to planktonic S. aureus is an important consideration in the development of treatments of these infections. It is well known that bacteria in biofilms are more resistant to antimicrobials, and the degree and nature of the responses is crucial to understanding the basis of this resistance. While certain antimicrobials such as antibiotics have specific mechanisms that induce pathways related to those mechanisms, and others such as hypochlorite are highly toxic, a wide variety of compounds exhibit intermediate effects that affect multiple systems. Responses to these substances are important to understand if new therapeutics are to be designed. Here, we investigated antibacterial and antibiofilm effects of cinnamaldehyde (CmAl), an antibacterial agent commonly used in foods. CmAl affects multiple bacterial systems, providing a model for the characterization of these intermediate responses. We measured CmAl activity on established biofilm and planktonic bacteria using recombinant bioluminescent S. aureus and performed RNA-seq on CmAl-treated biofilms and planktonic bacteria. RNA-seq results revealed response pathways that differ between these states, including phosphate uptake. The results of this study demonstrate how CmAl differentially affects S. aureus biofilms compared to planktonic forms. • Benzyl aldehydes such as cinnamaldehyde (CmAl) have long been known to have antimicrobial properties. • CmAl and chemically altered derivatives of CmAl affect multiple systems in the bacterial cell and are being engineered as antibiotics, including modified forms that inhibit specific enzymes such as Mycobacterium tuberculosis DXR. Several of these derivatives act on multiple structures and pathways distinct from standard-of-care antibiotics. • Here, we show that biofilm and planktonic Staphylococcus aureus respond quite differently to CmAl treatment, and that biofilm Staphylococcus aureus exhibits a much more restricted response than the planktonic form. • These differences, which include the up-regulation of tryptophan, glyoxylate, and glycerolipid metabolism in biofilms but not planktonic bacteria, may necessitate modification of CmAl-based antibiotics for the treatment of biofilm infections as opposed to non-biofilm infections. For example, certain imidazole-conjugates of CmAl inhibit the bacterial protein FtsZ, which is essential for cell division.