Effects of a Nanoscale Plasma Coating on Virulence Gene Expression in Pathogenic Biofilms

Introduction: In our previous studies, trimethylsilane (TMS) and TMS+O₂ (1:4) plasma nanocoatings were found to reduce the numbers of Listeria monocytogenes in biofilms by 99%. On the surface of TMS and TMS+O₂wafers, an increase in carbon, silicon and oxygen elements was detected and distorted cells were found, indicating deleterious effects of the coatings on cells. 

Purpose: The objective of this study was to investigate if the nanocoatings affect virulence gene expression in L. monocytogenes and Escherichia coli O157:H7. 

Methods: L. monocytogenes and E. coli O157:H7 were allowed to form biofilms on stainless steel (SS) wafers for 48 h. RNA extraction and reverse transcription were conducted on cells released from the biofilms. The expression of the hlyA, rpoB, inlA, inlB and actA genes in L. monocytogenes, and stx1, stx2, eaeA and arcA in E. coli O157:H7 was analyzed. Agar pour plating, and laser confocal and scanning electron microscopies were performed to investigate the mechanism of action of the nanocoatings on these pathogens. 

Results: On TMS and TMS+O₂ SS, L. monocytogenes numbers dropped from 10⁷ to 10⁵ CFU/wafer, distorted cells were found but no significant reduction in the expression of hlyA and rpoB was detected compared to the uncoated group. The TMS treatment showed a 0.5 log reduction in E. coli O157:H7 with some distorted cells but no significant difference in the expression of stx1, stx2 and eaeA genes was found. 

Significance: With the change in surface elements, the surface attractive forces may increase vastly enough to distort and kill adjacent cells without affecting the expression of virulence genes. The results imply that TMS and TMS+O₂ coatings can reduce the formation of biofilms without leading to resistance to this type of coating.