Clove Oil Modulates Biofilm-Associated Gene Expression in Oral Staphylococcus Aureus Compared with Tetracycline

Abstract

Oral Staphylococcus aureus can persist through adhesion and biofilm-associated pathways, and antimicrobial exposure below the minimum inhibitory concentration may alter virulence-gene transcription without completely suppressing growth. This study evaluated the effects of commercial clove oil and tetracycline on the relative expression of fnbA, icaC, and icaD in clinical oral S. aureus. Two hundred oral specimens were cultured, 75 isolates were identified as S. aureus, and four isolates (1, 5, 7, and 8) were selected for MIC/sub-MIC and transcriptional analysis. MICs were determined by resazurin-based broth microdilution. Isolate-specific sub-MIC exposures were followed by one-step RT-qPCR using 16S rRNA as the reference transcript and the 2^(−ΔΔCt) method. Clove-oil exposure reduced all three targets across the four isolates, with mean fold changes of 0.531 for fnbA, 0.445 for icaC, and 0.560 for icaD. Tetracycline increased fnbA and icaD to 1.178- and 1.555-fold, respectively, while reducing icaC to 0.596-fold. Exact Friedman tests showed overall condition effects for fnbA and icaD (P=0.0046) and icaC (P=0.0417), whereas Holm-adjusted pairwise comparisons were not significant. Commercial clove oil therefore produced a consistent downward transcriptional pattern, while tetracycline produced gene-dependent responses. These findings support further investigation of clove-oil constituents as modulators of biofilm-associated virulence pathways.