SaeRS Gene Expression Following Exposure to Olive Leaf-Mediated Zinc Oxide Nanoparticles in Multidrug-Resistant...

This pilot study assessed the transcriptional responses of saeR and saeS to green-synthesized zinc oxide nanoparticles (ZnO NPs) prepared using Olea europaea leaf extract in four multidrug-resistant clinical isolates of Staphylococcus aureus. Antimicrobial susceptibility profiles and the prevalence of pvl, agrI, agrII, and agrIII were also determined.

Antimicrobial susceptibility testing was performed on 40 clinical isolates. Four multidrug-resistant isolates were exposed to ZnO NPs at a subinhibitory concentration (1/2 MIC), and saeR and saeS expression was quantified by RT-qPCR using 16S rRNA for normalization and paired comparative Ct calculations. Untreated and exposed ΔCt values from the same isolate were compared using exact two-sided Wilcoxon signed-rank tests. Resistance was highest to oxacillin (85.0%), fusidic acid (82.5%), ceftaroline (72.5%), and rifampin (70.0%), whereas gentamicin, doxycycline, tigecycline, and linezolid showed 97.5% susceptibility. The pvl gene was detected in 27.5% of isolates; agrI, agrII, and agrIII were detected in 17.5%, 20.0%, and 15.0%, respectively. saeR expression decreased numerically in all four isolates, but the paired comparison was not statistically significant (p = 0.125). saeS expression decreased in three isolates and increased in one isolate; this paired comparison was also not significant (p = 0.250).

The findings provide descriptive, isolate-specific evidence of transcriptional responses of saeR and saeS to sub-MIC ZnO-NP exposure in the four MDR S. aureus isolates examined and should not be generalized across S. aureus lineages. They do not establish direct SaeRS inhibition or reduction of virulence-associated phenotypes because only four isolates were assessed and no extract-only, Zn²⁺, chemically synthesized ZnO-NP, downstream virulence, protein-level, or functional controls were included. Larger controlled studies are required before biological or therapeutic implications can be drawn.