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In Vitro Effects of Centaurea ovina (Roudbari Cornflower) Aqueous and Ethanolic Extracts on Staphylococcus
Sara Sadeghi Keleshteri1, Mohammad Javad Mehdipour Moghaddam1,2, Akbar Norastehnia2
1Department of Biology, University Campus 2, University of Guilan, Rasht, Iran, guilan.ac.ir.
Objectives:
Staphylococcus saprophyticus frequently causes community-acquired urinary tract infections (UTIs) and is characterized by multidrug resistance (MDR) and biofilm formation. This study evaluated the in vitro antibacterial and antibiofilm effects of aqueous and ethanolic extracts of Centaurea ovina (Roudbari cornflower) against clinical S. saprophyticus isolates and measured changes in ureC and uafA transcript levels after exposure to the extracts.
Methods:
The aqueous and 80% ethanolic extracts of C. ovina were analyzed for total phenolics, flavonoids, flavonols, anthocyanins, and DPPH radical-scavenging activity. Antibacterial activity against three clinical isolates (SS1-SS3) was assessed using agar well diffusion and broth microdilution (MIC/MBC). Biofilm inhibition was measured by crystal violet staining. In the MDR isolate (SS2), ureC and uafA transcript levels were measured by SYBR Green qRT-PCR (2-ΔΔCt) after treatment with the ethanolic extract at a sub-MIC concentration (1/2MIC), with results normalized to 16S rRNA.
Results:
The ethanolic extract contained more flavonoids and flavonols and exhibited stronger DPPH scavenging activity than the aqueous extract, which had more total phenolics. In broth microdilution, the ethanolic extract inhibited SS1-SS3 growth at 48 mg/mL (MIC), whereas the aqueous extract did not reach an MIC within the tested range (MIC > 48 mg/mL). No bactericidal effect was observed for the ethanolic extract (MBC > 48 mg/mL). Both extracts reduced biofilm inhibition in a concentration-dependent manner. The ethanolic extract demonstrated significantly higher efficacy, achieving up to 85.6% inhibition (for SS2) at 48 mg/mL, compared with the aqueous extract, which reached up to 71.6% inhibition (for SS2) at the same concentration. In SS2, the ethanolic extract at the sub-MIC reduced ureC and uafA transcript levels to 0.278 and 0.272 times those of untreated controls, respectively.
Conclusions:
Both aqueous and ethanolic C. ovina extracts showed in vitro growth-inhibitory and antibiofilm activity against clinical S. saprophyticus isolates, with the ethanolic extract being more effective. This effect was associated with lower expression of two uropathogenesis-related genes in an MDR isolate. Further chemical analysis, testing at lower concentrations, and in vivo studies are needed before clinical use.
