DOI: 10.31015/jaefs.2026.3.20 ISSN: 2602-246X

The bactericidal potential of liquid extracts against Yersinia ruckeri: a comparative in vitro assessment

Faik Sertel Secer
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Enteric redmouth disease, caused by Yersinia ruckeri, is a major bacterial disease of farmed rainbow trout (Oncorhynchus mykiss), and rising antibiotic resistance has increased the need for alternative control agents. This study compared the in vitro activity of eight commercial plant liquid extracts (rosemary leaf, dandelion, milk thistle seed, turmeric, vitex fruit, sage, ginger, French maritime pine) against ten Y. ruckeri isolates from diseased farmed trout. Minimum inhibitory (MIC) and minimum bactericidal (MBC) concentrations were determined by broth microdilution in independent triplicates, and MBC/MIC ratios distinguished bactericidal from bacteriostatic action; oxytetracycline susceptibility was assessed in parallel by disk diffusion. All ten isolates were oxytetracycline–resistant (zones 6.33–11.67 mm; MIC 8–16 µg/mL). All extracts inhibited all isolates (MIC 1.95–31.25 µL/mL; MBC 3.90–125 µL/mL). Milk thistle seed, vitex fruit, French maritime pine and turmeric were most active (MIC50 3.90–7.80 µL/mL), whereas dandelion was least active (MIC50 15.62, MBC50 62.50 µL/mL). Activity differed significantly among extracts (Friedman: MIC p = 0.002, MBC p < 0.001; Kendall’s W = 0.32 and 0.36), and MBC/MIC was ≤4 in all extract–isolate combinations. Because these endpoints correspond to roughly 0.4–1.6 % (v/v), extract standardization and in vivo efficacy are required before any practical application can be considered.

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