Campylobacteriosis is a zoonosis caused by Campylobacter spp. and it is one of the most common intestinal infections of humans in Europe. Due to adaptation of C. jejuni to stress conditions and antimicrobial resistance to one or more antibiotics, research for new antibiotics and active substances that can revive the function of existing antibiotics is needed. These substances can also be found in nature; in our case in extracts and their fractions of the plant Peucedanum ostruthium. We evaluated the antimicrobial and modulatory effectiveness on P. ostruthium with minimal inhibitory concentration (MIC) by the microdilution method in broth. Extracts exhibited from medium to weak antimicrobial activity as the minimal inhibitory concentrations were 500 mg/L or more. The exceptions were two fractions of ethanol extract; E0 (250 mg/L) and E4 (125 mg/L). We have proven that CmeABC pump is the target of P. ostruthium extracts by testing antimicrobial activity on mutants with interrupted gene frame shifts of efflux pumps. By comparing MICs of antibiotics and antibiotics in combinations with three basic extracts we proved week modulatory effects. By testing the accumulation of ethidium bromide in four different concentrations (1/4 MIC, 1/8 MIC, 1/16 MIC and 1/32 MIC) in the C. jejuni cells we found that P. ostruthium extracts function as inhibitors of efflux pumps. By testing membrane integrity we proved that the extracts of P. ostruthium increase the permeability of the C. jejuni cell membrane.
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