Luteolin Showed a Resistance Elimination Effect on Gentamicin by Decreasing mRNA Expression in .

is a common inhabitant of mucosal surfaces in animals and causes a variety of infections, including endometritis, mastitis, and liver abscessation, in dairy cows. Many antimicrobial agents are used for treatment of infections caused by ; however, antibiotic resistance has recently become a serious problem. The objective of this study was to characterize the effect of the efflux pump-encoding multidrug and toxic compound extrusion () gene on antibiotic resistance in isolates from cows with signs of endometritis. As a compound from plants, luteolin showed antimicrobial activities in and ; therefore, we also investigated whether luteolin can eliminate antibiotic resistance. We constructed a deletion mutant in BM-H06-3 to identify the function of in antibiotic resistance. mRNA expression was measured to identify the mechanism of luteolin in gentamicin resistance elimination effect in . The isolate BM-H06-3 became susceptible to gentamicin, amikacin, streptomycin, erythromycin, and roxithromycin after deletion. No synergistic effect between luteolin and gentamicin was observed in eight isolates, which were randomly selected from 34 isolates, but the isolates became susceptible to gentamicin after luteolin treatment at a subinhibitory concentration (1/4 minimum inhibitory concentration [MIC]) for 36 hr. Furthermore, luteolin can decrease mRNA expression after luteolin treatment at a subinhibitory concentration (1/4 MIC). We found that the gene was involved in antibiotic resistance and that luteolin induces a resistance elimination effect in . Therefore, luteolin may be a potential agent to inhibit efflux pumps in multidrug-resistant .