Functional Characterization of a Novel SMR-Type Efflux Pump RanQ, Mediating Quaternary Ammonium Compound Resistance in Riemerella anatipestifer

( ) is a multidrug-resistant bacterium and an important pathogen responsible for major economic losses in the duck industry. Our previous study revealed that the efflux pump is an important resistance mechanism of Bioinformatics analysis indicated that the gene (denoted here as ), a putative small multidrug resistance (SMR)-type efflux pump, is highly conserved in strains and important for the multidrug resistance. In the present study, we characterized the gene in strain LZ-01. First, the deletion strain RA-LZ01Δ and complemented strain RA-LZ01cΔ were constructed. When compared with that of the wild-type (WT) strain RA-LZ01, the mutant strain Δ showed no significant influence on bacterial growth, virulence, invasion and adhesion, morphology biofilm formation ability, and glucose metabolism. In addition, the Δ mutant strain did not alter the drug resistance phenotype of the WT strain RA-LZ01 and displayed enhanced sensitivity toward structurally related quaternary ammonium compounds, such as benzalkonium chloride and methyl viologen, which show high efflux specificity and selectivity. This study may help elucidate the unprecedented biological functions of the SMR-type efflux pump in . Thus, if this determinant is horizontally transferred, it could cause the spread of quaternary ammonium compound resistance among bacterial species.