THE STAPHYLOCOCCUS QACH GENE-PRODUCT - A NEW MEMBER OF THE SMR FAMILYENCODING MULTIDRUG-RESISTANCE

The prevalence of disinfectant-resistant food-related microorganisms i s of concern to the food industry. The Staphylococcus saprohyticus str ain ST2H6 isolated from a poultry processing plant contained a 2.4-kb plasmid (p2H6) harbouring qacH, which encodes resistance to disinfecta nts based on quaternary ammonium compounds. The complete p2H6 nucleoti de sequence revealed an open reading Frame encoding a putative protein of 107 amino acid residues with strong similarity to members of the s mall multidrug resistance protein family. QacH also conferred high-lev el ethidium bromide resistance and low-level proflavine resistance and thus differed phenotypically from the similar proteins Smr and QacG. Fluorimetry indicated that the high-level ethidium bromide resistance was due to improved efflux energised by the proton motive force. Site- directed mutagenesis substituting the Asp-24 residue with Glu-24 had n o effect on resistance characteristics. An additional open reading fra me on p2H6 encoded a putative protein with similarity to rolling circl e replication proteins. (C) 1998 Federation of European Microbiologica l Societies. Published by Elsevier Science B.V. All rights reserved.