BACTERIAL-RESISTANCE TO DISINFECTANTS CONTAINING QUATERNARY AMMONIUM-COMPOUNDS

Quaternary ammonium compounds (QAC) are widely used as disinfectants i n both medical and food environments. Microbial contaminants are, ther efore, regularly exposed to their action and the isolation from clinic al and food sources of resistant bacteria continues to be reported in many countries. Resistance to QAC in clinical strains of staphylococci is encoded by one of at least three resistance genes, designated qacA , qacB and qacC. Using hybridisation analysis, we have shown that thes e QAC resistance genes are also distributed among staphylococcal strai ns in the food industry. In addition, we have discovered two new resis tance determinants in these food isolates, which are now being charact erised and sequenced. Although the general level of resistance of pure cultures is low, the resistant strains have originally been isolated after exposure to the recommended user concentration of a commercial b rand of QAC. We have also studied resistance to QAC in pseudomonads is olated from the food industry. Their level of resistance is much highe r than that found in staphylococci. About 30% of the collected strains were able to grow in 200 mu g.ml(-1) benzalkonium chloride, the lowes t recommended use concentration for this commonly used type of QAC. (C ) 1998 Elsevier Science Ltd. All rights reserved.