Interaction of Detergents and Disinfectants upon Surface Adhered Populations of Escherichia coli and Listeria monocytogenes

Abstract

The primary aim of this investigation was to identify and assess the interactions (synergies and antagonisms) that exist between 20 minute detergent and 5 minute disinfectant treatments upon three factory isolated strains of surface adhered (1-hour attached) and surface adapted (24-hour biofilm) populations of Escherichia coli and Listeria monocytogenes, plus a comparison with vero-toxin producing strains of E. coli, when used as part of a cleaning and disinfection regime. The detergents chosen for assessment were two non-ionic (91/4 - Alcohol Ethoxylate and KCL5 - Polyethoxylated Alcohol), two anionic (LX28 - Sodium Lauryl Sulphate and Nec28 - Sodium Laurylether Sulphate) and two novel bismuth thiols (BisEDT - 1:1 Bismuth nitrate 1,2-ethanedithiol and BisTOL - 2:1 Bismuth nitrate 3,4-dimercaptotoluene), developed at Winthrop University Hospital, New York. The disinfectants chosen for assessment were a quaternary ammonium compound (BAC - Benzyl alkonium Chloride) and a chlorine releasing agent (NaDCC - Sodium Dichloroisocyanurate). The investigation showed that there were no specific cleaning and disinfection regimes that will adequately target both E. coli and L. monocytogenes strains. It was also concluded that to maximise the removal and disinfection of persistent strains of a given microorganism, it may be necessary to design a regime to specifically target not just the species, but the strain involved and where possible requires mechanical cleaning. The novel bismuth thiols were seen to be promising detergents to aid in the removal of E. coli strains and warrant further attention for future studies. Finally, an investigation to identify possible mechanisms of resistance to disinfectant treatments following detergent treatment, showed that different detergents can induce expression of the stress response proteins, HSP60 and HSP70, at differing levels of expression after the same contact time and against different states of adherent populations, i.e. 1-hour attached or 24-hour biofilm populations.