Susceptibility of Listeria monocytogenes from traditional cheese-dairies to in-use sanitizers

The minimal inhibitory concentrations (MICs) and the minimal bactericidal concentrations (MBCs) of five sanitizers (alkyl amine acetate, phosphoric acid, anionic tension active and two chlorine/alkaline) against 15 isolates of Listeriamonocytogenes (including isolates found persistently in two dairies) were determined. Alkyl amine acetate was the only agent whose efficacy was poorly affected by the presence of organic matter. The values of MICs and MBCs of cells pre-exposed to sub-inhibitory and sub-lethal concentrations of the disinfectants, did not suggest adaptation. It is possible that factors other than resistance or adaptation to sanitizers could account for the persistence of particular clones of L. monocytogenes in these dairies.