Monitoring of bacterial load in terms of culturable and non-culturable cells on new materials placed in a delicatessen serve over counter

The aim of this study was to determine how quickly the surface of a refrigerated supermarket serve over counter becomes loaded with bacteria. New material made of polyvinyl chloride or stainless steel was placed on the surface on which foodstuffs are displayed for sale. One to three samples per week for 7 weeks were collected on gauze pads. CFUs were counted and total cells were quantified by real-time PCR. “Viable” cells using real-time PCR following pre-treatment with ethidium monoazide were quantified on stainless steel. Attachment strengths were assessed at the end of the experiment by constructing detachment curves. Whatever the material, on day 1 the microbial load reached values near those observed in the following weeks i.e. 103–104 log total cells/cm2. The number of cells deposited in one week was compensated for by the small reduction obtained by cleaning and disinfection (C&D). The mean difference between total and viable cells was 0.54 log CFUs/cm2. A big drop in CFUs following C&D was observed at the beginning of the experiment, despite no visible decrease in the number of viable cells, but the CFU reduction decreased over time. Nevertheless, the low efficiency of C&D on the dominant microbiota did not indicate the fate of pathogenic bacteria on these materials. Our data suggest that dead cells do not adhere quite so well as viable cells. Although no growth was observed and the attached bacterial community cannot therefore be considered a biofilm, attached cells shared certain properties attributed to biofilms i.e. their resistance to C&D increased over time and they followed a biphasic detachment curve.

► Stainless steel and polyvinyl chloride sheets were placed in a serve over counter.
► Cleaning and disinfection had no detectable impact on total and viable cells number.
► Cleaning and disinfection led to loss of culturability which decreased over time.
► Higher attachment strengths were observed on polyvinyl chloride.
► Growth was not detected but attached cells had biofilm properties.