Moisture, sawdust, and bleach regulate the persistence of Escherichia coli O157:H7 on floor surfaces in butcher shops

Survival of Escherichia coli O157:H7 on typical butcher shop ceramic floor tiles contaminated with meat juice was compared in the presence and absence of sawdust, and under different moisture and cleaning regimes. Floor tiles from a butcher shop were cut into 5 × 5 cm pieces, and half were cleaned with commercial bleach diluted with water at 60 °C to simulate mopping. A coating of commercial sawdust was applied to half of the tiles, while the other half were left bare. Meat juice collected from beef joints was inoculated with E. coli O157:H7 (strain #3704), and subsequently applied onto tiles at a density of 6.47 log10 CFU cm−2. Thereafter, tiles were stored at room temperature (20 ± 2 °C), with half maintained under moist conditions [relative humidity (RH) close to 100%] and the other half gradually air-dried (RH 70 ± 5%). Viable E. coli O157:H7 persisted on all tiles over 72 h, although die-off rate varied with environmental conditions. Desiccation of surfaces resulted in a more rapid decline in E. coli O157:H7 numbers, while cleaning of the tiles with bleach prior to contaminating also affected pathogen recovery. Overall, greater numbers of cells were recovered from tiles when no sawdust had been applied; however the presence of sawdust only reduced survival on tiles under dry conditions, and damp sawdust actually increased survival. This highlights the importance of regular cleaning and removal of sawdust to reduce pathogen persistence.