Effect of environmental conditions on the survival and transfer of Enterococcus faecium between wheat flour and selected contact surfaces

Abstract

Low moisture food safety issues are frequently associated with Salmonella and its cross-contamination. As a non-pathogenic surrogate, the survival levels and transfer of Enterococcus faecium NRRL B-2354 on stainless steel (SS) and polypropylene (PP) coupons were investigated. The transfer rates of E. faecium between coupons and wheat flour were also determined at different temperature (13, 25, 37, and 49 °C) and humidity levels (45, 55, 65, and 75%). Results showed that survival of E. faecium on the coupons was not significantly affected by the selected material type. At 25 °C and 45% humidity, E. faecium with an inoculation level of ∼10⁷ CFU/cm² decreased by 2.69 ± 0.28 Log CFU/cm² and 2.85 ± 0.32 Log CFU/cm² on SS and PP surface after 96 h, respectively. While temperature did not significantly influence the transfer rate, humidity did. The highest transfer rate from coupons to wheat flour (5.10 ± 0.23%) occurred at 75% relative humidity. Rougher surfaces reduced the transfer rate from coupons to wheat flour, but not the reverse. Moreover, the transfer rate from coupons to wheat flour was significantly higher than the reverse. These findings highlight the significant role of environmental factors and surface properties in cross-contamination.