Recovery and transfer of Salmonella typhimurium from four different domestic food contact surfaces.

Domestic food contact surfaces can play an important role in the transmission of foodborne disease, yet debate continues as to which surface materials pose the greatest risk to consumer health in terms of cross-contamination during food preparation. Salmonella Typhimurium was inoculated onto stainless steel, Formica, polypropylene, or wooden surfaces (25 cm2) in the presence or absence of protein (tryptic soy broth supplemented with 5% horse serum) and held at room temperature. The pathogen was recovered from the test surfaces immediately after inoculation (T=0) and every hour for up to 6 h, by a conventional microbiological sampling technique and by direct transfer onto a model ready-to-eat food (cucumber slices). On all surfaces, pathogen numbers declined during the 6-h holding period, with the most rapid reductions occurring within the first hour. The presence of protein significantly increased (P < 0.05) the number of bacteria recovered from all surface types. However, regardless of application medium or holding time, the number of bacteria recovered from Formica (in all cases) and stainless steel (in most cases) was significantly higher than were the numbers on polypropylene or wood. Similarly, regardless of application medium or holding time, significantly higher bacterial numbers were transferred to the model food from Formica or stainless steel than from polypropylene or wooden surfaces. These differences were greater when the bacteria were applied in a protein-rich medium and the test surfaces held for 1 h or more. The results of this study emphasize that differences, both in recoverability and in the number of bacteria transferred to the model food rather than simply reflecting differences in pathogen survival, may also reflect differences in the ability of the test bacteria to remobilize from the different surface types. However, the results also demonstrate a fundamental problem when choosing food contact surfaces, i.e., that those characteristics that make a surface "easy to clean" may also render it more likely to release contaminating pathogens during common food preparation practices.