Effect of environmental stress on the ability of Listeria monocytogenes Scott A to attach to food contact surfaces
The attachment and detachment of Listeria monocytogenes Scott A to Buna-N rubber and stainless steel under varying conditions of temperature and pH were investigated. Numbers of attached cells increased with increasing attachment temperatures (10° to 45°C) and time (up to 120 min) for both Buna-N rubber and stainless steel. Cells attached at higher levels on stainless steel at all temperature and pH levels investigated. Rate of attachment was found to be significantly lower at 10°C than 30° and 45°C on Buna-N rubber. When L. monocytogenes was grown at 10°, 30°, and 42°C before exposure to Buna-N rubber at 30°C, differences in rates of adhesion were not significant. A downward shift in the cell suspension holding temperature immediately prior to attachment to Buna-N rubber at 10°C resulted in reduced adhered cell populations. A similar upward shift did not affect attachment at 45°C. Altering the pH of the attachment environment within the pH range of 4 to 9 did not affect the maximum levels of attached cells to Buna-N rubber. However, the measured rates of adhesion indicated slower attachment occurs under alkaline conditions. Growth pH was also found to significantly affect rates of attachment and maximum adhered cell populations to Buna-N rubber. Compared to Buna-N rubber, the rate of attachment to stainless steel was markedly more rapid for all temperature and pH conditions studied and could not be calculated. The ease of removal for cells adhered to Buna-N rubber was significantly affected by growth temperature, but not growth pH. Significant differences in detachment were also found between Buna-N rubber and stainless steel, inferring a stronger attachment to Buna-N rubber. Cell surface hydrophobicity was affected by both growth temperature and growth pH, but differences in hydrophobicity could not be correlated to differences in rates of attachment. Addition of 0.01% trypsin to the attachment medium during cell suspension exposure to both test surfaces resulted in a 99.9% reduction in the adhered cell population when compared to controls. This suggests that proteins may play a role in the initial attachment process for L. monocytogenes.