Use of conductimetry to rapidly determine relative stress sensitivity in Salmonella isolates

摘要

AIMS: To compare conventional plate counting and indirect conductimetry as techniques for ranking the resistance of Salmonella spp. to processing stressors. METHODS AND RESULTS: Forty Salmonella isolates were subjected to three separate stressors used in food processing; irradiation, heat and high hydrostatic pressure (HHP). Total viable counts (TVC) using conventional plate counts and time to detection (TTD) using indirect conductimetry were determined. A significant negative correlation between TVC and TTD was seen with irradiation (P < 0.01) and heat (P < 0.05) but not HHP. CONCLUSIONS: For a group of salmonellas, indirect conductimetry can rapidly determine a ranking of isolate sensitivity to irradiation and heat. However, for HHP, the resultsindicated that conventional plate counting alone cannot be used to determine sensitivity. SIGNIFICANCE AND IMPACT OF THE STUDY: The resistance of micro-organisms to processing systems must be ranked to allow the selection of appropriate isolates for process validation. TTD measurements allow rapid screening of salmonellas to rank isolates for resistance to irradiation and heat stress. However, following HHP, the TVC of survivors is independent of the time required for growth to a set cell density and therefore it cannot be used as the sole measure of relative stress resistance.