Comparison of adenosine triphosphate (ATP) bioluminescence and aerobic plate counts (APC) on plastic cutting boards*

Abstract

The objective of this study was to compare the adenosine triphosphate (ATP) bioluminescence method with aerobic plate count (APC). Three plastic cutting boards (30 × 35 cm) divided into 42 equal areas of 5 × 5 cm were used as food-contact surfaces. A culture of Lactobacillus rhamnosus ATCC 7469 with a starting concentration of 10⁹ colony-forming units (cfu/mL) was used as a source of cells and ATP. The culture was diluted in phosphate buffer saline to obtain four more initial target concentrations 10⁷, 10⁵, 10³ and 10¹ cfu/mL. After inoculation of the boards, recovery of microorganism was achieved by swabbing the surface with sterile cotton-tipped swabs for the APC assay, and PocketSwab Plus (Charm Sciences Inc., Lawrence, MA) for the bioluminescence test. Recovery after 15 min of inoculation gave average bioluminescence readings of 1.08 log₁₀, 2.99 log₁₀, 4.97 log₁₀ and 5.84 log₁₀ relative light units that corresponded to average recovered APC readings of 3.71 × 10³, 5.39 × 10⁵, 7.44 × 10⁷ and 9.30 × 10⁹ cfu on a 25-cm² surface area. Controls taken prior to the inoculation of the boards gave estimated average APC readings of <10 cfu and bioluminescence readings equal to zero. The correlation coefficient, r = 0.98, suggested a strong relationship between the two methods. A linear regression analysis showed a positive linear relationship between the two methods in the range of 10³–10⁷ cfu. A sensitive ratio test with a value of 1.016 gave an indication that ATP is as good as APC in evaluating sanitation on plastic cutting boards.