A comparison of surface sampling methods for detecting coliforms on food contact surfaces

Abstract

Newly developed self-contained swab-based methods were assessed for their ability to detect low levels of coliform bacteria on food contact surfaces. Their performance, under controlled laboratory conditions, was compared to a range of conventional microbiological methods, including traditional hygiene swabs, dipslides and sampling sponges. Stainless steel surfaces were inoculated with known levels of coliform bacteria and were sampled immediately after inoculation whilst still wet, or after they had been allowed to air-dry for 1 h. The sampling sponge was the least effective means of detecting coliforms on a wet surface, having a minimum detection limit of approximately 100 cfu cm−2, whereas all other test methods were able to detect the presence of <3·5 cfu cm−2. Allowing inoculated surfaces to dry resulted in a marked reduction in the minimum detection limits of all test methods although this was less for dipslides and the newly developed media-based hygiene swabs. A novel chemiluminescent swab-based assay was capable of providing results in 5 h, comparable to those obtained using traditional spread plates. The results of this study suggest that during the hygienic assessment of food contact surfaces when testing for coliforms, newly developed self-contained swab-based methods, including one giving results in 5 h, could prove a valuable tool for use within an integrated cleaning monitoring strategy.