Evaluation of the effectiveness of commercially available contact plates for monitoring microbial environments

Aim:  The aim of this study was to measure the efficiency of contact plates to recover microbial contaminants from stainless steel surface.
Materials and Methods:  Three commercially available contact plates were used to recover two biological indicators from stainless steel sheets. The method used was standardised and validated to provide robust results. Parameters such as wetness, fertility and loss of water were also investigated for possible correlation with recovery efficiency.
Results:  The percentage of recovery from the contact plates was low and differences in recovery efficiency between brands depended upon the test organism. The poor recovery was probably due to the inability of the dried micro-organism to transfer to the plate, rather than the inability of the plate to grow the micro-organism. Wetness might help in improving recovery.
Conclusions:  The use of a validated protocol allowed robust investigations into the recovery efficiency of contact plates.
Significance and Impact of the Study:  The poor and variable recovery rates are of concern as they cast doubt on the comparability and reliability of environmental monitoring results where different commercial contact plates have been used.