Membrane filter contact technique for bacteriological sampling of moist surfaces

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Abstract
We used a membrane filter contact technique to pick up and grow bacteria from artificially contaminated surfaces. We were able to recover individual colony-forming units (CFU) of Staphylococcus aureus from a moist agar surface more efficiently with 3- and 5- micron membrane filters than with Rodac plates, velvet pads, velveteen pads, or smaller-pore membrane filters. The effective transfer of bacteria with the 3- and 5-micron membrane filters was 0.96 +/- 0.04 (standard error of the mean) and 0.99 +/- 0.04, respectively, as compared to 0.49 +/- 0.03 for Rodac plates, 0.09 +/- 0.01 velvet pad imprints, 0.05 +/- 0.01 for velveteen pad imprints, 0.27 +/- 0.02 for velvet pad rinses, 0.005 +/- 0.001 for velveteen pad rinses, 0.39 +/- 0.02 for 0.45-micron filters, and 0.85 +/-0.05 for 1.2 micron filters. In addition, the recovery of S. aureus from contaminated bovine muscle surfaces with the 5-microns membrane filter was similar to that of quantitative dilutions of biopsy material and was significantly higher than the recovery from Rodac plates. The 5-microns membrane filters on a paddle recovered 52 +/- 5 CFU/cm2 from artificially contaminated bovine skeletal muscle, the quantitative dilutions of biopsy recovered 69 +/- 5 CFU/cm2, and the Rodac plate recovered 5 +/- 3 CFU/cm2. Sampling of moist surfaces by the membrane filter contact technique is easy to perform and highly efficient; our data suggest that it could be employed for cultures of clinical surfaces such as surgical wounds or burns.