Membrane filter contact technique for bacteriological sampling of moist surfaces

Abstract

A membrane filter contact technique was used to pick up and grow bacteria from artificially contaminated surfaces. One was able to recover individual colony-forming units (CFU) of Staphylococcus aureus from a moist agar surface more efficiently with 3 and 5 .mu.m 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 .mu.m 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 .mu.m filters and 0.85 .+-. 0.05 for 1.2 .mu.m filters. The recovery of S. aureus from contaminated bovine muscle surfaces with the 5 .mu.m membrane filter was similar to that of quantitative dilutions of biopsy material and was significantly higher than the recovery from Rodac plates. The 5 .mu.m 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/m2 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; the data suggest that it could be employed for quantitative cultures of clinical surfaces such as surgical wounds or burns.