Experimental evaluation of the velvet pad rinse technique as a microbiological sampling method

The use of velvet pads glued to aluminium foil has been evaluated as a microbiological sampling method in quantitative bacterial recovery experiments, and the efficiency and precision have been determined. The velvet pads uptake of Staphylococcus epidermidis was 0.93 (or 93 per cent) after sampling from a test surface on blood agar, while the release by subsequent imprinting on blood agar was 0.02, the median effective transfer being 0.02. A mechanical rinse and shake procedure of the velvet pad in 0.9 per cent saline followed by centrifugation and surface plating significantly increased the median release to 0.66, the median effective transfer being 0.61. There was no difference in uptake, release and effective transfer between a pure culture of S. epidermidis and a mixed culture of S. epiderimidis and Escherichia coli. Storage of the velvet pad in 0.9 per cent saline for 2 h at room temperature did not influence bacterial recovery significantly, in contrast to a significant decrease after storage in saline for 24 h or storage in a dry Petri dish for 2 h. The high and fairly constant efficiency of bacterial recovery of the velvet pad rinse technique suggests that it could be employed clinically.