Impact of swab material on microbial surface sampling

Efficient microbial sampling from surfaces for subsequent detection and quantification is crucial in fields such as food safety and hygiene monitoring. Cotton swabs are traditionally used for sample collection, but today there are numerous swabs of alternative material and different sizes available. Recovery efficiencies of swabs for different applications have been compared in several studies. However, the results are often contradictory. We have compared 15 different swabs made of cotton (n = 5), flocked nylon (n = 3) and foam (n = 7), for sampling of Listeria monocytogenes and mengovirus on small (4 cm²) and large (100 cm²) areas of window glass, ridged plastic and absorbing wood. Molecular quantification methods (qPCR and RT-qPCR) were applied, and all sampling and sample processing were standardized. Specific swabs gave higher DNA/RNA yields than others, depending on both the surface characteristics and the collected target. The highest DNA yields were achieved by applying Selefa or Puritan cotton swabs for Listeria sampling on 4 cm² areas of window glass and ridged plastic. Certain foam swabs (Critical swab with medium head and Macrofoam) gave the highest yields when sampling Listeria on 4 cm² areas of wood and on 100 cm² areas of ridged plastic and wood. Most foam swabs, and especially Sigma Virocult, were advantageous for virus sampling, regardless of surface. Nylon-flocked swabs showed poor recovery regardless of surface characteristics. The recovery varied substantially between swabs made of the same material, suggesting that a single swab may not be representative for a certain swab material.