Microbiological sampling of towels: comparison of 7 methods.

Pull-out roller towels were infected with bacteria and examined with 5 non-destructive methods. In addition to three traditional methods, the agar contact method (A), the swab method (S) and the tape method (T), two lesser known methods have been applied: the rinsing box method (R), new developed in the laboratory, and the filter method (F). In the first (R), the towel is fixed between the lid and the cup of a metal box containing a rinsing liquid; shaking the box completes the test. In the second (F) the liquid is forced through the towel by vacuum. In both experiments the rinsing liquid is tested for contamination. Destructive methods, mainly with a peristaltic blender ("stomacher") (P) or rotary mixer (M), were used as reference for calculating ratios of recovery. With the methods A, S and T, a low ratio of recovery, resp. 5, 10 and 2%, was obtained for Escherichia coli and Staphylococcus aureus. With method R, ratios for the two species were 60-90%, and also for a Micrococcus species and for spores of Bacillus subtilis. With method F the ratio for E. coli and Micrococcus sp. was even slightly higher than 100%. Recovery with method M was about the same as with P. It is concluded that the rinsing box method as well as the filter method are well suited to the purpose of microbiologically testing towels; the lower recovery of the first is compensated by its simplicity.