title: [Test for the efficacy of disinfectants at surfaces in test models. I. (communication:) Dependence of experimental results on the method of demonstration of surviving germs (swab and rinsing) (author's transl)].
abstract: For the testing of disinfectants at surfaces, the germs having survived at the surface are demonstrated by means of swabs according to the guide-lines of the Deutsche Gesellschaft fur Hygiene und Mikrobiologie (DGHM): after the period of exposure to the disinfectant, the surfaces were rubbed off with a damp swab, and the frictional surface of the swab was plated out on nutrient agar. The effectiveness of this technique was compared with the effectiveness of a rinsing method in a test model. In the rinsing process, the objects to be tested for surviving germs were shaken together with a suspension and with glass beads. Then the content of germs in the suspension was quantitatively determined by means of dilution tests and pour plates. The findings were evaluated according to the guide-lines for evaluation of the DGHM (less than or equal to 10 surviving germs = adequate efficacy). For the findings obtained by rinsing, the average number of surviving germs was also determined. For maldehyde solutions were used as disinfectants for the test models (time of exposure: 4 hours; temperature 22 to 25 degrees C). These disinfecting experiments were performed on raw smoothed as well as on varnished beech-wood. The experimental results showed that the criterion "less than or equal to X surviving germs" in itself does not mean clear evidence of the efficacy of a disinfectant. The one and only decisive criterion is the frequency of the statement that a certain disinfectant or a corresponding dilution of this disinfectant has shown adequate efficacy. Therefore, one single test according to the guide-lines of the DGHM is insufficient. The frequency of the finding "adequate efficacy" is not only dependent on the concentration of the disinfectant but also on the technique used for the demonstration of surviving germs. The swab method (according to the guide-lines of the DGHM) occasionally resulted in the finding "adequate efficacy" already if 10(4) to 10(5) surviving germs were demonstrable by the rinsing method. The range of formaldehyde concentrations for which the finding of adequate efficacy were present with a frequency between 20% (minimum) and 80% (maximum) amounted to 0.2-0.5% (varnished surface) and 1.1-2.5% (raw surface), respectively for the swab method. The respective figures for the rinsing method were 0.8-1.3% and 4.8-6.5%, respectively. When using the swab method, there is a slower increase in the efficacy of the disinfectant with concentration as compared with the rinsing method. The rinsing method is, therefore, more representative of the efficacy of a disinfectant than the swab method. On account of the results of this study, it is recommended for model experiments to recover the surviving germs quantitatively by the rinsing method and to determine their number.
mesh_terms: D004202:Disinfectants; D004353:Drug Evaluation, Preclinical; D005069:Evaluation Studies as Topic; D005557:Formaldehyde / Q000494:pharmacology*; D013048:Specimen Handling / Q000379:methods*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification
chemical_list: D004202:Disinfectants; D005557:Formaldehyde
vernacular_title: Wirksamkeitsprüfung von Desinfektionsmitteln an Oberflächen in Modellversuchen. I. Mitteilung Abhängigkeit der Versuchsergebnisse von der Methodik des Nachweises überlebender Keime (Tupferabstrich bzw. Abschwemmung)