The assessment of the bactericidal activity of surface disinfectants. II. Two other practical tests.

The Dutch quantitative carrier test (QCT) prescribes the rinsing technique for counting the surviving bacteria after disinfection. This method is compared with the Leuven test, which uses the impression technique in order to determine the survival on the disinfected surfaces, and with a novel quantitative surface disinfection test (QSDT). The QSDT combines the preparatory and disinfection phase of the Leuven test with the postexposure rinsing technique of the QCT. The results of the three tests correlate very well as is shown by Kendall's rank correlation test. The QCT and the Leuven test yield equivalent results: neither the median of the results, nor the paired results apart differ statistically for the same exposure time of 30 min. On the contrary the results of the novel QSDT differ in a statistically significant way from those of both other techniques, but the QSDT is more severe than the QCT and the Leuven test in the case of Staphylococcus aureus, whereas in the case of Pseudomonas aeruginosa it is the less severe one. This phenomenon can hardly be explained and emphasizes the importance of the resuscitation of sublethally damaged germs in the postexposure phase of testing.