Antimicrobial testing often involves supplementing test cultures with organic soil load, typically in the form of equine or bovine blood serum, to simulate light to moderately “dirty” conditions. EPA requires that a minimum organic soil load of 5% be tested for one-step cleaner/disinfectants. In theory, this additional soil should make for a more challenging test, but does such a low soil concentration – added directly to a concentrated microbial culture – really impact study outcomes?


Scientists at Antimicrobial Test Laboratories set out to answer this question by comparing Use-Dilution Test results of a quaternary ammonium-based disinfectant tested against Staphylococcus aureus supplemented with 0%, 5% and 10% organic soil. A total of 60 carriers were tested per concentration at a contact time of 5 minutes.



The data shows soil load definitely affects antimicrobial efficacy.  In our testing, only the test without soil load produced a result that met EPA performance standards for S. aureus. Contact the lab for more information on this topic or to discuss how soil load might affect your test results.