Methods for the efficacy testing of industrial biocides — 1. Evaluation of wet-state preservatives

A number of national and international methods developed during the last 15 years for evaluating the wet-state microbiological resistance of a wide range of aqueous formulations are compared and critically reviewed. General principles for testing the efficacy of biocidal additives in industrial aqueous-based products have been drawn from them and described. These principles were validated by the testing of five commonly available biocides in five different products. An emulsion paint, a metalworking fluid and a starch-based adhesive were tested for resistance to wet-state bacterial infection, and a bituminous emulsion and a ready-mixed ceramic tile adhesive were examined for resistance to wet-state surface fungal growth. The results not only indicate relative differences in the susceptibility of such products to microbiological infection but emphasise the effect of preconditioning the biocide in the test formulation prior to inoculation with the challenge organisms.