FACTORS INVOLVED IN BACTERICIDAL ACTIVITIES OF FORMALDEHYDE AND FORMALDEHYDE CONDENSATE ISOTHIAZOLONE MIXTURES

Enhanced antimocrobial activities of formaldehyde (FA) and 5-chloro-2- methyl-4-isothiazolin-3-one (IT) mixtures were determined in tryptic s oy broth (TSB), minimal salt-based medium, saline, and soluble oil emu lsion using a Pseudomonas aeruginosa strain as a test organism. The ap parent higher activity of mixture was the result of simultaneous and c ombined action of the biocides. The involvement of sulfhydryl groups a s targets in the mode of action of both biocides was investigated usin g S-nitroso thioglycollic acid as a covalent modifier of exterior sulf hydryl groups of the cells. The results suggest their involvement in t he mode of action of IT. These studies also indicate a considerable in dependent action by both biocides when the mixture is used with absenc e of cross-resistance in resistant isolates and independent induction of resistance in Pseudomonas aeruginosa to these biocides. Replacement of FA in the mixture with 1, 3,5-tris (2-hydroxyethyl)-hexahydrotriaz ine at equimolar concentrations of FA in TSB showed essentially the sa me levels of increased activity with no apparent adverse effects on th e antimicrobial activity of IT from the amine portion of the molecule. Furthermore, in-vitro studies also indicated direct protection of IT by FA and FA condensate biocides in the presence of nucleophiles.