Twenty-six strains of bacteria were isolated from IPBC-, Bethoxazin- and creosote-enrichment. These were found to fall into six principal clades: enterics, pseudomonads, Stenotrophomonas, Actinomycetes, Alcaligenes and Bacillus. Of these, only the last group was largely incapable of the dehalogenation of IPBC. Six representative strains were chosen for further study, and the ability of these six bacteria to degrade IPBC was elucidated. The Bacillus and actinomycete were less capable of IPBC degradation than the four other clades. The IC50s of IPBC; its degradation product PBC; a representative biocide, Bethoxazin; a representative disinfectant, BAC; and a representative antibiotic, tetracycline, to the six bacteria were measured. No significant correlation between IPBC-resistance and coresistance to the other chemicals was found. A scheme for rational investigation of coformulants is presented. An effective coformulant targeted against those bacteria that would otherwise degrade a principal biocide should have acceptable bacteriocidal activity. However, it is also advantageous for bacterial resistance mechanisms against the coformulant and the principal biocide to be dissimilar, so to reduce the evolution of coresistance, and hence increase the sustainability of the biocidal product in the long term.

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