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The Role of Coformulants in Preventing Bacterial Biotransformation of IPBC
2002 - IRG/WP 02-10436
The inhibitory effects of disodium tetraborate decahydrate and benzalkonium chloride (BAC), two common coformulants of IPBC in antisapstain treatments, on an IPBC-transforming enterobacterial isolate ‘W1’ were determined by their effect on the specific growth rate constant in vitro. The IC50s of IPBC, BAC and borate were found to be 0.46, 0.026 and 5.7 mM respectively. The IC50 of the Arch antistain product AntibluTM Select was 0.024 mM, based on its BAC content. Although their IC50’s were significantly different, it was clear that the vast majority of the bacterial toxicity of the AntibluTM Select was due to its BAC content. The degradation of 0.4 mM IPBC by the bacterium W1, as measured by the accumulation of its degradation product, iodide, in liquid culture, was completely inhibited by BAC concentrations greater than 18 μM, and the toxicity of the spent culture medium to Aspergillus niger, as measured by an antibiotic assay disc assay, was not ameliorated above this concentration. Below 18 μM, the toxicity of the spent broth was significantly reduced, and the accumulation of iodide occurred rapidly. Demonstrating the toxicity of BAC to bacteria, and its consequent inhibition of IPBC degradation in vitro, are indicative of the importance of coformulation in controlling bacteria that might otherwise cause preservative loss, and of their significance in determining the ultimate environmental fate of cobiocides.
S R Cook, D J Dickinson

The fungal degradation of quaternary ammonium compounds in wood
1998 - IRG/WP 98-10263
This work focuses on the biodegradation of didecyldimethylammonium chloride (DDAC) by the mould fungus Gliocladium roseum within a woody matrix. Three sawdust types, distinguished by their treatment and amount of DDAC retained, were inoculated with the fungus and their DDAC loss was measured over 11 weeks. The rates of degradation varied depending on the sawdust; however, a significant loss of DDAC was observed for all three. A metabolic by-product coincided with the fungal degradation of DDAC. The metabolite was separated using preparative HPLC and identified by proton-NMR and infrared spectroscopy to be a hydroxylated QAC.
J W Dubois, J N R Ruddick

Studies on the Toxicity of IPBC and Other Biocides to Bacteria
2004 - IRG/WP 04-10544
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.
S R Cook, D J Dickinson

The Bacterial Biotransformation of IPBC
2002 - IRG/WP 02-10437
The bacterial biotransformation of the biocide IPBC, widely used as an antisapstain wood preservative, was investigated in bacteria isolated from failed wood, soil experiencing IPBC wash-off, and John Innes No. 2 compost. Nine strains of bacteria were isolated, belonging to the genera Alcaligenes, Enterobacter, Microbacterium and Pseudomonas. The sole organic degradation product in an enteric bacterium ‘W1’, isolated from failed wood, was PBC, which was produced at 1:1 stoichiometry. No further degradation products were isolated: PBC appeared to be the terminal product of transformation. Incubation of 0.8 mM IPBC in mineral medium with W1 for 90 hr caused the IPBC concentration to fall to undetectable levels, and the toxicity of spent broth was reduced to zero for four target fungi as measured by an antibiotic assay disc bioassay. Furthermore, the toxicity of PBC to the fungi as bioassayed, was c. 1/1000 that of IPBC. The widespread ability of common soil and wood bacteria to transform IPBC to less toxic products is an important contribution to an understanding the environmental fate of IPBC and its continued use under the auspices of the European Biocidal Products Directive (BPD).
S R Cook, J Sullivan, D J Dickinson