Abstract
Isothiazolones are used as preservatives in various modern industrial products. Although microorganisms that exhibit resistance towards these biocides have been identified, the underlying resistance mechanisms are still unclear. Therefore, we investigated the resistance properties of the following Burkholderia cepacia strains to Kathon (a representative of isothiazolones): a wild-type (WT) strain; a laboratory resistance strain (BC-IR) induced from WT; and an isolated strain (BC-327) screened from industrial contamination samples. The bacterial cell structure was disrupted by 50 μg ml⁻¹ Kathon treatment. BC-IR and BC-327 did not display resistance in the presence of 1 ml L⁻¹ Tween 80, 1 ml L⁻¹ Triton X-100, 0.1 % sodium dodecyl sulfate or 1 mmol L⁻¹ EDTA-2Na. Additionally, BC-IR and BC-327 exhibited lower relative conductivity from 10 to 180 min. The types as well as the levels of outer-membrane proteins (OMPs) were altered among WT, BC-IR and BC-327. Finally, the two Kathon-resistance strains BC-IR and BC-327 presented higher resistance capacity to H₂O₂. We measured the levels of peroxide-sensor genes and observed that the transcriptional activator oxyR, superoxide dismutase sod1, sod2, catalase cat1 and cat3 were all up-regulated under oxidative conditions for all strains. Taken together, OMPs and peroxide-sensor genes in B. cepacia contributed to isothiazolone resistance; However, the laboratory strain BC-IR exhibited a different resistance mechanism and properties compared to the isolated strain BC-327.
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