Cytotoxicity assessment of residual high-level disinfectants.

Some studies show the uptake of disinfectants on medical devices but no studies on their cytotoxicity have been reported. This study aimed to assess that cytotoxicity in a 3-dimensional culture system using HeLa cells grown in matrices composed of collagen. Plastic materials were soaked in the use solutions of the widely used high-level disinfectants, glutaraldehyde (GA), ortho-phthalaldehyde (OPA) and peracetic acid (PAA). After being rinsed, they were allowed to dry and were embedded into the cell medium to investigate the cytotoxicity of the residual disinfectants. Cytotoxicity was observed with the polyvinyl chloride, polyurethane and silicon tubes soaked in GA and OPA, indicating that both disinfectants were absorbed in the test pieces, whereas for PAA, none was observed. As for the polytetrafluoroethylene (PTFE) tubes, no disinfectant displayed cytotoxicity. GA and OPA are primary irritants, having a potential to cause anaphylaxis and other forms of allergic reactions. There should be consideration not only about the toxicity of the residual disinfectant from poor rinsing, but also about the toxicity that would result from the disinfectants that were absorbed and consequently released from the medical devices or materials.

Comparison of the cytotoxicity of high-level disinfectants by the MTT assay and direct contact assay.

Most critical instruments are not designed for heat sterilization and autoclaving. These items are usually treated with chemical agents such as peracetic acid(PAA), glutaraldehyde (GA) and ortho-phthalaldehyde (OPA). MTT assay is often used to evaluate the in vitro cytotoxicity of these chemical agents. In this study, disinfectants were allowed to come in direct contact with cells. Their cytotoxicity was evaluated based on cell viability and adhesive properties. The results obtained from the direct contact method were compared with those obtained from the conventional MTT assay wherein the disinfectants were added into a nutrient medium. It was found that the two methods yielded very different results, especially when aldehyde- and halogen-containing disinfectants were tested, and that toxicity may be underestimated in the MTT assay. Hence, it can be assumed that the direct contact assay is more accurate when evaluating the cytotoxicity of residual chemicals. It was also observed that the cytotoxicity of PAA was lower than that of GA and OPA.