Application of post-discharge region of atmospheric pressure argon and air plasma jet in the contamination control of Candida albicans biofilms

Introduction:Candida species are responsible for about 80% of hospital fungal infections. Non-thermal plasmas operated at atmospheric pressure are increasingly used as an alternative to existing antimicrobial strategy. This work investigates the action of post-discharge region of a non-thermal atmospheric plasma jet, generated by a gliding arc reactor, on biofilms of standard strain of Candida albicans grown on polyurethane substrate. Methods Samples were divided into three groups: (i) non-treated; (ii) treated with argon plasma, and (iii) treated with argon plus air plasma. Subsequently to plasma treatment, counting of colony-forming units (CFU/ml) and cell viability tests were performed. In addition, the surface morphology of the samples was evaluated by scanning electron microscopy (SEM) and optical profilometry (OP). Results Reduction in CFU/ml of 85% and 88.1% were observed in groups ii and iii, respectively. Cell viability after treatment also showed reduction of 33% in group ii and 8% in group iii, in comparison with group i (100%). The SEM images allow observation of the effect of plasma chemistry on biofilm structure, and OP images showed a reduction of its surface roughness, which suggests a possible loss of biofilm mass. Conclusion The treatment in post-discharge region and the chemistries of plasma jet tested in this work were effective in controlling Candida albicans biofilm contamination. Finally, it was evidenced that argon plus air plasma was the most efficient to reduce cell viability.

引言：念珠菌属（Candida species）引发的感染约占医院真菌感染的80%。大气压下运行的非热等离子体正日益成为现有抗菌策略的替代方案。本研究探讨了滑动电弧反应器（gliding arc reactor）产生的非热大气压等离子体射流的放电后区域对聚氨酯基底上培养的白色念珠菌（Candida albicans）标准菌株生物膜的作用效果。
方法：将样品分为三组：(i) 未处理组；(ii) 氩等离子体处理组；(iii) 氩气加空气等离子体处理组。等离子体处理完成后，开展菌落形成单位（CFU/ml）计数与细胞活力检测。此外，通过扫描电子显微镜（SEM）与光学轮廓仪（OP）评估样品的表面形貌。
结果：第(ii)组与第(iii)组的菌落形成单位分别降低了85%与88.1%。与第(i)组（活力为100%）相比，第(ii)组处理后的细胞活力下降了33%，第(iii)组则下降了8%。扫描电子显微镜图像可观测到等离子体化学效应对生物膜结构的影响，光学轮廓仪图像显示样品表面粗糙度降低，这表明生物膜质量可能出现损失。
结论：本研究中所测试的放电后区域处理方式与等离子体射流的化学环境，均可有效抑制白色念珠菌生物膜污染。最终证实，氩气加空气等离子体在降低细胞活力方面效果最优。