Control Of Multidrug-Resistant Acinetobacter Baumannii: A Biocidal Efficacy Study Of Low-Temperature Air Plasma

Objective This study is designed to evaluate the efficacy and the mechanism of an atmospheric-pressure air plasma in inactivation of the multidrug-resistant Aci netobacter baumannii and to provide a laboratory basis for the application of at mospheric pressure air plasma in clinical dermatology or skin trauma.Method After culturing overnight,the concentration of A.baumannii was diluted to 10⁶ CFU ml^-1.2 ml of the bacteria suspension was put in the 35 mm diam eter dishes and exposed to the non-thermal atmospheric-pressure plasma for 30 s,1,3,5,and10 min,respectively.After plasma treatment,the inactivation of A.b aumanni was evaluated by plate counting method.The bacteria suspensions were diluted to appropriate concentrations by serial 10-fold attenuations with sterile water.Then,100?l of diluted samples were spread on the Luria-Bertani?LB?A gar plates by the sterile triangular glass rods.The plates were then incubated at37°C for 12 h under atmospheric conditions.The overnight culture plates were counted to derive the inactivation efficiency driven by plasma.A variety of rea gents were used to estimate cytobiological variation after plasma treatment,whic h included LIVE/DEAD BacLight Bacterial Viability assay,resazurin and ROS a ssay kit.The morphological changes of cells were observed by using scanning e lectron microscopy?SEM?.Besides,the concentration of the long-lived reactive s pecies in liquid induced by plasma,such as nitrate,hydrogen peroxide,and ozo ne,are also measured.Results The air plasma showed significant antimicrobial effects on multidrug-resi stant Acinetobacter baumannii.Nearly a 100%?6-log?reduction was obtained by colony count assay after the bacteria were treated with air plasma for 10 minut es.Whereas,the results acquired by resazurin asssay showed 7%of bacteria re mained metabolic capacity after the same time of plasma exposure.The differen ce between the two outcomes may indicate that some bacteria may be induced i nto a physiologically viable but non-culturable?VBNC?state to protect them fro m environmental stresses.SEM revealed that the plasma may induce the cell mo rphological change.But morphological change was not the only process of cell death induced by plasma.The concentrations of long-lived RS plasma induced in the liquid,such as H₂O₂,O₃,and NO₃^-,dramatically increased to different exte nts.After 10 minutes plasma exposure,the concentration of NO₃^-,H₂O₂ and O₃increases from 0 to 307.6 mg/L,49.2mg/L and 1.6 mg/L,respectively.Conclusions The air plasma showed significant antimicrobial effects on multidrug-resistant Acinetobacter baumannii.As the increase of the treatment time,the survival number of the Acinetobacter baumannii decreased gradually.The sterilization efficiency may relate with the reactive species plasma induced in water.