ANDREI CRISTIAN LUPU, ANDRA-CRISTINA BOSTANARU, MIHAI MARES, LAURA URSU, CONSTANTIN ROMAN, RALUCA MINDRU, LIVIU DAN MIRON ULTRASTRUCTURAL ASPECTS OF YERSINIA RUCKERI CELLS AFTER TREATMENT WITH NON-THERMAL PLASMA-ACTIVATED WATER Yersinia ruckeri is the causative agent of enteric red mouth disease (ERM, yersiniosis), one of the most important diseases that affects particularly farmed salmonids species. Numerous articles have demonstrated that Y. ruckeri can cause both epizootics and zoonosis. Y. ruckeri shows the ability to survive outside the host in nutrient-limiting environments for long periods due to biofilms forming capacity with adherence to solid supports but also for the adherence to the host tissues. Considering these aspects, the control of Y. ruckeri can be a problem, because of its resistance. Recently, non-thermal plasma activated water (PAW) proved to be active against Gram-negative bacteria and this fact could be also useful in Y. ruckeri control. The purpose of this in vitro study was to test the antimicrobial efficacy of PAW against Y. ruckeri and to explore the ultrastructural changes in these bacteria. Ultrastructural changes in Y. ruckeri cells, probably related to the action of PAW, included modifications in the shape and texture of the outer membrane. These changes in the bacterial membrane have been linked with the inactivation of bacteria by PAW exposure.