Ar + NO microwave discharges are used for sterilization and the results are compared with additional experiments with Ar, O(2) and N(2)-O(2) plasma mixtures. The NO* species produced in the Ar – NO mixtures remain up to long distances from the source, thus improving the sterilization efficiency of the process. E. coli individuals exposed to the Ar + NO plasma undergo morphological damage and cell lysis. Combined effects of etching ( by O* and Ar* species) and UV radiation ( from deactivation of NO* species) are responsible for the higher activity found for this plasma mixture.