Pulsed corona discharge (PCD) of moderate frequency in air has a bactericidal and bacteriostatic effect on Escherichia сoli М17 cultures at both cellular and population levels. PCD exposure inhibits forming a microbial community and results in the destruction of formed biofilms. The paper presents data of electron microscopy investigations of cells’ and biofilms’ ultrastructure after PCD treatment over a 90 second period. The morphological properties of opportunistic bacteria E. сoli M17 cells altered after sub-lethal and lethal thermal exposure. Refs 32. Figs 6.