New series of quinolines 2, 6, 7, 9, 14-17, 20, 21; pyrano[3,2-c]quinolines 3, 4, 5, 11; furo[3,2-c]quinolines 8, 18; oxazino[5,6-c]quinoline 19 and thieno[3,4-b]quinoline 22 were prepared and the impact of synthesized compounds on some pathogenic microorganisms isolated from clinical samples was studied. Compounds 4, 11 and 14 were found to be the most active against all tested microorganisms. The compound 14 which showed higher activity was selected to study its action on the ultrastructure of Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans. Death of numerous cells, destruction of the cell wall, cell contents poured into the medium and impairment of metabolism, were observed.