RESUMEN
Three bactreiophages of Pseudomonas aeruginosa were isolated from sewage and named as PaP1, PaP2 and PaP3. All belong to double-strand DNA phages, their genome is about 47kb, 34kb and 24kb respectively. The titre (pfu/mL) of three phages is respectively 109, 1011 and 1011, PaP1 is lytic phage, both PaP2 and PaP3 are lysogenic. Under electron microscope, All show icosahedral heads with diameter of 70nm, 55nm and 65nm respectively. PaPl belongs taxonomically to Myoviridae, and both of PaP2 and PaP3 belong to Pedoviridae. The phage-re-sistance and substitution phenomenon of the resistant flora for the sensitive were observed, and the mutation frequence of Pseudomonas aeruginosa resistant to the phage is about 1.4 ? 10-7 ~ 7.9 ?10-7 determined by end-point -titer method.