The invention covers new bacteriophage strains specific against bacteria belonging to the species Proteus mirabilis, deposited with the Polish Collection of Microorganisms (PCM) under the access numbers: F/00084 (72APm5211), F/00085 (39APmC32), F/00086 (65APm2833), for use for use in the prophylaxis and therapy. In accordance with the invention the above mentioned bacteriophage strains, in form of complete particles of the single bacteriophage strain, in form of bacteriophage lysates, optionally in form of purified bacteriophage proteins, in particular lytic enzymes that degrade the bacterial cell wall and enzymes that decompose bacterial extracellular polysaccharides, are intended for use in therapy as anti-bacterial agents, in particular against bacteria of the species Proteus mirabilis, especially the drug- and multidrug- resistant strains of the species, advantageously in urinary tract infections. In accordance with the invention the above mentioned bacteriophage strains, in form of a coctail comprising t
