**6.3 Endolysin as therapeutic agent**

*Staphylococcus aureus* is a serious threat to human and animal health, and there is an urgent need to develop new antibacterial agents to combat this pathogen. The aim of this study was to obtain active recombinant hemolysin from a novel bacteriophage (IME-SA1) and to conduct a clinical study of its effectiveness against bovine mastitis. We have isolated phages that are toxic and specific for *Staphylococcus aureus*. The optimal infection multiplier is 0.01. Electro-microscopic examination showed that IME-SA1 belongs to the Myoviridae family with the same head (98 nm) and a long tail (200 nm). Experimental lysis experiments showed a phage incubation time of 20 minutes and a burst size of 80. If the host bacterium is in the early stages of exponential growth, the multiplicity of infection is 0.01, resulting in complete lysis of the bacterium after 9 hours. We cloned the endricin gene (804 bp) into the pET-32a bacterial expression vector and succeeded in obtaining recombinant Trx-SA1 endricin with a molecule size of about 47 kDa. Preliminary results from a milk treatment study indicated that Trx-SA1 can effectively control mild clinical mastitis caused by *Staphylococcus aureus*. Endolicin Trx-SA1 may be another strategy for the treatment of infections (including MRSA) caused by *Staphylococcus aureus* [60]*.*
