Experimental Study Of Staphylococcus Aureus Lytic Bacteriophage In The Treatment Of Mastitis

Staphylococcus aureus is a common and dangerous pathogen that causes varietyof local and systemic infections. S. aureus is also one of the main pathogens causingmastitis. With the extensive use and misuse of antibiotics, the antibiotics resistant of S.aureus has become serious, making the treatment of mastitis caused by this bacteriamore and more difficult. Therefore, there is an urgent need to develop new noveltherapeutic agents to control antibiotic-resistant S. aureus-induced mastitis. Becauseof the ability of killing pathogens quickly and specifically, phage shows a greatpotential to treat drug-resistant infections.In this study, one S. aureus, named4P-1, has been isolated from cows sufferingfrom mastitis. And a new lytic phage, named2Y-10, was isolated from sewagesamples by using4P-1as the host bacteria. The biological characteristics indicatedthat the phage2Y-10has an isometrically hexagonal head of48±5nm in diameterpocesses and a tail of approximately160±5nm. The genome of2Y-10was dsDNAand the size was about39.3kb. The incubation period of2Y-10infecting4P-1wasabout30min and the lytic period was approximately70min. The optimum pH valueof this phage is7.0. In addition,2Y-10could maintain a high activity at even50°C for1h. The phage was insensitive to chloroform and ether. The optional MOI of2Y-10against4P-1was0.01~0.001.Furthermore, S. aureus isolates4P-1, was used to establish the mouse model ofmastitis through perfusion bacteria to mammary gland. Evaluation for the modelestablished by different doses of bacteria showed that105cfu (25μL) of4P-1couldcause mastitis with typical pathological changes: mammary alveolus destroyedseriously. Large number of inflammatory cell could be found in the histopathologicalsection. There was a large number of bacteria within mammary gland, reaching2.3×108cfu/g, and the level of TNF-α was increased significantly. Then,2Y-10wasused to treat this model by mammary gland perfusion. The results showed that thenumber of bacteria in mammary gland declined significantly by using105PFU of2Y-10at1h before and after attacking bacteria. Damage in mammary gland tissueswas alleviated significantly with infiltration of inflammatory cell, relieving congestion, and improving edema of alveolar walls. Besides, inflammatory cytokines TNF-αreduced significantly. Further more, the phage with the number of105PFU given tomammary gland after attacking bacteria6h could also alleviate the damage caused bymastitis.In this study, phage was used to treat mouse model of mastitis caused by S.aureus. This study showed that it is feasible to prevent and treat mastitis using lyticbacteriophages. And this research laid the groundwork for follow-up.