Biological Characterization and Therapeutic Evaluation of Staphylococcus aureus Bacteriophages in the Treatment of Mastitis in Mice
Bacteriophages(phages),natural viruses that lyse bacteria,are utilized to treat bacterial diseases.This work aims to identify bacteriophages effective in the treatment of mouse mastitis,providing a reference for the prevention and control of bovine mastitis.Two bacteriophages,φFJ04 and φAH12,were isolated and purified from sewage and fecal samples,using laboratory-preserved Staphylococcus aureus AA292 as the host bacterium.The biological characteristics of the phages were analyzed:φFJ04 exhibited an optimal multiplicity of infection(MOI)of 1,a burst size of 149,temperature tolerance between 40℃ and 50℃,pH tolerance from 3 to 10,and lysed 63 out of 90 strains.φAH12 showed an optimal MOI of 1,a burst size of 448,temperature tolerance at 40℃,pH tolerance from 4 to 12,and lysed 28 out of 90 strains.Whole genome sequencing revealed that φFJ04 genomic DNA has a total length of 38 540 bp with a G+C content of 33.79％,containing 48 ORFs,while φAH12 genomic DNA has a total length of 264 664 bp with a G+C content of 24.7％,containing 282 ORFs.The genomes of φFJ04 and φAH12 lack integrative elements,virulence genes,and antibiotic resistance genes,making them suitable for in vivo therapy.The bactericidal efficacy of the phages was evaluated and showed that a cocktail composed of φFJ04 and φAH12 completely eradicated 104 CFU/mL of S.aureus within 6 h.Administration of a cocktail containing 108 PFU/mL of phages significantly improved mouse mastitis induced by 108 CFU/mL of strain AA292,resulting in a reduction of the bacterial load in the mammary tissue of the treatment group by 2.8 log1o CFU/g,achieving a bactericidal effect of approximately 99.84％.Histologic examination(HE staining)revealed that the treatment group had more intact mammary alveolar structures and significantly reduced mammary epithelial cell desquamation,providing insight into the prevention and treatment of bovine mastitis.
Staphylococcus aureusIsolation and identification of phageAnalysis of biological characteristicsWhole-genome sequencingTreatment of mouse mastitis
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