The aim of this study was to investigate the effect of Escherichia coli bacteriophage Φ199 combined with clindamycin hydrochlo-ride on bactericide I.The biological characteristics of bacteriophage Φ199 with Escherichia coli O157:H7 as the host bacterium were stud-ied,and the antibacterial effect of bacteriophage Φ199 combined with clindamycin hydrochloride was evaluated.The results showed that phage Φ199 was a muscle-tailed bacteriophage with a head diameter of about 50 nm and a tail length of about 100 nm.Bacteriophage Φ199 could survive stably at 40-60 ℃ and maintain lysis activity in the pH range of 3-12,indicating that phage Φ199 had a wide temperature tol-erance and good acid-base tolerance.The optimal MOI of phage Φ199 was 1,and the one-step growth curve showed that the incubation peri-od was 5 min,the lysis period was 5 min,and the lysis amount was 44.The phage was able to inhibit the growth of bacteria within 3 h.In addition,the results of the antibiotic combination showed that the combination of bacteriophage Φ199 and clindamycin hydrochloride had a synergistic effect,which could reduce the effective concentration of antibiotics to 1/2 MIC when combined with the bacteriophage with a titer of 106-107 PFU/mL,and to 1/4 MIC when combined with a titer of 108 PFU/mL.