Biological characteristics of mycobacteriophage Leo and its bactericidal effect on Mycobacterium tuberculosis / 中国人兽共患病学报

ABSTRACT

To investigate the biological characteristics of mycobacteriophage Leo and its bactericidal effect on Mycobacterium tuberculosis for cocktail therapy ,we observed mycobacteriophage plaques after amplifying phage by double‐layer agar plate method .The morphological characteristics were observed by electron microscopy .Mycobacteriophage Leo DNA was extracted and then digested by restriction enzyme to identify the nucleic acid type .Leo was amplified in different multiplicity of infection (MOI) to find the optimal MOI and the minimum MOI .One step growth experiment was carried out to find the latent period and burst size of Leo .The frequency of Mycobacterium smegmatis mutation treated with mycobacteriophage Leo was inspected by the endpoint titration test .The effect of temperature and alcohol on Leo survival was surveyed .The ability of Leo to crack host bacteria at different pH values was examined .The effect of Leo on Mycobacterium tuberculosis was determined by bacteri‐cidal assay .Results showed that the Leo plaque was round and transparent with a diameter of 1 .5 nm .Leo has an isometric head (70 ± 3 .0 nm in diameter) and a flexible tail (211 ± 31 .7 nm in length) .Its genome could be digested by restriction en‐zyme of Hind Ⅲ and Bgl Ⅰ .The optimal MOI and the minimum MOI of Leo were 0 .000 01 and 0 .000 1 ,respectively .The mutation frequency was 10-7 .The latent period was 150 min ,and the burst size was 74 .Leo could not only crack host bacteria in solid medium at pH 7 .4 but also at pH 5 .0 .After 72 hours ,the amount of Mycobacterium tuberculosis in Leo group was less than that in control group (P<0 .05) .In conclusion ,Leo has a bactericidal effect on Mycobacterium tuberculosis and could be a candidate of phage cocktails .