RESUMO
Objective:To analyze the changes in biological characteristics including infectivity, growth and pathogenicity of Chlamydia muridarum ( Cm) after serial passage in vitro in special conditions in order to provide reference for screening attenuated live vaccines and virulence-related genes. Methods:Wild-type Cm strain (G0) was cultured for several passages using conventional cell culture method under alternate unassisted and assisted culture conditions. Then, the 28th generation (G28) of Cm was selected and compared with the parental G0 strain in terms of centrifugation dependence, attaching ability, intracellular growth curve, plaque size and fallopian tube lesions after genital tract infection in a mouse model. Results:Compared with the parental G0 strain, the G28 strain showed significantly decreased dependence on centrifugation during cell infection ( P<0.05) and increased attachment capacity to cells ( P<0.05). No significant differences were observed in the growth curves 32 h after cell infection or in the plaque sizes between the parental G0 and G28 strains. In the in vivo virulence test, fallopian tube lesions were observed in 87.5% of G0-infected mice and 37.5% of G28-infected mice ( P<0.05). Conclusions:Compared with the parental G0 strain, the G28 strain showed significantly enhanced in vitro infection ability, but decreased in vivo pathogenicity, which brought hope for further identification of virulence genes, isolation of attenuated strains with single genotype and development of live attenuated Chlamydia vaccines.