To test if the newly identified likely T3S substrates, and possible effectors, of C. trachomatis (CT053, CT105, CT142, CT143, CT144, CT161, CT338, CT429, CT656, and CT849) were expressed during infection, and to gain insights of when they could be acting during the developmental cycle, we analyzed by RT-qPCR the mRNA levels of their encoding genes during the developmental cycle of strain L2/434, at 2, 6, 12, 20, 30 and 42 h post-infection. This evidence concerns the gene SPAG17 and infection.