Long-term effects of natural amino acids on infection with Chlamydia trachomatis

Supplementation of culture media with leucine, isoleucine, methionine, or phenylalanine was previously found to inhibit Chlamydia trachomatis growth in HEp-2 cells. Here, we investigated the long-term effects of these additives on C. trachomatis infection in the same cell model. Amino acid addition 30 h post-infection (pi) effectively suppressed the generation of infectious progeny monitored for 10 days pi. With the exception of phenylalanine, amino acid treatment beginning at 2 h pi for up to 15 days led to a complete lack of infectious progeny. Phenylalanine treatment resulted in residual minimal infectivity. In extended supplementation experiments, very small aberrant chlamydial inclusions formed, whose numbers decreased considerably over time, and the production of infectious chlamydiae could not be rescued even upon amino acid withdrawal. Interestingly, a state of chlamydial persistence was induced under these conditions, as 16S rRNA transcripts were detected throughout treatment. However, expression of several key chlamydial genes including omp1, groEL, omcB, and those functioning for chlamydial DNA replication and cytokinesis was generally very low or even undetected, particularly in monolayers treated with Leu, Ile, or Met. These data revealed a capacity of certain amino acids to eliminate infectious chlamydial progeny. Additionally, supplementation of certain amino acids resulted in the formation of a small persistent population. Extrapolating from these findings may help formulate an anti-chlamydial treatment based on nutritional elements.