[In vitro inhibition of Chlamydia trachomatis growth by liposome-encapsulated cyclines]

The antichlamydial activity of tetracycline (Tet) and doxycycline (Dox) encapsulated in cationic (CaL), anionic (AnL) and neutral (NtL) liposomes has been evaluated in vitro by adding serial dilutions of antibiotics (minimum inhibitory concentration, MIC: 0.12-0.007 microgram/ml; MBC: 4 to 0.25 micrograms/ml) to HeLa 229 cell monolayers inoculated with Chlamydia trachomatis L2/434/Bu (10(3) ufi/ml). Following 72 h incubation at 37 degrees C under a 5% CO2 atmosphere, the chlamydial inclusions were stained by the May-Giemsa method to determine the MICs. After a second and third passage, the MBC1 and MBC2 were determined in antibiotic-free medium. The chlamydial inclusions were then counted to assess the degree of growth inhibition at each antibiotic dilution tested for MBC1 and MBC2 determinations. The MIC, MBC1 and MBC2 of the various antichlamydial agents were as follows: Tet (0.12; 4; 4), AnL-Tet (0.01; 1; 1), NtL-Tet (0.03; 1; 2), Dox (0.06; 1; 2), CaL-Dox (0.03; 0.5; 2), AnL-Dox (0.01; 1; 2), and NtL-Dox (0.03; 0.5; 0.5). It was found that Tet and Dox liposome-encapsulated antibiotics were more active than their non-encapsulated counterparts, and the inclusion count showed a higher inhibitory activity of the former antibiotics on chlamydial growth. The inhibition of chlamydial growth by AnL-Tet may be of bactericidal nature. In conclusion, liposome-encapsulated drugs could be of value in the treatment of chlamydial infections.