Submitted to: Antimicrobial Agents and Chemotherapy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2001
Publication Date: 11/1/2000
Interpretive Summary: Tetracycline is a widely used, inexpensive antibiotic that has been the standard for treatment of chlamydiosis in humans, animals and birds. A number of isolates from swine in Nebraska were recently found to be highly resistant to tetracycline. It was found that these isolates would continue to replicate in the presence of tetracycline but would not differentiate into the stable infectious form. However, when the tetracycline was removed, the developmental cycle returned to normal. Also, it was found that the tetracycline resistant chlamydia would produce a mixed infection with human strains in the same cell. The results show that the tetra- cycline resistance in swine chlamydial strains is stable and that high levels of tetracycline may alter the replicative cycle, but will not stop it. Also, it was shown that a cell can be infected with two replicating strains which would establish a period where genetic material could be transferred from one strain to another.
Technical Abstract: Tetracycline (tet) is a front line antibiotic for the treatment of chlamydial infections in both humans and animals, and the emergence of tet resistant (tet**R) Chlamydia is of significant clinical importance. Recently, several tet**R chlamydial strains have been isolated from swine (Sus scrofa) raised in production facilities in Nebraska. Here, the intracellular development of two tet**R strains, R19 and R27, is characterized through the use of tissue culture and immunofluorescence. The strains grow in tet up to 4 ug/ml, while a tet sensitive (tet**s) swine strain (S45) and a strain of the human serovar L2 (LGV-434) grow in tet up to 0.1 ug/ml. Although inclusions form in the presence of tet, many contain large aberrant RBs that do not differentiate into infectious EBs. The percentage of inclusions containing typical developmental forms decreases with increasing tet concentrations, and at 3 ug/ml of tet, 100% of inclusions contain aberrant RBs. However, upon removal of the tet, the aberrant RBs revert to typical RBs and a productive developmental cycle ensues. In addition, inclusions were found that contained both C. suis R19 and C. trachomatis L2 after sequential infection, demonstrating that two biologically distinct chlamydial strains could both develop within a single inclusion.