Effect of Chloramphenicol, Rifampicin, and Nalidixic Acid on Chlamydia psittaci Growing in L Cells

Abstract

Chloramphenicol, rifampicin, and nalidixic acid inhibited the development of inclusions of Chlamydia psittaci in mouse fibroblasts (L cells); the first two inhibited in concentrations similar to those required for inhibiting the growth of free-living bacteria, the third, only in considerably higher ones. Examination of thin sections of infected L cells by electron microscopy showed that chloramphenicol and rifampicin completely inhibited reorganization of small chlamydial cells into large ones and the subsequent multiplication of large cells by binary fission. Nalidixic acid permitted a limited reorganization of small cells into large cells but strongly interfered with their division. Chloramphenicol inhibited synthesis of proteins in C. psittaci well before it had any effect on synthesis of RNA or DNA, rifampicin inhibited synthesis of RNA first and synthesis of protein soon thereafter, and nalidixic acid showed no specificity in inhibiting macromolecular synthesis in C. psittaci. After contact for 1–2 hr with each antibiotic, C. psittaci synthesized all three macromolecules at significantly reduced rates. The inhibitory effect of these antibiotics on chlamydial multiplication was reversible.