FIG 7.

Iron-depletion-induced persistence enhances the susceptibility of C. trachomatis to azithromycin treatment. Subinhibitory doses of azithromycin (AZM) were added to Chlamydia-infected cells (18 hpi) either alone or following the addition of 10 μg/ml ampicillin (AMP) or 100 μM the iron chelator DPP at the time of infection. EBs were harvested at 44 hpi from treated cells, or cells were washed and Chlamydia cells were allowed to recover for an additional 48 h. Inclusion-forming units (IFU) were then calculated by conducting serial dilutions, infecting fresh monolayers, and counting new inclusions at 24 hpi. The dotted line represents the limit of detection for the assay. Data were gathered over three separate experiments, the data plotted represent the results of three independent biological replicates, and error bars represent the standard deviations from the means. **, P < 0.01.