FIGURE 4.

The intracellular activities of antibiotics, as determined by qPCR. Vero cells were spinfected (MOI 1:3,000) with F. tularensis LVS, treated for 1 h with 20 μg/ml gentamicin following 3 PBS washes. Fresh supplemented DMEM containing 20 μg/ml gentamicin and the tested antibiotic at a twofold dilution was added. After 24 h, the cell fractions were harvested, and a sample of 100 μl cell extract was added to 100 μl Triton buffer and heated for 30 min at 100°C. DNA was then purified and subjected to qPCR to determine PCR-equivalent cfu values. MIECs were defined as no growth based on the initial infected concentration. Ciprofloxacin (A), doxycycline (B), chloramphenicol (C), and erythromycin (D). All experiment were performed in duplicate. The numbers of repetitions for each antibiotic is stated in Table 1. The graphs are representatives of the repetitions.