A 1:1000 dilution of the 6 hour culture was made in LB broth and
grown with agitation at 37°C overnight. A 1:200 dilution of the overnight culture was made in LB broth and divided into 16×100 glass tubes. Depending on the assay, the cultures were grown to either early-log (OD600 = 0.15) or late-log (OD600 = 0.6) with agitation before tetracycline addition. Growth curves Growth curves for H 89 each isolate were determined by diluting overnight cultures 1:200, growing to early-log phase (OD600 = 0.15), and adding serial dilutions of tetracycline (0–256 μg/ml); this corresponds to the early-log growth phase to be tested, and was necessary to determine the effect of the antibiotic at this time point. Cultures were shaken
continuously, and growth curve measurements (OD600) were taken every hour for 24 hours using a Bioscreen C instrument (Growth Curves LTD, Raisio, Finland). Differences between the no-antibiotic control and the other sample conditions during the logarithmic growth phase (0–9 hours) were determined by a one-way ANOVA with Dunnett’s post-test using GraphPad Prism 5 (GraphPad Software, Rucaparib San Diego, CA). P values less than 0.05 were considered significant. Experimental conditions The effect of tetracycline during early-log growth phase was examined using overnight cultures that were diluted 1:200 medroxyprogesterone in LB, subcultured into four tubes, and grown
to OD600 = 0.15. An aliquot was taken for RNA analysis from each culture and placed in RNAProtect (QIAGEN, Germantown, MD). Tetracycline was then added to a final concentration of 0 (control), 1, 4, and 16 μg/ml to the four tubes for each isolate, and these were incubated with agitation at 37°C for 30 min (final OD600 = ~0.30). Aliquots for RNA analysis were taken from each bacterial culture and placed in RNAProtect. An additional aliquot was taken from each culture for a cell culture invasion assay. To test the effect of tetracycline during late-log growth phase, each overnight culture was diluted 1:200 in LB, split into four tubes, and grown to OD600 = 0.15. An aliquot was taken for RNA analysis from each culture and placed in RNAProtect. After these cultures grew to OD600 = 0.