Fig. 4

Recovery of tryptophan-starved C. trachomatis strain D after rescue with supernatant from indole positive/indole negative bacteria. Monolayers of HEp-2 cells were seeded in the presence of tryptophan-depleted media 24 h before infection. Cells were infected with C. trachomatis D, at an MOI of 0.5, and were incubated for 36 h. The Chlamydia infected cultures were allowed to recover for 36 h in the presence of (a) supernatant from indole producing P. intermedia and P. nigrescens, and a non-indole producer P. bivia. Data are presented in dilution of 1:10,000. P. bivia is significantly different (p < 0.0001). Indole concentrations measured from the growth medium of P. intermedia and P. nigrescens were 300 μM and 250 μM respectively. b A control of the bacterial growth broth (BHI) was added as well. All treatments were added in different dilutions of 1:1000, 1:5000 and 1:10,000 (Additional file 3: Figure S3). Infected cells and culture supernatants were sonicated and used to infect a new HEp-2 cell monolayer for enumeration of recoverable IFUs. Data are presented as the mean ± SD IFU/ml (n = 9) determinations. Statistical significance determined via multiple t testing using the Holm-Sidak method, with alpha = 0.05. Each row was analyzed individually, without assuming a consistent SD