FIG 1 .

Phenotypes induced by E. coli volatile compounds in representative bacteria. (A) Variations of the previously described 2-petri-dish assay (17) used to evaluate the impact of volatile compounds on antibiotic resistance, growth and morphotype, motility, and biofilm formation as described in Materials and Methods. *, 20-µl bacterial inoculum. AB, antibiotic. (B) Volatile-mediated modulation of biofilm formation by exposed E. coli MG1655F′, P. aeruginosa PAO1, S. aureus HG001, and B. subtilis 3610 to 12 volatile compounds (listed in Table 1). E. coli graph: B, 1% 1-butanol; b, 0.1% 1-butanol; D, 0.15% indole; d, 0.015% indole. P. aeruginosa graph: B, 1% 1-butanol; b, 0.1% 1-butanol. S. aureus graph: B, 1% 1-butanol; b, 0.1% 1-butanol. B. subtilis graph: F, 1% hexadecane; f, 0.1% hexadecane. The data represent means ± standard deviations (SD) from at least 3 independent experiments in which the OD₅₉₅ of the nonexposed bacteria was defined as 1. For statistical analysis, P < 0.05 (*), P < 0.01 (**), and P < 0.0001 (***) by one-tailed unpaired Student’s t test in comparison with H₂O. (C) Aerial exposure to TMA increases resistance to tetracycline in all tested bacteria. Shown is growth of E. coli MG1655, P. aeruginosa PAO1, S. aureus HG001, and B. subtilis 168 on inhibitory concentrations of tetracycline upon exposure to H₂O, NH₃ (1%), or TMA (0.5%). Pictures were taken after 24 h of aerial exposure to the volatile source in the 2-petri-dish experimental design presented in panel A.