FIG 1.

The B. glumae ΔdbcA strain is sensitive to colistin. (A) Growth curve of B. glumae 336gr-1 and ΔdbcA strains in LB broth buffered to pH 7.0 with 70 mM Tris. Equal amounts of cells (5 × 10⁷ CFU/ml) were used to inoculate LB broth, and bacterial growth was analyzed at 6-h intervals. (B) Serially log₁₀-diluted cells of B. glumae 336gr-1 and ΔdbcA strains transformed with control vector pSCrhaB2 (vec) or pSC301 (dbcA) were spotted and grown on MH2 agar medium containing 100 μg/ml trimethoprim and the indicated concentration of colistin. The 500 μg/ml colistin plate also contained 0.0004% rhamnose. (C) Colistin E-strips were used to determine the colistin MIC for B. glumae 336gr-1 transformed with pBBR1MCS-2 (vec), and the ΔdbcA strain transformed with pBBR1MCS-2, pMCS501, pRP101, pRP102, or pRP103 (see Table 1). Bacterial strains were grown in MH2 agar containing 100 μg/ml Kan. Bgl, B. glumae; Bth, B. thailandensis; Ec, E. coli.