FIG 2.

Effect of β-lactams and lactivicin derivatives on the production of β-lactamase by S. maltophilia clinical isolates N531 (upper panel) and K279a (lower panel). Bacteria were incubated in the presence of inducer (100 μg · ml⁻¹ cefoxitin, 10 μg · ml⁻¹ imipenem, 50 μg · ml⁻¹ LTV13, and 0.35 μg · ml⁻¹ LTV17), cell extracts were prepared, and β-lactamase activity in cell extracts was measured as described previously (22) using 100 μM meropenem as the substrate. Protein concentrations were determined using Bio-Rad protein assay dye reagent concentrate, and an extinction coefficient at 299 nm of 9,600 AU/M/cm for meropenem was used to calculate the specific meropenem hydrolyzing activity in each cell extract. Data presented are means ± standard errors of the means; n = 3.