Figure 6

Quantitative measurement of the β-lactamase activity produced by the M. catarrhalis WT isolate O35E and tat mutant strains. The β-lactamase activity of strains was measured using the chromogenic compound nitrocefin. Bacterial suspensions were mixed with a 250 μg/mL nitrocefin solution and the absorbance at 486 nm (A₄₈₆) was immediately measured and recorded as time “0” (open bars). The A₄₈₆ of the samples was measured again after a 30-min incubation at room temperature (black bars). Panel A: The β-lactamase activity of O35E is compared to that of the tatA mutant strain, O35E.TA, carrying the plasmid pWW115 (control), pRB.TatA (specifies a WT copy of tatA), and pRB.TAT (harbors the entire tatABC locus). Panel B: The β-lactamase activity of O35E is compared to that of the tatB mutant, O35E.TB, carrying the plasmid pWW115, pRB.TatB (specifies a WT copy of tatB), and pRB.TAT. Panel C: The β-lactamase activity of O35E is compared to that of the tatC mutant, O35E.TC, carrying the plasmid pWW115 and pRB.TatC (contains a WT copy of tatC). The strain O35E.Bro, which lacks expression of the β-lactamase BRO-2, was used as a negative control in all experiments in addition to the broth-only control. The results are expressed as the mean A₄₈₆ ± standard error. Asterisks indicate that the reduction in the β-lactamase activity of mutants is statistically significant (P < 0.05) when compared to the WT strain O35E.