Growth of the M. catarrhalis WT isolate O35E and tat mutant strains in the presence of the β-lactam antibiotic carbenicillin. The ability of tat mutants to grow in the presence of carbenicillin (cab) was tested by spotting equivalent numbers of bacteria onto Todd-Hewitt agar plates supplemented with the antibiotic (TH + cab). As control, bacteria were also spotted onto agar plates without carbenicillin (TH). These plates were incubated for 48 hrs at 37°C to accommodate the slower growth rate of the tat mutants. Panel A: Growth of O35E is compared to that of its tatA isogenic 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: Growth of O35E is compared to that of its tatB isogenic mutant strain, O35E.TB, carrying the plasmid pWW115, pRB.TatB (specifies a WT copy of tatB), and pRB.TAT. Panel C: Growth of O35E is compared to that of its tatC isogenic mutant strain, O35E.TC, carrying the plasmid pWW115 and pRB.TatC (contains a WT copy of tatC). Growth of the bro-2 isogenic mutant strain O35E.Bro is also shown. The results are shown as a composite image representative of individual experiments that were performed in duplicate on at least 3 separate occasions.