Analysis of mutant and recombinant M. catarrhalis strains. (A) Schematic showing the mcbABCI locus in the O12E chromosome and the position of the oligonucleotide primers used to construct the three different in-frame deletion mutations in this locus. The extent of the deletion in each ORF is indicated. (B) Bacteriocin production assay using O35E as the indicator strain together with the following test strains: panel 1, O12E; panel 2, O12EΔmcbA; panel 3, O12EΔmcbB; panel 4, O12EΔmcbC. Panel C, Use of recombinant M. catarrhalis strains to demonstrate that expression of McbI in O35E confers protection against killing by strain O12E. M. catarrhalis O12E was used as the test strain in a bacteriocin production assay with three different M. catarrhalis strains as the indicator. Panels: A, O35E wild-type; B, O35E(pWW115) [vector-only control]; C, O35E(pAA113) [expressing McbI].