Competitive survival of wild-type and ΔoxyRS E. coli in normal and oxidase-deficient neutrophils. Bacterial strains employed were wild-type (ATCC 11775 carrying a β-lactamase plasmid, pBAD18, solid lines and filled symbols) and the ΔoxyRS mutant described in Figure 5 (dashed lines, open symbols). A mixture of equal numbers of each strain was opsonized and incubated with neutrophils as described in Figure 5. At indicated times, samples were obtained to determine microbial viability by streaking dilutions of a neutrophil lysate onto replicate Mueller-Hinton agar plates containing carbenicillin (100 μg/ml to select for wild-type survivors) or kanamycin (10 μg/ml to select for ΔoxyRS survivors). (a) Normal neutrophils (n = 8). (b) Oxidase-deficient neutrophils (n = 4). Data points reflect the geometric mean ± SE of the n independent experiments.