FIG 4.

The AbaAL44 katX gene promotes bacterial resistance to hydrogen peroxide stress and neutrophil-mediated killing. (A) Mid-log-phase A. baumannii 17978 VU, 17978 UN, 17978 UN ΔkatX/EV, or 17978 UN ΔkatX/pkatX variants were incubated in LB medium supplemented with 1 mM hydrogen peroxide at a starting inoculum of 1 × 10⁷ CFU/ml. Following a 30-min incubation, remaining viable bacteria were enumerated. (B) Differentiated neutrophil-like HL-60 cells were incubated with mid-log-phase A. baumannii 17978 VU, 17978 UN, 17978 UN ΔkatX/EV, or 17978 UN ΔkatX/pkatX variants at an MOI of 2. At 90 min postincubation, HL-60 cells were lysed, and neutrophil-mediated killing of bacteria was assessed by determining the number of viable bacteria in each well. Data are represented as bacterial survival relative to that for A. baumannii 17978 VU. In both panels, N = 3 or 4 biological replicates per group per experiment. Experiments were repeated for a total of at least two times, with graphs depicting average data. Columns depict the mean, and error bars show standard deviation of the mean. All means were compared to all other means using a one-way ANOVA adjusted for multiple comparisons. *, P < 0.05; ***, P < 0.001; ****, P < 0.0001; ns, not significant.