FIGURE 2.

Neutrophils kill L. monocytogenes regardless of LLO expression. L. monocytogenes (Lm; wt, Δhly, and LLO⁺) were incubated alone (Lm) or with neutrophils (Lm + PMNs) in 10% DS/HBSS⁺ at 37°C at a MOI of 1 (A) and 10 (B, C). At the indicated times, Triton X-100 was added, and cell lysates were plated to enumerate CFUs. This measured the viability of L. monocytogenes in the absence (Lm) and the presence (Lm + PMNs [Total]) of neutrophils. To measure the viability of intracellular bacteria (Lm + PMNs [Intra.]), the last hour of incubation at 37°C was carried out with gentamicin. Cells were then washed before lysis and CFU enumeration. (A–C) At least three independent experiments were performed in triplicate. Results are expressed relative to the inoculum. Statistical analyses were performed respective to CFUs enumerated in the absence of neutrophils (Lm) at each corresponding time point. *p < 0.05.