Acinetobacter baumannii, which causes serious
infections in immunocompromised patients, expresses high-affinity
iron acquisition functions needed for growth under
iron-limiting laboratory conditions. In this study, we determined that the initial interaction of the ATCC 19606(T) type strain with A549 human alveolar epithelial cells is independent of the production of BasD and BauA,
proteins needed for
acinetobactin biosynthesis and transport, respectively. In contrast, these
proteins are required for this strain to persist within epithelial cells and cause their apoptotic death.
Infection assays using Galleria mellonella larvae showed that impairment of
acinetobactin biosynthesis and transport functions significantly reduces the ability of ATCC 19606(T) cells to persist and kill this host, a defect that was corrected by adding inorganic
iron to the inocula. The results obtained with these ex vivo and in vivo approaches were validated using a mouse
sepsis model, which showed that expression of the
acinetobactin-mediated
iron acquisition system is critical for ATCC 19606(T) to establish an
infection and kill this vertebrate host. These observations demonstrate that the virulence of the ATCC 19606(T) strain depends on the expression of a fully active
acinetobactin-mediated system. Interestingly, the three models also showed that impairment of BasD production results in an intermediate virulence phenotype compared to those of the parental strain and the BauA mutant. This observation suggests that
acinetobactin intermediates or precursors play a virulence role, although their contribution to
iron acquisition is less relevant than that of mature
acinetobactin.