c-di-GMP protects against intranasal Acinetobacter baumannii infection in mice by chemokine induction and enhanced neutrophil recruitment.

Acinetobacter baumannii has emerged as a major cause of both community-associated and nosocomial infections worldwide. A. baumannii rapidly develops resistance to multiple antibiotics; as a result, infections by this pathogen have become increasingly difficult to treat. In this study, we evaluated the effect of 3',5'-cyclic diguanylic acid (c-di-GMP), a bacterial second messenger and immunomodulator, in the host defense against A. baumannii infection in a mouse model of intranasal infection. Our results showed that 50 μg of c-di-GMP administered 18 h prior to infection provided the best protection against intranasal infection with A. baumannii. Mechanistically, administration of c-di-GMP induced the production of chemokines KC, MCP-1, MIP-1α, MIP-2 and RANTES, and enhanced neutrophil recruitment in the lung. Moreover, depletion of neutrophils abolished the protective role of c-di-GMP. Taken together, our data suggest that c-di-GMP confers resistance against intranasal A. baumannii infection in mice through a neutrophil-dependent mechanism and that c-di-GMP should be further explored as an immunomodulator for the treatment of A. baumannii infection.