Macrophage cellular and transcriptional responses to infection with necrotizing fasciitis-causing multidrug-resistant isolates of Acinetobacter baumannii 4576

Abstract Description The opportunistic nosocomial pathogen Acinetobacter baumannii has come to the forefront of concern within the public health community. A. baumannii (Ab) strains have been isolated from rare but fatal cases of necrotizing fasciitis (NF) and these NFAb strains possess enhanced mechanisms of resistance, limiting therapeutic efficacy. Macrophages are key players in the early immune response to A. baumannii infections, but their response to NFAb strains is unclear. We sought to reveal the cellular interactions between human macrophages and NFAb isolates. Monocyte-derived THP-1 macrophages were incubated with NFAb-1, NFAb-2 or type strains, 19606 or 17978, with or without cytochalasin D pre-treatment. Following a colistin-protection assay, viable intra- and extracellular bacteria were quantified after 2 or 24h. Bulk RNA sequencing of infected THP-1 cells was used to identify differential gene expression relative to mock infection. All bacterial isolates were found to enter macrophages, with NFAb-1 displaying greater intracellular survival than 19606. Bacterial entry primarily occurred via macrophage-driven phagocytosis and increased expression of microtubule-associated products was found with NFAb infection. All bacterial strains showed extracellular escape and viability post-antibiotic treatment. This work demonstrates that macrophage function during A. baumannii infections, particularly NF, may provide a means for pathogenic bacteria to evade extracellular antimicrobial defenses. Funding Sources Supported by the South Carolina IDeA Networks of Biomedical Research Excellence, The Infectious Disease Society of America Foundation, and the National Institute of Health Award (SC3GM125556). Topic Categories Innate Immune Responses and Host Defense: Cellular Mechanisms (INC)