Abstract
We investigated the intracellular survival of multidrug-resistant Acinetobacter baumannii (MDRAB) clinical isolates in macrophages, after phagocytosis, to determine their virulence characteristics. After ATCC 19606 and 5 clinical isolates of MDRAB were phagocytosed by mouse and human macrophages, the bacterial count of MDRAB strains, R4 and R5, increased in the mouse macrophages, 24 hours after phagocytosis. Bacterial count of the strains, R1 and R2, was almost equal 4 and 24 hours after phagocytosis. Intracellular reactive oxygen species was detected in the macrophages after phagocytosis of these bacteria. Further, the strains R1, R2, R4, and R5 showed higher catalase activity than ATCC 19606. Additionally, strains R1, R4, and R5 grew more efficiently than ATCC 19606 in the presence of H2O2, whereas growth of strains R2 and R3 was marginally more than that of ATCC 19606 in the presence of H2O2. The MDRAB clinical isolates altered the expression of TNF-α, IL-1β, IL-6, and MIP-2 mRNA induced in J774A.1 cells, 24 hours after phagocytosis. These results provide insights into the renewed virulence characteristics of MDRAB clinical isolates. Finally, tigecycline killed MDRAB phagocytosed by the macrophages more effectively than colistin, although colistin and tigecycline are both considered effective antibiotics for the treatment of MDRAB.
Highlights
We investigated the intracellular survival of multidrug-resistant Acinetobacter baumannii (MDRAB) clinical isolates in macrophages, after phagocytosis, to determine their virulence characteristics
We examined the MDRAB clinical isolate counts in J774A.1 and human macrophages at 4 and 24 hours after phagocytosis
We examined whether A. baumannii was phagocytosed by the macrophages or they invaded into the macrophages
Summary
We investigated the intracellular survival of multidrug-resistant Acinetobacter baumannii (MDRAB) clinical isolates in macrophages, after phagocytosis, to determine their virulence characteristics. The clinical isolates show different degrees of biofilm formation in the presence of sub-minimum inhibitory concentrations of antibiotics[18] These results suggest that A. baumannii is emerging as a highly pathogenic bacterium and that the characteristics of A. baumannii vary in different environmental stress conditions, such as multiple antimicrobial agents and host immune responses. Phagocytic cells such as neutrophils and macrophages represent the first line of defence against invading bacterial pathogens in the host[19]. The uptake of A. baumannii by alveolar macrophages and murine macrophage cell line J774A.1 has been explored[25], few studies have focused on the intracellular survival of A. baumannii in macrophages because it is regarded as an extracellular pathogen
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