Interaction of Aeromonas spp. human isolates with murine macrophages

This study aimed to evaluate phagocytic and bactericidal activity of macrophages originated from murine J774 macrophage cell line against 26 strains of Aeromonas caviae, Aeromonas veronii biotype sobria and Aeromonas hydrophila isolated from human fecal specimens. The analysis of phagocytic index (PI) indicated these strains were phagocytosed in low numbers, below 1.1 x 10(-3) for 65% strains of A. veronii biotype sobria and A. hydrophila. The highest PI value (0.019) was noted in murine macrophages infected with 19% of A. caviae isolates. Analysis of the number of viable bacteria in phagocytes revealed that 31% of Aeromonas spp. strains could replicate for an initial 3 h after gentamicin treatment. Opsonisation of the bacteria with non-immune serum did not affect phagocytic activity and bacterial killing. Stimulation of macrophages with gamma-interferon (IFN-gamma) at a concentration of 10 IU/ml caused the highest increase in phagocytic activity, but had no effect on the rate of bacteria elimination by murine macrophages. Aeromonas spp. isolates showed an invasive ability toward non-phagocytic epithelial cells. These findings indicate that Aeromonas spp. strains have evolved mechanisms to avoid phagocytosis, suggesting that murine macrophages, even activated by IFN-gamma, have a limited ability to eliminate these bacteria, which may invade epithelial cells and spread in the illeum.