Long-term treatment with Alcaligenes faecalis A12C improves host resistance to pathogens in septic rats: possible contribution of curdlan-like immune-trainer

Abstract

Curdlan, a β-1,3/1,6-glucan found in Alcaligenes faecalis (A. faecalis) wall, activates innate and humoral immunity. The aim of this study is to evaluate whether pre-treated rats with A.faecalis A12C could prevent sepsis disturbances and identify the immunomodulatory mechanisms involved. Experiments occurred in two stages: a survival study with 16 rats randomly divided into septic (SC) (n = 8) and septic pre-treated (SA) (n = 8) groups; and 45 rats divided into four groups: healthy (AGUSAN) (n = 9), septic (AGUIC) (n = 13), septic pre-treated (AGUIA) (n = 14), and healthy pre-treated (AGUSTO) (n = 9). Sepsis was induced by cecal ligation and puncture after 30 days of A.faecalis A12C pre-treatment or without. SA group had a higher survival rate (58%) vs SC group (16%) (P < 0.05). Overall, AGUIA showed better status than AGUIC (P < 0.01). Higher monocytosis was found in AGUIA and AGUSTO vs AGUIC and AGUSAN, respectively (P < 0.05). A gradual increase in curdlan fecal concentration was observed in AGUIA during pre-treatment. Fecal concentrations of E. coli significantly decreased in AGUIA and AGUSTO. Bacterial load in urine, peritoneal, and bronchoalveolar lavage fluids (PLF and BALF) decreased (P < 0.05) in AGUIA vs AGUIC. Finally, lower inflammation was observed in serum, BALF, and PLF, with reduced IL-6, IL-10, IL-1β, and TNF-α, along with less damage in lungs and peritoneum in AGUIA vs AGUIC. These findings suggest the connection between curdlan -produced by A. faecalis A12C- with the immune system and the reduction in severity of experimental sepsis.