Probiotic Properties of Alcaligenes faecalis Isolated from Argyrosomus regius in Experimental Peritonitis (Rat Model)

Abstract

A strain of Alcaligenes faecalis A12C (A. faecalis A12C) isolated from Argyrosomus regius is a probiotic in fish. Previous experiments showed that A. faecalis A12C had inhibitory effects on the growth of multidrug-resistant bacteria. We aimed to confirm whether A. faecalis A12C is safe and has adequate intestinal colonization in experimental rats, and evaluate its efficacy in an animal model of peritonitis. We used 30 male rats, randomly divided into 6 groups (n = 5): three groups (HA7, HA15, HA30) received A. faecalis A12C in drinking water (6 × 10⁸ CFU/mL) for 7 days, and three control groups received drinking water only. All groups were evaluated at 7, 15, and 30 days. Survival after A. faecalis A12C administration was 100% in all groups. Mild eosinophilia (1.5%, p < 0.01) and increased aspartate aminotransferase (86 IU/L, p < 0.05) were observed in HA7, followed by progressive normalization. No histological signs of organ injury were found. We observed significant E. coli decline in faeces, parallel to an increase in A. faecalis A12C at 7 days. E. coli had a tendency to recover initial values, while A. faecalis A12C disappeared from the intestinal microbiota at 30 days. To evaluate its efficacy against peritonitis, we studied two additional groups of animals: IA group pretreated with A. faecalis A12C before E. coli intra-abdominal inoculation, and IC group inoculated with no A. faecalis A12C. We found an increase in C-reactive protein, alanine aminotransferase, urea, and eosinophils in IC animals when compared with IA. Peritonitis was more evident in IC than in IA animals. Our findings suggest that A. faecalis A12C altered clinically relevant parameters in sepsis and was associated with a lesser spread of infection.

Keywords: Alcaligenes faecalis; Argyrosomus regius; Escherichia coli; Peritonitis; Probiotic; Rat.

Fig. 1

Experimental design and timeline. HC7, HC15, and HC30 Healthy control groups assessed at 7 days, 15 days, and 30 days, respectively. HA7, HA15, and HA30 groups treated with A. faecalis A12C and assessed at 7 days, 15 days, and 30 days after the first dose of probiotics. IC Infected Control Group, IA Group treated with A. faecalis A12C and infected. Black tip arrow extra orogastric administration of water or A. faecalis A12C suspension. E euthanatized

Fig. 2

Faeces concentration of E. coli and A. faecalis A12C at different times in groups treated with A. faecalis A12C and assessed at 0d, 0 days (just before administration of A. faecalis A12C), and 7d 7 days, 15d 15 days, and 30d 30 days, after the first dose of probiotic. Box and whisker diagrams depict the smallest observation, lower quartile, median, upper quartile, and largest observation.*P < 0.003, **P < 0.0005

Fig. 3

Loss of bodyweight, expressed as difference in grams between weight just in the moment of E. coli inoculation (7 days), and at euthanatized time (15 days) a, or as percentage of grams lost during the same period of time b. IC Infected control group, IA Infected group pretreated with A. faecalis A12C. Box and whisker diagrams depict the smallest observation, lower quartile, median, upper quartile, and largest observation

Fig. 4

Percentage of eosinophils and serum levels of urea, ALTL (alanine aminotransferase) and CRP (C reactive protein), in Infected Control Group (IC) and Infected group pretreated with A. faecalis A12C (IA). **P < 0.01, *P < 0.05

Fig. 5

Representative histological images of hematoxilin and eosin stained sections of jejuna peritoneum a, b, mesenteric lymph nodes c, d, and splenic hilum e, f. Dulling of the peritoneal surface, and swelling of mesothelial cell (black arrow) in jejunal peritoneum a and splenic hilum peritoneum e, plus focal desquamation of mesothelial cells (white arrow) in splenic hilum peritoneum e. Mixed polymorphonuclear infiltrate (black arrow) in mesenteric lymphondes c, in a rat from IC group. No sign of inflammation or tissue alteration (red arrow) in peritoneal surface of jejunal peritoneum b, neither mesenteric lymph nodes d nor splenic hilum f in a rat from IA group. × 200 magnification a, b, c, d, and e; × 40 magnification f