Ethical approval was granted through the local committee of animal care and use at the College of Veterinary Medicine within the University of Baghdad (Number P-G/649, 24/3/2024) during this study.

S. rubidea was isolated from one hundred fecal cattle samples in Baghdad, each sample was inoculated onto the chrome agar, MacConkey agar, and Nutrient agar, then incubated at 37˚C for 24 - 48 hrs. [14] . The Serratia isolates were identified at the species level using the traditional morphological, and biochemical tests, vitek2 compact system, and PCR [15] . Citrobacter freundii was obtained from the University of Baghdad’s College of Veterinary Medicine’s microbiology department accession No. OR766039.

Prodigiosin preparation was extracted by [16] . The Serratia rubidea was cultured on ten nutrient agar plates and incubated at room temperature (28˚C) for 2 days. Observe the colonies growing in confluence with the bright red color. Only the colonies with the bright red color were harvested from all plates in sterile saline and collected in centrifuge tubes. The cells were centrifuged at 3000 rpm for 20 min. The suspension was then digested in a glass test tube by adding 1 N (NaOH) twice the volume of the suspension and then put in a water bath at 100˚C for 1 hour, the pigment was removed from the suspension by adding the equal volume of ethanol, the tubes were centrifuged for 20 min at 3000 rpm. To obtain a color solution free of turbidity, petroleum ether was added and thoroughly mixed with the colored solution. The mixture was then vigorously shaken and blended using a vortex mixer. For layer separation, the tubes were allowed to settle for 10 minutes. In an evaporating dish, the top layer was collected. By heating a water bath to 100˚C, an acquired solvent was evaporated till dry residue was left. Put the leftovers in 5 ml of acidified ethanol. Crud prodigiosin concentration is estimated using spectrophotometer absorbance fixed at 535 nm [16] .

Twenty-four healthy Swiss mice of both sexes aged between 7 - 8 weeks, weighted 13 - 17 g were divided into 4 groups (each group 6 mice). Groups [3] [4] were inoculation with an infectious dose of Citrobacter freundii (1 × 10⁶ cfu/ml orally [17] . 2^nd group positive control inoculation with infectious dose Citrobacter freundii (1 × 10⁶ cfu/ml orally) [17] . 1^st group negative control was injected with (1ml PBS). After 24 hours post-infection with C. freundii, the Group 3 and Group 4 groups administered crud prodigiosin extract as follows: the 4^th group administered (1000 µg/ml I.P). 3^rd group administered (500 µg/ml I.P). Blood samples were collected on days 3, 7 and 14 from all mice groups, and sera were separated for estimating IL-6, IL-10, and IgM concentration by ELISA kits (Elabscience, China, for mice). Two mice from each group were used for histopathological changes at day 7, specimens were taken from the liver, kidney, spleen, and intestine. The tissues were fixed in a 10% formalin solution immediately after removal [18] .

Data were subjected to analysis using SAS (Statistical Analysis System—version 9.1). Two-way ANOVA with interaction and least significant differences (LSD) was performed to assess significant differences among means. Results are expressed as mean ± standard error. P < 0.05 is considered statistically significant [19] .

Thirty isolates of S. rubidea out of one hundred fecal samples from cattle and the colonies of S. rubidea were observed in red colonies on nutrient ( Figure 1 ). While dark pink to red on MacConkey agar and Chrome agar.

To confirm the identification of S. rubidea vitek 2 compact system was done and gave 99% Probability to Serratia rubidae. The isolate of Serratia rubidea was registered by GenBank under Accession No. (OR757107.1). This isolate was used for crud prodigiosin extract, the prodigiosin production was high at 28˚C for 48 h yielding a final concentration of 130 mg/L, and two concentrations were prepared (1000 and 500 µg/ml).

The IL-6 concentration results for groups Group 2 and Group 4 showed a significant increase on days 7 and 14, with significant differences (P < 0.05) compared to the negative control group. Group 3 showed a moderate increase at day 7, relative to Group 1 (the control group); Group 2 (Positive control) showed the highest IL-6 concentration at days 3 and 7, with 824.71 pg/ml and 955.28 pg/ml, followed by Group 4 at days 3 and 7, with 817.73 pg/ml at day 7 and 952 pg/ml, as indicated in Figure 2 .

Comparing the IL-10 concentration data for groups Group 2 and Group 4 to the negative control group on days 3, 7, and 14 revealed no significant variations. Figure 3 shows that, in comparison to the other groups, Group 4 had the lowest level of IL-10 concentration on days 3, 7, and 14 (64.83, 52.41, and 41.48 pg/ml), followed by Group 2 which also had the lowest concentration of IL-10 on the same days (64.81, 55.20, and 42.08 pg/ml). Group 3 had the highest IL-10 concentration on days 3, 7, and 14 (129.91, 450.06, and 835.54 pg/ml) ( Figure 3 ).

Results revealed that the differences among groups within each period were significant (P < 0.05). The concentration of IgM at all periods in the Group 4 (60.01 pg/ml) and Group 2 (59.35 pg/ml) did not differ significantly but they were significantly (P < 0.05) higher than other groups. Concerning the differences among periods within each group, results showed that the IgM in Group 2 and Group 4 increased significantly with advanced period while the Group 3 showed significant decreasing (62.46 pg/ml) at 14 days as compared with 7 days (95.43 pg/ml). On the other hand, the differences among periods in G1 were not significant ( Figure 4 ).

Following a 7-day histological examination revealed that all groups under investigation had varying histopathological alterations. Group 2: the liver shows marked portal fibrosis with marked bridge formation, proliferation of choanocytes, and degeneration with necrosis of hepatocytes ( Figure 5 ). Also, the liver shows marked vascular degeneration of hepatocytes, aggregation of MNCs, and portal congestion ( Figure 6 ). The liver of G2 shows marked deterioration with damage to the cytoarchitecture of the hepatic ( Figure 7 ). Kidney shows marked focal nephritis characterized by local necrosis of renal tubules with aggregation of MNcs ( Figure 8 ). kidney marked interstitial nephritis with necrosis of renal tissue and aggregation of MNCs and tubular dilation ( Figure 9 ). spleen shows marked sinusoidal congestion with distention, and slight atrophy of lymphoid follicles with marked irregular shapes ( Figure 10 ). enteritis marked thickening of villi with marked hyperplasia of lining cells with severe infiltration of mononuclear leukocytes ( Figure 11 ). Group 4: liver marked disarrangement of hepatic cords with sinusoidal dilation and degeneration of hepatocytes ( Figure 12 ). also marked disarrangement of hepatic cords with atrophy of hepatocytes and sinusoidal congestion ( Figure 13 ). kidney marked nephritis with severe tissue damage and aggregation of MNCs, degeneration with necrosis of lining cells of renal tubules, degeneration of podocytes of glomerulus ( Figure 14 ). Spleen showed marked lymphoid hyperplasia within follicles of splenic white pulp and congestion with dilation of splenic sinuses with proliferation of megakaryocytes ( Figure 15 ). The intestine showed hypernulcation of enterocytes ( Figure 16 ). Group 3: liver severe per central cellular swelling with necrosis of hepatocytes (Red arrows) and per central vein (V) aggregation of MNCs ( Figure 17 ). kidney marked dilation of bowman capsule with tubular dilation with accumulation of non-cellular eosinophilic substance ( Figure 18 ). spleen shows splenic sinus dilation with the proliferation of megakaryocytes ( Figure 19 ). The intestine shows hyperplasia of lining cells of intestinal glands involving paneth cells ( Figure 20 ).