Immunomodulatory Effects of Probiotics on Salmonella enterica Serovar Typhimurium Isolated from Diarrheal Children in Albino Male Mice

         This study aimed to determine the frequency of Salmonella Typhimurium and its multi-drug resistance (MDR) status as a diarrheal causative pathogen in children younger than five years old, as well as to investigate the role of four probiotic microorganisms(L.acidophillus,L.casei,S.cerevisiae,S.boulardi) in controlling such infection.For this purpose, 128 stool samples of patients (76 males and 52 females)
was included in this study. They were children suffering from diarrhea and fever who admitted to the “Central Pediatric Hospital” in Baghdad during the period from April to September, 2012. Their ages ranged from six days up to five years. The immunological effects of probiotics and MDR  S. Typhimurium isolate in the experimentally infected and probiotic-treated mice were investigated via assessing the level of ten cytokines (IFN-γ, IL-1β, IL-4, IL-10, IL-12, IL-17A, IL-21, GM-CSF, RANTES and IP-10) in the lavage of small intestine.Accordingly, five groups of mice were used in the in vivo part of this study; Mice in group I received probiotic for 7 successive days, challenged with S. Typhimurium on day 8, and dissected on days 14 and 21.  Group II was similarly treated, but the probiotic was continued for 14 days. Group III was given the probiotic only, and group IV was challenged with S. Typhimurium,while group V was the control.Results obtained in this study could be summarized as follows:
1. Out of 128 stool samples, S. Typhimurium was isolated and identified in 9 samples only (7.03%). All isolates were totally resistant to nalidixic acid, with the exception of one isolate which showed intermediate sensitivity.Furthermore, only one of these isolates (symbolized B) was found to be resistant to three antibiotics (ampicillin, amoxicillin and nalidixic acid).Therefore, this isolate was considered as an MDR isolate and selected for further experiments in the study.
2. When the susceptibility of MDR S. Typhimurium isolate B was further assessed in vitro by using four probiotics (Saccharomyces cerevisiae, S. boulardi, Lactobacillus acidophilus and L. casei), results showed that S. cerevisiae and L. acidophilus were the most efficient by recording the highest inhibition zones (12.6 and 16.3 mm, respectively), therefore, they were further investigated for their anti-S. Typhimurium effects in vitro and in vivo.
3. By using the unconcentrated and (one-fold, two-fold, three-fold) concentrated filtrates of these two probiotics, it was found that the three-fold filtrates were most efficient in their antibacterial activity  by recording the highest inhibition zones (25.0 mm for S. cerevisiae and 31.0 mm for L. acidophilus.
4. Significant increases in the values of liver index were observed in mice of group I treated with L. acidophilus at 21 days (10.73%) compared to the corresponding group treated with S. cerevisiae (7.41%) or other four groups. For spleen, index value in L. acidophilus groups was higher than the corresponding groups in S. cerevisiae. Mice treated with a probiotic alone or in a combination with the pathogen showed significant increases in the spleen index values of all groups compared to the untreated mice (group V).
5. Both probiotics were effective in reducing S. Typhimurium colony forming units per plate (cfu/plate) in the liver and spleen. In liver, mice in group IV showed a count of 224.4 cfu/plate, which was significantly higher than any count in groups of L. acidophilus and S. cerevisiae. Group II mice recorded better results than group I mice, while the lowest counts (21.6 and 27.8 cfu/plate for L. acidophilus and S. cerevisiae, respectively), were observed at day 21.
6. The ten investigated cytokines showed different levels in the small intestine wash; such differences were subjected to the group of mice under investigation and type of probiotics used. In addition, variations in IFN-γ/IL-4, IFN-γ/IL-10, IL-4/IL-10 and IL-17A/IL-10 were also observed.