الفهرس 
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Abstract
The sharp increase in antibiotic resistance imposes a global threat to human health and the discovery of effective antimicrobial alternatives is needed. The use of probiotics to combat bacterial pathogens has gained a rising interest.
Pathogenic Escherichia coli is causative of multiple clinical syndromes such as diarrheal diseases, meningitis and urinary tract infections. In this work, we evaluated the efficacy of probiotics to control multidrug-resistant E. coli and reduce their ability to form biofilms.
Six E.coli resistant to at least five antibiotics (Ceftazidime, Ampicillin, Clarithromycin, Amoxicillin + Clavulanic Acid and Ceftriaxone) were isolated in this work. Preparations of cell-free spent media (CFSM) of six probiotics belonging to the genus Bifidobacterium and Lactobacillus which were grown in Man-Rogosa-Sharpe (MRS) broth exhibited strong antibacterial activity (inhibition zones of 11.77–23.10 mm) against all E. coli isolates. Two E. coli isolates, namely E. coli WW1 and E. coli IC2, which were most resistant to all antibiotics were subjected to antibiofilm experiments.
Interestingly, the CFSM of MRS fermented by all probiotics resulted in inhibition of biofilm formation while B. longum caused highest inhibition (57.94%) in case of E. coli IC2 biofilms and L. plantarum was responsible for 64.57% reduction of E. coli WW1 biofilms. On the other hand, CFSM of skim milk fermented by L. helveticus and L. rhamnosus exhibited a slight inhibitory activity against IC2 isolate (inhibition percentage of 31.52 and 17. 68, respectively) while WW1 isolate biofilms was reduced by CFSM of milk fermented by B. longum and L. helveticus (70.81 and 69.49 reduction percentage, respectively)
The protective effect of probiotics against E. coli infections in mice as evident by histopathology of the organs, shows that the E. coli-infected control mice group which did not receive any probiotic treatments (group 9), had more severe disease symptoms in all organs (intestine, kidney, liver, and spleen) but most of the probiotic–treated mice experienced less disease severity.
For example, the probiotic group 6 (L. rhamnosus EMCC 1105) showed the highest protection and reduction of disease severity in intestinal cells, the probiotic group 3 (B. bifidum EMCC 1334) showed the highest protection and reduction of disease severity in kidney and liver cells, whereas the probiotic group 2 (L. acidophilus EMCC 1324) showed the highest protection and reduction of disease severity in spleen cells. On the other hand, probiotics have immunomodulatory effect on lymphocytes and phagocytic cells. The count of total and differential white blood cells in case of the probiotic group 7 were the highest for lymphocytes (66%) and WBCs (5.2x103), and the highest for phagocytic activity (90%), and phagocytic index (4.6). These results support the effective use of probiotics against E. coli infection