Aim: The increasing prevalence of multi-drug resistant (MDR) Escherichia coli is one of the intractable, economic veterinary and public health obstacle of the 21st century. As a component of the gut microbiota (GM), it is aimed in this study to establish a rat model to examine the role of E. coli in contributing to the increasing antimicrobial resistance of GM. Methods and Results: Ten rats were divided into two equal groups (RG-1 and RG-2), and their GM was characterized before and after an amoxicillin treatment. The first treatment was applied on all rats, administering to each an equal count of Multiple Drug Resistant E. coli (MDR E. coli). The second treatment was restricted to rats of the RG-2 group, treating them with amoxicillin, effective 48 hrs following the MDR E. coli administration, to examine the persistence of MDR E. coli and the posttreatment profile of the GM resistome. Stool samples, collected at different times, were aerobically cultured at 37°C, and the bacterial cultures were tested against ten antibiotics from different classes. The bacterial isolates were analysed by matrix-assisted laser desorption ionisation time-of-flight mass spectrophotometry (MALDI-TOF MS) and some by 16S RNA sequencing. In four phyla, 12 genera and 16 species were identified by culturing 8020 fecal colonies. The rat GM was dominantly inhabited by the genus Enterococcus, encoding resistance to amoxicillin, D-cycloserin, gentamicin, carbenicillin and kanamycin. The GM of rats in the two groups had significantly greater antimicrobial resistant colony count (p<0.01) after administration of exogenous MDR E. coli compared to that before treatment. The amoxicillin treatment in the second group was efficient in reduction of the bacterial density, associated with enhanced resistance diversity. The Bacteriodetes emerged as a new resistant phylum after the amoxicillin treatment. Conclusions: In conclusion, the administration of MDR E. coli caused a change in the resistome of the GM, and the additional treatment with amoxicillin increased the drug resistantcolony forming units, and led to the isolation of new antimicrobial resistant species. Significance and Impact of Study: This study proves the significance of a rat model in studying the role of ingestion of MDR microorganism, in absence and presence of antimicrobial treatment, on the drug resistome of the GM. The impact of this pioneer study on future control of the problem of drug resistance in GM, due to ingestion of MDR microorganisms by animals and humans, in absence and presence of antimicrobial treatment, is in accord with recent influx of documentations in this research scope.
