Assessment of Bacterial Density, Diversity, and Antibiotic Resistance-Dissemination from Multidrug-Resistant Escherichia coli to Rat’s Gut Microbiota in Presence and Absence of Antibiotic Treatment: a Useful Animal Model for Future Investigations

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. INTRODUCTION Escherichia coli resides mainly in the mammalian gut, with a rare presence in the gut of reptiles, avians and fish. This bacterium is quite diversified and can contaminate the ecosystems of animals and humans, including water, soil, plants and feed and food1. The Gut Microbiota (GM) can produce vitamins (B12 and K) for the host, in exchange of seeking shelter and nutrients for their growth. The association of E. coli with its host is not a self-to-self association, since some of its strains are antigenic, causing serious illnesses such as urinary tract infections (UTIs), abdominal sepsis, meningitis, septicaemia, haemolytic-uremic syndrome and diarrhoea1–6. Furthermore, the acquisition of various β-lactamases genes in this bacteria has currently worsened the severity of the resulting diseases, thereby increasing the duration of morbidity and causing unproductive exposure to antimicrobials used in treatment7. Certain E. coli strains, originating from animals, such as E. coli O157:H7, E. coli–bearing blaCTX-M gene and E. coli encoding blaAmpC genes, can cause serious human infections, in addition to their