A new model of intestinal colonization using larvae: testing hyperepidemic ESBL- and carbapenemase-producing clones.

Finding strategies for decolonizing gut carriers of multidrug-resistant (MDR-) is a public-health priority. In this context, novel approaches should be validated in preclinical gut colonization models before being translated to humans. However, the use of mice presents limitations. Here, we used for the first time larvae to design a new model of intestinal colonization (28-days duration, T28). Three hyperepidemic MDR- producing extended-spectrum β-lactamases (ESBLs) or carbapenemases were administered via contaminated food to larvae for the first 7 days (T7): -4901.28 (ST131, CTX-M-15), -042 (ST410, OXA-181) and -050 (ST167, NDM-5). Growth curve analyses showed that larvae became rapidly colonized with all strains (T7, ~10 CFU/mL), but bacterial load remained high after the removal of contaminated food only in -4901.28 and -042 (T28, ~10 CFU/mL). Moreover, larvae receiving a force-feeding treatment with cocktail (on T7 and T10 via gauge needle) were decolonized by -4901.28 (-susceptible); however, -042 and -050 (-resistant) did not. Initial microbiota (before administering contaminated food) was very rich of bacterial genera (e.g., , ), but patterns were heterogeneous (Shannon diversity index: range 1.1-2.7) and diverse to each other (Bray-Curtis dissimilarity index ≥30%). However, when larvae were challenged with the MDR- with or without administering bacteriophages the microbiota showed a non-significant reduction of the diversity during the 28-day experiments. In conclusion, the larvae model promises to be a feasible and high-throughput approach to study novel gut decolonization strategies for MDR- reducing the number of subsequent confirmatory mammalian experiments.