Age-driven shifts of the camel gut microbiome and resistome in extensively reared dromedary camels

ABSTRACT Camels are uniquely adapted to arid environments and are commonly raised in extensive grazing systems. The composition of their gut microbiome and antimicrobial resistance genes (ARGs) is expected to change with host development, but age-related patterns have not been well described. In this study, we analyzed fecal samples from juvenile (approximately 6 months old) and adult (6 years) dromedary camels kept under the same grazing management, with no recorded therapeutic antibiotic treatments during the study period. Shotgun metagenomic sequencing was used to profile bacterial communities, ARGs, and mobile genetic elements (MGEs). Juvenile camels showed lower alpha diversity and greater inter-individual variation than adults, and their gut communities were dominated by facultative anaerobes such as Escherichia and Streptococcus . Adult camels carried more stable, fiber-adapted communities enriched in Bacteroidaceae and Prevotellaceae. In parallel with these microbiome changes, the resistome also differed by age. Juveniles carried a wider range of ARGs, with higher contributions from multidrug efflux pumps and vancomycin resistance genes. Adults had a smaller and more concentrated set of ARGs, mainly β-lactamase and tetracycline resistance genes, together with lower ARG richness and diversity. MGEs also showed distinct age-related patterns: transposase genes were more common in juveniles, whereas insertion sequence-associated genes were more abundant in adults, suggesting age-specific routes of potential ARG mobility. Overall, these data indicate that maturation of the camel gut microbiome is accompanied by a reduction and focusing of the resistome and by a shift in the dominant types of MGEs. This study provides an age-stratified reference for ARG reservoirs and MGE-associated ARG mobility in camels studied under conditions with no recorded therapeutic antibiotic treatments and may be useful for future work on antimicrobial resistance in extensively managed livestock. IMPORTANCE Antimicrobial resistance is often studied in animals heavily exposed to antibiotics, leaving a gap in our understanding of its natural development. Camels, rarely treated with antibiotics, offer a unique model. By comparing juvenile and adult gut microbiomes, we found that early-life communities are diverse, unstable, and rich in mobile resistance genes, while adult communities are more stable and carry fewer mobile elements. These findings establish a natural baseline for how resistance genes emerge and settle without drug pressure, providing critical insights for One Health strategies aimed at limiting the spread of resistance in livestock and wildlife.