Impact of narrow-spectrum penicillin V on the oral and faecal resistome in a young child treated for otitis media.

OBJECTIVES: Antibiotic overuse has led to the global emergence of antimicrobial-resistant bacteria, and children are among the most frequent users of antibiotics. Most studies with broad-spectrum antibiotics show a severe impact on resistome development in patients. Although narrow-spectrum antibiotics are believed to have fewer side effects, their impact on the microbiome and resistome is mostly unknown. The aim of this study was to investigate the impact of the narrow-spectrum antibiotic phenoxymethylpenicillin (penicillin V) on the microbiome and resistome of a child treated for acute otitis media. METHODS: Oral and faecal samples were collected from a 1-year-old child before (Day 0) and after (Days 5 and 30) receiving penicillin V for otitis media. Metagenomic sequencing data were analysed to determine taxonomic profiling using Kraken and Bracken software, and resistance profiling using KMA in combination with the ResFinder database. RESULTS: In the oral samples, antimicrobial resistance genes (ARGs) belonging to four classes were identified at baseline. At Day 5, the abundance of some ARGs was increased, whereas some remained unchanged and others could no longer be detected. At Day 30, most ARGs had returned to baseline levels or lower. In the faecal samples, seven ARGs were observed at baseline and five at Day 5. At Day 30, the number of ARGs had increased to 21. CONCLUSIONS: Following penicillin V, we observed a remarkable enrichment of the aecal resistome, indicating that even narrow-spectrum antibiotics may have important consequences in selecting for a more resistant microbiome.