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A metagenomics study analyzed the effects of azithromycin and amoxicillin on the gut microbiome, which revealed sustained alteration in microbial communities and increases in putative resistance genes, suggesting a potential spillover effect on untreated housemates.
Jessica Chopyk, PhD, Department of Pathology, University of California San Diego, San Francisco, CA, and colleagues noted that the impact of antibiotics on the gut microbiome is significant and could last a lifetime, as indicated by their impact on some of the most prevalent bacteria in the intestinal system.
The researchers enlisted 56 individuals, including 24 housemate pairs and 8 individuals from different households. They were given either amoxicillin or azithromycin, or placebo (vitamin C) for either 3 or 7 days daily. Fecal samples were taken on day 0, 3, 7, week 8, and at 6 months. A total of 282 samples was sequenced.
The most prevalent bacterial genera among all participants were Bacteriodes, Bifidobacterium, Ruminococcus, Eubacteriana, Prevotella, Faecalibacterrium, and Blautia. The azithromyin-treated participants had significantly lower BIFs than those who received amoxicillin, with the relative abundance of Bacteroids being higher after 3 days.
The untreated Bifidobacterium relative in the housemates of individuals given azithromycin for 3 or 7 days showed a statistically lower relative abundance at week 8, suggesting relapse.
Chopyk and his colleagues hypothesized that the correlation between stable Bifidobacterium populations and improved gut health could have significant implications for the gut of individuals receiving antibiotic treatment.
The scientists examined the presence of genes linked to antibiotic resistance (to over 81 class of drugs) in samples collected before, during, and after exposure to amoxicillin or azithromycin. They discovered an average of 2% or more increases in various antibacterial resistance genes.
Compared to non-household controls, azithromycin exposure resulted in a significantly higher number of genes associated with resistance to macrolide, long-acting substance (LDH), lincosamide, and stretogramin at days 7, 8, and 6 of month.
The researchers examined the impact of antibiotics on the phage community’s composition and found no significant relationship between the frequency of three Caudobacteria families and duration of antibacterial use.
Their virome analysis did not support their hypothesis that the transmission of lytic phages from the treated participant could have caused the apparent reduction in Bifidobacteria in the housemate. They suggested that noise infiltration could be an alternative explanation, given the low relative abundances of Biffidies.
Chopyk and others noted that while much has been said about the effects of common antibiotics on the gut microbiome, there is still not enough knowledge about potential medium-term changes that can be observed in those who are taking the same antibiotic.