Effect of antibiotics on the human microbiome: a systematic review

•Quinolone and metronidazole are associated with consistent changes in microbiota.•Combination antibiotic treatment may result in longer periods of dysbiosis.•Paediatric studies investigating antibiotics and the microbiome are lacking.•Longitudinal follow-up, particularly long term, is essential for microbiome studies. Global antibiotic use has been increasing for decades. The gut microbiome, a key contributor to health, can be altered by antibiotics, which have been associated with both short- and long-term effects on the intestinal microbiome. The aim of this study was to summarize the effects of antibiotics on the diversity and composition of the human microbiota at different anatomical sites. A systematic review was conducted according to PRISMA guidelines. PubMed, Scopus and Web of Science online databases were searched for studies that described the microbiome of any human bodily site pre- and post-antibiotic treatment using 16S rRNA gene sequencing. Increases or decreases in diversity, dissimilarity of microbial communities, and changes in taxonomic composition following antibiotic treatment were recorded as outcome measures. The review identified consistent changes in the microbiota following quinolone and metronidazole treatment, and showed that combination treatment may result in longer-term dysbiosis. The importance of longitudinal analysis, and a lack of studies in paediatric populations was highlighted. Heterogeneity in the methodology of included studies could have contributed to the inconsistent findings regarding the effect of most antibiotic classes on the microbiome. It is recommended that studies investigating the effect of antibiotics on the microbiome need to exclude participants exposed to antibiotics within 4 months preceding collection and analysis of baseline samples, and to include longitudinal analysis, particularly in the longer term. Further explorations need to be made into the functional implications of antibiotic-induced dysbiosis in the microbiome. PROSPERO (https://www.crd.york.ac.uk/prospero; Registration:CRD42020168991).