Short-term effect of antibiotics on human gut microbiota.
Level 4 - case-series / case-control
Prospective uncontrolled pre-post observational study
PubMed 24748167 · doi:10.1371/journal.pone.0095476
What was done
Fecal samples were collected from 21 patients immediately before and one week after treatment with broad-spectrum antibiotics (fluoroquinolones and beta-lactams). Total microbial load was quantified using quantitative PCR, and microbial community composition was analyzed using 16S rRNA gene pyrosequencing.
What was found
Fluoroquinolones and beta-lactams significantly decreased microbial diversity by 25% and reduced the core phylogenetic microbiota from 29 to 12 taxa. At the phylum level, antibiotics increased the Bacteroidetes/Firmicutes ratio (p = 0.0007, FDR = 0.002). At the species level, both antibiotic types increased the proportion of several unknown taxa belonging to the genus Bacteroides (p = 0.0003, FDR < 0.016). Additionally, beta-lactams significantly increased average microbial load two-fold (p = 0.04).
Why it matters
This study shows that short-term broad-spectrum antibiotic therapy reduces overall diversity while selectively favoring Gram-negative Bacteroides taxa and unexpectedly increasing total bacterial load under beta-lactam treatment.
Limits
The study had a small sample size (n = 21) and lacked an untreated control group. Clinical indications for antibiotic prescription and long-term recovery dynamics were not described in the abstract.
Cited by
- context Approximately 40% to 50% of the microbes in the human gut are made up of gram-negative bacteria.