Nutrients mediate caffeine inhibition of Escherichia coli.

The consumption of coffee and other caffeinated drinks is increasingly popular across the globe. In the United States, 90% of adults consume at least one caffeinated beverage a day. While caffeine consumption of up to 400 mg/d is not generally associated with negative effects on human health, the impact of caffeine on the gut microbiome and individual gut microbiota remains unclear. We examined the effect of caffeine on the growth rate of Escherichia coli, a bacterium commonly found in the human gut, when grown aerobically or anaerobically in nutrient-rich or minimal medium. A significant negative correlation was observed between caffeine concentration and growth rate under all conditions, suggesting that caffeine can act as an antimicrobial agent when ingested. Caffeine reduced growth rates significantly more in nutrient-poor, but not in anoxic, conditions. Given the highly variable nutrient and oxygen conditions of the gut, these results suggest a need to further explore caffeine's inhibitory effects on the gut microbiome and its relation to human health.