Impact of acetaminophen on the growth kinetics and metabolite production of probiotic lactic acid bacteria.

Bacterial interactions within the human gut microbiota are dynamic and closely linked to host health. These interactions are time-dependent and can be modulated by probiotic bacteria through metabolite production, environmental modification such as pH changes, and niche occupation. However, commonly used human-targeted drugs may alter these microbial dynamics. This study evaluated the effect of acetaminophen, a widely used over-the-counter drug, on the growth dynamics of a probiotic lactic acid bacterium within synthetic gut microbiota communities. The growth of Lactococcus lactis subsp. lactis was analyzed in monoculture and in co-culture with the commensal species Clostridium butyricum using 2 mL batch microbioreactors. Biomass accumulation was monitored until stationary phase, while acetaminophen and lactic acid concentrations were quantified by LC-MS. Growth kinetics were characterized using four parameters: carrying capacity, biomass accumulation (AUC), maximum growth rate ( μ max ), and lag phase duration, which were estimated via regression analysis that coupled the 4Z Gompertz model and the exponential growth model. Co-cultures exhibited greater biomass accumulation and higher carrying capacity than monocultures, indicating mutualism between the species. A minimum effective concentration assay identified 66.1 mM acetaminophen as the concentration for subsequent experiments. Acetaminophen negatively affected all biomass-related kinetic parameters of L. lactis in mono- and co-culture, whereas C. butyricum growth remained unaffected in monoculture. LC-MS analysis suggested drug internalization without metabolic degradation. Lactic acid production reached a saturation concentration of 17.8 mM, indicating that metabolite-related probiotic activity may remain stable despite reduced biomass.