Evaluating the Impact of Over-the-Counter Aspirin on the Growth of Selected Intestinal Microbial Strains

The human intestinal microbiota varies in composition among individuals and is largely influenced by external factors such as diet, drugs and environment. While it is well-known to play a pivotal role in maintaining gut health, its interactions with non-antibiotic pharmaceuticals remain understudied. This in vitro study evaluates the effects of over-the-counter (OTC) aspirin (Cardiprin) on the growth dynamics of three commensal gut bacterial strains, Escherichia coli, Klebsiella pneumoniae and Enterococcus faecalis. Employing a dual-method approach of disk diffusion assay (DDA) and colony-forming unit (CFU) analysis, the study evaluates aspirin’s effects at physiologically relevant (300 µg/mL) and high (1000 µg/mL) concentrations. DDA demonstrated consistent inhibition zones across all strains and highlighted aspirin’s weak antibacterial potency, while CFU analyses revealed strain-specific responses. At 300 µg/mL of aspirin, E. coli and E. faecalis exhibited growth comparable to baseline while K. pneumoniae uniquely showed enhanced growth. However, at a higher concentration of 1000 µg/mL, growth of all strains were inhibited to different extents. These results underscore the need for further investigation into the therapeutic and unintended effects of oral aspirin on gut microbial growth.