Abstract: Antibiotic contamination has a serious impact on microbial ecology. Fermentation is an important biological process under anaerobic conditions, but its response to antibiotic contamination remains unclear. In this study, we investigated the effects of different concentrations of antibiotics on the fermentation metabolism of Clostridium butyricum and Bacillus coagulans, two spore-producing microorganisms of the thick-walled phylum Clostridium perfringens, using the typical β-lactam antibiotic amoxicillin as an example. We measured the changes of the growth curves, carbon source consumption, organic acid production, and pH of both strains of bacteria during the fermentation process. The results showed that amoxicillin inhibited the growth and carbon source consumption of both C. butyricum and B. coagulans, with less effect on bacterial morphology. 50 mg·L^-1 amoxicillin caused the growth of C. butyricum to stop, whereas B. coagulans could continue to grow after 24 h of incubation. In terms of organic acid metabolism, the effect of amoxicillin on B. coagulans was more significant. Butyric, formic, lactic and acetic acid production of both strains was inhibited, but lactic acid production in B. coagulans was significantly increased under the addition of low concentration (1 mg·L^-1) of amoxicillin.

Key words: Clostridium butyricum, Bacillus coagulans, antibiotics, fermentation metabolism