Changes in resistance to and antimicrobial activity of antibiotics during in vitro human digestion

This study was performed to determine changes in (i) the antimicrobial activity of antibiotics (tetracycline, ofloxacin and penicillin) and (ii) the resistance of Staphylococcus aureus RN4220 (SA RN4220) and methicillin-resistant S. aureus (MRSA) to these antibiotics during in vitro human digestion.

A human gastrointestinal digestion model simulating the conditions of the mouth, stomach, small intestine and large intestine (with intestinal microbial application) was used in this study. Antimicrobial susceptibility testing was performed by the disk diffusion method according to Clinical and Laboratory Standards Institute (CLSI) guidelines.

Concentrations of the three antibiotics decreased during digestion. In particular, the three antibiotics were unstable under conditions of stomach to large intestine digestion, and thus a decrease in antibiotic concentration could cause a reduction in antimicrobial activity during in vitro human digestion. The resistance of SA RN4220 and MRSA to the three antibiotics increased after in vitro human digestion. SA RN4220 and MRSA showed less resistance to ofloxacin compared with tetracycline and penicillin during in vitro human digestion.

These results may help to explain the factors affecting antimicrobial activity and resistance to antibiotics during digestion in the human alimentary canal.