IncI2 plasmid transfer and changes of intestinal microbiota in mice under β-lactam antibiotic pressure.

Background: β-lactam antibiotics represent the most widely utilized class of antimicrobial agents in livestock and poultry breeding. However, the effects of β-lactam antibiotics on conjugation transfer of IncI2 plasmids and the homeostasis of the mouse intestinal microbiota have not been thoroughly investigated.

Results: The results revealed that the transfer of IncI2 plasmid was the highest for intra-specific E. coli and inter-specific transfer to Salmonella and K. pneumoniae occurred at much lower levels in the absence of β-lactam antibiotic selective pressure. Furthermore, inter-species and intra-species transfer of IncI2 plasmid was enhanced in the presence of sub-MIC levels of amoxicillin/clavulanate and cephalexin whereas ampicillin promoted only inter-species transfer. These results were consistent with in vivo observations where amoxicillin/clavulanate and cephalexin but not ampicillin promoted conjugation. Meanwhile, the intestinal microbiota was also disturbed following antibiotic treatment and Proteobacteria abundance increased while Bacteroides decreased. The gut microbiota could also be partially restored to initial levels after antibiotic cessation for 14 days.

Conclusions: These findings highlight the potential risk of β-lactam antibiotics in promoting the spread of resistance plasmids and causing disruption to the intestinal microbiota.