Antibiotic residues and R-plasmid selection: are in vitro methods good models?

Area of Science:

• Microbiology
• Genetics
• Infectious Diseases

Background:

• Antibiotic resistance plasmids can spread rapidly within bacterial populations.
• Understanding the dynamics of plasmid-mediated resistance in vivo is crucial for public health.
• In vitro studies may not accurately reflect bacterial interactions within a host organism.

Purpose of the Study:

• To investigate the in vivo dynamics of tetracycline resistance plasmid transfer in E. coli within the gut of axenic mice.
• To compare in vivo bacterial interactions with previously reported in vitro findings.
• To assess the selective advantage or disadvantage of a tetracycline resistance plasmid in the absence of antibiotic pressure.

Main Methods:

• Inoculation of axenic mice with three E. coli clones, including one with a tetracycline resistance plasmid.
• Monitoring bacterial populations in mouse feces over time.
• Comparing results with in vitro chemostat experiments.

Main Results:

• The tetracycline resistance plasmid-bearing E. coli strain became dominant in mouse feces without antibiotic pressure.
• In contrast, in vitro studies showed plasmid-free strains outcompeting plasmid-bearing strains.
• The presence of the resistance plasmid did not disadvantage the E. coli strain in the mouse gut environment.

Conclusions:

• In vivo bacterial interactions, particularly in the gut, differ significantly from in vitro conditions.
• Extrapolation of in vitro findings to in vivo scenarios should be done cautiously.
• In vivo studies are essential for determining the no-effect level of antibiotic residues on R-factor selection.