Selection for florfenicol resistance at sub-MIC concentrations in Pasteurella multocida

Area of Science:

• Veterinary Microbiology
• Antimicrobial Resistance Research
• Molecular Biology

Background:

• Antimicrobial resistance (AMR) poses a significant global health threat, impacting both human and animal populations.
• The transfer of resistance genes between bacteria in different environments is a critical concern.
• Limited data exists on AMR selection by sub-inhibitory concentrations of veterinary antimicrobials in non-laboratory bacterial strains.

Purpose of the Study:

• To determine the minimum selective concentration (MSC) of florfenicol for Pasteurella multocida.
• To investigate whether sub-inhibitory florfenicol concentrations promote de novo resistance development.
• To identify challenges in adapting AMR experimental protocols across different bacterial species.

Main Methods:

• Competition experiments were conducted between a florfenicol-susceptible wild-type Pasteurella multocida strain and a floR-resistant mutant.
• Minimum Inhibitory Concentration (MIC) was determined for florfenicol against P. multocida.
• Sub-inhibitory concentrations were tested to assess selection for resistance.

Main Results:

• The minimum selective concentration for florfenicol in wild-type Pasteurella multocida was determined to be 0.06 mg/L (1/6 x MIC).
• Sub-inhibitory concentrations of florfenicol did not significantly select for the de novo development of resistance in P. multocida.
• Challenges were encountered when adapting experimental protocols for AMR selection studies between different bacterial species.

Conclusions:

• Low-level, sub-inhibitory concentrations of florfenicol can exert selective pressure for antimicrobial resistance in Pasteurella multocida.
• Developing standardized methods for detecting AMR in novel bacterial species requires careful consideration of inter-species protocol adaptation.
• Findings have implications for antimicrobial stewardship, policy on animal feed contamination, and AMR surveillance.