Wild-type cutoff for Apramycin against Escherichia coli

Area of Science:

• Veterinary Microbiology
• Antimicrobial Resistance
• Molecular Diagnostics

Background:

• Apramycin has been a key treatment for swine E. coli infections since the 1980s.
• Emerging multidrug-resistant E. coli necessitates proper apramycin use and susceptibility testing.
• This study addresses the need for reliable interpretive criteria for apramycin in veterinary medicine.

Purpose of the Study:

• To establish a wild-type cutoff for apramycin against E. coli using CLSI guidelines.
• To determine the prevalence of apramycin resistance genes in swine E. coli isolates.
• To provide reliable interpretive criteria for apramycin susceptibility testing.

Main Methods:

• Broth microdilution testing was performed on 1230 E. coli clinical isolates from swine.
• PCR was used to detect resistance genes (aac(3)-IV, npmA, apmA) in 310 selected E. coli strains.
• Statistical analysis based on CLSI document M07-A9 was employed to define the wild-type cutoff.

Main Results:

• The minimum inhibitory concentration (MIC) distribution showed MIC50 and MIC90 values of 16 and 64 μg/mL, respectively.
• The aac(3)-IV gene was the only detected resistance gene, found predominantly in isolates with MICs ≥ 64 μg/mL.
• A wild-type cutoff for apramycin against E. coli was determined to be 32 μg/mL.

Conclusions:

• The established wild-type cutoff of 32 μg/mL for apramycin against E. coli is reliable.
• The prevalence of the aac(3)-IV gene supports the validity of the new cutoff.
• This wild-type cutoff provides essential interpretive criteria for apramycin susceptibility testing in E. coli.