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Table 3 Interpretive criteria for E coli using disk diffusion susceptibility testing reported as inhibition zone diameters (mm)

From: Methodological comparisons for antimicrobial resistance surveillance in feedlot cattle

Antimicrobial [Disk] (μg) Susceptible Intermediate Resistant Reference
Ampicillin 10 ≥17 14-16 ≤13 CLSI M100-S22, 2012
Amoxicillin- Clavulanate 20/10 ≥18 14-17 ≤13 CLSI M100-S22, 2012
Ceftazidine 30 ≥18 15-17 ≤14 CLSI M100-S18, 2008
Ceftiofur 30 ≥21 18-20 ≤17 CLSI M31-A4, 2013
Enrofloxacin 5 ≥21 17-20 ≤16 *CLSI M31-A4, 2013
Florfenicol 30 ≥19 15-18 ≤14 *CLSI M31- A4, 2013
Neomycin 30 ≥17 - ≤12 *CLSI M31-A3, 2008
Streptomycin 10 ≥15 12-14 ≤11 CLSI M100-S18, 2008
Sulfisoxazole 300 ≥17 13-16 ≤12 CLSI M100-S22, 2012
Tetracycline 30 ≥15 12-14 ≤11 CLSI M31-A4, 2013
Trimethoprim-Sulfamethoxazole 1.25/23.75 ≥16 11-15 ≤10 CLSI M100-S22, 2012
  1. *Interpretive criteria for M. haemolytica used in lieu of E. coli since CLSI does not define breakpoints for E. coli in cattle for these antimicrobial drugs.
  2. CLSI = Clinical and Laboratory Standards Institute.
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