Antibiotic Susceptibility Testing Protocol

Antimicrobial susceptibility was tested on 8 antibiotics listed by the European Food Safety Authority (EFSA) [20 (link)], namely, ampicillin, gentamicin, kanamycin, streptomycin, erythromycin, clindamycin, tetracycline, and chloramphenicol, and evaluated using the commercial E-test MIC Test Strip (Liofilchem, Roseto degli Abruzzi, Italy). The concentration on the strips ranged from 0.016 to 256 ug/mL for all antibiotics, except streptomycin (0.064–1024 ug/mL). The MIC test strips were placed on the surface of the inoculated agar and incubated at 37 °C for 48 h. The minimal inhibitory concentrations (MICs) were interpreted as the point at which the ellipse intersected the strip, as described in the MIC Test Strip technical guide.