Antibiotic Susceptibility Testing of LAB

Minimum inhibitory concentrations were determined using an E-test (BioMerieux, Lyon, France) for nine antibiotics: tetracycline, erythromycin, streptomycin, gentamicin, clindamycin, ampicillin, kanamycin, chloramphenicol and vancomycin. Concentrations for all antibiotics were 0.016–256 μg/mL, except for streptomycin at 0.064–1024 μg/mL. The LAB isolates were diluted to final concentrations of 10⁶–10⁷ CFU/mL and then inoculated onto Iso-Sensitest agar (Oxoid, Basingstoke, UK) supplemented with MRS agar (Georgieva et al., 2015 (link)), and incubated at 37 °C for 24 h. Breakpoint values were interpreted according to EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) (2012) (Table S1).