Determination of phenotypic resistance profiles
The resistance profiles were determined using the microdilution method.
The minimum inhibitory concentration (MIC) was determined for a panel of
eleven antimicrobials: ampicillin, cefotaxime, tetracycline,
chloramphenicol, ciprofloxacin, streptomycin, kanamycin, gentamicin,
nalidixic acid, sulfamethoxazole, and nitrofurantoin. The selection of
drugs, their concentration, and interpretation of results were carried
out in accordance with the CLSI standards (CLSI, 2015), and E.
coli ATCC25922 was used as a quality control. A double-disk diffusion
test using cefotaxime, cefotaxime/clavulanic acid, ceftazidime, and
ceftazidime/clavulanic acid was used to confirm the extended-spectrum
β-lactamase (ESBL) phenotype (CLSI, 2015). Multidrug-resistant strains
were defined as being resistant to at least one antimicrobial agent in
three or more antimicrobial classes (Magiorakos et al., 2012).