Amoxicillin clavulanic acid

Non-typhoidal Salmonella isolates were tested for susceptibility toward 14 antimicrobials belonging to 10 different classes. The SOPs were strictly followed, in accordance with the guidelines of the Clinical and Laboratory Standards Institute (CLSI) for standard disk diffusion assays (CLSI, 2017 ). Muller-Hinton agar (Liofilchem^®, 2014 s.r.l., Italy) was used. Bacterial inoculum was adjusted to be equivalent to a 0.5 McFarland standard (corresponding to 1–2 × 10⁸ CFU/mL). Escherichia coli ATCC 25922 strain was used for quality control. The following AM disks (Liofilchem^®, 2014 s.r.l., Italy) were used: ampicillin (10 μg), amoxicillin-clavulanic acid (20 μg/10 μg), ceftazidime (30 μg), ceftriaxone (30 μg), chloramphenicol (30 μg), ciprofloxacin (5 μg), gentamicin (10 μg), imipenem (10 μg), nalidixic acid (30 μg), streptomycin (10 μg), sulphonamide (300 μg), tetracycline (30 μg), and trimethoprim-sulfamethoxazole (1.25 μg/23.75 μg). The results of susceptibility testing were interpreted based on the CLSI criteria (CLSI, 2017 ). Minimum inhibitory concentration (MIC) of azithromycin was determined by agar dilution method according to the CLSI performance standards (CLSI, 2015 ). Isolates that were resistant to at least three different classes of antimicrobials were considered as MDR.

Because the disc diffusion method only allows the analysis of the impact of a single concentration of an antibiotic, in the second stage of the experiment, the E-test strips with exponentially decreasing antibiotic concentrations were applied for all of the antibiotics that were previously used in the disc diffusion test.
The cultures with the E-tests were exposed and incubated in the same way as described for the disc diffusion method. The E-tests containing cefoxitin, amoxicillin, amoxicillin/clavulanic acid, erythromycin, clindamycin, tetracycline, ciprofloxacin, gentamicin, and teicoplanin were obtained from Liofilchem (Roseto degli Abruzzi, Italy). The analyses were performed on M–H agar in accordance with the E-test manufacturer’s recommendations.
The location of the Petri dishes in the RMF reactor chamber and the location of antibiotic discs and E-tests in Petri dishes are presented in Figure 7.