Neomycin

The antimicrobial susceptibility of all isolated Enterobacteriaceae strains was tested following Clinical and Laboratory Standards Institute (CLSI) guidelines [17 ]. The isolates were tested against a panel of 12 antimicrobials: Nalidixic acid (NA, 30 µg), flumequin (UB, 30 µg), ciprofloxacin (CIP, 5 µg), ampicillin (AM, 10 µg), amoxicillin/clavulanic acid (AMC, 20/10 µg), ceftiofur (XNL, 30 µg), tetracycline (TE, 30 µg), trimethoprim/sulfamethoxazole (SXT, 1.25/23.75 µg), neomycin (N, 30 µg), gentamicin (CN, 15 µg), chloramphenicol (C, 30 µg), and colistin (CT, 50 µg) (Bio-Rad, Marnes la Coquette, France). Results were obtained after incubating samples for 16–18 h at 37°C and were interpreted according to CLSI previously cited guidelines. E. coli ATCC 25922 was used as a quality control strain.

The antibiotic susceptibility of the MRSA isolates was determined by the disk diffusion method on Mueller-Hinton agar (MHA, CONDA, Spain), according to the recommendations of the Clinical and Laboratory Standards Institute (CLSI). The disk diffusion assay was done with 14 antibiotics: bacitracin (10 U), enrofloxacin (5 μg) (OXOID), streptomycin (10 μg), spiramycin (100 μg), sulfadiazine (25 μg), chloramphenicol (30 μg) (BD), doxycycline (30 μg), erythromycin (15 μg), gentamicin (10 μg), neomycin (30 μg), penicillin (10 U), tetracycline (30 μg), cefoxitin (30 μg), and trimethoprim/sulfamethoxazole (1.25 μg/23.75 μg, respectively) (BIO-RAD). Minimum inhibitory concentrations (MIC) for cefoxitin and vancomycin was determined by using MIC Test Strip (Liofilchem) on inoculated Mueller Hinton agar plates and the results were interpreted according EUCAST breakpoints. S. aureus strain ATCC 25923 and Enterococcus faecalis strain ATCC 29212 were used as controls in the susceptibility test.