Ampicillin sulbactam

To test antibiotic resistance in Campylobacter spp., the broth microdilution method was used with 5 % sheep blood. For all other pathogens, antimicrobial susceptibilities were determined by the agar dilution method according to the Clinical and Laboratory Standards Institute (CLSI) Guidelines, 2015 [20 ]. All isolates of Salmonella spp. were tested for their minimum inhibitory concentrations (MICs) of ampicillin, ampicillin-sulbactam, ceftriaxone, cefotaxime, nalidixic acid, ciprofloxacin, levofloxacin, co-trimoxazole, azithromycin, chloramphenicol and tetracycline (Oxoid); DEC were tested for ampicillin, ampicillin-sulbactam, cefotaxime, ciprofloxacin, levofloxacin, chloramphenicol, tetracycline, cefazolin, cefuroxime, imipenem, amikacin and gentamicin (Oxoid); Campylobacter spp. were tested for ciprofloxacin, azithromycin, tetracycline, erythromycin and doxycycline (Oxoid); and Aeromonas spp. were tested for cefotaxime, ciprofloxacin, levofloxacin, co-trimoxazole, chloramphenicol, tetracycline, cefazolin, cefuroxime, imipenem, amikacin and gentamicin (Oxoid). ATCC 25922, 35218, 700603 and 27853 were used as quality control strains. Antibiotic susceptibility was interpreted according to CLSI guidelines, 2015 [20 ].

Antimicrobial susceptibility profiles of the isolates were determined using the disk diffusion method according to the standard procedures of the Clinical and Laboratory Standards Institute (CLSI, 2013 ). Escherichia coli (ATCC25922) (Microbiologics, USA) was used as the quality control strain. The following 17 antibiotic discs (Oxoid) were used: amikacin, amoxicillin+clavulanic acid, ampicillin+sulbactam, azithromycin, cefepime, cefixime, cefotaxime, cefoxitin, cefperazone, ceftazidime, ceftriaxone, chloramphenicol, gentamycin, imipenem, levofloxacin, meropenem, and trimethoprim-sulphamethexazole. MDR was defined according to the guidelines of the European Society of Clinical Microbiology and Infectious Diseases (Magiorakos et al., 2012 (link)).

A modification of the standard disk diffusion method (rAST) was evaluated for the detection of antimicrobial resistance. The rAST followed CLSI standards in all aspects, except for the inoculum preparation. CLSI guideline recommends preparing the inoculum for AST with a direct suspension of isolated colonies selected from 18–24 h agar plate incubation [6 ]. In this study, we used colonies selected from a rapid culture grown (4–6 h agar plate incubation). The inoculum was prepared from the rapid culture grown on a 150 mm Mueller–Hinton Agar (bioMérieux, France), and then, disks were applied and plates incubated at 35°C ± 1° and incubated for 18 h. The following antimicrobial agents were evaluated for GN: amikacin 30 μg, amoxicillin-clavulanate 20/10 μg, ampicillin 10 μg, ampicillin-sulbactam 10/10 μg, cefepime 30 μg, ceftazidime 30 μg, cefuroxime 30 μg, ciprofloxacin 5 μg, gentamicin 10 μg, meropenem 10 μg, piperacillin-tazobactam 100/10 μg, and trimethoprim-sulfamethoxazole 23.75/1.25 μg (Oxoid®, Thermo-Fisher, USA). For GP, cefoxitin 30 μg, clarithromycin 15 μg, clindamycin 2 μg, doxycycline 30 μg, erythromycin 15 μg, gentamicin 10 μg, levofloxacin 5 μg, rifampicin 5 μg, and trimethoprim-sulfamethoxazole 23.75/1.25 μg (Oxoid®) were evaluated. The inhibition zones were analyzed after 18–24 h, and the results were interpreted by CLSI proposed breakpoints [6 ].