Ofloxacin

Antimicrobial susceptibility testing of E. coli isolates were performed by the Kirby-Bauer disk diffusion assay on Mueller-Hinton agar medium (Oxoid, Basingstoke, England) as recommended by Clinical Laboratory Standard Institute (CLSI, 2011), against 15 antimicrobial agents from different categories including: amikacin (30 μg), amoxicillin (10 μg), amoxicillin-clavulanic acid (30 μg), ceftazidime (30 μg), ceftriaxone (30 μg) cefuroxime (30 μg), chloramphenicol (30 μg), ciprofloxacin (5 μg), gentamicin (10 μg), nalidixic acid (30 μg), nitrofurantoin (50 μg), ofloxacin (5 μg), tetracycline (30 μg), tobramicin (10 μg) and trimethoprim- sulfamethoxazole (25 μg) (Oxoid, Basingstoke, England). E. coli isolate was considered non-susceptible to an antimicrobial agent when it tested resistant, intermediate or non-susceptible when using clinical breakpoints as interpretive criteria, provided by the CLSI, (2011). MDR patterns of E. coli isolates were defined as non-susceptibility to at least one agent in three or more antimicrobial categories (Magiorakos et al., 2012 ).

The in vitro antimicrobial susceptibilities of all identified Salmonella isolates to the commonly prescribed antibiotics in Nigeria were investigated by disk diffusion method, as described by the Clinical and Laboratory Standard Institute (CLSI) guidelines [23 ]. The following antibiotic discs were used: cefpodoxime (CPD) (30 µg), cefoxitin (FOX) (30 µg), cefotaxime (CTX) (30 µg), ceftazidime (CAZ) 30 µg, ampicillin (AMP) 10 µg, ciprofloxacin (CPR) 5 µg, augmentin (AUG) 30 µg, ofloxacin (OFL) 5 µg, imipenem (IMP) 10 µg, ertapenem (ETR) 10 µg, doripenem (DOR) 10 µg, amikacin 30 µg (AMK), and gentamycin (GEN) 10 µg (Oxoid, Hampshire, UK). Each of the antibiotic’s discs was placed aseptically on Mueller Hinton agar (HIMEDIA, Mumbai, India) plates that were previously inoculated with the Salmonella suspension equal to 0.5 McFarland standard and the plates were incubated aerobically at 37 °C for 18–24 h. The diameter of the zones of inhibitions was measured in millimetres and compared with a zone interpretation chart of CLSI [23 ]. E. coli ATCC® 25922™ was used as a control.

Antimicrobial susceptibility tests of the three ESBL-producing isolates and seven non-ESBL-producing isolates were evaluated using the disk diffusion method to Piperacillin 100 μg (PIP), Moxalactam 30 μg (MOX), Ceftazidime 30 μg (CAZ), Cefixime 5 μg (CFM), Cefepime 30 μg (FEP), Cefotaxime 30 μg (CTX), Cephalexin 30 μg (CL), Caphazolin 30 μg (CZ), Ceftriaxone 30 μg (CRO), Cefoxitin 30 μg (FOX), Piperacillin/Tazobactam 100/10 μg (TZP), Cefuroxime 30 μg (CXM), Cefaclor 30 μg (CEC), Ampicillin/Sulbactam 10/10 μg (SAM), Cefoperazone 75 μg (CFP), Ceftizoxime 30 μg (ZOX), Aztreonam 30 μg (ATM), Meropenem 10 μg (MEM), Imipenem 10 μg (IPM), Kanamycin 30 μg (K), Streptomycin 10 μg (S), Ofloxacin 5 μg (OFX), Norfloxacin 10 μg (NOR), CiprOfloxacin 5 μg (CIP); Gatifloxacin 5 μg (GTX), Chloramphenicol 30 μg (C), Azithromycin 15 μg (AZM), Doxycycline 30 μg (TE), Minocycline 30 μg (MH), Compound Sulfamethoxazole 23.75/1.25 μg (SMZ), and Trimethoprim 5 μg (TMP) (Oxoid, Basingstoke, United Kingdom). The results were interpreted according to the Clinical and Laboratory Standards Institute (CLSI) breakpoints. Escherichia coli ATCC 25,922 was used as a control for antimicrobial susceptibility testing.

All E. coli isolates were tested for antimicrobial susceptibility using the disc diffusion method as described in details in our previous study^{5 (link)}. The antimicrobial agents that were tested included amikacin (AK, 30 μg), ampicillin (AMP, 10 μg), cephalothin (CF, 30 μg), cefotaxime (CTX, 30 μg), ceftazidime (CAZ, 30 μg), sulfamethoxazole/trimethoprim (SXT, 1.25/23.75 μg), gentamicin (GM, 10 μg), norfloxacin (NOR, 10 μg) and ofloxacin (OFX, 5 μg) (Oxoid Ltd.; Basingstoke, UK). Extended spectrum β-lactamase (ESBL) production was also determined by the double-disc diffusion test according to the standard method of the Clinical and Laboratory Standards Institute.