Antibiotic Susceptibility Testing Protocol

Antibiotic susceptibility test was carried out by using disc diffusion (Kirby–Bauer) method on Mueller–Hinton agar plates. Bacterial suspension was prepared in 0.5 McFarland turbidity standard for each isolate and was swabbed on already prepared nutrient agar plates. The plates contained the impregnated antibiotics discs (Oxoid, UK), which were incubated at 37 °C for 24 h. The experiment used 14 antibiotics: streptomycin (10 μg), amikacin (30 μg), gentamicin (10 μg), ciprofloxacin (5 μg), pefloxacin (5 μg), ofloxacin (5 μg), erythromycin (15 μg), nitrofurantoin (300 μg), oxacillin (50 μg), cloxacillin (10 μg), colistin sulfate (25 μg), cefepime (5 μg), ceftazidime (30 μg), and cefotaxime (75 μg). Zones of diameter were measured and interpreted as susceptible, intermediate, and resistant in accordance with the recommendation of Clinical and Laboratory Standard Institute.¹¹