Impenem

Antibiotic susceptibility testing was performed according to the Clinical Laboratory Standard Institute (CLSI) guidelines using Kirby-Bauer method (CLSI, 2014) (12 ). Antibiotics used were benzyl penicillin (10U), piperacillin tazobactam (100-10 μg), amoxicillin clavulanic acid (20-10 μg), impenem (10 μg), ceftriaxone (30 μg) chloramphenicol (30 μg), tetracycline (30 μg), moxifloxacin (5 μg), ciprofloxacin (5 μg), levofloxacin (5 μg) vancomycin (5 μg) and metronidazole (4 μg) (Oxoid, UK). Inoculated Mueller Hinton agar plates (HiMedia, India) were incubated at 37°C for 24 hours in the anaerobic jar using Anaerogen gas packs (90% N2 /10% CO2) (Oxoid, UK). E. coli ATCC 25922 was used as standard strain to check the standardization of the disks.

The antimicrobial susceptibility profile for Salmonella isolates (n = 75) was investigated against 8 different antimicrobial agents using the Kirby–Bauer disc diffusion method (Oxoid Ltd., Basingstoke, UK). The sensitivity pattern was interpreted according to the guidelines of Clinical and Laboratory Standards Institute [40 ]. The antibiotics selected were those commonly used in the poultry industry, including Cefotaxime (CTX, 30 μg), Ceftriaxone (CRO, 30 μg), Ampicillin–Sulbactam (SAM, 10 μg), Amoxicillin–clavulanic (AMC, 30 μg), Impenem (IPM, 10 μg), Sulfamethoxazole–trimethoprim (SXT, 25 μg), Ciprofloxacin (CIP, 5 μg) and (Gentamicin CN, 10 μg) (Oxoid Ltd., Basingstoke, UK). The diameter of the inhibition zone was measured compared with the zone size interpretation chart and was graded as susceptible (S), intermediate (I), and resistant (R).