Cefazolin

Disk diffusion antimicrobial susceptibility tests were performed on the confirmed S. aureus isolates. The common used antibiotics for treating respiratory disease in farm animals were chosen for the antimicrobial susceptibility tests, including ampicillin (10 μg), cloxacillin (5 μg), cefoxitin (30 μg), cefazolin (30 μg), gentamicin (10 μg), vancomycin (30 μg), and tetracycline (30 μg) (Oxoid Ltd., Hampshire, UK). Briefly, S. aureus colonies were picked and subcultured by streaking on nutrient agar (Himedia Laboratories, Mumbai, India) and incubating the plate at 37°C for 18–24 hr. Then, a sterilized loop was used to pick four or five colonies from the nutrient agar and they were suspended in 2 ml of Mueller-Hinton broth (Difco Laboratories, Inc., NJ, USA). After adjusting to a turbidity of 0.5 McFarland standards, a sterile swab was dipped into the tube and streaked on Mueller-Hinton agar (Difco Laboratories, Inc., NJ, USA). Then, the appropriate antimicrobial-impregnated disks were placed on the surface of the agar, and the plate was incubated at 37°C for 18–24 hr. Thereafter, we measured the zones of inhibition and determined the antimicrobial susceptibility of the isolates using interpretative standards for Staphylococcus species. The results were reported as susceptible, intermediate, or resistant [8 , 9 ].

Based on the instructions of the Clinical and Laboratory Standards Institute [44 ], the Kirby–Bauer diffusion method was used to evaluate the antimicrobial agents (AMs) susceptibilities of Cronobacter isolates by diluting antibiotics and analyzing the sensitivities of the disks displayed in Mueller–Hinton agar (Huankai). A total of 16 antimicrobial agents (Oxoid, Hampshire, United Kingdom) were detected in this experiment: ampicillin (AMP, 10 μg), ampicillin/sulbactam (SAM, 10 μg), cefepime (FEP, 30 μg), ceftriaxone (CRO, 30 μg), cefazolin (KZ, 30 μg), cephalothin (KF, 30 μg), gentamicin (CN, 10 μg), tobramycin (TOB, 10 μg), amikacin (AMK, 30 μg), ciprofloxacin (CIP, 5 μg), imipenem (IPM, 10 μg), trimethoprim/sulfameth-oxazole (SXT, 25 μg), aztreonam (ATM, 30 μg), amoxicillin-clavulanic acid (AMC, 30 μg), chloramphenicol (C, 30 μg), and tetracycline (TE, 30 μg). We characterized the susceptibilities of the analyzed isolates after 24 h at 37 °C by measuring the inhibition region and illuminating the diameters according to the guidelines.

Patterns of antimicrobial resistance of the S. epidermidis strains were studied using the Kirby-Bauer method. A simple disk diffusion technique on the Mueller-Hinton agar (Merck, Germany) medium was used for this purpose. susceptibility of S. epidermidis isolates was tested against several types of antibiotic agents including penicillin (10 μg/disk), cefazolin (30 μg/disk), clindamycin (2 μg/disk), mupirocin (30 μg/disk), azithromycin (15 μg/disk), erythromycin (15 μg/disk), tetracycline (30 μg/disk), ciprofloxacin (5 μg/disk), trimethoprim-sulfamethoxazole (25 μg/disk), nitrofurantoin (300 μg/disk), and rifampin (5 μg/disk) (Oxoid, UK). The instructions of the Clinical and Laboratory Standards Institute were used for this purpose [46 ]. The plates containing the disks were allowed to stand for at least 30 min before incubated at 37 °C for 24 h. The diameter of the zone of inhibition produced by each antibiotic disc was measured and interpreted using the CLSI zone diameter interpretative standards [46 ]. S. epidermidis ATCC 12228 was used as a quality control organism in antimicrobial susceptibility determination.

Susceptibility of GNB isolates to ten antibiotics such as cefazolin (30 µg), cefotaxime (30 µg), ceftazidime (30 µg), amoxicillin-clavulanic acid (20/30µg), nitrofurantoin (10 µg), trimethoprim-sulfamethoxazole (1.25/23.75 µg), ciprofloxacin (5 µg), imipenem (10 µg), and meropenem (10 µg) (Oxoid, Basingstoke, UK) and cefotaxime-clavulanate, (30/10µg) (Abtek, Liverpool, UK) was performed on Mueller Hinton agar (Condalab, Madrid, Spain) using the Kirby Bauer disk diffusion technique in accordance with the guidelines of Clinical and Laboratory Standards Institute (CLSI) (CLSI, 2021). The bacterial growth around the discs was observed, and the diameter of the zone of inhibition was measured using a caliper and interpreted according to the 2021 CLSI guideline. Isolates that showed non-susceptibility to at least one agent in three or more antibiotic classes were classified as having multi-drug resistance (MDR) [18 (link)].