Aztreonam

Using the Clinical and Laboratory Standards Institute (CLSI) guidelines [9 ], an antibiogram assay was performed on the isolated K. pneumoniae colonies. The antibiotic discs contained ampicillin (30 µg), cotrimoxazole (25 µg), cefixime (5 µg), cefotaxime (30 µg), ceftriaxone (30 µg), ceftazidime (30 µg), gentamicin (10 µg), amikacin (30 µg), tetracycline (30 µg), doxycycline (30 µg), minocycline (30 µg), tigecycline (15 µg), ciprofloxacin (5 µg), levofloxacin (5 µg), ampicillin/sulbactam (100/10 µg), piperacillin/tazobactam (100/10 µg), imipenem (10 µg), meropenem (10 µg), ertapenem (10 µg), doripenem (10 µg), aztreonam (30 µg), colistin (10 µg), and fosfomycin (200 µg) (Mast Diagnostics, United Kingdom) [4 , 10 ].
The minimum inhibitory concentration (MIC) of imipenem, meropenem, and colistin for isolates resistant to carbapenems was determined by using E-test (Liofilchem, Italy) according to the 2021 CLSI guidelines [9 ].

Standard discs of 17 antibiotics were obtained from Mast Diagnostics (Merseyside, Liverpool, UK) to be used in this assay; amikacin (30 µg), ampicillin (10 µg), augmentin (30 µg), aztreonam (30 µg), cefoxitin (30 µg), cefepime (30 µg), ceftazidime (30 µg), cephalothin (30 µg), chloramphenicol (30 µg), ciprofloxacin (5 µg), cotrimoxazole (25 µg), fucidic acid (10 µg), gentamicin (10 µg), imipenem (10 µg), oxacillin (1 µg), piperacillin (100 µg), and vancomycin (30 µg).
Antimicrobial activity of four cLfs isolated from milk of four different breeds of Saudi camels (cLf1, cLf2, cLf3, and cLf4), bLf, hLf, and the standard antibiotics against S. typhimurium and S. sonnei was tested by agar disc-diffusion technique. Plates of Mueller-Hinton (MH) agar were overlaid with 2 × 10⁶ CFU/ml of Salmonella typhimurium LT2 and Shigella sonnei. Wells of about 5 mm diameter were made on inoculated plates then different concentrations of lactoferrins (0.00, 0.125, 0.250, 0.50, 0.750, 1, 1.5, 2, 2.5, and 3 mg/ml) were added, and left to diffuse in agar at 4 °C for 2 h before plates finally incubated overnight at 37 °C. The diameters of clear inhibition zones were measured in millimeters. Antibacterial effects of different lactoferrins on growth of S. typhimurium and S. sonnei after 1, 3, 6, 12, and 24 h of incubation at 37 °C were monitored spectrophotometrically (measuring OD at 620 nm).

Initially, all Isolates were tested using the Kirby Bauer disk diffusion method according to the Clinical Laboratory Standards Institute (2013) . E. coli ATCC25922 was used as control strains. The tested antibiotics included: ampicillin, ampicillin/sulbactam, amoxicillin/clavulanate, ticarcillin, piperacillin, piperacillin/tazobactam, cephalothin, cefuroxime, cefoxitin, ceftriaxone, cefotaxime, ceftazidime, cefepime, meropenem, and aztreonam (Mast Diagnostics, Merseyside, UK). co-trimoxazole, gentamicin, nalidixic acid, ciprofloxacin, imipenem, meropenem, tetracycline, and nitrofurantoin (Oxoid Ltd., Basingstoke, UK). MIC values were extrapolated by the BIOMIC automated reading system and software package (Giles Scientific, New York, NY, USA).
The disk diffusion method was applied to assess ESBL production in all the Isolates with cefotaxime (30 ug) and ceftazidime (30 ug) alone and in combination with clavulanic acid (10 ug) as recommended by the Clinical and Laboratory Standards Institute (CLSI).