Ampicillin

A bacterial suspension of density equivalent to a MacFarland of 0.5 was used to inoculate an MH agar plate using a sterile swab. An Etest® (Biomérieux, Marcy-l’Etoile, France) containing ciprofloxacin was loaded onto the agar and incubated overnight at 37 °C before MIC determination. In parallel, an antibiogram of Enterococci was performed by disk diffusion method using the following molecules (Bio-Rad, Hercules, CA, USA): ampicillin (2 µg), imipenem (10 µg), norfloxacin (10 µg), rifampicin (5 µg), erythromycin (10 µg), clindamycin (2 µg), quinuspristin-dalfopristin (15 µg), tigecycline (15 µg), linezolid (10 µg), levofloxacin (5 µg), gentamicin (30 µg), streptomycin (300 µg), vancomycin (5 µg), teicoplanin (30 µg), nitrofurantoin (100 µg), fosfomycin (200 µg). The interpretations were carried out according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines (https://www.eucast.org/clinical_breakpoints, 2022).

Antibiotic susceptibility testing was performed by the disc diffusion method on Mueller Hinton agar according the standard recommendations of the French Society of Microbiology (CA-SFM, 2010) [8 ]. The following antibiotic discs were tested: ampicillin, amoxicillin+ acid clavulanic, ticarcillin, cefalotin, cefoxitin, cefuroxime, cefotaxim, imipenem, nalidixic acid, aztreonam, norfloxacin, ciprofloxacin, gentamycin, tetracycline, trimethoprim-sulfamethoxazole, streptomycin (Bio-Rad, France). For carbapenems, ertapenem (10 μg/ml) antibiotic discs were used (Bio-Rad, France). The zones of inhibition were measured to assess resistance or susceptibility.

Antibiotic susceptibility was determined by the disk diffusion method, on Mueller-Hinton (MH) agar, in accordance with the guidelines of the Antibiogram Committee of the French Society for Microbiology (CA-SFM 2006)³⁹ . The following antimicrobial drugs (Bio-Rad, Marnes-la-Coquette, France) were tested: ampicillin (AMP), cefalotin (CEF), cefotaxime (CTX), streptomycin (STR), chloramphenicol (CHL), azithromycin (AZM), sulfonamides (SUL), trimethoprim-sulfamethoxazole (SXT), vibriostatic agent O/129 (O129), tetracycline (TET), nalidixic acid (NAL), ciprofloxacin (CIP), nitrofurantoin (FUR), polymyxin B (PB) and colistin (CS). Escherichia coli CIP 76.24 (ATCC 25922) was used as a control.

The confirmed S. aureus isolates were subjected to antibiotic sensitivity test with linezolid (Bio-Rad), methicillin, ampicillin, ampicillin-sulbactum, amoxicillin-clavulanic acid, ticarcillin-clavulanic acid, imipenem-ethylenediaminetetraacetic acid, piperacillin-tazobactam, cefotaxime, ceftizoxime, ceftriaxone, ceftriaxone-tazobactam, enrofloxacin, ciprofloxacin, vancomycin and gentamicin antibiotic discs procured from HiMedia, India following CLSI (Clinical & Laboratory Standards Institute) guidelines [21 ].

The disk diffusion assay was performed in accordance with the method described by the antibiogram committee of the “French Society of Microbiology” CA-SFM/2014. All isolates were tested for their susceptibility to the following antibiotics: Amoxicillin/clavulanic acid (20/10 μg), ampicillin (10 μg), erythromycin (15 IU), tetracycline (30 IU), gentamicin (10 μg), ciprofloxacin (5 μg), and chloramphenicol (30 μg) (Bio-Rad, France).
From a pure culture of 18-24 h, the bacterial suspension was adjusted to match the 0.5 McFarland turbidity standard. A sterile swab was immersed into the adjusted suspension and then seeded by swabbing onto the entire surface of Mueller-Hinton agar supplemented with 5% defibrinated horse blood and β-NAD (MH-F). After streaking, the inoculum was dried for 5-10 min, and four antimicrobial disks were placed onto the surface of the plate. The plates were incubated at 37°C for 24 h under a microaerophilic atmosphere. Inhibition zones were measured by a caliper, and diameters were interpreted as recommended by the Antibiogram Committee of the French Society of Microbiology [8 ]. C. jejuni ATCC 33560 and C. coli ATCC 33876 were used as control strains.

Rosin acid was supplied from the local market (Egypt). The commercial grade rosin is provided in a solid grains form of resin obtained from conifers as reported elsewhere³² . Tetrahydrofuran is supplied by Sigma Aldrich. Ampicillin and gentamicin were suplied from (Bio-Rad, France). All used microorganisms were obtained from the Environmental Research Department, Theodor Bilharz Research Institute (TBRI), Egypt. All reagents were analytically pure and were not further purified.