Minimum inhibitory concentration (MIC)

Minimum inhibitory concentration (MIC) was determined using disc diffusion method or conventional broth dilution assay. Kirby–Bauer disk-diffusion method was applied by swabbing bacteria on the surface of brain heart infusion agar or nutrient agar plates. Then, paper discs of 6-mm in diameter, previously loaded with MEW at levels of 0.5, 1, 2, 4 and 10 μg/disc with appropriate distances separating them from each other. Likewise, other discs previously saturated with NEW at similar levels were laid on another plate. The plates were incubated at 37 °C for 24 h and the diameters of the inhibition zones (mm) were measured using a transparent ruler (Bauer et al. 1966; Ehinmidu 2003). The conventional broth dilution assay (Lana et al. 2006) against the previously mentioned G⁺ and G⁻ bacteria was carried out simultaneously.

MIC of an antimicrobial is taken as the lowest concentration (μg/disc) in case of the disc diffusion method or (μg/ml) in case of conventional broth dilution assay, that will inhibit the visible growth of a microorganism after overnight incubation. The MICs of some specific antibiotic were simultaneously assessed against the targeted bacteria as follows: Ciprofloxacin (L. monocytogens, P. aeruginosa, S. typhimurium), Chloramphenicol (L. ivanovii, B. subtilis). Penicillin G (St. pyogenes), Gentamycin (K. oxytoca, E. coli) and Vancomycin (S. aureus, B. cereus).