Antibiotic-resistance Detection

Antibiotic resistance of bacteria was carried out against 30 antibiotics by the standard disc diffusion method. The strains were grown in Luria–Bertani (LB) medium containing (g L⁻¹): casein peptone (10.0) yeast extract (5.0) and NaCl (5.0) at 30 °C for 24 h. Then, the bacterial suspensions were adjusted to OD_600nm 0.5 (ca. 10⁷–10⁸ CFU x dm⁻³), and 100 µl was spread onto Mueller–Hinton agar plates (Oxoid). The antibiotic-impregnated discs (Oxoid) were put on these freshly prepared bacterial lawns and incubated at 30 °C for 24 and 48 h. The degree of resistance or sensitivity of the strains was determined by the measurements of lightened zones (expressed in mm) around the disc and by comparing with the standard antibiotic disc sensitivity testing method (EUCAST 2011). The strains which showed resistance or intermediate were classified as “resistant.” All others were classified as sensitive. The antibiotics used in this test are presented in Table 1.

List of antibiotics used in this study