Methicillin sodium salt

Antimicrobial stock solutions of vancomycin hydrochloride (Sigma, MO), clindamycin hydrochloride (RPI Corp., IL), ciprofloxacin hydrochloride (Sigma-Aldrich, WY), tobramycin sulfate (Sigma, MO), methicillin sodium salt (Sigma, MO), and linezolid (AK Scientific, CA) were diluted in phosphate-buffered saline to a maximum concentration of 100 μg/ml. The stock solutions of the antifungal drugs amphotericin B and fluconazole were diluted in PBS to maximum concentrations of 16 μg/ml and 2 mg/ml, respectively. Any subsequent dilutions needed for the antimicrobial susceptibility assays were made in PBS. To study the effect of drugs in preventing biofilm formation, 50 nl of drugs was printed at 2-fold dilutions on top of the hydrogel spots after initial printing of the cells. The microarray(s) containing drugs was then incubated in a humidified hybridization cassette for a maximum of 24 h, gently washed in PBS, stained with FUN-1, and analyzed using the microarray scanner.

The β-lactam antibiotics (Figure 4) methicillin sodium salt (≥95% purity) and penicillin G sodium salt (>96% purity) were purchased from Sigma-Aldrich (Darmstadt, Germany). Concentrations of the antibiotics from 1000 to 0.12 mg/L were prepared by dissolving the medicines in 2% (v/v) dimethyl sulfoxide (DMSO, Loba Chemie, Mumbai, India) and diluting with Mueller–Hinton broth (MHB; Sigma-Aldrich, Darmstadt, Germany).
The ten EOCs (Figure 4) used in this study, 1,8-cineole (99% purity), eugenol (≥98% purity), linalool (≥96% purity), linalyl acetate (≥97% purity), thymol (≥99% purity), menthone (98% purity), menthol (>99% purity), and β-caryophyllene (>95% purity), were purchased from ErnestoVentós, S.A. (Barcelona, Spain), whereas carvacrol (99% purity) and trans-anethole (99% purity) were obtained from Sigma-Aldrich (Darmstadt, Germany). Concentrations of the EOCs from 500 to 0.12 µL/mL were prepared by dissolving constituents in 1% (v/v) Tween 80 (Sigma-Aldrich, Darmstadt, Germany) and diluting with MHB. Using the known densities of EOCs, the results were expressed in mg/mL.