S epidermidis

Minimal inhibitory concentration (MIC) of each antibacterial agents was determined by standardized broth microdilution method with inoculum of 5 × 10⁵ CFU/mL and incubated for 24 h at 35 °C according to the recommendation of CLSI (Clinical Laboratory Standards Institute) [35 ]. The antibacterial activity of the thiosemicarbazides 1–9 and antibiotics (amoxicillin, gentamicin, levofloxacin, linezolid, and vancomycin) was tested on the Gram-positive strains (Microbiologics, St. Cloud, MN, USA) (S. aureus ATCC 25923, S. aureus ATCC 6538, S. epidermidis ATCC 12228, B. subtilis ATCC 6633, B. cereus ATCC 10876, M. luteus ATCC 10240), the Gram-negative strains (Microbiologics, St. Cloud, MN, USA) (E. coli ATCC 25922, K. pneumoniae ATCC 13883, P. mirabilis ATCC 12453, P. aeruginosa ATCC 9027), and clinical isolates of S. aureus (Medical University of Lublin, Lublin, Poland) (MSSA-1, MSSA-2, MSSA-3, MSSA-4, MRSA-1). Similarly to previous experiments with the thiosemicarbazides 1–5, cefuroxime was used as positive control antibiotic [23 (link)], whereas sterile distilled water served as negative controls.

Plant species were brought from the CONAF conservation reserve on Rapa Nui. Upon receipt in the Laboratory of Biomedicine and Biocatalysis of the Pontifica Universidad Católica de Valparaíso, rhizomes and leaves were weighed, washed in sterile water, chopped, and stored at −80 °C. Adult Human Dermal Fibroblasts (HDFa) were obtained from Thermo Fisher Scientific (Thermo, Waltham, MA, USA). Bacterial strains S. aureus (ATCC 25955) and S. epidermidis (ATCC 35984) were purchased from Microbiologics^® (Microbiologics, MN, USA). The LDH Cytotoxicity Assay Kit was purchased from Thermo Scientific (Thermo, Waltham, MA, USA). Gallic acid, TROLOX, AAPH, n-Hexane, ethyl acetate and DPPH were purchased form Sigma-Aldrich (St. Louis, MO, USA). Culture medium 106, LSGS supplement, antibiotics penicillin and streptomycin, Trypticase Soy Agar (TSA), and Trypticase Soy Broth (TSB) were purchased from Oxoid, Thermo Fisher Scientific (Thermo, Waltham, MA, USA). All other reagents used in this study were purchased from Merck Co. (Kenilworth, NJ, USA).