Antimicrobial Efficacy of QA Derivatives

The antibacterial activity of QA and its derivatives against Escherichia coli MTCC 443, Yersinia enterocolitica MTCC 859, Staphylococcus aureus MTCC 96, and Bacillus sp. MTCC 441 was determined by the disk diffusion method. The nutrient agar media was prepared, autoclaved, and poured into the sterilized Petri plates (90 mm, HiMedia, India). The media was allowed to gel. A known quantity (50 µL) of the fresh broth cultured bacterial cell (24–48-h-old culture) suspension was spread-plated and allowed to air-dry in a laminar air flow bench (Horizontal, Micro flow, Pvt. Ltd. India) after covering the media with the Petri lid. Stock solutions (2000 μg/mL) of each treatment were prepared in dimethyl sulfoxide (DMSO: 10%) to make various dilutions (100–1,500 μg/mL). A filter paper disk (5–6 mm diameter) was impregnated with 20 µL of a known concentration of each treatment and was shade-dried. These disks were then placed on the agar plate. The plates were incubated at an appropriate temperature (37°C ± 2°C) in a BOD incubator (Remi Lab. Incubator, Ludhiana, India). The filter paper discs containing DMSO (10%) served as control, while streptomycin (10 μg/mL) was used as the standard antibiotic. After incubating the plates, the diameters of the zone of inhibition (mm) were measured (De Zoysa et al., 2019 (link)).