Investigation of Antibacterial Activity and Synergistic Antibacterial Potential of Sericin Protein Extracts ^†

Abstract

Many antibacterial agents have been continuously used by various industries in order to extend shelf life by controlling spoilage bacteria and reducing the risk of pathogenic bacteria. However, there are concerns related to safety and various health-related issues. The sericin in silk cocoons is considered as a waste product in the silk industry and is usually thrown away. Sericin is known to possess a number of important biochemical properties. Considering this, in the present study, sericin protein was extracted from silk cocoons via a degumming process, and its antibacterial activity was investigated against a number of foodborne pathogenic bacteria using standard procedures. Its synergistic antibacterial activity was also investigated using both sericin protein and standard antibiotics such as ampicillin, azithromycin, cephalexin, erythromycin, gentamycin, kanamycin, and streptomycin. The results showed that sericin extract displayed a prominent antibacterial effect against all the tested foodborne pathogenic bacteria, with the diameter of inhibition zones ranging from 9.44 ± 0.04 mm to 12.09 ± 0.58 mm, and the results were comparable with those of the standard antibiotics. The sericin extract at 500 µg/disc displayed the highest inhibition zones against both the tested E. coli (12.09 ± 0.58 mm) and the L. monocytogenes (11.51 ± 0.35 mm). Furthermore, sericin along with the standard antibiotics at (25 µg + 5 µg respectively)/disk displayed significant antibacterial potential against all the tested foodborne pathogenic bacteria, with the highest inhibition zone against Salmonella Typhimurium (26.59 ± 0.74 mm). The minimum inhibitory concentration and the minimum bactericidal concentration values of the sericin extract ranged from 0.0625 to 1.0 mg/mL. These data suggested that sericin extract has promising antibacterial potential that can be utilized in various industries as an effective antibacterial agent.