Trials for Replacing Antibiotics Used in Production of Tissue Culture Vaccines by Natural Antibacterial and Antifungal Extracts

The continuous use of antibiotics for tissue culture adapted vaccines production has led to the increase in the bacterial resistance to these antibiotics. This study aims to evaluate the antimicrobial potential of thyme (Thymus vulgaris) and clove (Syzygium aromaticum) on bacterial and fungal contamination, in the production of tissue culture vaccines. The active agents in each plant were extracted by the conventional extraction technique using ethanol and water as solvents followed by concentration (steam distillation and boiling). The antimicrobial activities of different solvent extracts were determined in well agar diffusion technique using Staphylococcus aureus (S. aureus), Escherichia coli (E. coli), and Candida albicans as model for gram positive, gram negative and fungal contamination, respectively. The cytotoxic effects of the different solvent extracts were tested on VERO and MDBK cell culture. The obtained results indicated that water and ethanolic extracts from thyme and clove plants showed significant antimicrobial activities (P < 0.05) as they could inhibit the growth of E. coli, S. aureus and Candida albicans. Ethanolic extract of thyme had the maximum zone of inhibition against E. coli (2.40±0.20) and Candida albicans (3.07±0.3), and the lowest inhibition zone against S. aureus (1.53±0.23), whereas the thyme water extract didn’t show any antimicrobial activity. The ethanolic extract of clove showed the greatest zone of inhibition against Candida albicans (2.63±0.2), E. coli (2.63±0.2), while the lowest was against S. aureus (1.87±0.3). Water extract of clove showed the greatest zone of inhibition against E. coli and S. aureus (1.93±0.4, and 2.47±0.1), respectively and 0.97±0.1 against Candida albicans. The ethanolic extracts of thyme and clove showed changes in the cell wall until concentration 1 mg/ml for clove and 10 µg/ml for thyme on VERO cells; while the cytotoxic effect on MDBK cells was observed till the concentration of 100 µg/ml for clove and thyme water extracts. In conclusion, the antimicrobial potential of clove  water extract on bacterial and fungal contaminant could replace antibiotics in the production of tissue culture vaccines at a concentration of 10 µg/ml.