10 Development of an Essential Oil-Based Intranasal Spray Against Bovine Respiratory Pathogens: in vitro Selection Based on Antimicrobial, Antiviral, Immunomodulatory, and Antibiofilm Activities

Abstract

Abstract The objective of this study was to screen and select candidate essential oils (EOs) for the development of an intranasal EO spray against bacterial and viral pathogens associated with bovine respiratory disease (BRD) as an alternative to antibiotics. The effects of previously selected EOs (N = 6; ajowan, cinnamon leaf, citronella, grapefruit, fennel, and thyme) on bovine nasopharyngeal microbiota culture was evaluated using 16S rRNA gene sequencing. The microbiota culture was prepared by growing nasopharyngeal swabs obtained from finishing beef heifers in brain heart infusion broth with and without the presence of EOs (0.025%, vol/vol). The sequencing was performed on genomic DNA extracted from the microbiota culture harvested after 24 h incubation. These EOs were then evaluated for their immunomodulation effect on bovine turbinate (BT) cells by analyzing the concentrations of 15 cytokines and chemokines in cell culture after 24 h incubation. The EOs were further characterized by assessing their antibiofilm activity against E. coli UMN026 using a crystal violet assay. Finally, 15 EOs were screened for their antiviral activity against the bovine viral diarrhea virus 1 (BVDV1) using BT cells and a fluorescence-based method. Ajowan, fennel, and thyme resulted in a moderate reduction of overall nasopharyngeal microbiota growth, and significant alterations of both α- and β-diversity, and relative abundance of predominant bacterial families (e.g., boosting Enterobacteriaceae while suppressing Moraxellaceae) compared with control (P < 0.05). Only IL-6 and IL-8 cytokine concentrations were affected by EOs (P < 0.05). Ajowan, thyme, fennel, and cinnamon leaf exhibited antibiofilm activity at the concentration of 0.05%. Reduction of BVDV1 viral replication on BT cells was observed with thyme (strong), ajowan, and citronella (moderate; 0.0125%). Accordingly, ajowan, thyme, fennel, cinnamon leaf, and citronella EOs were selected for development as an intranasal EO spray to prevent and control BRD pathogens in feedlot cattle.