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Essential oils inhibit the bovine respiratory pathogens Mannheimia haemolytica, Pasteurella multocida and Histophilus somni and have limited effects on commensal bacteria and turbinate cells in vitro

S. Amat, D. Baines, E. Timsit, J. Hallewell, T.W. Alexander
Journal of applied microbiology 2019 v.126 no.6 pp. 1668-1682
Haemophilus somni, Mannheimia haemolytica serotype 1, Pasteurella multocida, antimicrobial properties, bacteria, bovine respiratory disease, cattle, cell lines, chemical composition, cytotoxicity, essential oils, feedlots, fennel, gas chromatography-mass spectrometry, growth retardation, minimum inhibitory concentration, multiple drug resistance, nasopharynx, pathogens, serotypes, thyme
AIMS: The objective of this study was to determine antimicrobial activities of essential oils (EOs) against bovine respiratory disease (BRD) pathogens and nasopharyngeal commensal bacteria, as well as cytotoxicity in bovine turbinate (BT) cells in vitro. METHODS AND RESULTS: The chemical composition of 16 EOs was determined using gas chromatography–mass spectrometry. All EOs were first evaluated for growth inhibition of a single BRD pathogen Mannheimia haemolytica serotype 1 strain (L024A). The most inhibitory EOs (n = 6) were then tested for antimicrobial activity against multidrug‐resistant strains of M. haemolytica (serotypes 1, 2 and 6); the BRD pathogens Pasteurella multocida and Histophilus somni, as well as commensal bacteria that were isolated from the nasopharynx of feedlot cattle. The cytotoxicity of 10 EOs was also evaluated using a BT cell line. The EOs ajowan, thyme and fennel most effectively inhibited all BRD pathogens tested including multidrug‐resistant strains with minimum inhibitory concentrations (MIC) of ≤0·025% (volume/volume, v/v). For these EOs, the MIC was 2–32 fold greater against commensal bacteria, compared to BRD‐associated pathogens. No cytotoxic effects of EOs against BT cells were observed within the tested range of concentrations (0·0125–0·4%, v/v). CONCLUSIONS: The EOs ajowan, thyme and fennel inhibited M. haemolytica, P. multocida and H. somni at a concentration of 0·025% and had minimal antimicrobial activity against nasopharyngeal commensal bacteria and cytotoxicity against BT cells. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrated that EOs may have potential for intra‐nasal administration to mitigate bovine respiratory pathogens in feedlot cattle.