249 Antimicrobial activities of commercial essential oils against the bovine respiratory pathogen Mannheimia haemolytica and analysis of their chemical composition and cytotoxicity on bovine turbinate cells
Bibliographic record
Abstract
Recent studies have shown the emergence of bacterial pathogens associated with bovine respiratory disease (BRD) that are resistant to all classes of antibiotics used to treat BRD. Therefore, there is an impetus to develop alternatives to antibiotics for use in the beef industry. Essential oils (EO) may offer a potential mitigation strategy against BRD bacterial pathogens through direct inhibition and also attenuation of resistance to antibiotics. The purpose of this study was to determine the chemical composition of commercial EOs (N = 16) and their in vitro antimicrobial activities against the model BRD pathogen Mannheimia haemolytica, as well as any cytotoxicity in bovine turbinate (BT) upper respiratory cells. The EO chemical composition was determined using gas chromatography-mass spectrometry. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the 16 EOs against M. haemolytica serotype 1 were determined using the broth dilution method with serial dilutions ranging from 0.2% to 0.006% (v/v). Based on MIC and MBC, the most inhibitory EOs (N = 7; ajowan, cinnamon leaf, citronella, fennel, ginger grass, lavender, and thyme) were further characterized by evaluating their vapor-phase antimicrobial activities against M. haemolytica, impact on M. haemolytica morphology, and cytotoxicity against BT cells at concentrations between 0.0125% and 0.4% (v/v). A variety of volatile compounds were detected from the EOs, with some containing thymol and eugenol, which are known to have antibacterial activities. Thymol was most abundant in ajowan and thyme EOs (>46% of EO content), and eugenol was most predominant in cinnamon leaf EO (84% of EO content). The MIC ranged between 0.025% and 0.2%. The lowest MIC (0.025%) was observed with ajowan, fennel, and thyme EOs. Cinnamon leaf and citronella EOs showed MIC value of 0.05%. All MIC values were the same as MBC for all EOs. Ajowan, thyme, and cinnamon leaf EOs completely or moderately inhibited M. haemolytica in their vapor-phase. Scanning electron microscopy revealed noticeable changes in cell structure between EO treated and non-treated cells. The cells treated with ajowan and thyme EOs displayed the greatest morphological cell damage compared to other EOs. None of the selected EOs exhibited noticeable cytotoxicity on BT cells within the tested concentrations. Our results indicate that ajowan, thyme, and cinnamon leaf EOs may have potential to be used as antibiotic alternatives to control BRD bacterial pathogens.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".