Date of Project

4-6-2026

Document Type

Honors Thesis

School Name

Donna and Allan Lansing School of Nursing and Health Sciences

Department

Medical Laboratory Science

Major Advisor

Karen Golemboski

Abstract

Antibiotic resistance increasingly threatens the effectiveness of conventional antibiotics, particularly against hospital-acquired infections (HAIs). Essential oils have emerged as promising antibiotic adjuvants due to their diverse mechanisms of action and lower potential to promote resistance. This study sought to explore the significance of the antibiotic class when formulating combinations with essential oils. Thyme and cinnamon essential oils were evaluated in combination with cefepime, a β-lactam antibiotic, and levofloxacin, a fluoroquinolone, against Staphylococcus epidermidis and Pseudomonas aeruginosa. Synergistic effects were assessed using checkerboard assays and by calculating fractional inhibitory concentration indices (FICIs). Log₂ fold-reduction analyses were employed to visualize the interaction between each agent. Several combinations demonstrated synergy (FICI ≤ 0.5). For S. epidermidis, levofloxacin combinations showed the strongest synergy, whereas synergy against P. aeruginosa was observed only with cefepime combinations. Statistical analysis indicated no significant overall advantage based solely on antibiotic class. However, combinations that led to balanced, bidirectional reductions in minimum inhibitory concentrations (MICs) consistently produced the greatest synergy. These findings suggest a more organism-focused approach and highlight the importance of bacterial traits and resistance mechanisms in developing effective combination therapies. This study reinforces the potential of essential oils as antibiotic adjuvants and offers valuable insights for future research aimed at addressing antibiotic resistance.

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Available for download on Tuesday, April 06, 2027

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