Antimicrobial effects of Melaleuca alternifolia (tea tree) essential oil against biofilm-forming multidrug-resistant cystic fibrosis-associated Pseudomonas aeruginosa as a single agent and in combination with commonly nebulized antibiotics

Document Type

Journal Article

Publication Title

Letters in Applied Microbiology

Volume

75

Issue

3

First Page

578

Last Page

587

PubMed ID

34687564

Publisher

Wiley

School

School of Medical and Health Sciences

RAS ID

42643

Funders

Conquer Cystic Fibrosis Research Grant

Comments

Haines, R. R., Putsathit, P., Tai, A. S., & Hammer, K. A. (2022). Antimicrobial effects of Melaleuca alternifolia (tea tree) essential oil against biofilm‐forming multidrug‐resistant cystic fibrosis‐associated Pseudomonas aeruginosa as a single agent and in combination with commonly nebulized antibiotics. Letters in Applied Microbiology, 75(3), 578-587. https://doi.org/10.1111/lam.13589

Abstract

Broth microdilution assays were used to determine minimum inhibitory concentrations (MICs) and fractional inhibitory concentration indices (FICIs) of tea tree oil (TTO), tobramycin, colistin and aztreonam (ATM) against clinical cystic fibrosis-associated Pseudomonas aeruginosa (CFPA) isolates (n = 20). The minimum biofilm eradication concentration (MBEC) and fractional biofilm eradication concentration index (FBECI) were also determined using a similar microbroth dilution checkerboard assay, with biofilms formed using the MBEC device®. TTO was effective at lower concentrations against multidrug-resistant (MDR) CFPA isolates (n = 3) in a biofilm compared to in a planktonic state (MBEC 18·7-fold lower than MIC). CFPA within biofilm was less susceptible to ATM, colistin and tobramycin compared to planktonic cells (MBEC 6·3-fold, 9·3-fold, and 2·1-fold higher than MIC respectively). All combinations of essential oil and antibiotic showed indifferent relationships (FICI 0·52–1·72) when tested against planktonic MDR CFPA isolates (n = 5). Against CFPA isolates (n = 3) in biofilm, combinations of TTO/aztreonam and TTO/colistin showed indifferent relationships (mean FBECI 0·85 and 0·60 respectively), whereas TTO/tobramycin showed a synergistic relationship (mean FBECI 0·42). The antibiofilm properties of TTO and the synergistic relationship seen between TTO and tobramycin against CFPA in vitro make inhaled TTO a promising candidate as a potential therapeutic agent.

DOI

10.1111/lam.13589

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