Chemical composition and in vitro antimicrobial activity of Cupressus sempervirens and Eucalyptus camaldulensis essential oils against colistin-resistant Escherichia coli and methicillin-resistant Staphylococci recovered from different animal diseases in Tunisia

Sana Dhaouadi1, Salsabil Chedli1, Soufiene Chaari2, Ameur Cherif1, and Ramzi Boubaker elandoulsi1

1 University Manouba, ISBST, BVBGR-LR11ES31, Biotechpole Sidi Thabet, 2020 Ariana, Tunisia; 2 Medivet, Souliman, Nabeul, Tunisia 
*correspondence to:

Context and problematic: Bovine mastitis, calf diarrhea and avian colibacillosis caused by staphylococciand Escherichia coliE. coli, respectively,are among the most important diseases affecting dairy cows, calves and poultry leading to high economic losses. Emerging resistance to colistin and methicillin in E. coli and Staphylococci, respectively, is a growing problem in veterinary medicine. Thus, using natural products such as essential oils (EOs) as an alternative option for the treatment of animal diseases appears to be very promising.

Objectives:This study aimed to determine the chemical composition and to evaluate the antibacterial activity of Cupressus sempervirens and Eucalyptus camaldulensisEOsagainst methicillin-resistant Staphylococci and colistin-resistant E. coli isolatesrecovered from cows with mastitis, calves with diarrhea and chickens with colibacillosis.

Methodology:The chemical composition of EOs was analyzed by gas chromatography with mass spectrometry detection. The antibacterial activity of Cupressus sempervirens and Eucalyptus camaldulensisEOs against E. coli and Staphylococcus isolates was assessed by disk diffusion test and broth microdilution method. Then, Minimal inhibitory concentration (MICs) and Minimal bactericidal concentrations (MBCs) were determined for each of the EOs.

Results:Compounds were identified in C.  sempervirens and E. camaldulensis EOs, respectively: α-Pinène (58,3 and 30,2 %), Cinéole 1.8 (6,25 and 52,1 %), Limonène (2,92 and 5,18%), being predominant. Inhibition zones of EOs in E. coli isolates varied from 6 to 18 mm for C.  sempervirens and 14 to 20 mm for E. camaldulensis. In staphylococci, the diameters of inhibition varied from 17 to 35 mm for C.  sempervirens and 16 to 30 mm for E. camaldulensis. MICs for E. camaldulensis EO ranged from 80μg/mL to ≥640 μg/mL and from 160 μg/mL to ≥640 μg/mL for C.  sempervirens EO in E. coli isolates. Whereas MICs for E. camaldulensis EO ranged from 20μg/mL to ≥640 μg/mL and from 80 μg/mL to ≥640 μg/mL for C.  sempervirens EO in Staphylococci isolates. MBCs/MICs ratios revealed a bactericidal activity of the two EOs tested.

Conclusion: C.  sempervirens and E. camaldulensis EOs were active against methicillin-resistant Staphylococci and colistin-resistant E. coli isolates recovered from diseased animals. These findings showed that the use of these EOs as alternatives to antibiotics might be very promising for the development of new therapeutic options against antibiotic-resistant bacteria in veterinary medicine.

Keywords: Antimicrobial activity, essential oils, E. coli, Staphylococci, animal diseases.