Evaluation of antibacterial activity of essential oils extracted from Thymus satureioides and Mentha pulegium against antibiotic resistance bacteria from raw sheep milk

Abstract

Aims: This study evaluated in vitro resistance and susceptibility of Enterobacteriaceae (Escherichia coli and Klebsiella oxytoca strains) and Staphylococci strains, isolated from sheep's milk, against antibiotics and essential oils from Thymus satureioides and Mentha pulegium. Methodology and results: Antibiotic resistance tests were done using disc diffusion while essential oils were extracted by steam distillation and yields were calculated relative to plant dry matter. Gas chromatography-mass spectrometry (GC-MS) was used to analyze each oil's chemical composition. Amoxicillin + Clavulanic acid (AMC), Cefotaxime (CTX), Cefoxitine (FOX), Nalidixic acid (NA), Gentamicin (CN), Ciprofloxacin (CIP) and Ofloxacin (OFX) were very effective against the E. coli strains tested. Half of the strains were resistant to AMC, 60% to Ticarcillin (TIC) and 80% to Tetracycline (TE). Klebsiella oxytoca was resistant against AMC, FOX and TIC (100%). Antibiotic-resistant testing on Staphylococci strains indicated Staphylococcus capitis and S. chromogenes as the most sensitive. Staphylococcus aureus, S. xylosus and S. cohnii ureal exhibited less resistance to Oxacilin (OX), TE, Pristinamycin (PT), Erythromycin (E) and Penicillin (P). Mentha pulegium resulted in a higher yield of essential oil of 3.2% oil compared to T. satureioides with only 1.85% yield. The monoterpene oxygenated derivatives, monoterpene hydrocarbons and phenols are found in essential oil extracts. Thymus satureioides essential oil had high antibacterial activity even at low concentrations (0.2; 0.55 g/mL). The minimal bactericidal concentration (MBC) values indicate that the essential oils from the plants analyzed had bactericidal effects on all strains tested and are similar to the minimal inhibitory concentration (MIC) values. Conclusion, significance and impact of study:The high antibacterial properties of these medicinal plants, against bacteria isolated from sheep's milk, provide an opportunity to use these medicinal plants in the breeding sector, as additives and preservatives in the dairy industry.