Ambrosio Carmen M S, de Alencar Severino M, Moreno Andrea M, Da Gloria Eduardo M
a Department of Agri-Food industry, Food and Nutrition, "Luiz de Queiroz" College of Agriculture, University of São Paulo, Piracicaba/São Paulo 13418-900, Brazil.
b School of Veterinary Medicine and Animal Science, University of São Paulo, São Paulo 05508-270, Brazil.
Can J Microbiol. 2018 Nov;64(11):844-855. doi: 10.1139/cjm-2018-0021. Epub 2018 Jun 12.
Essential oils (EOs), as substitutes for antibiotics in animal diets, should have selective antibacterial activity between pathogenic and beneficial bacteria from the animal gut. Thus, this study evaluated the selective antibacterial activity of Eucalyptus globulus (EG) and Pimenta pseudocaryophyllus (PP) EOs on Enterococcus faecalis as a surrogate model of pathogenic bacterium and on Lactobacillus rhamnosus as a beneficial bacterium model. The EOs antibacterial activity was evaluated by determination of minimal inhibitory concentrations (MICs), minimal bactericidal concentration (MBCs), and fractional inhibitory concentration (FIC) indices. The time-kill and sequential exposure assays were also performed, but using only the EG oil, which was the best selective EO, since it had a MIC lower on E. faecalis (7.4 mg/mL) than on L. rhamnosus (14.8 mg/mL). FIC index values showed that the combination of the two EOs had an indifferent effect (1.25 and 2.03) on E. faecalis and an additive effect (1.00) on L. rhamnosus. The time-kill assay showed that EG oil was able to kill E. faecalis within 15 min of treatment (∼5 log reduction) and caused a reduction ∼3 log of L. rhamnosus viability. The sequential exposure assay showed that EG oil (at MIC/2) produced higher reduction on E. faecalis viability (∼3 log) than on L. rhamnosus (∼2 log) as well. Therefore, L. rhamnosus presented higher tolerance to the antibacterial activity of EG oil than E. faecalis did.
精油（EOs）作为动物饲料中抗生素的替代品，应对动物肠道中的病原菌和有益菌具有选择性抗菌活性。因此，本研究评估了蓝桉（EG）和假丁香番荔枝（PP）精油对粪肠球菌（作为病原菌的替代模型）和鼠李糖乳杆菌（作为有益菌模型）的选择性抗菌活性。通过测定最低抑菌浓度（MICs）、最低杀菌浓度（MBCs）和分级抑菌浓度（FIC）指数来评估精油的抗菌活性。还进行了时间杀菌和连续暴露试验，但仅使用了EG油，因为它是最佳的选择性精油，其对粪肠球菌的MIC（7.4 mg/mL）低于对鼠李糖乳杆菌的MIC（14.8 mg/mL）。FIC指数值表明，两种精油的组合对粪肠球菌有无关作用（1.25和2.03），对鼠李糖乳杆菌有相加作用（1.00）。时间杀菌试验表明，EG油在处理15分钟内能够杀死粪肠球菌（约5个对数级减少），并使鼠李糖乳杆菌的活力降低约3个对数级。连续暴露试验表明，EG油（在MIC/2）对粪肠球菌活力的降低幅度（约3个对数级）也高于对鼠李糖乳杆菌的降低幅度（约2个对数级）。因此，鼠李糖乳杆菌对EG油抗菌活性的耐受性高于粪肠球菌。
