Determination of Minimum Inhibitory Concentration of Thyme Essential Oil Against Salmonella Enteritidis and the Effects of the Essential oil at Sub-Inhibitory Concentration on Bacterial Invasion in Broiler Chickens: An Experimental Study.

BACKGROUND: Salmonella Enteritidis (SE) in chickens is associated with growth depression and mortality of young chicks. Moreover, poultry products are identified as a prominent source of SE, which can cause food-borne diseases in humans. Therefore, considering the economic and public health significance of SE, control of this bacterial infection is important. OBJECTIVES: This study aims to assess colonization and invasion of SE after exposure to the thyme essential oils in experimentally infected broiler chickens. METHODS: Minimum inhibitory concentration (MIC) of thyme essential oils was measured by broth microdilution method. A total of 75 one-day-old Ross 308 chicks were randomized to three experimental groups of 25 (A, B and C). At 9 days old, groups A and B were challenged with 108 colony-forming unit (CFU) of SE with and without previous exposure to thyme essential oils at 50% MIC. Group C (control) received a bacteria-free buffer. On days 9, 16 and 24 after the challenge, cloacal swabs and samples from visceral organs were collected from slaughtered birds and evaluated for the presence of Salmonella. RESULTS: The MIC of thyme essential oil for SE was obtained 1.25 mg/mL. Results of experimental infection showed a significant reduction of SE in the cloaca, ceca, liver, and spleen of group A compared to group B throughout the sampling times. On day 16 after infection, Salmonella was isolated at 1 and 7.4 log CFU/g of cloacal swabs and at 3.2 and 9.2 log CFU/g of ceca in groups A and group B, respectively. CONCLUSIONS: According to the results, previous exposure of SE to the thyme essential oil at a sub-inhibitory concentration can reduce the colonization and invasion of this pathogen in broiler chickens. [ABSTRACT FROM AUTHOR]