Equol‐Producing Bacteria in the Chicken Intestine: PCR Analysis on the Bacteria Quantitatively Correlating With Equol Concentration in Daidzein‐Fed Laying Hens

Equol is a microbial metabolite from daidzein, an isoflavone, in the animal intestine. This study aimed to identify equol-producing bacteria in the intestines of chickens. Sixteen 181-day-old Hy-Line Brown laying hens were given a basal diet formulated excluding soy products for 2 weeks and subsequently given the diets supplemented with 0-, 100-, 1000-, and 10,000-ppm daidzein for 10 days. Plasma and egg yolk equol concentration was significantly increased with dietary daidzein supplementation. Gene abundance of two major bacterial enzymes catalyzing the conversion of daidzein to equol, dihydrodaidzein reductase, and tetrahydro daidzein reductase was measured using polymerase chain reaction (PCR) analysis, with the abundance increasing with dietary daidzein supplementation (p < 0.05). After sequencing the PCR amplicons, six possible bacteria were identified, and they were further identified and quantified using a specific primer for each bacterial gene. As a result, Adlercreutzia equolifaciens and Slackia equolifaciens were identified, and their bacterial relative abundance increased with dietary daidzein concentration and plasma equol levels (p < 0.05). A. equolifaciens and S. equolifaciens are known as equol-producing bacteria, and the present study was the first to show that these bacteria could also contribute to equol production in chickens.