Dietary intake of heat-killed Lactococcus lactis H61 prevents age-related hearing loss in C57BL/6J mice

Age-related hearing loss (AHL) is a common disorder associated with aging. In this study, we investigated the effect of intake of heat-killed Lactococcus lactis strain H61 on AHL in C57BL/6J mice. Measurement of auditory brainstem response (ABR) demonstrated that 9-month-old female mice fed a diet containing 0.05% strain H61 for 6 months maintained a significantly lower ABR threshold than control mice. Age-related loss of neurons and hair cells in the cochlea was suppressed by the intake of strain H61. Faecal analysis of bacterial flora revealed that the intake of strain H61 increased the prevalence of Lactobacillaceae, which is positively correlated with hearing ability in mice. Furthermore, plasma free fatty acid levels were found to be negatively correlated with hearing ability. These results suggest that intake of heat-killed strain H61 altered the intestinal flora and affected plasma metabolite levels, including fatty acid levels, and suppressed AHL in the mice.