The gut microbial composition in humans in hot occupational settings and the effects of drinking buttermilk

Abstract: The principal aims of the present study were to examine the latent heat stress relieving capacity of drinking buttermilk and to observe the human gut microbiota in hot occupational condition. A human crossover intervention study with 12 volunteers was studied, each of them performed 3 hours of physical work in a heat chamber. During the working period, the volunteers were given buttermilk, water or no liquid. Rectal and saliva samples were obtained after and during 3 hours of physical work. The results showed no significant differences in diversity indices of three treatment groups, we detected, by means of salivary cortisol level analysis, significantly differences between the Buttermilk and Dehydrated groups, as well as Water and Dehydrated groups at the last time-point (P = 0.017). When it comes to qPCR results, Lactobacillus and Enterobacteriaceae were detected in 9 (75%) and 12 (100%) subjects, with the medians of 4.039 (Buttermilk), 4.02 (Dehydrated), 4.081 (Water) and 7.407 (Buttermilk), 6.763 (Dehydrated), 7.64 (Water) log 16S rRNA gene copies/g rectal samples respectively. The PCA score and scatter plots indicated that the microbiota differed widely between individuals with regard to both composition and diversity. While the PLS score and loading scatter plots based on cortisol, core temperature and T-RFLP data explicated that the observations separated in groups which representing three treatments of same subject. However, the relationship between the stress indicators (core temperature and salivary cortisol level) and the gut microbial diversity was not clearly shown.