Is the gut microbiota bacterial abundance and composition associated with intestinal epithelial injury, systemic inflammatory profile, and gastrointestinal symptoms in response to exertional-heat stress?

Objectives: The study aimed to examine if the α-diversity and relative abundance of the gastrointestinal bacterial taxa is associated with the response magnitude of markers characteristic of exercise-induced gastrointestinal syndrome in response to exertional-heat stress. Design: Cross-sectional. Methods: Twenty-two endurance-trained athletes completed 2 h running at 60% V.O2max in hot ambient conditions (35.2 °C, 25% relative humidity). Faecal samples were collected pre-exercise to determine bacterial taxonomy by 16S rRNA amplicon sequencing (Illumina MiSeq platform). Data were processed using the QIIME2 pipeline (v2019.1) establishing taxonomic classification with >95% confidence using SILVA. Pre- and post-exercise blood samples were used to determine plasma I-FABP and cortisol concentrations, and systemic inflammatory response profile. Markers of physiological and thermoregulatory strain, and gastrointestinal symptoms were measured every 10 min during exercise. Associations were determined by partial correlation controlled for body mass variables. Results: Positive associations between Tenericutes (r(18) = 0.446, p = 0.049) and Verrucomicrobia (r(18) = 0.450, p = 0.046) phylum, Akkermansiaceae (r(18) = 0.486, p = 0.030) and Ruminococcaceae (r(18) = 0.449, p = 0.047) family and aligned genus groups with I-FABP were observed. Whilst, associations between Faecalibacterium (r(12) = 0.668, p = 0.009) and Ruminoclostridium-9 (r(12) = −0.577, p = 0.031) genus with systemic inflammatory profile were observed. Association between bacterial phyla, family, and genus groups were also observed for gastrointestinal symptoms and markers of thermoregulatory strain (r(18) >0.400, p < 0.05). Conclusions: The relative abundance of several commensal bacterial groups showed modest favourable (i.e., low perturbations) or detrimental associations with the magnitude of gastrointestinal integrity perturbations and symptoms, and potentially influences body temperature change, in response to exertional-heat stress.