Quantification and Correlation Analysis of <i>Bacteroides</i> Species with Diabetes-Related Amino Acids in Individuals with Prediabetes and Type 2 Diabetes Mellitus

<b><i>Background:</i></b> The relationship between gut microbiota and diabetes-related amino acids significantly impacts insulin resistance and obesity. We aimed to quantify two <i>Bacteroidetes</i> species and their correlation with branched-chain amino acids, aromatic amino acids, and glutamate in prediabetes (preDM) and type 2 diabetes mellitus (T2DM). <b><i>Methods:</i></b> Fecal samples were collected from 68 participants, including 21 with T2DM, 23 with preDM, and 24 with normal glycemic tolerance (NGT). The abundance of <i>Bacteroides vulgatus</i> and <i>Bacteroides thetaiotaomicron</i> was determined by quantitative real-time polymerase chain reaction. Plasma amino acid measurements were performed using liquid chromatography coupled with tandem mass spectrometry. <b><i>Results:</i></b> The quantities of <i>B. vulgatus</i> and <i>B. thetaiotaomicron</i> were reduced in preDM and T2DM than in NGT subjects, but it was not statistically significant. The concentrations of leucine, valine, and tyrosine were significantly higher in preDM and T2DM than in NGT subjects (<i>P</i> < 0.05). A negative correlation was observed between <i>B. thetaiotaomicron</i> abundance and two aromatic amino acids (tyrosine, <i>r</i> = -0.28, <i>P</i> = 0.04; phenylalanine, <i>r</i> = -0.26, <i>P</i> = 0.05). <b><i>Conclusions:</i></b> These findings imply that, since gut microbiota varies throughout ethnic groups, further research with many participants will be required to determine the abundance of <i>B. vulgatus</i> and <i>B. thetaiotaomicron</i> in preDM and T2DM and their association with diabetes-related amino acids.