Described herein is a set of oligonucleotide probes. Also included are methods of using the oligonucleotide probes in profiling the microbiota of the GI tract of a subject and methods of diagnosing or monitoring a disease or condition in a subject or predicting or assessing the risk of a subject developing a disease or condition. Kits comprising the oligonucleotide probe set described herein are also provided.