A method for assessing whether a person has type-2 diabetes, comprising 1) acquiring a faecal sample of the person, wherein the faecal sample is being stored on a solid support for up to 5 days, wherein the solid support is an FTA card for example FTA Elute, 2) amplifying nucleic acid for 16S rRNA of bacteria of interest from the faecal sample; 3) detecting and quantifying the bacteria of interest in the faecal sample by nucleic acid sequencing technique; and 4) assessing whether the person has type-2 diabetes, wherein the assessment is done by a. calculating a ratio for the amount of butyrate-producing bacteria to the amount of sulphate reduction/oxidative stress resistance bacteria in the faecal sample, wherein an increase of the ratio from that of a healthy individual indicates the person has type-2 diabetes, or b. normalizing detected value of the 16S rRNA from the bacteria of interest in the faecal sample to that of a control genomic DNA sequence, wherein a change in normalized value from that of a healthy individual indicates the person has type-2 diabetes; and wherein the amplifying step is carried out directly from punches excised from the solid support containing the faecal sample, wherein the amplifying step is performed in the presence of cyclodextrin, and wherein the bacteria of interest are selected from: Type-2 Diabetes-enriched Control-enriched Akkermansia muciniphila Clostridiales sp. SS3/4 Bacteroides intestinalis Eubacterium rectale Bacteroides sp. 20_3 Faecalibacterium prausnitzii Clostridium bolteae Haemophilus parainfluenzae Clostridium hathewayi Roseburia intestinalis Clostridium ramosum Roseburia inulinivorans Clostridium sp. HGF2 Faecalibacterium sp. Clostridium symbiosum Desulfovibrio sp. 3_1_syn3 Eggerthella lenta Escherichia coli Alistipes sp. 1) acquiring a faecal sample of the person, wherein the faecal sample is being stored on a solid support for up to 5 days, wherein the solid support is an FTA card for example FTA Elute, 2) amplifying nucleic acid for 16S rRNA of bacteria of interest from the faecal sample; 3) detecting and quantifying the bacteria of interest in the faecal sample by nucleic acid sequencing technique; and 4) assessing whether the person has type-2 diabetes, wherein the assessment is done by a. calculating a ratio for the amount of butyrate-producing bacteria to the amount of sulphate reduction/oxidative stress resistance bacteria in the faecal sample, wherein an increase of the ratio from that of a healthy individual indicates the person has type-2 diabetes, or b. normalizing detected value of the 16S rRNA from the bacteria of interest in the faecal sample to that of a control genomic DNA sequence, wherein a change in normalized value from that of a healthy individual indicates the person has type-2 diabetes; and a. calculating a ratio for the amount of butyrate-producing bacteria to the amount of sulphate reduction/oxidative stress resistance bacteria in the faecal sample, wherein an increase of the ratio from that of a healthy individual indicates the person has type-2 diabetes, or b. normalizing detected value of the 16S rRNA from the bacteria of interest in the faecal sample to that of a control genomic DNA sequence, wherein a change in normalized value from that of a healthy individual indicates the person has type-2 diabetes; and