Takuya Takahashi

Clostridium perfringens is a widespread pathogen, but the precise quantification of this subdominant gut microbe remains difficult due to its low fecal count (particularly in asymptomatic subjects) and also due to the presence of abundant polymerase-inhibitory substances in human feces. Also, information on the intestinal carriage of toxigenic C. perfringens strains in healthy subjects is sparse. Therefore, we developed a sensitive quantitative real-time PCR assays for quantification of C. perfringens in human feces by targeting its α-toxin and enterotoxin genes. To validate the assays, we finally observed the occurrence of α-toxigenic and enterotoxigenic C. perfringens in the fecal microbiota of healthy Japanese infants and young adults. The plc-specific qPCR assay was newly validated, while primers for 16S rRNA and cpe genes were retrieved from literature. The assays were validated for specificity and sensitivity in pre-inoculated fecal samples, and were finally applied to quantify C. perfringens in stool samples from apparently healthy infants (n 124) and young adults (n 221). The qPCR assays were highly specific and sensitive, with a minimum detection limit of 103 bacterial cells/g feces. Alpha-toxigenic C. perfringens was detected in 36 % infants and 33 % adults, with counts ranging widely (103-107 bacterial cells/g). Intriguingly, the mean count of α-toxigenic C. perfringens was significantly higher in infants (6.0 ± 1.5 log10 bacterial cells/g), as compared to that in adults (4.8 ± 1.2). Moreover, the prevalence of enterotoxigenic C. perfringens was also found to be significantly higher in infants, as compared to that in adults. The mean enterotoxigenic C. perfringens count was 5.9 ± 1.9 and 4.8 ± 0.8 log10 bacterial cells/g in infants and adults, respectively. These data indicate that some healthy infants and young adults carry α-toxigenic and enterotoxigenic C. perfringens at significant levels, and may be predisposed to related diseases. Thus, high fecal carriage of toxigenic C. perfringens in healthy children warrants further investigation on its potential sources and clinical significance in these subjects. In summary, we present a novel qPCR assay for sensitive and accurate quantification of α-toxigenic and enterotoxigenic C. perfringens in human feces, which should facilitate prospective studies of the gut microbiota.

A novel intraluminal colon tumor model was established in mice by intrarectal instillation of colon cancer cells followed by short term induction of colitis by an irritant agent. Male BALB/c mice were fed a diet containing 3% (w/w) dextran sulfate sodium (DSS) for 7 days to induce colitis, and colon 26 cells (1–2±10⁶ cells/mouse) were infused intrarectally after the mice had been deprived of food for the last 18 h of DSS treatment. The tumor incidence (%) and size (mean volume±SD, mm³) at the rectal mucosa were 35% (2±3), 95% (96±79), 95% (141 ±137) and 94% (325±270) at 1, 2, 3 and 4 weeks after instillation of tumor cells, respectively. Histopathological analyses revealed that a solid tumor was formed initially at the rectal mucosa at 1 week after instillation, then became invasive into the submucosal and muscular tissues at 3 weeks after implantation. Intrarectal instillation of human colon cancer cells, LS174T (1x10⁷ cells/mouse), mixed with “Matrigel” (0±5 mg/mouse), an extracellular matrix solution, in SCID mice led to formation of rectal tumors at 4 weeks after instillation, and immunohistochemical analysis revealed that the tumor cells expressed human carcinoembryonic antigen, suggesting that the tumor nodule was derived from the instilled LS174T cells. Oral or intravenous administration of a camptothecin (CPT) derivative, CPT‐11, resulted in a significant reduction in tumor incidence and tumor volume in the colon 26‐in‐traluminal implantation system. In conclusion, it was suggested that the present intraluminal colon tumor model is useful for examination of chemotherapeutic agents and also intraluminal factors (dietary compounds, intestinal microflora, etc.) that might function to suppress or enhance the growth of colorectal cancer in situ.