The gut microbiota predispose to the pathophysiology of acute postradiotherapy diarrhea.
BACKGROUND
Severe diarrhea may complicate pelvic radiotherapy and force interruption of treatment. As there is no current clinical or experimental information on the role of the gut microbiota in this pathogenesis, we conducted a pilot observational study on the fecal microbiota in patients receiving pelvic radiotherapy.


METHODS
The study involved 10 patients who underwent 5 wk of radiotherapy for abdominal tumors and 5 controls. Four fecal samples were collected from each individual: before, during, at the end, and 2 wk after treatment. Following the amplification of the bacterial 16S rRNA gene from the samples, DNA fingerprinting and cloning-sequencing techniques were used to determine their microbial profile and composition, respectively.


RESULTS
Six patients suffered acute postradiotherapy diarrhea and 4 did not. In patients without diarrhea, as well as in healthy volunteers, microbial diversity was stable over a period of 7 wk. However, patients exhibiting diarrhea showed a progressive modification in their microbial diversity. A radical drop in similarity index was observed at the end (P= 0.026) and still 2 wk after radiotherapy (P= 0.014). Interestingly, cluster analysis of the microbial profile in the first sample (S1) (collected before radiotherapy) displayed a dendogram where patients that presented diarrhea clustered separately from those that did not develop diarrhea after radiotherapy. Moreover, sequence analysis of dominant bacteria in the S1 sample confirmed differences between the diarrhea and nondiarrhea groups.


CONCLUSIONS
In this set of patients, susceptibility or protection against diarrhea after radiotherapy could be linked to different initial microbial colonization.
Unité d'Ecologie et de Physiologie du système Digestif, INRA, Jouy-en-Josas, France.
Chaysavanh
C
Manichanh
Encarna
E
Varela
Cristina
C
Martinez
Maria
M
Antolin
Marta
M
Llopis
Joël
J
Doré
Jordi
J
Giralt
Francisco
F
Guarner
Juan-Ramon
JR
Malagelada
D000008:Abdominal Neoplasms / Q000532:radiotherapy; D000368:Aged; D004269:DNA, Bacterial / Q000032:analysis; D003967:Diarrhea / Q000209:etiology* / Q000503:physiopathology*; D005243:Feces / Q000382:microbiology; D005260:Female; D005784:Gene Amplification; D006801:Humans; D007422:Intestines / Q000382:microbiology*; D008297:Male; D008875:Middle Aged; D010388:Pelvis / Q000528:radiation effects; D011878:Radiotherapy / Q000009:adverse effects*
D004269:DNA, Bacterial