Vancomycin (VAN) treatment in
Clostridioides difficile
infection (CDI) suffers from a relatively high rate of recurrence, with a variety of reasons behind this, including biofilm-induced recurrent infections.
C. difficile
can form monophyletic or symbiotic biofilms with other microbes in the gut, and these biofilms protect
C. difficile
from being killed by antibiotics. In this study, we analyzed the ecological relationship between
Bacteroides thetaiotaomicron
and
C. difficile
and their formation of symbiotic biofilm in the VAN environment. The production of symbiotic biofilm formed by
C. difficile
and
B. thetaiotaomicron
was higher than that of
C. difficile
and
B. thetaiotaomicron
alone in the VAN environment. In symbiotic biofilms,
C. difficile
was characterized by increased production of the toxin protein TcdA and TcdB, up-regulation of the expression levels of the virulence genes
tcdA
and
tcdB
, enhanced bacterial cell swimming motility and c-di-GMP content, and increased adhesion to Caco-2 cells. The scanning electron microscope (SEM) combined with confocal laser scanning microscopy (CLSM) results indicated that the symbiotic biofilm was elevated in thickness, dense, and had an increased amount of mixed bacteria, while the fluorescence in situ hybridization (FISH) probe and plate colony counting results further indicated that the symbiotic biofilm had a significant increase in the amount of
C. difficile
cells, and was able to better tolerate the killing of the simulated intestinal fluid. Taken together,
C. difficile
and
B. thetaiotaomicron
become collaborative in the VAN environment, and targeted deletion or attenuation of host gut
B. thetaiotaomicron
content may improve the actual efficacy of VAN in CDI treatment.