Aggregation substance promotes colonic mucosal invasion of Enterococcus faecalis in an ex vivo model

Background. Bacterial translocation through the gastrointestinal tract is t he crucial step in the pathogenesis of intraabdominal infections, We assess ed whether aggregation substance (AS), a bacterial adhesin and virulence fa ctor of Enterococcus faecalis, promotes bacterial translocation and colonic mucosal invasion in an ex vivo experiment. Methods. Colonic mucosa of male Wistar rats was placed in a modified Ussing system. The mucosal side of the chamber was filled with a suspension of E. faecalis OG1X:pAM721 (AS-positive) or E. faecalis OG1X (AS-negative). The serosal side was filled with sterile Dulbecco's modified Eagle's medium. Fo r assessment of colonic mucosal invasion the mucosal side was incubated for 2.5 h with a suspension of AS-positive or AS-negative enterococci. After b eing washed, a solution of gentamicin and penicillin G in tissue culture me dium was added on both sides in order to kill extracellular bacteria. Subse quently, the mucosa was removed from the system, washed, lysed with Triton X-100, and homogenized. Viable intramural bacteria were quantified by plati ng serial dilutions of the homogenate on Todd-Hewitt broth agar plates. To quantify bacterial translocation samples which were taken at various time p oints from the serosal side were plated on Todd-Hewitt broth agar plates an d colony forming units (CFU) were determined. Results. Invasion of the AS-positive E. faecalis strain OG1X:pAR1721 into t he colonic mucosa was significantly higher than invasion rates of the AS-ne gative strain OG1X (2.88 log(10) CFU/ml vs 1.73 log(10) CFU/ml; P = 0.02). However, none of the tested strains was found to translocate from the mucos al to the serosal side within the incubation time of 4 h. Conclusions. The aggregation substance promotes invasion of E. faecalis int o colonic mucosa, (C) 2000 Academic Press.