Altering and assessing persistence of genetically modified E. coli MG1655 in the large bowel

One of the primary factors limiting the efficacy of probiotic therapies is short persistence time. Utilizing a novel method for assessment of persistence in the large bowel independent of survival of the organisms in the upper GI tract, we tested whether overexpression of the type 1 pilus, a colonization factor, or the presence of secretory immunoglobulin A (sIgA) might increase the persistence time of a laboratory strain of E. coli in the gut. For this purpose, cecal ostomies were created in mice and bacteria were placed in the ostomies, with or without sIgA. The persistence of the bacteria was assessed by evaluating the length of time after placement in which the bacteria were found in fecal samples. E. coli MG1655 expressing pili with the mannose-specific adhesin persisted in vivo significantly longer [mean (hours) +/- SEM: 91.50 +/- 15.98, n = 12] than bacteria expressing pili without adhesin [43.67 +/- 8.22, n = 12] (P = 0.01) and significantly longer than bacteria expressing neither pili nor adhesin [22.00 +/- 4.22, n = 12] (P = 0.0004). Although the persistence time of bacteria was not significantly affected by the presence of sIgA, the sIgA did cause a relative increase in retention of inert particles. These results, combined with an acute increase in stool production and stool water content in those animals not receiving sIgA following introduction of bacteria, suggest that sIgA might have anti-inflammatory properties in the gut when administered with enteric bacteria. Modifying expression of probiotic colonization factors may provide substantial benefit to patients with digestive tract diseases by virtue of increased persistence of the probiotic and, in the case of sIgA, an anti-inflammatory effect. This novel in vivo model may be useful in evaluating persistence time in a variety of current and future probiotic regimens.