Incorporation of secretory immunoglobulin A into biofilms can decrease their resistance to ciprofloxacin.

Extracellular matrices utilized by biofilms growing on inert surfaces are generally produced entirely by the bacteria growing within those biofilms, whereas symbiotic (mutualistic) biofilms growing in or on a wide range of plants and animals utilize host-derived macromolecules, such as mucoid substances, as components of their extracellular matrix. Incorporation of host-derived molecules may have a profound effect on the resistance to antibiotics of symbiotic biofilms, which may have important implications for medicine and biology. As an initial probe of the potential effects of host-derived molecules in the extracellular matrix on the sensitivity of biofilms to antibiotics, an in vitro model was used to evaluate the effects of ciprofloxacin on biofilms grown in the presence and absence of SIgA, a host-derived glycoprotein associated with biofilms in the mammalian gut. In five out of six strains of Escherichia coli tested, the incorporation of SIgA into the biofilms apparently reduced the resistance of the bacteria to ciprofloxacin. On the other hand, SIgA generally increased the resistance of planktonic bacteria to ciprofloxacin, perhaps due in part to the SIgA-mediated aggregation of the bacteria. These findings suggest that incorporation of host-derived molecules into the extracellular matrix of symbiotic biofilms might profoundly alter the properties of those biofilms, including the resistance of those biofilms to antibiotics.

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.

Secretory IgA and mucin-mediated biofilm formation by environmental strains of Escherichia coli: role of type 1 pili.

Recent studies suggest the importance of secretory IgA (SIgA) and mucin in the mediation of biofilm formation by commensal bacteria within the mammalian gut. Studies using a variety of strains of Escherichia coli have indicated that the interaction between E. coli and SIgA is dependent on the type 1 pilus. In this study, the importance of the pilus in SIgA-mediated biofilm formation by a laboratory strain (MG1655) and environmental (fecal) strains of E. coli was evaluated. Transient expression of the type 1 pilus by the laboratory strain of E. coli failed to facilitate SIgA-mediated biofilm formation, whereas constitutive expression of the type 1 pilus by the laboratory strain was sufficient. In contrast, transient expression of the type 1 pilus was sufficient to facilitate SIgA-mediated biofilm formation by environmental isolates. The "threshold" for mucin-mediated biofilm formation appeared to be lower than that for SIgA-mediated biofilm formation, perhaps reflecting disparate roles of mucin and SIgA in mediating biofilm formation in the gut. These studies also provide the first procedures for the growth of bacterial biofilms on live epithelial cells in vitro, an important development that may facilitate future studies on the effects of bacterial biofilms on epithelial cells.