| The novel hypothesis that antimicrobial growth promoters (AGP) function by modulating the mammalian immune system was tested. Sampling methods to characterize the mucosa-associated microbiota of the murine intestine by terminal restriction fragment length polymorphism (T-RFLP) analysis indicated that direct plug extraction was superior to wash methods. Using T-RFLP analysis, non-therapeutic administration of chlortetracycline (CTC) and sulfamethazine to beef cattle did not affect the composition of bacterial communities associated with intestinal mucosa and in digesta, with exception of those associated with mucosa of the proximal jejunum. Similarly, oral administration of non-therapeutic concentrations of CTC did not affect the mucosa-associated microbiota of the murine intestine. Oral administration of non-therapeutic concentrations of CTC prevented weight loss, reduced pathologic changes, modulated transcription levels of inflammatory cytokines in C. rodentium-infected mice, and did not consistently affect the colonic microbiota. These findings support the hypothesis that AGP primarily function by modulating the intestinal immune system. |
