ACKNOWLEDGMENTS. We thank Daniele Provenzano, Tracy Raivio, Jon Dennis, and members of the S.P. laboratory for helpful discussions and Shahna Tariq and Karen Gahir for technical assistance. We thank Marcia Craig for critically reviewing the manuscript, and Kim Ellison and Randy Irvin (University of Alberta) for providing us with bacterial strains. Work in the S.P. laboratory is supported by Canadian Institute for Health Research Operating Grant MOP-84473 and by Alberta Innovates–Health Solutions (funded by the Alberta Heritage Foundation for Medical Research Endowment Fund). S.P. is the recipient of the Alberta Heritage Foundation for Medical Research Scholar Award