[1] Univ Washington, Dept Microbiol, Seattle, WA 98195 USA
[2] Univ Minnesota, Sch Med, Dept Med, Minneapolis, MN 55455 USA
[3] Univ Minnesota, Sch Med, Vet Adm Med Ctr, Minneapolis, MN 55455 USA
[4] SUNY Stony Brook, Dept Ecol & Evolut, Stony Brook, NY 11794 USA