Table 2.

Siderophore cross-feeding of various serotype Typhimurium strainsa

MediumConcn of 2,2′-bipyridyl (μM)StrainRelevant genotypeResults with the following siderophores:
Ferrioxamine BFerrioxamine EFerrioxamine GCoprogenEnterobactin
RK804entB tonB1314555
RK804(pIRS618)entB tonB+2625232830
WR1024ent fhuB555530
RK809entB foxA8552830
EWMc400SL1344/nrWild type++++ND
TML/nrWild type++++ND
  • a Approximately 106 cells of each strain tested were spread over the surface of Vogel-Bonner or EWM agar. Sterile filter paper discs (diameter, 5 mm), each impregnated with 1 μg of a siderophore, were placed on the agar surfaces.

  • b For the Vogel-Bonner medium bioassays, the sizes (in millimeters) of growth zones around siderophore discs were recorded after 18 h of incubation at 37°C; a value of 5 mm indicates that there was no growth stimulation.

  • c In the EWM bioassays, growth was too diffuse to measure accurately as discrete zones, and so the results were recorded as follows: +, obvious growth; (+), limited growth around the disc; and −, no observable growth after 3 to 4 h of incubation at 37°C. ND, growth stimulation not determined.