S. enterica sv. Typhimurium strain aPTVS150 was used in this study.
The parental source of aPTVS150 was S. enterica sv. Typhimurium
χ3895, generously made available by R. Curtis (Hassan and Curtiss Iii,
1990). The strain lacks adenylate cyclase and cyclic AMP receptor protein
rendering it avirulent yet still immunogenic. This strain has been
previously utilized as surrogate in other model systems (Islam et al,
2004). A derivative isolate, aPTVS177, is a rifampicin-resistant strain
from aPTVS150 selected via spontaneous mutation for tolerance to
80 mg/L, which facilitates detection and recovery and minimizes interference
from background bacteria during greenhouse trials and field
studies. Lab studies verified that aPTVS177 had an in vitro growth rate
in several media indistinguishable from the parent strain and a plating
efficiency exceeding 85% following 20 generations without rifampicin
amendment in the selective/differential growth media or on plant
surfaces (data not shown). The use of aPTVS177 in both, greenhouse
and field studies was approved by the Office of Environmental Health
and Safety (EH&S) and the Institutional Biosafety Committee of the
University of California, Davis.