Survival of Escherichia coliO157:H7 Transformed with Either the pAK1-luxor pXEN-13 Plasmids in In VitroBovine Ruminal and Fecal Microbial Fermentations

AbstractThe use of luminescent plasmids in bacteria may serve as a viable model for the real-time validation of various pre-harvest interventions on the colonization or shedding patterns of Escherichia coliO157:H7 within cattle. The objective of this study was to determine if the growth characteristics of E. coliO157:H7 in mixed ruminal and fecal microbial fluid cultures would be altered when transformed with one of the two luminescent plasmids: pAK1-lux(PAK) or pXEN-13 (XEN). Transformants harboring the luminescent plasmids were compared to the non-transformed parental strain (wild type [WT]) after incubating in mixed ruminal or fecal microbial fluid media for 6 h in triplicate (n=3). The transformants and WT exhibited similar growth rates. Within mixed ruminal microbial fluid fermentations and mixed fecal microbial fluid, all transformants grew similarly (p=0.28) through the 6-h study. The reflective light unit (RLU; photons/pixel per second) photonic emissions of each plasmid within ruminal fluid differed at 0 h (p=0.002) and 2 h (p=0.02) and within fecal fluid at 0 h (p=0.009) and 2 h (p=0.04). The RLU remained the same within rumen fluid at 4 h (p=0.22) and 6 h (p=0.80) and within fecal fluid at 4 h (p=0.06) and 6 h (p=0.29). Growth of E. coliO157:H7 transformed with the bioluminescent plasmids was not altered in comparison to the WT, suggesting that both plasmids may serve as useful models for in vivostudies.